CA1169304A - Preparing substrate surface for electroless plating - Google Patents
Preparing substrate surface for electroless platingInfo
- Publication number
- CA1169304A CA1169304A CA000406066A CA406066A CA1169304A CA 1169304 A CA1169304 A CA 1169304A CA 000406066 A CA000406066 A CA 000406066A CA 406066 A CA406066 A CA 406066A CA 1169304 A CA1169304 A CA 1169304A
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- bath
- catalyzing
- nickel
- cobalt
- rinsing
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Abstract
Abstract of the Disclosure Polyalloy catalytic coating formulations are included in a multiple bath system or composite bath in order to prepare a metallic substrate surface to enhance subsequent plating thereover of nickel, cobalt or polyalloys including nickel or cobalt. Within this bath system, these catalytic formulations are rinsed Subsequent to their application onto the substrate and prior to the electoless deposition thereover. Improved products such as printed wiring boards are provided that are resistant to the development of bridging within the circuitry pattern and to undesirable increases in the conductivity of the board at locations other than on the circuitry pattern to produce printed wiring boards that are extremely resistent to developing short circuiting problems. Such properties are achieved, in large measure, because copper specks that are left embedded on the non-conductive board do not have any substantial electroless plating thereon.
Description
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SPECIFICATI~:)N
Background and Description of the Invention The present invention generally relates to the treatment of metal substrates so as to render them catalytic to subsequent eleciroless aeposition of metals thereonto, and is especially well suited to the electroless deposition of nickel, cobalt, or polyallovs containing nickel and/or cobalt onto copper that had previously been plated onto a non-conductive substrate in an electronic circuitry pattern. In an important embodiment o~ this invention, printed wiring boards are prepared which are less likely to develop electrical short circuiting problems than plates prepared without the use of these catalytic solutions.
Copper-plated circuits tend to oxidize, making it highly desirable to overplate the copper with a more durable metal to thereby enhance the circuitsl corrosion resistance, abrasion resistance, and solderability or bondability to aluminum or gold wire by ultrasonic means or the like, while at the same time maintaining or enhancing adequate conductivity.
Early procedures for providing overplatings included Plectro plating techniques which require electrically connecting each indiviaual circuit of the printed wiring board to a current source T~hile electroless overplating does not require such inefficient handling techniques, and avoids other drawbacks of electroplating such as non-unirorrnity of coating at board locations relatively re~note from the power source and exposed copper at the elec~rode connection sites, it has been found ~' .
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that such electroless overpl~tirlgs do not readily adhere to copper or copper alloys.
When electrolessly overplating the copper circuitry of a printed wiring board or a printed circuit board with a nickel-phosphorus or nickel-boron deposit, general im-provement has been found to be attained by dipping copper clad boards into a bath of an activator without rinsing in order to coat the copper clad board with a slightly alkaline film prior to nickel overplating in a slightly acidic electro-less nickel bath. Activators known to be useful in this regard include a bath having dimethylamine borane to activate reduction of nickel onto the copper. A serious drawback of this procedure is that it activates the entire board including the insulating portions thereof to also activate the reduction of nickel onto portions of the board that are not in the circuitry pattern for carrying current, which leads to short circuiting or bridging, especially when the insulating portions have metal specks therein which serve as sites for plating initiation and bridging between specks and between specks and portions of the circuitry.
It is believed that one important reason for the un-desirable plating in the non-circuitry portions is the fact that it is not possible to rinse the plate after treatment with such activators primarily because such a rinsin~ step would simply remove essentially all of the activator before it has had a chance to enhance the subsequent electroless step.
Copper specks are often embedded into the surface of the board and they typically can not be seen by the human eye.
Specks that remain on the board at the time it is over-plated with nickel or the like serve as sites for electroless ~'~
. -2-~93~4 metal deposition at locations that are not within the circuitry pattern and which can eventually lead to short circuiting of the circuitry.
Another approach that has been taken in attempting to improve the electroless overplating of nickel or the like onto copper clad boards includes the use of baths having matPrials, known generally as catalyzing agents, which operate to make the copper surface more receptive to the electroless deposition o~ metals thereover~ A known catalyzing agent is a palladium chloride dip which, although it effectively catalyzes the copper, has been found that adhesion between the copper and the subsequently electrolessly deposited metal is tenuous; and, as a result, when circuits made in this manner are subjected to rugged mechanical handling, or heat shock such as that developed during dip soldering, there is a tendency for the conductive layer to crack or pop free of the non-conductive base, thereby diarupting the circuit. Discussions relative to catalyzing agents are ~ound in Schneble et al U.S~ Patent No. 3,226,256 and Weisenberger U.S. Patent No. 3,431,120 It has now been discovered that certain formulation~ perform quite effectively as catalyzing agen~æ
in order to enhance the adhesion of nickel 9 cobalt, or polyalloys of nickel and/or cobalt over copper`surfaces, especially those copper surfaces found on printed wiring ; boards for use in preparing printed circuitry, while at the same time permitting a procedure whereby these catalyzing agents in conjunction with a rinse will enhance verdeposition only upon the metal carrying components of the circuit board to the exclusion of other metal imbedded in ~he board.
These results are achieved in accordance with the prese,nt invention basically by employing catalyzing formulations ;,, . . ~
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that include nickel or cobalt and a source of a secondary, inhibitor-type of metal such as tin, molybdenum, copper or tungsten, together with a reducing agent. Such catalyzing formulat1ons can be applied to a copper surface and rinsed to form a catalytic film for enhancing electro-less overplating in a bath that deposits nickel or cobalt, either alone or in combination with other metals, onto the circuitry pattern but discourages overplating onto portions of the board not within the circuitry pattern.
Accordingly, an object of this invention is to pro-vide a formulation and a method for improving electroless plating and products produced in accordance therewith.
Another object of the present invention is to pro-vide a formulation, method, and product having improved adhesion of an electrolessly deposited metal over copper, copper alloys, or the like.
Another object of this invention is to provide an improved catalyzing agent, its method of use, and products produced therewith.
Ano-ther object of the present invention is to provide an improved catalyzing agent, method, and product which exhibi-t enhanced adhesion and simultaneously allow for rinsing just prior to electroless overplating for reducing the tendency to bridge or short circuit.
Another object of the present invention is an im-proved method for providing a catalytic surface onto platea copper, which surFace can be subsequently treated by electro-less deposi-tion of nickel, cobalt, and/or polyalloys includ-ing either.
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Another object of this invention is to pro~id~ an improved catalyzing agent which includes nickel or cobalt and tin, molybdenum, copper or -tungsten together with a reducing agent, which catalyzing agent is suitable for in-corporation into a bath.
These and othex objects of the present invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings wherein:
The Figure is a generally schematic view depicting a production flow in accordance with this invention and products at various stages of production.
Catalyzing agents in accordance with this invention are, in general, polymetallic formulations of deposition-enhancing nickel and/or cobalt metal, and of secondary or inhibitor-type metals such as tin, molybaenum, copper and tungsten. As such, these catalyzing agents are related to the electroless polyalloy plating-formulations shown in Malloxy U.S. Patent No. 4,019,910. Typically, the formulations will be put to use within an aqueous bath which also includes a reducing agent for electrole~ss baths.
Any of these metals can be added as soluble salts, salts of low solubility within the particular electroless bath system in which they are intended to be used, esters, or substantially any other source suitable for electroless systems.
In an important aspect of this invention/ boron is added to the system as a third metal by means of a boron-containing reducing agent.
Suitable salts of nickel or cobalt include sulfates, chlorides, sulfamates or other anions compatible with these electroless systems. These same anions usually pro~ide an ~i~
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acceptable source of sal-ts of the secondary metals, inclllding for example stannous chloride, stannous fluorobora-te, sodium stannate, cuprous chloride, cuprous sulfate, and cupric salts, although it is preferred that these secondary metals be provided in the form o~ ester complexes of polyhydric compounds which are prepared hy conventional techniques involving reaction between an oxyacid and a pol~hydric acid or alcohol. The oxyacids are generally inorganic acids of the particular metal cation, for example, the tungstic, molybdic or boric acids. Representative O of the polyhydric acids or alcohols which may be employed are carboxylic acids or alcohols which contain at least two hydroxy groups and from about four to about fifteen carbon atoms per molecule. Typical polyhydric compou~ds include acids such as tartaric, gluconic, or glucoheptonlc acid, or alcohols such as mannitol, 2,3-butanediol or 1,2,3-propanetriol. Of these various polyhydric compounds, the carboxylic acids are generally preferred, and a particularly suitable one is gluco-heptonic acid. The ester complexes may also be, and in certain instances preferrably are, in the form o~ a polyester, that is O as ester complex formed by reacting two or more mols of the oxyacid with one mol of the polyhydric compoundl Ester complexes of these general types are formed and are generally believed to exist in aqueous solution as a complex equilibrium mixture where the cation of the oxyacid forms one or more ester linkages either with two hydroxyl groups of the polyhydric compound or with one hydroxyl group and one carboxylic acid group when the polyhydric compound is an acid, for example glucoheptonic acid. Such an ester complex has been found to be quite stable when used within baths pre-pared with the catalyzing formulations.
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Catalyzing baths for use in connection with the catalyzing agent formulations of this invention will usually include a reducing agent for the cations in the bath. While reducing agents such as hydrazine may be used, it has been found to be most advantageous if the reducing agent is a boron compound whereby boron cations are provided to the system and assist in forming the catalyzing film, together with the nickel or cobalt and the secondary metal~ Various boron-containing compounds can be used;theY are preferably any of those employed as reducing agents in electroless nickel or cobalt plating baths. Typical examples include boron hydrides, amine boranes or lower alkyl substituted amine boranes such as dimethyl-or diethyl-amine horane. Generally, of the various boron compounds which may be employed, the alkylamine boranes are preferred, particularly dimethylamine borane.
In general, when these various a~ents are combined with water and formulated into a catalyzing bath, -the total bath will usually be alkaline although slightly acidic baths can be put to ractice, a typical pH range being between 5.5 and 13, preferably between about 8 and about 11. Operating temperatures are between room temperature and the boiling temperature of the bath, a typical temperature range being between about 20 and 100C. These baths are, in ~eneral, capable of operating as electroless polyalloy plating baths;
their catalyzing function is achieved in part by using relatively low concentrations of active ingred;ents and by limiting the time period during which the article being sub-jected to the catalyzing agent remains within the bath. Very ~ :l6~3~
generally, active ingredient concen~rations about one-tcnth those of plating baths can be ~ormulated. The time period is such that the catalytic agent will form a coatiny to the extent that the surface is ~Inuc1eated~ typically with a tertiary polyalloy; in order to provide a film that is not necessarily observable to the ~naided eye but which will perform as catalyzing agent even after rinsing a substrate that had been immersed in the bath. Generally, catalyzing bath immersion will continue for between about 10 to 9~ seconds, usually no more than 60 seconds, at approximately 0.1 mil/hour, the most appropriate time and rate depending upon the particular catalyzing system being used, the temperature of the bath, the pH of the bath, and the precise make-up of the material being overplated.
Plating baths prepared with formulations according to this invention may, if desired, contain conventional bath additives which are commonly employed in electroless plating baths. Included are bath stabilizers such as sulfur contain-ing compounds, for example thiourea, as well as pH regulators such as an acid or a base, complexing agents for the metal ~0 ions maintained within the bath, such as ethylene diamine tetracetic acid, potassium pyrophospha-te or polyamines, or sulfide ion controllers such as lead. Buffering agents can also be added to add to the pH stability of the bath.
In proceeding with the ~ethod according to this in-vention, a metal substrate that is not normally receptive to electroless nickel or cobalt plating baths is rendered catalytic whereby nickel or cobalt can be electrolessly de-posited thereover. Not only does the method include catalyz-ing a surface and improving adhesion between the nickel or ~ :~6930~
cobalt and the overcoated metal, but also it allows for rinsing after application of the catalytic coating in order to enhance the quality of produets produced thereby.
As an aid for illustrating this invention, reference is made to the ~igure, which generally depicts the catalyzing and overplating of a copper clad board, generally designated 11, that had been prepared by conventional plating techniques to plate about 1/4 ounce of copper per square foot of plating area. These conventional plating techniques prepare a copper elad board by a process which ineludes removing copper from a plate 12 at those locations that are not within a eircuitry pattern 13, which, in general tends to leave copper specks or partieles 14 lying on the surface of plate 12 and often em-bedded into that surface.
Typical conventional techniques (not depicted) ean inelude adhering copper to the plate, for example an expoxy fiberglass plate, at whieh stage procedures sueh as drilling holes 15 can be proceeded with, and this ean be followed by laying down a resist and plating copper onto the board. The copper plating can be entirely electroless, but the length of time needed to plate a suitable thickness is shortened if an electroless co per deposition is followed by an electrodeposition of copper. Then, by etchingl lifting-off, or the like, the copper that had been plated onto the non-circuitry portions of the plate 12 is removed in order to leave an isolated eircuitry pattern to form the copper elad board 11.
Conventional further treatment that is not depicted -can include cleaning the copper clad board in a mildly ~ ~6930~
alkaline detergent bath Eor on the or~er of about five minutes at an elevated temperature that will not damage surfactants in the bath. After rinsing with water to remove residual carry-over, the plates are oEten either mechanically scrubbed or are dipped in an etching agent such as ammonium persulfate at a concentration of about 1 pound per gallon in order to etch off surface oxides and render the copper more active for subsequent deposition, which step would typically be followed by rinsing with tap water or the like. Next, a copper clad plate would usually be acid dipped as insurance that any residual surface materials are removed and in order to re-activate the copper. A mineral acid bath, such as 10% sulfuric acid, or a dry acid salt such as sodium bisulfate salts can be used, followed by rinsing for about one minute with, for example, deionized water. Even if every one of these further treatments are conducted on the copper clad board 11, the residual specks or particles of copper remain on the plate portion 12 off of the circui-try pattern 13~
Copper clad b~ard 11 is treated with the catalyzing agent in accordance with -this invention, with the general objective of forming a catalyzing film thereon to, generally ~peaking, nucleate the copper surface with what may be in the nature of a monomolecular layer. Typically, this treating step will include immersing the board ll into a bath 16 having the catalyzing agent according to this invention. This treating step should not be of such a length that electroless plating actually occurs, but should be of a duration adequate to provide a catalytic coa-ting of the board as shown at 17.
When the bath immersion technique is used, a typical suitable time period will be between about lO and 60 seconas, the exact 3 0 ~
time that is most sui~able depending upon the particular catalyzing systems being used, the temperature of the bath, the pH of the bath, the reducing agent used, and the make-up of the copper clad board.
The catalyzing treatment time is also dependent somewhat upon the temperature o the bath in which the catalyzing agent is used, with typical temperature ranges being between about 20C. to substantially boiling, or about 100C., preferred temperature ranges therewithin varying somewhat depending upon the particular reducing agent included within the bath.
After treatment with the catalyzing agent, the board 17 is subjected to a rinsing step, illustrated in the Figure by spray nozzle 18, although any means or method for rinsing may be used, such as running through a water bath for a very short period of time. This rinsing step will not significantly affect the catalytic surface formed by the catalyzing agent at the circuitry pattern 13 or the particles or specks of metal 14, but the rinsing step does wash away all of the plating solu~ion, especially that on the insulator board 12, which is not nucleated or catalyzed, on~y the metal portions having been nucleated. It is possi-ble to then pass the rinsPd board 17 into subsequent baths, - even those having hypophosphite, which is not possible when activator solutions such as dimethylamine borane are used instead of cataly~ing agents of this invention.
It has been found that the catalyzing agents, when used according to the method of this invention, can be combined with this subsequent rinsing step in order to obtain a result that catalyzes plating on the circuitry pattern by - nucleating, or providing active sites thereon, while at the ~ e time avoiding enh~ncement of deposition, t~pically discouraging 930~
deposition, at those locations on the surface of the board 12 that are not wi~hin a circuitry pattern 13. ~s a resultr a~ter the catalyzing agent films are electrolessly plated over with nickel, cobalt, or polyalloys including either or both, the electroless overplating is selectively deposited onto only the nucleated metal and does not spread onto the irlsulator board by way of forming plated bridges between specks and/or the circuitry pattern, which undesirable spreading out or extending is otherwise started at and encouraged by the specks within a catalyzed board environment provided by other systems. In this way, a finished printed circuit or wiring board can be made with precisely overplated circuitry pattern, one that does no~
have substantial excess deposits outside of the pattern which can and often do lead to short circuiting within the circuitry pattern and a generally undesirable increase in the conductivity of the board 12 outside of the pattern.
Rinsing solutions suitable for use in -the rinsing step will typically be aqueous, and the rinsing step itself should be long enough to significantly reduce the effect of catalyzlng agent that had been placed onto the non-circuit portion during the immersion step. The maximum rinsing time desired will be determined by convenience and economics in general, there being a point at which lengthy rinsing times will become expensivev On the whole, lengthy rinsing will not reduce the extent -that the surfaces are catalyzed since it is the surfaces themselves that are transformed rather than a rinsable film being placed thereon. The catalytic surface will be removed only by etching off or otherwise removing the copper or the like from the board.
Multiple rinsing can be carried out, and the rinsing can be in a still bath, under a running ba-th, or tne like. Rinsing times will vary somewhat depending upon the overa]l make-up of the plates, the materials, other physical 3 ~ ~
conditions, and whether the rinsing solution is running or still, typical times generally ranging be-tween about 2 seconds and about 45 seconds for each rinse. The pre-Eerred rinsing times will depend upon the catalyzing agent being used, the extent to which the catalyzing agent has adhered to the copper prior to rinsing, and the solventizing ability of the particular rinsing agent being used. Usually, a cool water rinsing agent, such as tap water or deionized water at ar~ient temperature, is preferred primarily because of the ready availability and low cost of water. If desired, wetting agents could be added, provided they do not interfere with the subsequent electroless plating.
Once rinsing in accordance with this invention has been accomplished, the selective electroless plating step is ready to be carried out. Catalytic flims formed in ac-cordance with the preceeding steps are especially receptive to electroless deposition of nickel plating or cobalt plating within any number of baths, such as nickel-phosphorous baths, electroless cobalt plating baths, or pollyalloy type baths, including ones listed in U.S. Patenk No. 4,019,910. The rinsed board 17 is electrolessly plated in a conventional manner, such as within a plating hath 19, whereby an over-coated layer 20 is added to the copper circuitry pattern 13 in order to form an overcoated circuit board 21, shown in the Figure emerging from the bath 19, which has subs-tantially no overplating deposits that are not within the precise circuitry pattern 13, except for any specks 22 that had been catalyzea and overplated but not spread out or expanded into a bridging or short circuiting path, the specks 14 and 22 being illustrated in exaggerated size for drawing clarity.
Included within the electroless plating bath 19 can be a source of nickel cations or cobalt cations, a source of other metal cations when polyalloy deposition is to be accomplishedt a pH regulator, a reducing agent, a complexing agent, water, bath stabilizers, sulfide ion controllers, or other suitable bath ingredients. Details concerning many of these various ingredients and the conditions suitable for such baths are discussed in U.S.
Patent No. 4,019,910. ~lso, a typical nickel-phosphorus electro-less plating bath usually would form a binary coating having be-10 tween about 88 to 95 weight percent nickel and between about 12 to 5 weight percent phosphorus.
If desired, especially when preparing printed circuit boards of high quality, it is possible, usually after one or more rinsing steps, to plate over the overcoating of nickel, cobalt, or polyalloy with another metal, such as gold, in order to enhance the solderability and corrosion resistance of the circuit. When final plating is completed, the substrate formed by this invention, such ; as a printed circuit or wiring boardr will be allowed to dry or will be dried according to any desired drying procedure.
While there is no desire to be bound by any theory concerning the operation of this invention, it is believed that the inclusion of metals generally accepted as being inhibitors, especially in the case of the molybdenum, tungsten or tin secondary metals, cooperate with the plating enhancement abilities of the nickel or cobalt within the catalyzing agent io render catalytic the other-wise non-catalytic surfaces, especially copper circuitry patterns.
The combination of the nickel or cobalt with the inhibitor-type secondary metals is believed to bring about the catalyzing properties attained by this invention by nucleating the otherwise non-catalytic surface and thus render the surface itself catalytic rather than merely lay a film over such surface tnat will be washed off during -1~-3 ~ ~
a subsequent rinsing step. It is believed that this particular combination within the system of this invention enhances the deposition efficiency of the system to the extent that a catalyzing surface is actually formed ~rom a surface that previously was non-catalytic. Once such a catalytic surface is formed, it is possible to electrolessly plate thereover because the overplating reaction is thereby encouraged, the catalyzed surface being much more favorable to deposition thereover than the original non-catalytic surface, especially when such overdeposition is that ~f a polyalloy. The components of the system cooperate with each other to efficiently - utilize the attributes of each to the extent that the system will successfulIy transform a non-catalytic surface into a catalyzed one.
As far as the mechanism by which the catalyzing agent itself renders the circuitry pattern more receptive to over-plating, it is believed that galvanic initiation plays a part in instituting the overplating surface. In a general sense, the catalyzing agent transforms the copper surface to the extent it is rendered catalytic for the subsequent overplating step. The ultimate result is a preferential catalyzing of the copper within the circuitry pattern It is believed-that the results attributable to the invention areenhanced by including boron within the sensi-tizing agent formulation, which inclusion can be most readily accomplished by using a boron-containing reducing agent~
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It is also possible that p}lysical ~ttri~ es of t~e v~rious materials involved in the process contribute to this ef~ect.
An in~ersion within the catalyzing agent bath wets all of the board, but the surface textures of the board within and out of the circuitry pattern are different, which would in-dicate that the effects of the subsequent rinsing step on the mzke-up of the catalyzing agent left on the board will be different too.
Baths incorporating the catalyzing agents according to this invention are typically alkal~ It is believed that operating with pH any lower than about 5.5 can lead to bridg-ing or plating in bet~een portions of the circuitry pattern, and a pH that is too high, say above about 13, would be un-necessarily severe. The preferred pH range is between about and about 11. The concentration of the deposition-enhancing metals such as nickel compounas within a bath according to the invention can be between about 0.001 and about 0.3 mol/literJ
usually between about 0 002 to about 0.125 mol/liter. A
typical ranye for the secondary metals such as the tin com-pounds within such baths is between about 0.001 to about 0.5 mol/liter, generally between about 0.002 and about 0.250 mol/liter. Reducing agent concentrations such as those for dimethylamine borane can be between about 0.001 and abol~t 0.2 mol/liter, usually be~ween about 0.002 and 0.1 mol/liter~ The up~er limits of the various constituents are ~etermined by economics and solubility, ana the lower limits by minimal eI~ectiveness.
While the Figure and ihis specification ~eal ~rimarily ~ith the preparation of prinied circuit boards, the invention is suitable for use whenever it is desired to catalyze a metal 3 0 ~
surface, particularly a copper surface, for subseql~ent overplating wi~h nickel, cobalt, or ~olyalloys including same. Eventual end uses for pro~ucts produced accor~ing to this invention incluae boards for carrying electrical circuit components within games, watches/ or magnetic memory devices in computer-type applications. These may bé in the Iorm of 2-sided printed etched boards which can have plating through holes therein. The following ex~nples are offered to illustrate the present invention:
E X k M P L E
Nickel - Molybdenum - Boron A catalyzing agent immersion bath was prepared to include 0.01 moi/liter molybdenum ester of gluconic acid, 0.05 mol/liter nickel sulfate, 0.1 mol/liter potassium pyrophosphate, which is a buffer and complexing agent, and 0 004 mol/liter dimethylamine borane reducing agent. The operating pH was 9.0, and the operating tem~erature was 40~C. This bath formed an adherent catalytic lilm on copper alloys that was then overplated with e]ectroless nickel.
Printea circuit boards were prepared an~ exhibited an en-hance~ adhesion between the copper and its nickel-containing overcoating. The use of printed circuits thus prepared were lound to be more consistently iess susceptible to developing short c;rcuits during use.
E X A M P ~ E 2 - _cXel - Tungsten - Boron Another catalyzing bath was ~repared and used generally in accord~nce with Example 1, this catalyzing agent bath including 0.005 mol/liter tun~sten ester of 3 0 ~
glucoheptonic acid, 0.02 mol/liter nickel sulfate, 0.05 mol/liter po~asium pyrophosphate, 0.04 mol/liter dimethyl-amine borane, with the balance of the bath being essentially water. The bath was operated at a 2H of 9.0, and the operating temperature was 40C.
Nickel - Tungsten - Boron Another bath that had been prepared and is suitable for use as a catalyzing agent bath includes 0.2 mol/liter of a tungsten ester of glucoheptonic acid, 0.1 mol/liter of nickel sulfate, 0.06 mol/liter of dime~hylamine borane and ~ ppm of thiourea. The operating conditions were a pH of 9.6 and a ~temperature of 90C., and the catalytic film pre-pared thereby should include 77.4 weight percent nickel, 20.0 weight percen-t tungsten, and 2.6 weight percent boron.
Nickel - Tungsten - Tin - Boron Another suitable catalytic agent bath includes deionized, carbon 'reated and filtered water containing 0.2 mol/liter tungsten ester of g}ucoheptonic acid, 0.1 mol/liter nickel slllfate, 0.025 mol/liter stannous chloride, 0.06 mol/liter dimethylamine borane, and 1 ppm of thiourea, the operating temperature being 90C an~ the pH being about 7.5.
This bath produces a catalytic film believe~ t~ be analyzable as 71.9 weight percent nickelr 16.0 weight percent tungsten, 4.2 weight percent tin, and 1.9 weight percent boron 3 ~ ~
Nickel - Tin - Boron A suitable catalytic plating aqueous bath includes 0.1 mol/liter of nickel sulfate, 0.1 mol/liter of stannous chloride, 0.06 mol/liter of dimethylamine borane, 0.2 mol/liter of potassium pyrophosphate, 1 ppm of thiourea, and 0.1 mol/liter of a diboron ester of glucoheptonie acid, which was pre-pared by charging approximately 2 mols of boric acid and 1 mol of sodium glucoheptonate into an esterification vessel eontaining about 600 milliliters of water as a solvent, followed by stirring while maintaining the temperature at about 25C for 30 mlnutes, after whieh it was diluted to a final volume of 1 liter with additional water. This bath produces a eatalytie film whieh has been analyzed in thicker, plating, operations as 92.8 weight percent nickel, 6.1 weight percent tin, and 1.1 weight percent boron.
Nickel - Molybdenum ~ Boron An aqueous catalyzing agent bath was produced to include 0.001 mol/liter of a molybdenum ester of glueohep-tonie acid, 0.1 mol/liter of nickel sulfate, 0.06 mol/liter : of dimethylamine borane, and 0.3 mol/liter of lactic acid, the operating pH being 10.0, and the operating temperature being 90C. This bath produces a catalytic film which has been analyzed in thicker, plating, operations as 79.8 weight percent nickel, 20 weight percent molybdenum, and 0.2 weight . percent boron.
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Nickel - Mol bdenum - Copper - Boron y A catalyzing agent bath was prepared by adding the following to deionized, carbon treated and filtered water:
0 001 mol/liter of molybdenum ester of glucoheptonic acid, 0.1 mol/liter of nickel sulfate, 0.0005 mol/liter of copper sulfate, 0.06 mol/liter of dimethylamine borane, and 0.3 mol/liter of lactic acid. The operating temperature was 90C and the operating pH was lQ. This bath has been analyzed to produce a coating of 77.87 weight percent nickel, 20 ~7eigh percent molybdenum, 1.8 weight percent copper, and 0.33 weight percent boron.
NicXel - Tin - Boron A tin-containing catalyzing bath is prepared by adding to water 0.001 mol/liter of nickel ion, 0.02 mol/liter of sodium stannate (tetravalent) complex of gluconic ~cid, and 0.02 mol/liter of dimethylamine borane. A very similar bath is prepared when 0.002 mol/liter of dimethylamine borane is included therein.
Nickel - Tin - Boron Another useful catalvzing agent bath includes 0.001 mol/liter of the stannate ester of glucoheptonic acid, 0.1 mol/liter of nickel sulfate J 0. 06 mol/liter of dimethylamine borane, and 0.3 mol/liter of lactic acid, with the operating temperature being 90~C and the operating pH being 10Ø
1 il~930~1 Cobalt~- Tungsten - Boron A complexing ayent agueous bath for subsequent cobalt overcoating has 0.2 mol/~ter ofthe tungsten ester of sluc~heptonic acid, 0.1 mol/liter of cobalt sulfate, 0.06 m~l/liter of dimethylamine borane, ana 1 ppm of thiourea.
The operating pH is about 9.6 at a temperature of about 90C, coating analysis being about 81 weight percent cobalt, 18 weight percent tungsten and 1 weight percent boron. After application of a catalyzing film with this bath, subsequent cobalt overplating can be accomplished by using a similar bath.
Cobalt - Molybdenum - Phosphorus Copper catalyzing bath can be prepared including 0.1 mol/liter of molybdenum ester of yluconic acid, 0.1 mol/liter o~ cobalt sulfate, and 0.28 mol/liter of sodium hypophosphite.
An operating pH is 10.0, and an operating temperature is 90 the film to be preparea having about 92.9 weiyht percent cobalt, 1.1 weight percent molybdenum, and 6 weight percent phosphorus. If aesired, the bath formulation is useful for coating over this catalytic coating after rinsing with cola water; typically incluain~ increasing the plating rate to about 0.2 to 0.3 mil/hour and reaucing the pH to an acidic level.
Cohalt - Tin - Boron An aqueous catalyzing agent bath can be prepared to include 0.1 mol~liter of robalt sulfate, 0.2 mol/liter of a sodium stannate complex of gluconic acid/ and 0. a mol/liter of dimethylamine borane. The operatlng temperature is 60C at a pH of about 7.
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E X A M P L E
After any o~ one of the catalyzing ayent baths of Examples 1 through 9 have been used to prepare a catalytic film on a copper substrate which remained in the bath for about 45 seconds, and after that film has been rinsed with - water twice for 15 second time periods, nickel can be electrolessly plated thereover using an aqueous bath having 0 1 mol/liter of nickel sulf~te, 0.2 mol/liter of citric acid and 0.17 mol/liter of sodium hypophosphite The operating pH is between about 4 5 and 5 0 at a temperature of 90C, and the plating rate is about 10 microns/minute which usually con-tinues for about 10 to 20 minutes. The overplating is generally complete, no bridging or coating over of copper specks on the board being observable.
After copper clad substrates are immersed in any of on~ of the cataiyzing agent baths of Examples 1 through 9 for about 45 seconds~ to prepare a catalytic ilm thereon, and after that film has been rinsed twicèwith running water, a nick~l overplating can be electrolessly formed thereover at about ~0C and a pH of 5 0 using an a~ueous bath having 0.1 mol/liter of nickel sulf~te, 0 25 mol/liter of succinic acid, and 0 04 mol/liter of dimethyla~ine borane~ This was followed by two running water rinses and further overplating with an electroless yold bath at 63C ana at a plating rate of about 1 micron/minute.
While in ~he Ioregoing s~ecification certain embodi-ments and examples of this inven~ion have been described in aetail, it will be appreciated that modifications and variations therefrom will be apparent to those skilled in this art. Accordingly, this invention is to be limited only by the scope of the appended claims.
SPECIFICATI~:)N
Background and Description of the Invention The present invention generally relates to the treatment of metal substrates so as to render them catalytic to subsequent eleciroless aeposition of metals thereonto, and is especially well suited to the electroless deposition of nickel, cobalt, or polyallovs containing nickel and/or cobalt onto copper that had previously been plated onto a non-conductive substrate in an electronic circuitry pattern. In an important embodiment o~ this invention, printed wiring boards are prepared which are less likely to develop electrical short circuiting problems than plates prepared without the use of these catalytic solutions.
Copper-plated circuits tend to oxidize, making it highly desirable to overplate the copper with a more durable metal to thereby enhance the circuitsl corrosion resistance, abrasion resistance, and solderability or bondability to aluminum or gold wire by ultrasonic means or the like, while at the same time maintaining or enhancing adequate conductivity.
Early procedures for providing overplatings included Plectro plating techniques which require electrically connecting each indiviaual circuit of the printed wiring board to a current source T~hile electroless overplating does not require such inefficient handling techniques, and avoids other drawbacks of electroplating such as non-unirorrnity of coating at board locations relatively re~note from the power source and exposed copper at the elec~rode connection sites, it has been found ~' .
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that such electroless overpl~tirlgs do not readily adhere to copper or copper alloys.
When electrolessly overplating the copper circuitry of a printed wiring board or a printed circuit board with a nickel-phosphorus or nickel-boron deposit, general im-provement has been found to be attained by dipping copper clad boards into a bath of an activator without rinsing in order to coat the copper clad board with a slightly alkaline film prior to nickel overplating in a slightly acidic electro-less nickel bath. Activators known to be useful in this regard include a bath having dimethylamine borane to activate reduction of nickel onto the copper. A serious drawback of this procedure is that it activates the entire board including the insulating portions thereof to also activate the reduction of nickel onto portions of the board that are not in the circuitry pattern for carrying current, which leads to short circuiting or bridging, especially when the insulating portions have metal specks therein which serve as sites for plating initiation and bridging between specks and between specks and portions of the circuitry.
It is believed that one important reason for the un-desirable plating in the non-circuitry portions is the fact that it is not possible to rinse the plate after treatment with such activators primarily because such a rinsin~ step would simply remove essentially all of the activator before it has had a chance to enhance the subsequent electroless step.
Copper specks are often embedded into the surface of the board and they typically can not be seen by the human eye.
Specks that remain on the board at the time it is over-plated with nickel or the like serve as sites for electroless ~'~
. -2-~93~4 metal deposition at locations that are not within the circuitry pattern and which can eventually lead to short circuiting of the circuitry.
Another approach that has been taken in attempting to improve the electroless overplating of nickel or the like onto copper clad boards includes the use of baths having matPrials, known generally as catalyzing agents, which operate to make the copper surface more receptive to the electroless deposition o~ metals thereover~ A known catalyzing agent is a palladium chloride dip which, although it effectively catalyzes the copper, has been found that adhesion between the copper and the subsequently electrolessly deposited metal is tenuous; and, as a result, when circuits made in this manner are subjected to rugged mechanical handling, or heat shock such as that developed during dip soldering, there is a tendency for the conductive layer to crack or pop free of the non-conductive base, thereby diarupting the circuit. Discussions relative to catalyzing agents are ~ound in Schneble et al U.S~ Patent No. 3,226,256 and Weisenberger U.S. Patent No. 3,431,120 It has now been discovered that certain formulation~ perform quite effectively as catalyzing agen~æ
in order to enhance the adhesion of nickel 9 cobalt, or polyalloys of nickel and/or cobalt over copper`surfaces, especially those copper surfaces found on printed wiring ; boards for use in preparing printed circuitry, while at the same time permitting a procedure whereby these catalyzing agents in conjunction with a rinse will enhance verdeposition only upon the metal carrying components of the circuit board to the exclusion of other metal imbedded in ~he board.
These results are achieved in accordance with the prese,nt invention basically by employing catalyzing formulations ;,, . . ~
`` ~16~30~
that include nickel or cobalt and a source of a secondary, inhibitor-type of metal such as tin, molybdenum, copper or tungsten, together with a reducing agent. Such catalyzing formulat1ons can be applied to a copper surface and rinsed to form a catalytic film for enhancing electro-less overplating in a bath that deposits nickel or cobalt, either alone or in combination with other metals, onto the circuitry pattern but discourages overplating onto portions of the board not within the circuitry pattern.
Accordingly, an object of this invention is to pro-vide a formulation and a method for improving electroless plating and products produced in accordance therewith.
Another object of the present invention is to pro-vide a formulation, method, and product having improved adhesion of an electrolessly deposited metal over copper, copper alloys, or the like.
Another object of this invention is to provide an improved catalyzing agent, its method of use, and products produced therewith.
Ano-ther object of the present invention is to provide an improved catalyzing agent, method, and product which exhibi-t enhanced adhesion and simultaneously allow for rinsing just prior to electroless overplating for reducing the tendency to bridge or short circuit.
Another object of the present invention is an im-proved method for providing a catalytic surface onto platea copper, which surFace can be subsequently treated by electro-less deposi-tion of nickel, cobalt, and/or polyalloys includ-ing either.
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Another object of this invention is to pro~id~ an improved catalyzing agent which includes nickel or cobalt and tin, molybdenum, copper or -tungsten together with a reducing agent, which catalyzing agent is suitable for in-corporation into a bath.
These and othex objects of the present invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings wherein:
The Figure is a generally schematic view depicting a production flow in accordance with this invention and products at various stages of production.
Catalyzing agents in accordance with this invention are, in general, polymetallic formulations of deposition-enhancing nickel and/or cobalt metal, and of secondary or inhibitor-type metals such as tin, molybaenum, copper and tungsten. As such, these catalyzing agents are related to the electroless polyalloy plating-formulations shown in Malloxy U.S. Patent No. 4,019,910. Typically, the formulations will be put to use within an aqueous bath which also includes a reducing agent for electrole~ss baths.
Any of these metals can be added as soluble salts, salts of low solubility within the particular electroless bath system in which they are intended to be used, esters, or substantially any other source suitable for electroless systems.
In an important aspect of this invention/ boron is added to the system as a third metal by means of a boron-containing reducing agent.
Suitable salts of nickel or cobalt include sulfates, chlorides, sulfamates or other anions compatible with these electroless systems. These same anions usually pro~ide an ~i~
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acceptable source of sal-ts of the secondary metals, inclllding for example stannous chloride, stannous fluorobora-te, sodium stannate, cuprous chloride, cuprous sulfate, and cupric salts, although it is preferred that these secondary metals be provided in the form o~ ester complexes of polyhydric compounds which are prepared hy conventional techniques involving reaction between an oxyacid and a pol~hydric acid or alcohol. The oxyacids are generally inorganic acids of the particular metal cation, for example, the tungstic, molybdic or boric acids. Representative O of the polyhydric acids or alcohols which may be employed are carboxylic acids or alcohols which contain at least two hydroxy groups and from about four to about fifteen carbon atoms per molecule. Typical polyhydric compou~ds include acids such as tartaric, gluconic, or glucoheptonlc acid, or alcohols such as mannitol, 2,3-butanediol or 1,2,3-propanetriol. Of these various polyhydric compounds, the carboxylic acids are generally preferred, and a particularly suitable one is gluco-heptonic acid. The ester complexes may also be, and in certain instances preferrably are, in the form o~ a polyester, that is O as ester complex formed by reacting two or more mols of the oxyacid with one mol of the polyhydric compoundl Ester complexes of these general types are formed and are generally believed to exist in aqueous solution as a complex equilibrium mixture where the cation of the oxyacid forms one or more ester linkages either with two hydroxyl groups of the polyhydric compound or with one hydroxyl group and one carboxylic acid group when the polyhydric compound is an acid, for example glucoheptonic acid. Such an ester complex has been found to be quite stable when used within baths pre-pared with the catalyzing formulations.
3~
Catalyzing baths for use in connection with the catalyzing agent formulations of this invention will usually include a reducing agent for the cations in the bath. While reducing agents such as hydrazine may be used, it has been found to be most advantageous if the reducing agent is a boron compound whereby boron cations are provided to the system and assist in forming the catalyzing film, together with the nickel or cobalt and the secondary metal~ Various boron-containing compounds can be used;theY are preferably any of those employed as reducing agents in electroless nickel or cobalt plating baths. Typical examples include boron hydrides, amine boranes or lower alkyl substituted amine boranes such as dimethyl-or diethyl-amine horane. Generally, of the various boron compounds which may be employed, the alkylamine boranes are preferred, particularly dimethylamine borane.
In general, when these various a~ents are combined with water and formulated into a catalyzing bath, -the total bath will usually be alkaline although slightly acidic baths can be put to ractice, a typical pH range being between 5.5 and 13, preferably between about 8 and about 11. Operating temperatures are between room temperature and the boiling temperature of the bath, a typical temperature range being between about 20 and 100C. These baths are, in ~eneral, capable of operating as electroless polyalloy plating baths;
their catalyzing function is achieved in part by using relatively low concentrations of active ingred;ents and by limiting the time period during which the article being sub-jected to the catalyzing agent remains within the bath. Very ~ :l6~3~
generally, active ingredient concen~rations about one-tcnth those of plating baths can be ~ormulated. The time period is such that the catalytic agent will form a coatiny to the extent that the surface is ~Inuc1eated~ typically with a tertiary polyalloy; in order to provide a film that is not necessarily observable to the ~naided eye but which will perform as catalyzing agent even after rinsing a substrate that had been immersed in the bath. Generally, catalyzing bath immersion will continue for between about 10 to 9~ seconds, usually no more than 60 seconds, at approximately 0.1 mil/hour, the most appropriate time and rate depending upon the particular catalyzing system being used, the temperature of the bath, the pH of the bath, and the precise make-up of the material being overplated.
Plating baths prepared with formulations according to this invention may, if desired, contain conventional bath additives which are commonly employed in electroless plating baths. Included are bath stabilizers such as sulfur contain-ing compounds, for example thiourea, as well as pH regulators such as an acid or a base, complexing agents for the metal ~0 ions maintained within the bath, such as ethylene diamine tetracetic acid, potassium pyrophospha-te or polyamines, or sulfide ion controllers such as lead. Buffering agents can also be added to add to the pH stability of the bath.
In proceeding with the ~ethod according to this in-vention, a metal substrate that is not normally receptive to electroless nickel or cobalt plating baths is rendered catalytic whereby nickel or cobalt can be electrolessly de-posited thereover. Not only does the method include catalyz-ing a surface and improving adhesion between the nickel or ~ :~6930~
cobalt and the overcoated metal, but also it allows for rinsing after application of the catalytic coating in order to enhance the quality of produets produced thereby.
As an aid for illustrating this invention, reference is made to the ~igure, which generally depicts the catalyzing and overplating of a copper clad board, generally designated 11, that had been prepared by conventional plating techniques to plate about 1/4 ounce of copper per square foot of plating area. These conventional plating techniques prepare a copper elad board by a process which ineludes removing copper from a plate 12 at those locations that are not within a eircuitry pattern 13, which, in general tends to leave copper specks or partieles 14 lying on the surface of plate 12 and often em-bedded into that surface.
Typical conventional techniques (not depicted) ean inelude adhering copper to the plate, for example an expoxy fiberglass plate, at whieh stage procedures sueh as drilling holes 15 can be proceeded with, and this ean be followed by laying down a resist and plating copper onto the board. The copper plating can be entirely electroless, but the length of time needed to plate a suitable thickness is shortened if an electroless co per deposition is followed by an electrodeposition of copper. Then, by etchingl lifting-off, or the like, the copper that had been plated onto the non-circuitry portions of the plate 12 is removed in order to leave an isolated eircuitry pattern to form the copper elad board 11.
Conventional further treatment that is not depicted -can include cleaning the copper clad board in a mildly ~ ~6930~
alkaline detergent bath Eor on the or~er of about five minutes at an elevated temperature that will not damage surfactants in the bath. After rinsing with water to remove residual carry-over, the plates are oEten either mechanically scrubbed or are dipped in an etching agent such as ammonium persulfate at a concentration of about 1 pound per gallon in order to etch off surface oxides and render the copper more active for subsequent deposition, which step would typically be followed by rinsing with tap water or the like. Next, a copper clad plate would usually be acid dipped as insurance that any residual surface materials are removed and in order to re-activate the copper. A mineral acid bath, such as 10% sulfuric acid, or a dry acid salt such as sodium bisulfate salts can be used, followed by rinsing for about one minute with, for example, deionized water. Even if every one of these further treatments are conducted on the copper clad board 11, the residual specks or particles of copper remain on the plate portion 12 off of the circui-try pattern 13~
Copper clad b~ard 11 is treated with the catalyzing agent in accordance with -this invention, with the general objective of forming a catalyzing film thereon to, generally ~peaking, nucleate the copper surface with what may be in the nature of a monomolecular layer. Typically, this treating step will include immersing the board ll into a bath 16 having the catalyzing agent according to this invention. This treating step should not be of such a length that electroless plating actually occurs, but should be of a duration adequate to provide a catalytic coa-ting of the board as shown at 17.
When the bath immersion technique is used, a typical suitable time period will be between about lO and 60 seconas, the exact 3 0 ~
time that is most sui~able depending upon the particular catalyzing systems being used, the temperature of the bath, the pH of the bath, the reducing agent used, and the make-up of the copper clad board.
The catalyzing treatment time is also dependent somewhat upon the temperature o the bath in which the catalyzing agent is used, with typical temperature ranges being between about 20C. to substantially boiling, or about 100C., preferred temperature ranges therewithin varying somewhat depending upon the particular reducing agent included within the bath.
After treatment with the catalyzing agent, the board 17 is subjected to a rinsing step, illustrated in the Figure by spray nozzle 18, although any means or method for rinsing may be used, such as running through a water bath for a very short period of time. This rinsing step will not significantly affect the catalytic surface formed by the catalyzing agent at the circuitry pattern 13 or the particles or specks of metal 14, but the rinsing step does wash away all of the plating solu~ion, especially that on the insulator board 12, which is not nucleated or catalyzed, on~y the metal portions having been nucleated. It is possi-ble to then pass the rinsPd board 17 into subsequent baths, - even those having hypophosphite, which is not possible when activator solutions such as dimethylamine borane are used instead of cataly~ing agents of this invention.
It has been found that the catalyzing agents, when used according to the method of this invention, can be combined with this subsequent rinsing step in order to obtain a result that catalyzes plating on the circuitry pattern by - nucleating, or providing active sites thereon, while at the ~ e time avoiding enh~ncement of deposition, t~pically discouraging 930~
deposition, at those locations on the surface of the board 12 that are not wi~hin a circuitry pattern 13. ~s a resultr a~ter the catalyzing agent films are electrolessly plated over with nickel, cobalt, or polyalloys including either or both, the electroless overplating is selectively deposited onto only the nucleated metal and does not spread onto the irlsulator board by way of forming plated bridges between specks and/or the circuitry pattern, which undesirable spreading out or extending is otherwise started at and encouraged by the specks within a catalyzed board environment provided by other systems. In this way, a finished printed circuit or wiring board can be made with precisely overplated circuitry pattern, one that does no~
have substantial excess deposits outside of the pattern which can and often do lead to short circuiting within the circuitry pattern and a generally undesirable increase in the conductivity of the board 12 outside of the pattern.
Rinsing solutions suitable for use in -the rinsing step will typically be aqueous, and the rinsing step itself should be long enough to significantly reduce the effect of catalyzlng agent that had been placed onto the non-circuit portion during the immersion step. The maximum rinsing time desired will be determined by convenience and economics in general, there being a point at which lengthy rinsing times will become expensivev On the whole, lengthy rinsing will not reduce the extent -that the surfaces are catalyzed since it is the surfaces themselves that are transformed rather than a rinsable film being placed thereon. The catalytic surface will be removed only by etching off or otherwise removing the copper or the like from the board.
Multiple rinsing can be carried out, and the rinsing can be in a still bath, under a running ba-th, or tne like. Rinsing times will vary somewhat depending upon the overa]l make-up of the plates, the materials, other physical 3 ~ ~
conditions, and whether the rinsing solution is running or still, typical times generally ranging be-tween about 2 seconds and about 45 seconds for each rinse. The pre-Eerred rinsing times will depend upon the catalyzing agent being used, the extent to which the catalyzing agent has adhered to the copper prior to rinsing, and the solventizing ability of the particular rinsing agent being used. Usually, a cool water rinsing agent, such as tap water or deionized water at ar~ient temperature, is preferred primarily because of the ready availability and low cost of water. If desired, wetting agents could be added, provided they do not interfere with the subsequent electroless plating.
Once rinsing in accordance with this invention has been accomplished, the selective electroless plating step is ready to be carried out. Catalytic flims formed in ac-cordance with the preceeding steps are especially receptive to electroless deposition of nickel plating or cobalt plating within any number of baths, such as nickel-phosphorous baths, electroless cobalt plating baths, or pollyalloy type baths, including ones listed in U.S. Patenk No. 4,019,910. The rinsed board 17 is electrolessly plated in a conventional manner, such as within a plating hath 19, whereby an over-coated layer 20 is added to the copper circuitry pattern 13 in order to form an overcoated circuit board 21, shown in the Figure emerging from the bath 19, which has subs-tantially no overplating deposits that are not within the precise circuitry pattern 13, except for any specks 22 that had been catalyzea and overplated but not spread out or expanded into a bridging or short circuiting path, the specks 14 and 22 being illustrated in exaggerated size for drawing clarity.
Included within the electroless plating bath 19 can be a source of nickel cations or cobalt cations, a source of other metal cations when polyalloy deposition is to be accomplishedt a pH regulator, a reducing agent, a complexing agent, water, bath stabilizers, sulfide ion controllers, or other suitable bath ingredients. Details concerning many of these various ingredients and the conditions suitable for such baths are discussed in U.S.
Patent No. 4,019,910. ~lso, a typical nickel-phosphorus electro-less plating bath usually would form a binary coating having be-10 tween about 88 to 95 weight percent nickel and between about 12 to 5 weight percent phosphorus.
If desired, especially when preparing printed circuit boards of high quality, it is possible, usually after one or more rinsing steps, to plate over the overcoating of nickel, cobalt, or polyalloy with another metal, such as gold, in order to enhance the solderability and corrosion resistance of the circuit. When final plating is completed, the substrate formed by this invention, such ; as a printed circuit or wiring boardr will be allowed to dry or will be dried according to any desired drying procedure.
While there is no desire to be bound by any theory concerning the operation of this invention, it is believed that the inclusion of metals generally accepted as being inhibitors, especially in the case of the molybdenum, tungsten or tin secondary metals, cooperate with the plating enhancement abilities of the nickel or cobalt within the catalyzing agent io render catalytic the other-wise non-catalytic surfaces, especially copper circuitry patterns.
The combination of the nickel or cobalt with the inhibitor-type secondary metals is believed to bring about the catalyzing properties attained by this invention by nucleating the otherwise non-catalytic surface and thus render the surface itself catalytic rather than merely lay a film over such surface tnat will be washed off during -1~-3 ~ ~
a subsequent rinsing step. It is believed that this particular combination within the system of this invention enhances the deposition efficiency of the system to the extent that a catalyzing surface is actually formed ~rom a surface that previously was non-catalytic. Once such a catalytic surface is formed, it is possible to electrolessly plate thereover because the overplating reaction is thereby encouraged, the catalyzed surface being much more favorable to deposition thereover than the original non-catalytic surface, especially when such overdeposition is that ~f a polyalloy. The components of the system cooperate with each other to efficiently - utilize the attributes of each to the extent that the system will successfulIy transform a non-catalytic surface into a catalyzed one.
As far as the mechanism by which the catalyzing agent itself renders the circuitry pattern more receptive to over-plating, it is believed that galvanic initiation plays a part in instituting the overplating surface. In a general sense, the catalyzing agent transforms the copper surface to the extent it is rendered catalytic for the subsequent overplating step. The ultimate result is a preferential catalyzing of the copper within the circuitry pattern It is believed-that the results attributable to the invention areenhanced by including boron within the sensi-tizing agent formulation, which inclusion can be most readily accomplished by using a boron-containing reducing agent~
~ 1693~
It is also possible that p}lysical ~ttri~ es of t~e v~rious materials involved in the process contribute to this ef~ect.
An in~ersion within the catalyzing agent bath wets all of the board, but the surface textures of the board within and out of the circuitry pattern are different, which would in-dicate that the effects of the subsequent rinsing step on the mzke-up of the catalyzing agent left on the board will be different too.
Baths incorporating the catalyzing agents according to this invention are typically alkal~ It is believed that operating with pH any lower than about 5.5 can lead to bridg-ing or plating in bet~een portions of the circuitry pattern, and a pH that is too high, say above about 13, would be un-necessarily severe. The preferred pH range is between about and about 11. The concentration of the deposition-enhancing metals such as nickel compounas within a bath according to the invention can be between about 0.001 and about 0.3 mol/literJ
usually between about 0 002 to about 0.125 mol/liter. A
typical ranye for the secondary metals such as the tin com-pounds within such baths is between about 0.001 to about 0.5 mol/liter, generally between about 0.002 and about 0.250 mol/liter. Reducing agent concentrations such as those for dimethylamine borane can be between about 0.001 and abol~t 0.2 mol/liter, usually be~ween about 0.002 and 0.1 mol/liter~ The up~er limits of the various constituents are ~etermined by economics and solubility, ana the lower limits by minimal eI~ectiveness.
While the Figure and ihis specification ~eal ~rimarily ~ith the preparation of prinied circuit boards, the invention is suitable for use whenever it is desired to catalyze a metal 3 0 ~
surface, particularly a copper surface, for subseql~ent overplating wi~h nickel, cobalt, or ~olyalloys including same. Eventual end uses for pro~ucts produced accor~ing to this invention incluae boards for carrying electrical circuit components within games, watches/ or magnetic memory devices in computer-type applications. These may bé in the Iorm of 2-sided printed etched boards which can have plating through holes therein. The following ex~nples are offered to illustrate the present invention:
E X k M P L E
Nickel - Molybdenum - Boron A catalyzing agent immersion bath was prepared to include 0.01 moi/liter molybdenum ester of gluconic acid, 0.05 mol/liter nickel sulfate, 0.1 mol/liter potassium pyrophosphate, which is a buffer and complexing agent, and 0 004 mol/liter dimethylamine borane reducing agent. The operating pH was 9.0, and the operating tem~erature was 40~C. This bath formed an adherent catalytic lilm on copper alloys that was then overplated with e]ectroless nickel.
Printea circuit boards were prepared an~ exhibited an en-hance~ adhesion between the copper and its nickel-containing overcoating. The use of printed circuits thus prepared were lound to be more consistently iess susceptible to developing short c;rcuits during use.
E X A M P ~ E 2 - _cXel - Tungsten - Boron Another catalyzing bath was ~repared and used generally in accord~nce with Example 1, this catalyzing agent bath including 0.005 mol/liter tun~sten ester of 3 0 ~
glucoheptonic acid, 0.02 mol/liter nickel sulfate, 0.05 mol/liter po~asium pyrophosphate, 0.04 mol/liter dimethyl-amine borane, with the balance of the bath being essentially water. The bath was operated at a 2H of 9.0, and the operating temperature was 40C.
Nickel - Tungsten - Boron Another bath that had been prepared and is suitable for use as a catalyzing agent bath includes 0.2 mol/liter of a tungsten ester of glucoheptonic acid, 0.1 mol/liter of nickel sulfate, 0.06 mol/liter of dime~hylamine borane and ~ ppm of thiourea. The operating conditions were a pH of 9.6 and a ~temperature of 90C., and the catalytic film pre-pared thereby should include 77.4 weight percent nickel, 20.0 weight percen-t tungsten, and 2.6 weight percent boron.
Nickel - Tungsten - Tin - Boron Another suitable catalytic agent bath includes deionized, carbon 'reated and filtered water containing 0.2 mol/liter tungsten ester of g}ucoheptonic acid, 0.1 mol/liter nickel slllfate, 0.025 mol/liter stannous chloride, 0.06 mol/liter dimethylamine borane, and 1 ppm of thiourea, the operating temperature being 90C an~ the pH being about 7.5.
This bath produces a catalytic film believe~ t~ be analyzable as 71.9 weight percent nickelr 16.0 weight percent tungsten, 4.2 weight percent tin, and 1.9 weight percent boron 3 ~ ~
Nickel - Tin - Boron A suitable catalytic plating aqueous bath includes 0.1 mol/liter of nickel sulfate, 0.1 mol/liter of stannous chloride, 0.06 mol/liter of dimethylamine borane, 0.2 mol/liter of potassium pyrophosphate, 1 ppm of thiourea, and 0.1 mol/liter of a diboron ester of glucoheptonie acid, which was pre-pared by charging approximately 2 mols of boric acid and 1 mol of sodium glucoheptonate into an esterification vessel eontaining about 600 milliliters of water as a solvent, followed by stirring while maintaining the temperature at about 25C for 30 mlnutes, after whieh it was diluted to a final volume of 1 liter with additional water. This bath produces a eatalytie film whieh has been analyzed in thicker, plating, operations as 92.8 weight percent nickel, 6.1 weight percent tin, and 1.1 weight percent boron.
Nickel - Molybdenum ~ Boron An aqueous catalyzing agent bath was produced to include 0.001 mol/liter of a molybdenum ester of glueohep-tonie acid, 0.1 mol/liter of nickel sulfate, 0.06 mol/liter : of dimethylamine borane, and 0.3 mol/liter of lactic acid, the operating pH being 10.0, and the operating temperature being 90C. This bath produces a catalytic film which has been analyzed in thicker, plating, operations as 79.8 weight percent nickel, 20 weight percent molybdenum, and 0.2 weight . percent boron.
.
~ '.
Nickel - Mol bdenum - Copper - Boron y A catalyzing agent bath was prepared by adding the following to deionized, carbon treated and filtered water:
0 001 mol/liter of molybdenum ester of glucoheptonic acid, 0.1 mol/liter of nickel sulfate, 0.0005 mol/liter of copper sulfate, 0.06 mol/liter of dimethylamine borane, and 0.3 mol/liter of lactic acid. The operating temperature was 90C and the operating pH was lQ. This bath has been analyzed to produce a coating of 77.87 weight percent nickel, 20 ~7eigh percent molybdenum, 1.8 weight percent copper, and 0.33 weight percent boron.
NicXel - Tin - Boron A tin-containing catalyzing bath is prepared by adding to water 0.001 mol/liter of nickel ion, 0.02 mol/liter of sodium stannate (tetravalent) complex of gluconic ~cid, and 0.02 mol/liter of dimethylamine borane. A very similar bath is prepared when 0.002 mol/liter of dimethylamine borane is included therein.
Nickel - Tin - Boron Another useful catalvzing agent bath includes 0.001 mol/liter of the stannate ester of glucoheptonic acid, 0.1 mol/liter of nickel sulfate J 0. 06 mol/liter of dimethylamine borane, and 0.3 mol/liter of lactic acid, with the operating temperature being 90~C and the operating pH being 10Ø
1 il~930~1 Cobalt~- Tungsten - Boron A complexing ayent agueous bath for subsequent cobalt overcoating has 0.2 mol/~ter ofthe tungsten ester of sluc~heptonic acid, 0.1 mol/liter of cobalt sulfate, 0.06 m~l/liter of dimethylamine borane, ana 1 ppm of thiourea.
The operating pH is about 9.6 at a temperature of about 90C, coating analysis being about 81 weight percent cobalt, 18 weight percent tungsten and 1 weight percent boron. After application of a catalyzing film with this bath, subsequent cobalt overplating can be accomplished by using a similar bath.
Cobalt - Molybdenum - Phosphorus Copper catalyzing bath can be prepared including 0.1 mol/liter of molybdenum ester of yluconic acid, 0.1 mol/liter o~ cobalt sulfate, and 0.28 mol/liter of sodium hypophosphite.
An operating pH is 10.0, and an operating temperature is 90 the film to be preparea having about 92.9 weiyht percent cobalt, 1.1 weight percent molybdenum, and 6 weight percent phosphorus. If aesired, the bath formulation is useful for coating over this catalytic coating after rinsing with cola water; typically incluain~ increasing the plating rate to about 0.2 to 0.3 mil/hour and reaucing the pH to an acidic level.
Cohalt - Tin - Boron An aqueous catalyzing agent bath can be prepared to include 0.1 mol~liter of robalt sulfate, 0.2 mol/liter of a sodium stannate complex of gluconic acid/ and 0. a mol/liter of dimethylamine borane. The operatlng temperature is 60C at a pH of about 7.
~ 1~93~
E X A M P L E
After any o~ one of the catalyzing ayent baths of Examples 1 through 9 have been used to prepare a catalytic film on a copper substrate which remained in the bath for about 45 seconds, and after that film has been rinsed with - water twice for 15 second time periods, nickel can be electrolessly plated thereover using an aqueous bath having 0 1 mol/liter of nickel sulf~te, 0.2 mol/liter of citric acid and 0.17 mol/liter of sodium hypophosphite The operating pH is between about 4 5 and 5 0 at a temperature of 90C, and the plating rate is about 10 microns/minute which usually con-tinues for about 10 to 20 minutes. The overplating is generally complete, no bridging or coating over of copper specks on the board being observable.
After copper clad substrates are immersed in any of on~ of the cataiyzing agent baths of Examples 1 through 9 for about 45 seconds~ to prepare a catalytic ilm thereon, and after that film has been rinsed twicèwith running water, a nick~l overplating can be electrolessly formed thereover at about ~0C and a pH of 5 0 using an a~ueous bath having 0.1 mol/liter of nickel sulf~te, 0 25 mol/liter of succinic acid, and 0 04 mol/liter of dimethyla~ine borane~ This was followed by two running water rinses and further overplating with an electroless yold bath at 63C ana at a plating rate of about 1 micron/minute.
While in ~he Ioregoing s~ecification certain embodi-ments and examples of this inven~ion have been described in aetail, it will be appreciated that modifications and variations therefrom will be apparent to those skilled in this art. Accordingly, this invention is to be limited only by the scope of the appended claims.
Claims (17)
1. A composite bath for catalyzing a metal surface for subsequent overplating with nickel, cobalt, or polyalloys including nickel or cobalt, said composite bath comprising: a polymetallic catalyzing bath including a primary metal selected from the group consisting of nickel, cobalt and combinations thereof, a secondary metal selected from the group consisting of tin, molybdenum, copper and tungsten, and a reducing agent for cations of said metals, said catalyzing bath including an ester complex of a polyhydric compound, said catalyzing bath being sufficient to nucleate the metal surface and insufficient to deposit a generally continuous plating film thereonto; said composite bath further including a rinsing bath downstream of the catalyzing bath for rinsing said metal surface with an aqueous rinsing agent for enhancing preferential catalyzing agent film formation onto said nucleated metal surface.
2. The composite bath of claim 1, further including a plating bath downstream of the rinsing bath for subsequent overplating of nickel, cobalt, or polyalloys including nickel or cobalt onto the nucleated metal surface.
3. The composite bath of claim 1, wherein said reducing agent is a boron-containing composition selected from the group consisting of boron hydrides, amine boranes, and lower alkyl substituted amine boranes.
4. The composite bath of claim 1, wherein said catalyzing bath is at a pH between about 5.5 and 13 and a temperature between about 20 and 100°C.
5. The composite bath of claim 1, wherein said catalyzing bath is an aqueous bath having between about 0.001 and about 0.3 mol/liter of the primary metal, between about 0.001 and about 0.5 mol/liter of the secondary metal, and between about 0.001 and about 0.2 mol/liter of the reducing agent, all as based on the total volume of the bath.
6. The composite bath of claim 1, wherein said catalyzing bath further includes a bath stabilizer, a pH
regulator, a complexing agent, a sulfide ion controller, or a buffering agent.
regulator, a complexing agent, a sulfide ion controller, or a buffering agent.
7. The composite bath of claim 1, wherein the metal surface is a copper-containing surface.
8. The composite bath of claim 1, wherein in the catalyzing bath the molar ratio of compounds containing the primary metal to compounds containing the secondary metal is between about 150 to 1 and about 1 to 100.
9. The composite bath of claim 1, wherein said polymetallic catalyzing bath includes copper only when it also includes one or more of tin, molybdenum or tungsten as said secondary metal.
10. A multiple bath system for nucleating a non-catalytic metal surface of a substrate in order to catalyze the metal surface for subsequent overplating with nickel, cobalt, or polyalloys including nickel or cobalt, said multiple bath system comprising: catalyzing means for receiving the substrate to nucleate the metal surface while avoiding deposit of a generally continuous plating film thereonto, said catalyzing means having a catalyzing bath including a polymetallic catalyzing agent including a primary metal selected from the group consisting of nickel, cobalt, and combinations thereof, a secondary metal selected from the group consisting of tin, molybdenun, copper and tungsten, and a reducing agent for cations of said metals, said catalyzing bath including copper only when it also includes one or more of tin, molybdenum or tungsten as said secondary metal, said catalyzing bath including an ester complex of a polyhydric compound, said catalyzing means providing for immersion of said substrate in said catalyzing bath for a time sufficient to nucleate said non-catalytic metal surface and insufficient to deposit a generally continuous plating film thereon-to;
means for rinsing the substrate having said nucleated non-catalytic metal surface, said rinsing means being downstream from said catalyzing means, said rinsing means including means for applying an aqueous rinsing agent to the substrate; and plating means for subsequent overplating of nickel, cobalt or polyalloys including nickel or cobalt onto the nucleated metal surface, said plating means being downstream from said catalyzing means and said rinsing means.
means for rinsing the substrate having said nucleated non-catalytic metal surface, said rinsing means being downstream from said catalyzing means, said rinsing means including means for applying an aqueous rinsing agent to the substrate; and plating means for subsequent overplating of nickel, cobalt or polyalloys including nickel or cobalt onto the nucleated metal surface, said plating means being downstream from said catalyzing means and said rinsing means.
11. The multiple bath system of claim 10, wherein said reducing agent is a boron containing composition selected from the group consisting of boron hydrides, amine boranes and lower alkyl substituted amine boranes.
12. The multiple bath system of claim 10, wherein said catalyzing bath is at a pH between about 5.5 and 13 and a temperature between about 20 and 100°C.
13. The multiple bath system of claim 10, wherein said catalyzing bath is an aqueous bath having between about 0.001 and about 0.3 mol/liter of the primary metal, between about 0.001 and about 0.5 mol/liter of the secondary metal, and between about 0.001 and about 0.2 mol/liter of the reducing agent, all as based on the total volume of the catalyzing bath.
14. The multiple bath system of claim 10, wherein said catalyzing bath further includes a bath stabilizer, a pH regulator, a complexing agent, a sulfide ion controller, or a buffering agent.
15. The multiple bath system of claim 10, wherein the metal surface is a copper-containing surface.
16. The multiple bath system of claim 10, wherein said rinsing means includes a running bath.
17. The multiple bath system of claim 10, wherein said rinsing means includes a still bath.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000406066A CA1169304A (en) | 1979-01-22 | 1982-06-25 | Preparing substrate surface for electroless plating |
| CA000438885A CA1176118A (en) | 1979-01-22 | 1983-10-12 | Preparing substrate surface for electroless plating and products produced thereby |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/005,169 US4232060A (en) | 1979-01-22 | 1979-01-22 | Method of preparing substrate surface for electroless plating and products produced thereby |
| US5,169 | 1979-01-22 | ||
| CA000343240A CA1139012A (en) | 1979-01-22 | 1980-01-08 | Method of preparing substrate surface for electroless plating and products produced thereby |
| CA000406066A CA1169304A (en) | 1979-01-22 | 1982-06-25 | Preparing substrate surface for electroless plating |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000343240A Division CA1139012A (en) | 1979-01-22 | 1980-01-08 | Method of preparing substrate surface for electroless plating and products produced thereby |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000438885A Division CA1176118A (en) | 1979-01-22 | 1983-10-12 | Preparing substrate surface for electroless plating and products produced thereby |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1169304A true CA1169304A (en) | 1984-06-19 |
Family
ID=27166537
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000406066A Expired CA1169304A (en) | 1979-01-22 | 1982-06-25 | Preparing substrate surface for electroless plating |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1169304A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113151811A (en) * | 2021-04-13 | 2021-07-23 | 赤壁市聚茂新材料科技有限公司 | Non-palladium activated nickel plating solution and nickel plating method |
-
1982
- 1982-06-25 CA CA000406066A patent/CA1169304A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113151811A (en) * | 2021-04-13 | 2021-07-23 | 赤壁市聚茂新材料科技有限公司 | Non-palladium activated nickel plating solution and nickel plating method |
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