CA2052931A1 - Process and programmable computer controlled system for electroless copper plating - Google Patents

Abstract

PROCESS AND PROGRAMMABLE COMPUTER CONTROLLED
SYSTEM FOR ELECTROLESS COPPER PLATING

ABSTRACT OF THE DISCLOSURE

A process is provided for maintaining the level of cyanide ion stabilizer in an electroless copper plating bath held at a constant predetermined temperature by making additions of predetermined amounts of cyanide ion feedstock at predetermined time intervals. The properties of the copper layer deposited on a substrate by means of the system are significantly improved in uniformity and structural strength. In addition, The plating rate and stability of the bath are far more uniform. A programmable computer system for controlling the process of the invention is also described.

Description

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: PROCESS AND PROGRAMMABLE COMPUT~R CONTROLLED
SYSTEM FOR ~LECTROL~SS COPPER PLATING_ 1. Field of tbe In,vention.
This invention relates to electroless copper plat-ing baths~and improved copper plated substrates, and ismore particularly concerned wi~h a process and a program-mable;computer controlled system for electroless copper plating and with substrates coated with copper using said ~ syst~m.

:~ 10 2. Back~ound of the Invq,n,tion., Electroless copper plating of substrates such a~ :
printed circuit:boards and the like is a well known process. Electrole~s copper plating baths contain a sourc~:o~ cupric ions, generally coppex sulfate, together with a reducing agent such ae formaldehyde, a complexing agent for the cupric ion o~ which ethylenediamine tetra acetic acid (EDTA) ie typical, sodium hydroxide to :con~rol pH, and various additives such as surfactant~ and stabilizing agents. ~ sta~ilizing agent which is common-20 ly used is a ~ource o~ cyanide ions such as sodiumcyanide.
Underkofler et al U.S. Patent 3,844,799 teach that, by maintaining the cyanide ion concentration of an electroles~ copper pla~ing bath between 0.0002 and 0.0004 molar, and at the same time maintaining the temperature of th~ bath between 70C. and 80C., it is poéeible j, 2 ~

to improve the propertie~ of the depo~ited copper layer.
The range of concentration of cyanide ion called for by this teaching is sufficiently broad to permit variations of up to 100 percent.
No details are given in the above patent as to how the concentration of cyanide ions was monitored in order to make additions to keep the concentration in the required range. A common method of analysis for cyanide ions employs a cyanide ion specific electrode and measure~ the rate at which silver metal is removed from a membrane in contact with the solution containing the cyanide ion. The accuracy of this method is affected by the presence of ions which may be present in the bath as additives or impurities. ~or example, the presence of ions such as sulfide, halide, thiocyanate or any ion which form~ an insoluble complex with silver, can cause significant interference with an accurate determination of the actual cyanide concentration, particularly where the latter is at a level as low as 0.0002 molar. Other method~ of analysis include ion chromatography, polarog-raphy, colorimetric, kjeldahl, and amperometric titra-tion. In general these methods lack the required accuracy andior are slow, i.e. re~quire significant time to carry out thereby causing significant delay in correct-ing a deficiency of cyanide ion in the bath.
This invention is ba~ed on the finding that if thep~, cupric ion and reducing agent concentration~ are maintained at constant levels in accordance with norm~l practice in the art, the rate at which the cyanide ion is consumed is directly related to the temperature at which the ba~h is maintained. The ra~e o~ consumption may be di~ferent in baths having different ~ompo~itions, but, in the case of any given bath wherein the above named para-meter~ are maintained con~tant, the rate of cyanide ion consumption at a given temperature is directly related to said temperature and is reproducible, i~e. the rate at a _3_ 2~52~1 given temperature sho~s ~ub~tantially the same pattern in all haths which have the same chemical compo~ition.
Accordingly, on the basis of the foregoing find-ings, for a given bath at a given temperature it is possible to predict how much cyanide ion m~st be added to the bath at any given elapsed time in order to restore the cyanide ion concentration in the bath to the initial desired level. Therefore, once the relationship of rate of cyanide ion consumption at a chosen bath temperature has been determined, it becomes unnecessary to do routine cyanide analysis of that bath, or any other bath of the same chemical composi~ion, during the operating life of the bath in order to determine how much cyanide ion must be added at any giYen time to maintain a desired cyanide ion concentration.
Based on the above findings r it has become possible in accordance with the invention to develop a sys~em in which the cyanide ion concentration in an electroless copper plating bath can be maintained substan-tlally constant over a prolonged working period withoutrecourse to repeated analysis for cyanide ion in the bath. In consequence, significant variation in cyanide ion content, which has been a feature of prior sy~tems due to the time cequired for analysi of ali~uots and resulting delay in correcting the cyanide ion concentra-tion after a deficiency is determined, has been eliminated. Fuc~her, ag will be de~cribed in detail below, the above findings have made po6sible the develop-ment of an automated system to maintain the desired level of cyanid~ ion concentration in an electroless copper plating bathO
It has also been found that the copper layer depo~ited on a subatrate in an electroles~ plating bath operated in accordance with the in~ention exhibits markedly improved physical proper~ies compared to a copper layer deposited using the same bath but operated 2~Y~2~2 ~ ~

~ithout the benefit of the presen~ inventionO Likewi~e, : the stability and plating rate of the bath are far more - uniform leading to potentially longer bath life and a more consistent productO

SUMMARY OF T~E INVENTION
The invention, in its broadest aspect, comprises a : process for the electroless deposition of copper onto a substrate surface from an electroless copper depositing bath comprising cupric ions, a reducing agent, a complex-ing agent and a stabilizing agent comprising cyanide ions, which process comprises the step~ of:
(a) establi6hing, for fixed values of cupric ion concentration, reducing agent concentration, temperature and pH of the bath, a characteristic relationship between cyanide ion con~umption in the bath and elapsed time of operation of the bath;
~b~ substantially uniformly maintaining the bath at the fixed value of temperature ~c) sub~tantially uniformly maintaining the concentration of cupric ion, the concen~ration of reduc-ing agent and the pH of the bath at the fixed values thereo~; and ~d) adding to the bath over the course of copper depo~ition therefrom an amount of cyanide ion su~icient to æubstantially replace the cyanide ion consumed in the bath based on the characteristic relationship established in (a) above, the additions being carried out at time intervals'su~ficient to sub~tantially uniformly maintain ~.
the cyanide ion concentration in the bath at the predeter mined level over the cour e of copper depo~ition from the bath.
The invention, in a particular aspect, comprises a computer controlled sy~tem for carrying out ~he procesE
of the inventionl said system comprising in combination:

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an electroles~ copper plating bath compris~
ing cupric ions, a reducing agent, a complexing agent and a stabilizing agent comprising cyanide ions, said bath also comprising heat control means for adjusting the temperature thereof;
storage means containing cyanide ion feed-stock and pump means associated wi~h said storage mean~
for delivering cyanide ions via a feed line to said plating bath;
programmable computer means for monitoring the temperature of said plating bath at a predetermined level and for controlling the addition of predetermined or calculated amounts of cyanide ion at predetermined intervals, said computer means including:
(a) means for producing base reference signals characteristic of a predetermined bath temperature:
(b) sensing means for producing signals characteristic of the tempera~ure of said bath, comparator means producing signals responsive to a difference between ~aid signals so produced and said base reference signalE~, and means sensitiva to said comparator response to cause said heat control means in said bath to make corrective adiustment to the temperature of said bath; and (c) means for producing at predetermined time intervals signals characteristic of predeter-mined or calculated amounts of cyanide feedstock to be added to said bath at said predetermined time intervals and means sen~itive to said signals to activ~te said pump means to deliver each of said predetermined or calculated amounts at each of said inter~als.
The invention also comprises a method of electro-le~ deposition of copper on a substrate using the above recited process and system and the improved stability and ~ ' :

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rate uniformity of the bath and properties of the copper layer so deposited.

; BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 show~ a plot of loss of cyanide ion versus temperature of a typical electroless copper plating bath.
FIGURE 2 shows a schematic rendering of a typical computerized control system in accordance with the inven-tion~
FIGURE 3 show~ in schematic form a breakdown of the components of the computer means shown in FIG~R~ 2.

DETAILED DESCRIPTION OF T~E INVENTION :
The cyanide ion CN- ha~ an exceptional ability to complex and sequester monovalent copper, so much so that it can even strip a chelating agent such as ~DTA
from a monovalent copper-EDTA complex. The resultant cuprous cyanide (CuCN) has such s'cability that it behaves as an inert 6ubstance in the plating bath. The cyanide ion reacts with monovalent copper so ~a~t that it will 20 often prevent other deR~abilizing reactions from occur-: ring in an electroles~ copper plating bath. However, the cyanide ion will also react with divalent copper in any one of a number o~ ways which result in consumptiorl of cyanide ion but do not csntribute to stabilizing of the plating bath. The following are typical of these unde~ir-able reactions with divalent copper, the cyanide being u~ed in the form of potas~ium cyanide for purpo~es of illu~;tration .

CuCN + 2 KCN~ ~ Cu(CN~3= + 2R+
CutCN)3= + KCN~ ~ Cu~CN)4= + K+
Cu++ ~ 2 KCN ~Cu~CN)2 + 2 K+
2 Cu(CN)2 - ~ 2 CuCN ~ 2 CN-3 Cu(CN)2 ---~ CuCN.Cu(CN)2 + 3 CN-~; :
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, ~7~ 2~2931 The above reactions and other related ones are the primary cau~e of consumption of cyanide in the electro-lesfi plating bathO The ra~e of consumption is related to the concentration of monovalent and divalent copper, the concentration of cyanide ion, the p~ of the bath, the reducing agent (formaldehyde) concentration. and the bath temperature. If the concentration of copper ion~ and reducing agent and the p~ of the bath are each maintained at a constant level during the operating life of the bath as is the normal practice commercially, the rate of con~umption is dependent only on the concentration of cyanide ion and the temperature of the bath. A~ set forth above, it ha~ been found that, or a bath having a given compo~ition, ther~ is a direct relation between rate o~ consumption and the tempera~ure of the bath.
Figure 1 shows a plot of lo~s of cyanide ion in one hour versu~ bath temperature for a typical electro-le~ plating bath having ~he following composition.
Part~ bv We iaht 2Q . cupric chloride5O25 -formaldehyde 2.40 EDTA 20.00 s~dium cyanide0.0017 sodium hydroxideS.00 ~urfactant 0,10 water to make 1000.00 The analyses for cyanide con~ent o~ the bath at the variou~ time~ and temperature8 were carried out ulng ion specific eleGtrode~ and by acidi~ication of aliquot~
followed by ~team di~tillation of hydrogen cyanide.
collection of the distillate in 8tandard alkali ~olutlon and back-titration with 6tandard acid to determine the amount of hydrogen cyanide 60 liberated.

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As noted previou~ly, the curve sho~n in Figure 1 is unique to a bath having the particular composition shown above and is consistently shown by all baths having that particular compo~ition. A similar but different plot will be obtained from a bath having a different composition.
Based on the data shown in Figure 1, a mathemati-cal e~uation is derived from which loss of cyanide ion at given in~ervals of time can be calculated for any particular temperature of the bath from which the data shown in the Figure wafi derived. This mathematical equation is then used a~ the ba~is for determining the amount and frequency with which cyanide ion mu~t be added ~ :`
to the bath in order to sub~tantially maintain the cyanide ion concentration at a predetermined level without the need to do any further analysis of ali~uots of the ~ath in order to control the level of cyanide ion.
The addition of the cyanide ion at the requisite intervals of time in accordance with the inventi~n can be carried out manually. Ho~ever, in a particular and ~referred embodiment, the required additions are carried out automa~ically using a computer controlled sy~tem.
Reference i8 made to Figure 2 which showfi in schematic form a control ~ystem in accordance with the invention. Electroless copper plating bath (2) is pro~ided with temperatare con~roller t~)~ temperature sensor probe6 (6) and (8), and a ~eed line (10) through which cyanide ion feedgtock can be delivered from ~torage vessel ~12) when pump ~14) is activated. The temperature oP bath ~2) i8 maintained at a predetermined level by a heater control system shown overall as (18). The various components of the computer sy~tem (16) are illustrated schematically in Figure 3 as will be discussed further hereinafter. The control of bath temperature is effected a~ follow~. At predetermined intervals signals character-istic of the temperature of the bath ~2) are fed by ,, , sensor (6) to the heater control wherein a comparator means compares tbe signals so received to ba~e reference signals characteristic of the predetermined temperature at which it is desired to maintain bath (2). If a difference between the siynal~ received from ~ensor (Ç) and the base reference signal6 is detected by the oomparator, the latter generate~ signals characteristic of the necessary adjustment to be made. These corrective signals are u~ed by the heater control sy~tem (18) which activates temperature control means (4) to allow the necessary correction to be made to the bath temperature, either up or down aR the case may be. Temperature sensor (8) produces signalæ characteristic of the bath tempera-ture and the~e signals are used to monitor the heater control sy~tem (18) or proper operation. The above described process of monitoring the temperature of the bath is carried out continuously at very short intervals, generally of about one ~econd, although the frequency of monitoring can vary over a wi~e range and is not critical to ~uccessful operation of the sy~tem.
In addition to monitoring the temperature of the bath, the computer system (16) is also programmed to make additions of cyanide ion at predetermined intervals of time based on the mathematical re:Lationship between the loæs of cyanide ion versus time for the operating life of the particular bath at the operat:ing temperature which is b~ing employed and monitored as described above. Timer means incorporated in the computer sys~em cauEes signal~
- to be generated at predetermined periods of time which signals are characteri#tic of the particular amount of cyanide ion which i~ to be added at any particular period of time. The signals 50 generated are fed to sensor mean~ associated with pump ~14) to cause said pump to be activated for a length of time sufficient to deliver the predetermined or calculated amount of cyanide ion to bath ~2) via feed line (10~. Fluid ~low sensor means (20) -lo~ 2 9 ~ ~

located in the feed line (lO) between pump (14) and bath ~2) is activated by movement of fluid in the feed line and generates signals which are fed to the computer (16) and serve to confirm that pump (14) is delivering cyanide ion feedstock when activated. The frequency with which the additions of predetermined or calculated amounts of cyanide ion are made can vary over a wide range. Advanta- -geously, the additions are programmed to be made at inter-vals of the order of o.nl to 120 minutes and preferably of the order of about 1 minute to about 60 minutes.
Advantageou~ly, the temperature at which the bath (2~ is maintained con~tant in accordance with the invention is in the ranye of about 25C~ to about 75C. and, preferably, is within the ran~e of about 30C. to about 60C. However, the bath temperature employed in the process o~ the invention is not critical and the above range~ are given for purpo~es of illustra~
tion only. The optimum temperature in any giYen in~tance can be determined by a proces~ o~ trial and error.
The level of concentration at which the cyanide ion ~present typically in the form of the pota~sium or ~odium salt) i8 maintained i8 advantageously in th~ ranye of about 0.1 to about lO0 ppm and, preferably, in the range of about 0.5 to about 50 ppm~ However, the~e concentration ranges are given for purposes of illustra-tion only and are not limiting and the process of the invention can be carried out with concentrations above or below these ranges.
The system of the invention ha~ an additional advantageou~ feature which centers around the significant and unexpecte~ finding that the rate o~ lo~ of cyanide ion i~ directly proportional to the actual concentration of cyanide ion, i.e. the greater the concentration the greater the rate of consumption. If the amount of cyanide ion added at a given time is greater or les~ than the amount actually needed at that par~icular time to .
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maintain the de~ired level, the error i~ quickly correct-ed because of the above factor. Thus, if the amount added is in exces~ of that required, the increased level of cyanide causes the rate of consumption to increa~e accordingly and thereby quickly overcome the error.
~onversely, if the amount added is less than actually required, the rate of consumption is lower than that at the higher desired level of cyanide ion and the error is again quickly corrected. This self-correcting effect is ; 10 an added and unexpected advantage in terms of the overall control achie~ed by the system of the present invention.
Figure 3 shows in schematic form a breakdown of the various components o~ the computer system shown overall as 116) in Figure 2, the functioning of which ~ystem has been discussed above. As shown in Figure 3, microproceæsor (22) serves to receive, proces~ and transmit appropriate 6ignals characteristic of a variety of functions. Timer means ~24) provide~ ~ignals to micro-processor ~22) at preset intervals which ~ignals are characteristic o~ the times at which one or other func-tion of the system is to be activated. The R~M/ROM
component ~26) contains the so~tware for operation of the system. The temperature monitoring component i8 prefer~
ably a cold junction compen~ated analog/digital convert-ing temperature control system with track and holdfeatures WhiCh receives signals from the temperature sensor ~8) lsee Figure 2~, converts these si~nals from analog to digital mode, ~ran6mits the same to micro-pro~e6sor (22~ for calculation o$ a temperature databa~e u~d to determine cyanide confiumption. ~he~e signals are also compared with base reference signal~ characteristic of the desired temperature leYel ~nd moni~ors the proper operation of the heater control system (18)~
Computer (22~ also generates signals, at predeter-mined time intervals which are transmitted to pump control component (30), which signals are cha~acteristic -12- 20~29 ~

of the time component for which pump (14) mu~t be activated to deliver ~he amount of cyanide ion from storage vessel (12~ to bath (2) which amount has been predetermined as required by the bath at the time in gue6tion to maintain the desired cyanide level in the bath. The component (30) is provided with the necessary logic to transmit the appropriate signal to the operating mechanism of the pump.
Unit (32) of the sys$em comprises a standard terminal keyboard for accessing the system and video display monitor to permit an operator to set up a program for the overall sys~em, to make any necessary changes to additions thereto and to monitor actual operating parame-ters of the system during operation thereof. In an al~ernative embodiment the overall system is entirely preprogrammed and need only respond to alarm conditions such as purnp failur2, heater failure, empty feedstock reser~oir, and the like.
The electronic components necessary to carry out the various ~unctions described above in re~pect of the s~stems shown and discu ed in regard to Figure~ 2 and 3 ~are well known and commercially available. A detailed discus6ion of the circuit~ involved in producing the afore~aid functions i8 accordingly omitted. Illustrative of commercially available components which can be employed in the computer ~y~tem dlescribed above are shown below. It is to be noted that the~e are given for purpo6es of exempllfication and the invention is not limited to the use o~ the~ particular pieces of equip-ment either individually or in combination.
Illustrative of commercially available timer units is that available under the name DIGI-TIMER from SSAC
Inc. Represen~ative of microprocessor units is the mch 18 available from Wintek Corporation and for the ROM/RAM
component the mcm 2814p and mcm 6206p units available from Motorola Semiconductors. A ~ypical display unit i~

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that available from Digital Equipment Corporation under the name VT 420 and a typical terminal keyboard is the RS232tRS423 COM-PAC available from Grayhill Inc. Repre-sentative of temperature control system components is the unit available from Protec Inc. as model dl5d, and repre-sentative of pump control system components is the unit available from Crydom Company as a series 6 module.
Programmable computer controlled means for monitor-ing and adjusting the levels of copper ion, formaldehyde, pH and other parameters of an electroless copper plating bath are already known and commonly used in the art and will not be described in detail herein. Such computer means generally include means for producing base refer-ence signals characteristic of a predetermined level of the parameters to be monitored, sensing means for produc-ing signals characteristic of the actual levels of each parameter in the plating bath, comparator means producing signals responsive to any difference between the signals so produced and the base reference signals, and means sensitive to said comparative response to indicate the need for any necessary adjustment to the actual levels of the various parameters in the bath. Such means may be incorporated into the system of the invention if desired or may be maintained separate therefrom.
The control process of the invention, when employed in the electroless deposition of copper on a substrate such as those employed in the manufacture of printed circuit board, gives ~ise to a deposited copper layer which has siynificantly improved properties compared with layers deposited by prior methods.
Illustratively, two identical substrates comprising epoxy fiberglass reinforced sheets having copper foil laminated on one side thereof were subjected to electroless copper plating. In the case of both substrates, the coating was carried out using a bath having the following-composition:

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2~2~1 Parts by Weight copper sulfate pentahydrate 9.83 formaldehyde 1~90 EDTA 20.00 : 5 sodium cyanide 0.002 60dium hydroxide 2.B0 surfactant 0.10 additive~ 0~02 water ~o make 1000.00 The bath was maintained at 60C. In the case of one substrate (A) the deposition was carried out u~ing a ~: computer control system of the invention. A layer of : thickness 1.0 mil. was depo~ited. In the ca~e of the other sub~rate (B~ the depo~ition to the same thickness : 15 was carried out without benefit of a control sy~tem of : - the invention and the cyanide level was maintained in the conventional manner with the cyanide in the caus$ic soda component wbich was added to the bath a~ required.
Plating times were o the order of 16 hour~ in both cases. The following proper~ie~ were then determined ~or the copper layer on each ~ubstrate after removal of the reinforcing layer by dissolution in concentrated sulfuric acid.
Ly Substrate A B
Ten~ile ~trength 51~000 psi 39,000 psi % elongation 10 7 : It;i~ to be understood that ~he above description ana exemplification ha~ been given for purpo~es of illu~tration only and i8 not to be con~idered a~ limit- -ing. Variou~ modifications wh.ich will be readily apparent to one skilled in the art can be made without departing from the ~cope o ~he inven~ion which latter i~
defined only by the claim~ which follow.
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Claims (7)

1. In a process for the electroless deposition of copper onto a substrate surface from an electroless copper depositing bath comprising cupric ions, a reducing agent, a complexing agent and a stabilizing agent compris-ing cyanide ion, the improvement wherein the concentra-tion of cyanide ion in said bath is substantially uniformly maintained at a predetermined level over the course of copper deposition from said bath, by a process comprising:
(a) establishing, for fixed values of cupric ion concentration, reducing agent concentration and pH of said bath, a characteristic relationship between cyanide ion consumption in said bath and time for a fixed bath temperature;
(b) substantially uniformly maintaining the temperature of said bath at the said fixed temperature (c) substantially uniformly maintaining the cupric ion concentration, reducing agent concentration and pH of said bath at the said fixed values thereof; and (d) adding to said bath over the course of copper deposition therefrom an amount of cyanide ion sufficient to substantially replace the cyanide ion consumed in said bath according to the characteristic relationship established in (a), said adding being carried out at time intervals sufficient to substantially uniformly maintain the cyanide ion concentration in said bath at said predetermined level over the course of copper deposition therefrom.

2. A system for maintaining a predetermined level of cyanide ion stabilizer in an electroless copper plating bath at a constant temperature said system comprising in combination:

an electroless copper plating bath compris-ing cupric ions, a reducing agent, a complexing agent and a stabilizing agent comprising cyanide ions, said bath also comprising heat control means for adjusting the temperature thereof;
storage means containing cyanide ion feedstock and pump means associated with said storage means for delivering cyanide solution via a feed line to said plating bath programmable computer means for monitoring the temperature of said plating bath and for controlling the addition of predetermined amounts of cyanide ions at predetermined or calculated intervals, said computer means including (a) means for producing base reference signals characteristic of a predetermined bath temperature;
(b) sensing means for producing signals characteristic of the temperature of said bath;
and (c) means for producing at predetermined time intervals signals characteristic of predeter-mined or calculated amounts of cyanide ion feedstock to be added to said bath at said predetermined time intervals and means sensitive to said signals to activate said pump means to deliver each of said predetermined or calculated amounts at each of said predetermined intervals.

3. A system according to Claim 2 which also comprises flow sensor means located in said feed line between said pump means and said plating tank said flow means generat-ing signals characteristic of rate of flow of cyanide ion feedstock in said feed line.

4. A system according to Claim 2 wherein the amount of cyanide ion feedstock added at any given time interval is the amount predetermined or calculated to be necessary at that particular time interval to restore the cyanide ion concentration in said bath to the level initially present therein.

5. A system according to Claim 2 which also comprises programmable computer means to monitor and adjust the pH
and concentrations of cupric ions and formaldehyde in said plating bath, said computer means including means for producing base reference signals characteristic of a predetermined level each of the aforesaid parameters, sensing means for producing signals characteristic of the actual levels of said parameters in said plating bath, comparator means producing signals responsive to any difference between said signals so produced and said base reference signals and means sensitive to said comparative response to indicate the need for any necessary adjust-ment to the actual levels of said parameters in said bath.

6. An improved process for the electroless deposition of copper which process comprises maintaining a predeter-mined level of cyanide ion at a constant predetermined temperature in the electroless copper plating bath employed in said deposition, said system comprising in combination:
an electroless copper plating bath compris-ing cupric ions, a reducing agent, a complexing agent and a stabilizing agent comprising cyanide ions, said bath also comprising heat control means for adjusting the temperature thereof;
storage means containing cyanide ion feed-stock and pump means associated with said storage means for delivering cyanide solution via a feed line to said plating bath programmable computer means for monitoring the temperature of said plating bath, said tempera-ture being held at a predetermined level and for controlling the addition of predetermined or calculated amounts of cyanide ions at predetermined intervals, said computer means including (a) means for producing base reference signals characteristic of a predetermined bath temperature;
(b) sensing means for producing signals characteristic of the temperature of said bath;
and (c) means for producing at predetermined time intervals signals characteristic of predeter-mined or calculated amounts of cyanide ion feed-stock to be added to said bath at said predeter-mined time intervals and means sensitive to said signals to activate said pump means to deliver each of said predetermined or caculated amounts at each of said predetermined intervals.

7. A substrate electrolessly coated with a layer of copper using the process of Claim 6.