CN102642097A

CN102642097A - Low-silver lead-free solder alloy

Info

Publication number: CN102642097A
Application number: CN2012101018963A
Authority: CN
Inventors: 卫国强; 肖德成
Original assignee: SHENZHEN TONGFANG ELECTRONIC NEW MATERIAL CO Ltd; South China University of Technology SCUT
Current assignee: SHENZHEN TONGFANG ELECTRONIC NEW MATERIAL CO Ltd; South China University of Technology SCUT
Priority date: 2012-04-09
Filing date: 2012-04-09
Publication date: 2012-08-22

Abstract

The invention discloses a low-silver lead-free solder alloy, which comprises the following components in percentage by mass: 0.5-0.8% of Ag, 0.5-0.7% of Cu, 1.5-2.5% of Bi, 0.05-0.5% of Dy, 0.04-0.08% of Ni, and the balance being Sn. The solder alloy provided by the invention has the following advantages that: 1) without changing a brazing process and increasing the activity of a soldering flux, the soldering joint quality similar to that of eutectic and near-eutectic Sn-Ag-Cu lead-free solder can be obtained; 2) without changing the melting temperature, by adjusting the ratio of Bi to Dy, solder alloys with different mechanical properties can be obtained so as to meet the needs of different service conditions of soldering joints; 3) through the addition of a trace of Ni, the growth rate of a soldering joint interface intermetallic compound and the dissolution rate of a substrate Cu can be reduced and the service reliability of the soldering joints is improved; and 4) the material cost is greatly reduced by greatly reducing the Ag content.

Description

A kind of low silver leadless solder alloy

Technical field

The present invention relates to technical field of electronic encapsulation, specifically be meant a kind of low silver leadless solder alloy that is used for Electronic Packaging.

Background technology

Along with the enforcement of RoHS of European Union and WEEE instruction, electronic product is unleaded to be globalization tendency.In the process of seeking Sn-Pb solder substitute; Sn-(3.0-4.0) Ag-(0.5-0.9) Cu eutectic and nearly eutectic lead-free brazing be owing to have lower fusion temperature (Tm=217 ℃), good soldering processes performance and good comprehensive mechanical property, therefore currently is used widely in electron trade.

But a large amount of research and production practices show that high Ag content will cause the alligatoring of eutectic structure in the process of setting in eutectic and nearly eutectic Sn-Ag-Cu lead-free brazing, particularly in slow cooling process in addition the first precipitated phase Ag3Sn that has a lath-shaped occur.Thick like this intermetallic compound reduces the mechanical property of solder joint, particularly shock resistance strongly.In addition, Ag belongs to noble metal, because the rare price that causes of resource constantly rises, has increased the material cost of lead-free brazing.

Present stage is the manufacturing cost and the shock proof ability of raising solder joint of reduction Sn-(3.0-4.0) Ag-(0.5-0.9) Cu eutectic and nearly eutectic lead-free brazing, and the Sn-0.3Ag-0.7Cu lead-free brazing has obtained the application of certain limit.But because the reduction greatly of Ag content causes the increase of solder fusion temperature, thereby brazing temperature is also increased accordingly, bring the fire damage problem of wiring board, electronic devices and components and assembling chip.On the other hand, because the reduction of Ag content, eutectic structure reduces in the solder joint solidified structure, and the intensity index of solder joint also reduces, so the Sn-0.3Ag-0.7Cu lead-free brazing can only use under specific assembling condition and service condition.At last, since the reduction of Ag content, Sn-0.3Ag-0.7Cu lead-free brazing substantial deviation eutectic composition, under identical soldering condition, the wetability of solder reduces, and the product defects rate increases.

Summary of the invention

The multi-element alloyed low silver leadless solder alloy that the purpose of this invention is to provide a kind of instead eutectic and nearly eutectic Sn-Ag-Cu lead-free brazing.

The object of the invention is realized through following technical scheme:

A kind of low silver leadless solder alloy is made up of Sn, Ag, Cu, Bi, Dy and Ni.

Said each component is by mass percentage: Ag is 0.5-0.8%, Cu: be 0.5-0.7%, Bi is 1.5-2.5%, and Dy is 0.05-0.5%, and Ni is 0.04-0.08%, and surplus is Sn.

Preferably, said Ag is 0.8%, Cu: be 0.5%, Bi is 2.0%, and Dy is 0.05%, and Ni is 0.05%, and surplus is Sn.

Preferably, said Ag is 0.5%, Cu: be 0.7%, Bi is 1.5%, and Dy is 0.1%, and Ni is 0.05%, and surplus is Sn.

Preferably, said Ag is 0.8%, Cu: be 0.5%, Bi is 1.0%, and Dy is 0.4%, and Ni is 0.05%, and surplus is Sn.

Preferably, said Ag is 0.5%, Cu: be 0.7%, Bi is 2.5%, and Dy is 0.05%, and Ni is 0.05%, and surplus is Sn.

Preferably, said Ag is 0.5%, Cu: be 0.5%, Bi is 1.0%, and Dy is 0.5%, and Ni is 0.05%, and surplus is Sn.

Lead-free solder alloy of the present invention compared with prior art has following advantage:

1) has and eutectic and close fusion temperature, wetting and spreading performance and the solder joint presentation quality of nearly eutectic Sn-Ag-Cu lead-free brazing; Therefore not changing soldering processes and increasing under the condition of flux activity, can obtain and eutectic and the close quality of welding spot of nearly eutectic Sn-Ag-Cu lead-free brazing;

2) under the prerequisite that does not change fusion temperature, through the ratio of adjustment Bi and Dy, can get the brazing filler metal alloy of different mechanical properties, satisfy the needs of the different service conditions of solder joint;

3) through the adding of micro-Ni, can reduce the growth rate of welding point interface intermetallic compound, reduce the rate of dissolution of substrate Cu, improve the solder joint service reliability;

4) therefore this brazing filler metal alloy reduces material cost owing to greatly reduce Ag content greatly.

The principle that the effect of each component and content limit among the present invention is (content is all by percentage to the quality) as follows:

Ag:Ag and Sn, Cu can form ternary eutectic, and the Ag content range of ternary eutectic but because Ag costs an arm and a leg, causes the solder cost to increase between 3.5-4.0%; Secondly, high Ag content causes welding spot reliability to reduce.If Ag content is too low, will reduce the wettability of brazing filler metal alloy, result of the test shows, and is little to the wetability influence of solder when Ag content is higher than 0.8%, therefore is preferably 0.5-0.8%.

Cu:Cu is a basic alloys element of forming lead-free brazing.Interpolation Cu can reduce the fusion temperature of solder, can reduce the rate of dissolution of matrix Cu simultaneously.In addition, Cu can form Cu6Sn5 mutually with Sn in solder, improves brazing filler metal alloy intensity, but too high Cu causes the solder fusing point to raise, and is preferably 0.5-0.7%.

Bi:Bi and Sn can form eutectic, reduce the solder fusing point; Bi is the positive absorption element in Sn base solder, can improve the wetability of solder, improves the soldering processes performance.But the Bi too high levels will cause the increase of brazing filler metal alloy intensity, plasticity to reduce, and solder is become fragile, and be preferably 1.5-2.5%.

Dy:Dy and Sn can form eutectic, and eutectic temperature is 215 ℃, and eutectic phase is β-Sn+DySn4.Therefore in Sn base solder, add Dy, can reduce the fusing point of solder, can adjust the mechanical property of brazing filler metal alloy again through the content that changes Dy.But add Dy solder will be become fragile, fusing point increases.Therefore, be preferably 0.05-0.5%.

Ni: in Sn base solder, add Ni, can reduce the rate of dissolution of matrix Cu during soldering, when Ni content is lower than 0.08%, can reduce the growth rate of compound between interface metal simultaneously, improve welding spot reliability.On the other hand, the adding of Ni can make the solder joint surface-brightening fine and close, remedies Ag content and reduces the influence that brings.Be preferably 0.04-0.08%.

Low silver leadless solder alloy of the present invention can be applicable to the various electron package structures such as THT, SMT, BGA, Flip-Chip in Electronic Packaging field, can reduce material cost greatly, improves welding spot reliability.

The specific embodiment

Below in conjunction with specific embodiment the present invention is done further concrete detailed description the in detail.

Embodiment 1

A kind of low silver leadless solder alloy, by mass fraction, its prescription is Ag:0.80%, Cu:0.50%, Bi:2.00%, Ni:0.05%, Dy:0.05%, surplus is Sn.Its preparation technology is following:

1) used raw material are Sn-10Cu intermediate alloy, Sn-1.12%Ni intermediate alloy, Sn-1.0%Dy intermediate alloy, pure Sn (99.95%), Ag (99.95%), Bi (99.99%);

2) the one-tenth assignment system brazing filler metal alloy 5000g of according to the form below 1;

3) at first pure Sn is put into crucible, place the resistance furnace heat fused to crucible then, heating-up temperature is 350-400 ℃;

4) treat that Sn melts fully after, add intermediate alloy and Ag, stir;

5) add metal Bi at last, and stir, be incubated 1h then;

6) in punching block, cast, the processing method by conventional lead-free brazing is processed into a material, bar and powder then.

The difference of embodiment 2～5 and embodiment 1 only is the prescription of alloy, and concrete composition is referring to table 1.

Table 1 lead-free solder alloy chemical composition (wt%)

Table 2 embodiment, comparative example lead-free brazing wettability

Table 3 embodiment, other performance of comparative example

Claims

1. a low silver leadless solder alloy is characterized in that, is made up of Sn, Ag, Cu, Bi, Dy and Ni.

2. according to the said alloy of claim 1, it is characterized in that, each component by mass percentage: Ag is 0.5-0.8%, Cu: be 0.5-0.7%, Bi is 1.5-2.5%, and Dy is 0.05-0.5%, and Ni is 0.04-0.08%, and surplus is Sn.

3. alloy according to claim 2 is characterized in that, said Ag is 0.8%, Cu: be 0.5%, Bi is 2.0%, and Dy is 0.05%, and Ni is 0.05%, and surplus is Sn.

4. alloy according to claim 2 is characterized in that, said Ag is 0.5%, Cu: be 0.7%, Bi is 1.5%, and Dy is 0.1%, and Ni is 0.05%, and surplus is Sn.

5. alloy according to claim 2 is characterized in that, said Ag is 0.8%, Cu: be 0.5%, Bi is 1.0%, and Dy is 0.4%, and Ni is 0.05%, and surplus is Sn.

6. alloy according to claim 2 is characterized in that, said Ag is 0.5%, Cu: be 0.7%, Bi is 2.5%, and Dy is 0.05%, and Ni is 0.05%, and surplus is Sn.

7. alloy according to claim 2 is characterized in that, said Ag is 0.5%, Cu: be 0.5%, Bi is 1.0%, and Dy is 0.5%, and Ni is 0.05%, and surplus is Sn.