# US 2013/0153646 A1 · Method for suppressing kirkendall voids formation at the interface between solder and copper pad

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- Number: US 2013/0153646 A1
- Document ID: US20130153646A1
- Status: Published application
- Kind: A1
- Application number: 13/442,865
- Filed: 2012-04-10
- Published: 2013-06-20
- Earliest claimed: 2011-12-14
- Assignees: Yuan Ze University
- Inventors: Cheng-En Ho
- Web page: https://patentgrep.com/patent/US20130153646A1

## CPC

- B23K 1/203: {Fluxing, i.e. applying flux onto surfaces}
- B23K 1/0016: {Soldering of electronic components}
- B23K 35/0222: {for use in soldering or brazing (B23K35/0205 takes precedence)}
- B23K 35/302: {Cu as the principal constituent}
- B23K 35/34: comprising compounds which yield metals when heated
- B23K 2101/42: Printed circuits
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM

## Abstract

The embodiment of the present invention relates to a method for suppressing Kirkendall voids formation in a solder joint. A solder alloy doped with 0.1˜0.7 weight percent (wt. %) of palladium (Pd) is utilized. Before soldering, the solder alloy is disposed on a copper (Cu) pad, possibly treated with a surface finish. Subsequently, the solder alloy is joined with the Cu pad, so as to form the solder joint with a Cu/Cu3Sn/(Cu,Pd)6Sn5/solder structure. The formation of Kirkendall voids at the Cu/Cu3Sn interface is greatly suppressed in the presence of Pd in the solder. As the amount of Pd doped is minimal, the properties and the processing conditions for soldering are not changed to a large extent, and the mechanical reliability of the solder joint is significantly improved. Therefore, the present invention is suitable for the microelectronic packaging applications.

## Claims

### Claim 1

A method for suppressing Kirkendall voids formation at the interface between a solder and a copper (Cu) pad, comprising:
doping the solder with an amount of palladium (Pd) ranging from 0.1 wt. % to 0.3 wt. % of the total weight of the solder; and
joining the palladium-containing solder to the copper pad, so as to form a solder joint that can suppress the formation of Kirkendall voids at the interface between the solder and the copper pad, wherein the solder joint possesses a structure of Cu/Cu3Sn/(Cu,Pd)6Sn5/solder, and the Kirkendall voids primarily form at the Cu/Cu3Sn interface.

### Claim 2

(canceled)

### Claim 3 (depends on 1)

The method according to claim 1, wherein the material of the solder comprises tin, tin-bismuth alloy, tin-lead alloy, tin-copper alloy, tin-silver alloy, tin-silver-copper alloy, or any combination thereof.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the material of the copper pad includes copper or copper-nickel alloy.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the copper pad includes a copper substrate and a surface finish disposed on the surface of the copper substrate.

### Claim 6 (depends on 1)

The method according to claim 1, wherein the surface finish comprises an organic solderability preservative (OSP) film.