Pulse plating process for deposition of gold-tin alloy

a technology of gold-tin alloy and pulse plating, which is applied in the field of pulse plating process for deposition of gold-tin alloy, can solve the problems of many prior art baths, inability to deposit eutectic alloys, and inability to achieve eutectic alloys

Inactive Publication Date: 2006-07-27
TECHNIC INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0021] This method is preferably used for electroplating a gold-tin alloy deposit on composite articles that include electroplatable and non-electroplatable portions in order t

Problems solved by technology

Prior art electroplating baths for the deposition of gold-tin alloy have been found by the current inventor to be incapable of depositing the eutectic alloy over a usable current density range.
This has been further confirmed by our work which has shown that prior art electrolytes will not typically yield the desired eutectic alloy.
Moreover, many prior art baths suffer from poor stability making them of little practical interest.
However, this bath gives deposits with less than 1% S

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0046] A eutectic gold-tin alloy electrodeposit is obtained from the following solution and under the following electroplating conditions.

Oxalic Acid70g / lTin (as tin sulfate)3g / lGold (as potassium gold cyanide)6g / lPolyethylene Imine (1200 MW)4ml / l 10% solutionCatechol1g / lpH adjusted with KOH4

[0047] The above electrolyte will deposit a matte to semibright 80-20 wt % gold-tin alloy at current densities up to 10 ASF at temperatures between 105° F (40.5° C.) and 120° F. (48.8° C.).

example 2

[0048] A eutectic gold-tin alloy electrodeposit is obtained from the following solution and under the following electroplating conditions.

Citric Acid100g / lTin (as tin sulfate)3g / lGold (as potassium gold cyanide)6g / lPolyethylene Imine (1200 MW)4ml / l 10% solutionCatechol1g / lpH adjusted with KOH4

[0049] The above electrolyte will deposit a matte to semibright 80-20 wt % gold-tin alloy at current densities up to about 10 ASF at temperatures between 100° F. (37.7° C.) to 120° F. (48.8° C.).

example 3

[0050] A eutectic gold-tin alloy electrodeposit is obtained from the following solution and under the following electroplating conditions.

Gluconic Acid70g / lTin (as tin sulfate)5g / lGold (as potassium gold cyanide)5g / lPolyethylene Imine (1200 MW)4ml / l 10% solutionCatechol1g / lpH adjusted with KOH4

[0051] The above electrolyte will deposit a matte to semibright 80-20 wt % gold-tin alloy at current densities up to 10 ASF at temperatures between 105° F. (40.5° C.) and 130° F. (54.4° C.).

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Abstract

The invention relates to a solution for use in connection with the deposition of a gold-tin alloy on an electroplatable substrate. This solution generally includes water, stannous tin ions, a complexing agent to render the stannous tin ions soluble, complexed gold ions, and an alloy stabilization agent that includes an imine functional group. The alloy stabilization agent is present in an amount sufficient to stabilize the composition of the gold-tin deposit over a usable current density range. The solution has a pH of between about 2 and about 10 and the deposit having a gold content less than about 90% by weight and a tin content greater than about 10% by weight. An advantageous way for providing the desired deposit is by a pulse plating technique.

Description

[0001] This application claims the benefit of provisional application 60 / 645,949 filed Jan. 21, 2005, the entire content of which is expressly incorporated herein by reference thereto.BACKGROUND OF THE INVENTION [0002] Gold-tin alloys are useful in many microelectronic applications including chip bonding and wafer bump plating. The 80-20 wt % (70-30 at %) gold-tin eutectic alloy is particularly desirable as a solder. The alloy may be applied by vacuum deposition or as a solid preform, however, electrodeposition, due to its low cost, is a preferred method of application. [0003] Prior art electroplating baths for the deposition of gold-tin alloy have been found by the current inventor to be incapable of depositing the eutectic alloy over a usable current density range. This was clearly demonstrated in “Film growth characterization of pulse electro deposited Au / Sn tin films” by Djurfors and Ivey (GaAs MANTECH, 2001), where in FIG. 1 they show a step transition from 16 at % Sn to 50 at ...

Claims

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Application Information

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IPC IPC(8): C25D3/62C25D5/18C25D3/60
CPCC25D3/60C25D3/62C25D5/18C25D5/617C25D5/627
Inventor HAYWARD, FRED C.
Owner TECHNIC INC
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