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Passivation of Lead Indium Solder Pads

IP.com Disclosure Number: IPCOM000089550D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

DiGiacomo, G: AUTHOR

Abstract

Lead-indium solder pads can be protected from organic acids (such as acetic acid) and from attack by water, which forms indium hydroxide (In(OH)(3)), by forming a layer of indium oxide (In(2)O(3)) on the surface of a solder pad. The oxide film is between 100 and 500 angstroms thick. The oxide film can be formed by exposing the solder pad to an oxygen atmosphere for 30 minutes at about 150 Degrees C.

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Passivation of Lead Indium Solder Pads

Lead-indium solder pads can be protected from organic acids (such as acetic acid) and from attack by water, which forms indium hydroxide (In(OH)(3)), by forming a layer of indium oxide (In(2)O(3)) on the surface of a solder pad. The oxide film is between 100 and 500 angstroms thick. The oxide film can be formed by exposing the solder pad to an oxygen atmosphere for 30 minutes at about 150 Degrees C.

When the solder has at least 25% indium, the indium oxidizes preferentially, and the lead is left unoxidized. The indium atoms diffuse through the lead-indium alloy to reach the surface of the pad and to react with oxygen. As the oxygen film forms, the site of the reaction is the oxide interface with the lead-indium alloy. The rate of diffusion of oxygen through the oxide layer controls the rate of the reaction. If the indium concentration is below 25%, lead participates in the surface oxidation process and becomes a minor component of the surface oxide.

The indium oxide film protects the underlying indium from attack by water, which forms indium hydroxide. A film as thin as 30 angstroms provides this protection. The thicker film protects the solder pad also from other corrosive species, such as C1/-/ and F/-/.

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