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Pb-In Solder Coating for Radial Finger Conduction Springs to Improve Thermal Contact and Prevent Degradation

IP.com Disclosure Number: IPCOM000044698D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

DiGiacomo, G: AUTHOR [+2]

Abstract

The use of a Pb-In solder alleviates problems due to oxide formation when attaching radial conduction springs to a substrate.

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Pb-In Solder Coating for Radial Finger Conduction Springs to Improve Thermal Contact and Prevent Degradation

The use of a Pb-In solder alleviates problems due to oxide formation when attaching radial conduction springs to a substrate.

Pb-60Sb is used to coat radial finger conduction springs to provide a large enough contact area between the chip and the spring, and the spring and ceramic cap. The large contact area is achieved as a result of solder melting during the cap brazing process (220OEC). The solder, however, forms a thick film of non-conductive oxides (for example, SnO and SnO2) with time so that the contact resistance increases to the point that it significantly impairs the thermal properties of the spring and its ability to function efficiently.

The problem can be solved by replacing the Pb-Sn alloy with Pb-In solder (In is allowed to vary between 30 and 40%) which covers a liquidus range of 170OE to 190OEC, falling around the Pb-60Sn liquidus of about 185OEC, and forms indium oxides and/or hydroxides having reasonably good thermal properties. No Pb oxide is formed in the process because it is thermodynamically unfavorable.

Even when the indium content is 5%, the indium oxide covers about 60% of the surface, and takes only about 10% indium to virtually cover the allow surface totally. The indium diffuses to the surface where it is oxidized (reaction sink). As a result, a Sn concentration graidient toward the surface is established which promotes the di...