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Copper Enhanced Solder Paste

IP.com Disclosure Number: IPCOM000037616D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Graham, AE: AUTHOR [+3]

Abstract

A process is given in which copper balls are added to lead / tin solder paste to increase electrical conductivity. Copper has substantial better (101% IACS vs. 11.9% IACS* for eutectic lead / tin solders) electrical conductivity than lead / tin solders and a network of copper in lead / tin solder will enhance the electrical conductivity of the metal system.

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Copper Enhanced Solder Paste

A process is given in which copper balls are added to lead / tin solder paste to increase electrical conductivity. Copper has substantial better (101% IACS vs.
11.9% IACS* for eutectic lead / tin solders) electrical conductivity than lead / tin solders and a network of copper in lead / tin solder will enhance the electrical conductivity of the metal system.

The copper is added to the solder paste and stirred to a uniform mixture results. The copper balls are of similar size and diameter of the lead / tin balls and are fully screen or stencilable. Reflow in the standard vapor phase furnace results in micro-alloying of the outer diameter of the copper balls with lead / tin yielding a ternary alloy of lead / tin / copper. This alloy is mainly a solid solution of lead, tin and copper. No deleterious intermetallic compounds are formed.

The copper balls may be tin coated prior to processing via Immersion Tinning . The following property enhancements result: 1. Initiate contact of individually tinned copper particles insures high electrically conductive continuums in composites (e.g. PTF) / toned adhesive circuit patterns. 2. The oxidation of individually tinned copper particles
(i.e., 3 um) is precluded.

3. The tinned continuum promotes subsequent soldering operations.

A network of copper in the lead / tin solder paste is formed after reflow as shown in the Figure. * International Annealed Copper Standard

Disclosed anonymously.

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