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Non-Corrosive, Water Soluble Flux for Flip Chip Soldering

IP.com Disclosure Number: IPCOM000050653D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Antoune, B: AUTHOR

Abstract

Flip-chip techniques are widely used for mounting semiconductor chips onto ceramic modules.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 91% of the total text.

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Non-Corrosive, Water Soluble Flux for Flip Chip Soldering

Flip-chip techniques are widely used for mounting semiconductor chips onto ceramic modules.

As generally practiced, the lead-tin solder balls are previously fluxed before the bonding takes place in a furnace.

There has been a real need in this industry for a non-corrosive, water-soluble flux, with the latter characteristic being particularly important because it permits important savings in equipment and solvant consumption.

A very popular flux consists of colophony dissolved in benzyl alcohol. However, if not corrosive, this flux is only solvent soluble. Colophony, a natural product, is mainly comprised of abietic acid and somers thereof. Up to now, these acids were believed to react with lead and tin oxides to provide undesired lead and/or tin abietates.

I have discovered that pure sodium abietate dissolved easily in alcohol and assured very good tin-lead ball joining. When heated (360 degrees C) in a nitrogen atmosphere, the abietate transforms in dehydroabietate; as a consequence, hydrogen atoms reduce the oxide, thus leading to pure lead-tin alloys, which are essential for good solder joints. On the other hand, pure sodium abietate and its reaction products are very water-soluble. The flux composition of sodium abietate (60% by weight) and isopropanol (40% by weight (+ 5%)) has demonstrated good manufacturing yields, although other alcohols and proportions are possible. Optimum temperature conditions...