Browse Prior Art Database

Method for Modified Solder Reflow Chip Joining

IP.com Disclosure Number: IPCOM000080776D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Dionne, E: AUTHOR [+4]

Abstract

The present method provides a modification in the conventional solder reflow chip joining of integrated circuit chips to substrates. Solder reflow chip joining involving the controlled collapse of a solder ball or pad is well known in the art and is described, for example, in U. S. Patent 3,392,442. The art has further recognized the need to limit the lateral flow of the solder pad being melted or reflowed during joining. U. S. Patent 3,495,133 describes a method for limiting the lateral flow of the melted pad during joining, by surrounding the pad with an area on the substrate which is nonwettable by the solder, e.g., glass dam. The present method takes an alternative approach.

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Method for Modified Solder Reflow Chip Joining

The present method provides a modification in the conventional solder reflow chip joining of integrated circuit chips to substrates. Solder reflow chip joining involving the controlled collapse of a solder ball or pad is well known in the art and is described, for example, in U. S. Patent 3,392,442. The art has further recognized the need to limit the lateral flow of the solder pad being melted or reflowed during joining. U. S. Patent 3,495,133 describes a method for limiting the lateral flow of the melted pad during joining, by surrounding the pad with an area on the substrate which is nonwettable by the solder, e.g., glass dam. The present method takes an alternative approach.

Instead of melting the entire solder ball or pad during reflow, the pad is coated with a eutectic lead-tin paste which initially melts at 185 degrees C. During joining the structure is heated to 220 degrees to 230 degrees C. At this temperature, the solder alloys at a higher lead content than in the initial eutectic. As the lead content rises, the melting point of the eutectic also rises so that eventually, if the temperature is maintained at 220 to 230 degrees C, the coating becomes essentially "self-solidifying". Since the lead pad has a higher melting point than the eutectic, it does not melt during this joining operation, and thereby provides the requisite standoff.

Alternatively, instead of a eutectic lead coating, a solder loaded flux o...