Browse Prior Art Database

Multiple Thermal Expansion Coefficient Substrates

IP.com Disclosure Number: IPCOM000061499D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Berding, JT: AUTHOR

Abstract

This article describes a printed circuit board having zones of differing effective thermal coefficients of expansion (TCE) to match the characteristics of different chips or circuit package mounted thereon. It makes use of metal core circuit card technology of the general kind previously published [1,2]. Ceramic and plastic packages expand at different rates: Ceramic Z .6-.8x10-5/ŒC Plastic > 2.5 x 10-5/ŒC If a printed circuit board 10 (Fig. 1) were to use both ceramic and plastic packages 12, 14 for surface mounting, a compromise TCE3 would be made in choosing a substrate to match only approximately the thermal expansion coefficients of the packages. The result would be at best a tolerable mismatch of coefficients with each package. Fig. 2 shows a scheme to alleviate this problem.

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Multiple Thermal Expansion Coefficient Substrates

This article describes a printed circuit board having zones of differing effective thermal coefficients of expansion (TCE) to match the characteristics of different chips or circuit package mounted thereon. It makes use of metal core circuit card technology of the general kind previously published [1,2]. Ceramic and plastic packages expand at different rates: Ceramic Z .6-.8x10-5/OEC Plastic > 2.5 x 10-5/OEC If a printed circuit board 10 (Fig. 1) were to use both ceramic and plastic packages 12, 14 for surface mounting, a compromise TCE3 would be made in choosing a substrate to match only approximately the thermal expansion coefficients of the packages.

The result would be at best a tolerable mismatch of coefficients with each package. Fig. 2 shows a scheme to alleviate this problem. In this figure, board 20 is drawn in partial cross-section to show a metal core 22. The core 22 has been selectively etched before being laminated, molded or otherwise encapsulated into the board 20 so that the board 20 can have different thermal expansion rates at different parts of the board, to match the components soldered onto the board.

In other words, the core 22 would be in the form of islands, strips or salients where needed and apertured or absent where not desired.

In this example, a low expansion coefficient alloy would be used for the core 22 located under ceramic module 12, while no such core (or a high expansion rate co...