Stress Relief in Solder Joints Due to the Application of a Flex Circuit

[+] Author and Article Information
E. Suhir

AT&T Bell Laboratories, Murray Hill, New Jersey 07974

J. Electron. Packag 113(3), 240-243 (Sep 01, 1991) (4 pages) doi:10.1115/1.2905401 History: Received December 14, 1990; Revised April 15, 1991; Online April 28, 2008


A stress analysis model is developed to assess the stresses in solder joints caused by thermal contraction mismatch between a low expansion flex-circuit (FC) and a high expansion rigid substrate. It is shown that application of low expansion FCs can result in significant stress relief for solder joints. This is due to the fact that the force acting on a joint cannot exceed the buckling force for the adjacent portion of the FC. It is shown that the strains in solder joints interconnecting FCs to rigid substrates can be made very small, thereby resulting in a substantially longer fatigue life of the interconnection. In the executed example these strains are about two orders of magnitude smaller, than in the case of a rigid board. The obtained results can be utilized as guidance in physical design of assemblies with FCs.

Copyright © 1991 by The American Society of Mechanical Engineers
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