Tailored Coefficient of Thermal Expansion Printed Wiring Boards to Improve the Solder Joint Life of Leadless Ceramic Chip Carriers

Abstract

A computer program was used to predict the coefficient of thermal expansion (CTE) of four printed wiring board (PWB) designs. Designs consisted of low CTE materials, E glass/epoxy and copper. Twenty PWBs were fabricated to duplicate four computer models. CTE was measured by a strain gauge technique developed at Boeing. The measured CTE was then compared with the predicted CTE value and a design curve developed. Following CTE verification, the PWBs were assembled with 20, 44, 68, and 84 I/O leadless ceramic chip carriers. The printed wiring assemblies were then thermal shocked from −55 to 125°C and continuously monitored to detect the first solder failure for each I/O chip carrier. The results illustrate the dependence of solder joint life on PWB CTE and verify the use of a computer model to design surface mount PWBs.

Citation

Williams, R.L. and Noblett, A.W. (1989), "Tailored Coefficient of Thermal Expansion Printed Wiring Boards to Improve the Solder Joint Life of Leadless Ceramic Chip Carriers", Circuit World, Vol. 15 No. 2, pp. 30-32. https://doi.org/10.1108/eb043970