SMTA International Conference Proceedings

Mechanical Reliability: Updated Results From A Spherical Bend Test Program

Authors: John McMahon, P.Eng., and Brian P. Standing
Company: Celestica Inc.
Date Published: 10/14/2012   Conference: SMTA International

Abstract: The increased temperatures associated with Lead free processes have introduced significant new challenges for PWB suppliers. Cost competitive, Lead free process compatible laminates are typically phenolic cured epoxy based composites, filled with ceramic particles or micro-clays. While Tg values are no longer the sole indicator of thermal resistance, high complexity assembly is now almost completely associated with 170-180 C Tg materials. These changes which are aimed at improving the materials resistance to thermal excursions and maintaining electrical integrity through primary attach and rework operations have produced harder resin systems that we now understand to have lower fracture toughness.

Celestica has been conducting an ongoing testing program to assess Lead free compatible materials and area array packages against the currently accepted levels of process strain. The latest phases of this work have been designed to extend our understanding of component construction dependencies, to begin investigations into some other package types and to compare more materials.

This paper outlines the theory and practice of the test vehicle design, the assembly and test method used to generate data and selected test results. There is also a discussion on the complexities involved in generating predictions of survivable strain in manufacturing operations.

Key Words: 

Pad Crater, Spherical bend test, Mechanical Failure Mode, Laminate Testing, Process Strain

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