scope:

This document describes specific guidelines for strain gage testing for Printed Wiring Board (PWB) assemblies in the board manufacturing process including, assembly, test, system integration and board shipping.

The suggested procedure enables board assemblers to conduct required strain gage testing independently, and provides a quantitative method for measuring board flexure, and assessing risk levels.

• The topics covered include:

• Test setup and equipment requirements

• Strain measurement

• Report format

This document assumes a surface mount device; Ball Grid Array (BGA), Small Outline Package (SOP) and Chip Scale (Size) Package (CSP) are typical device examples. Discrete Surface Mount Technology (SMT) devices, (e.g., capacitors, resistors, etc.) are outside the scope of this publication.

Purpose Strain gage testing allows objective analysis of the strain and strain rate levels that a SMT package is subjected to during PWB assembly, test and operation.

Characterization of worst-case PWB strain is critical due to the susceptibility of component solder joints to straininduced failures. Excessive strain can result in solder joint damage for all package substrate plating finishes. Such failures include solder ball cracking, trace damage, pad lifting (shown in Figure 1-1) and substrate cracking during board manufacturing and test processes.