TWO METHODS OF EVALUATING A PRINTED WIRING BOARD'S DIELECTRIC PERFORMANCE IN A LEAD FREE ASSEMBLY ENVIRONMENT
Author: Paul Reid Company: PWB Interconnect Solutions Inc. Date Published: 5/16/2008
ICSR (Soldering and Reliability)
Abstract: It has been demonstrated that lead-free assembly and rework of printed wiring boards (PWBs) can reduce reliability by up to 50%, in well fabricated product. There are two main reliability influences in lead-free applications, copper quality and material robustness. The reliability impact of copper quality is readily evaluated using thermal cycling, while monitoring resistance in test circuits, followed by a microscopic evaluation of plating variables and failure analysis. The reliability impact of materials, however, is not so directly evaluated. Although materials impart the z-axis expansion that causes failure, the material itself is not normally monitored in reliability testing. Traditionally material damage, in reliability testing of bare PWBs has been limited to random microscopic evaluation. Materials traditionally considered robust are now failing in a lead-free application. In response to the need to quantify the material’s role in reliability PWB Inc. developed two unique material test methods; cyclic time to delamination at 260°C (cT260) and detection of material degradation in representative test coupons by Dielectric Estimation and Laminate Analysis Method (DELAM). This article offers an overview of these two evaluation methods, their applications, and benefits.
Key Words: lead-free, material degradation, delamination, reliability, cT260, DELAM, IST