Pb-Free Thermal Cycle Acceleration Factors
Paper discusses the calculation of acceleration factors for different Pb-free solders, comparing results with those for eutectic SnPb.
DOWNLOAD
Authored By:
Phil Isaacs and Eddie Kobeda
IBM Corporation
Rochester, MN, USA, and Raleigh, NC, USA
Summary
Society is demanding tougher legislation to minimize or even eliminate perceived health risks to people. Since the European Union began drafting requirements in support of RoHS (Restriction of Hazardous Substances), companies have been scrambling to address the critical transition from eutectic SnPb to Pb-free solder for electronic assemblies. Activities have focused heavily on understanding fundamental material properties and their changes during higher temperature processing. The most important question that must be answered is how these new materials will perform in the equivalent customer environment.
This paper will discuss the calculation of acceleration factors for different Pb-free solders, comparing results with those for eutectic SnPb, while also evaluating several approaches and their ability to predict field reliability.
Conclusions
The available literature supports the use of several calculation methods to determine the acceleration factor for extrapolating from lab testing to life expectancy in the field for Pb-free solders. These methods have been used for SnPb solders and are readily extendable to Pb-free with the right constants and variables available in the literature today. As in the case for SnPb, calculations for Pb-free solder will experience similar limitations for extreme strain factors where predictions have in the past fallen short. Many claim with proper use and thoughtful data results within +/- 25% are very achievable.
Initially Published in the SMTA Proceedings
|
