Journal of SMT Article

LEAD-FREE ASSEMBLY OF SERVER CLASS PCBAs: QUALIFICATION TRIAL RESULTS

Authors: Matthew Kelly, Marie Cole, Jim Wilcox, David Braun
Company: IBM Corporation
Date Published: 4/30/2009   Volume: 22-2

Abstract: At present, insufficient long term thermomechanical reliability performance data exists to support high complexity, lead-free printed circuit board assembly (PCBA) for use within enterprise server and storage class applications. The majority of reported second level interconnect reliability experience with lead-free PCBAs has been generated without adherence to high complexity, high reliability product life specifications. As a result, many of the lead-free material and assembly process solutions deployed to date have not been characterized according to more stringent server and storage reliability requirements.

This paper reports the reliability testing results of a lead-free assembly qualification trial on a mid-range complexity, high reliability PCBA sourced with three different printed circuit board (PCB) surface finishes. Reported results include electrical functionality through accelerated thermal cycling (ATC), isothermal high temperature storage (HTS), as well as combination shock / vibration / ATC testing. Mechanical four-point bend test results and implications will be discussed. Construction analyses of various interconnect technologies is also included.

Through continued product vehicle study, the capability of leadfree processing is being systematically assessed for the extension of its applicability to higher complexity PCBAs. This work demonstrates that the reliability requirements can be met for mid-range server PCBAs as described in this paper. For extension to higher complexity assemblies or those with higher reliability requirements, additional work is required to understand the solder joint fatigue life of certain components and to overcome PTH holefill performance limitations.

Key words: Lead-free server PCBA, product vehicle qualification trial, mid-range complexity, high reliability, TSOP failure, alternate surface finishes.



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