Journal of SMT Article

MANUFACTURING AND RELIABILITY OF PB-FREE AND MIXED SYSTEM ASSEMBLIES (SNPB/PB-FREE) IN AVIONICS ENVIRONMENTS

Authors: Dave Nelson and Hector Pallavicini et al.
Company: Raytheon Company
Date Published: 1/1/2004   Volume: 17-1

Abstract: Due to environmental and political concerns, and although significant uncertainties remain about the potential for lead contained in electronic products to have any significant impact on the environment, the use of lead in electronic products is an increasingly visible topic. Because of processing or reliability limitations, entire product categories are being exempted from legislation banning the use of lead.

It appears that multi-track electronics manufacturing, where some assemblies will use traditional eutectic solder while others will use various lead-free alloys, is a certainty. A result of multi-track manufacturing will be products that require the use of both SnPb and lead-free components. The intent of this study is to provide the avionics industry with reliability data that addresses lead-free and mixed system assemblies.

A CCA test vehicle was designed to analyze several design and assembly process variables when subjected to environmental extremes. CCA variables included solder paste type, solder bump type, device type, and use of underfill materials. Solder paste included Sn63/Pb37 and (95.5Sn/3.8Ag/0.7Cu) alloys. Solder bumps were either SnPb or lead-free. Device types included area array components with pitches of 0.5, 0.75, 0.8 and 1.27 mm. Use of underfill material considered presence or absence of non-reworkable underfill.

Test vehicle design permitted real time solder joint interconnection monitoring by measuring resistance through daisy-chained loops. Thermal cycling was used to stress the CCA in environmental testing. The thermal cycle profile consisted of temperature extremes from -55 to 125° Celsius with a 15-minute dwell at hot, a 10-minute dwell at cold, and a 5-10° Celsius per minute ramp rate.

Key words: lead-free, manufacturing, reliability, avionics.



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