Journal of SMT Article


Author: Matthew Kelly et al.
Company: Celestica International
Date Published: 10/1/2002   Volume: 15-4

Abstract: With the transition from eutectic tin-lead solder to lead-free SnAgCu (SAC) solder alloys, which require higher melting temperatures, concerns from component and board suppliers, contract manufacturers, and original equipment manufacturers are emerging with respect to component body maximum peak temperatures and the effects these elevated temperatures have on the assembly during and after second level processing.

Implementing elevated reflow temperatures associated with lead-free solder processing has led to questions concerning current moisture sensitivity level classifications, component stability at temperatures in excess of 220°C, and overall reliability. A study was developed to monitor various component body and joint temperatures during lead-free reflow processing. Rework efforts will be covered in a NEMI study to help monitor temperature requirements in that area [1].

The goal of this study was to better understand the impact of new lead-free reflow processing configurations on current component and board material sets, using a range of functional product design complexities assembled with standard production equipment. The study focused on surface mount technology (SMT) reflow processing on fully populated assemblies with a range of component sizes and types. Areas to be discussed in this paper include tin-lead control assembly build benchmarking, lead-free reflow profile optimization, lead-free assembly verification build analysis, and component body temperature analysis. Results for different product types and the associated analysis will be presented for each phase of the study. Data to be presented will include visual inspection, X-ray, component temperature profiles, cross-sections, C-SAM, and pin pull results which compare eutectic tin-lead versus lead-free reflow processing differences.

Key words: SAC, lead-free, component body temperature.

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