Solder Selection for Reflowing Large Ceramic Substrates During PCB Assembly
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Large substrates are prone to warpage issues during reflow due to Coefficient of Thermal Expansion (CTE) mismatch with Printed Circuit Board (PCB) material subsequently affecting solder joint quality and reliability in the form of cracks and interface dislocations. This paper describes best solder paste alloy for reflowing larger dimension ceramic substrates during PCB assembly process to improve solder joint quality by minimizing CTE differences. Experiments have been carried out using various commercially available solder alloys for reflowing larger substrates (80 mm × 80 mm). Solder joint quality was inspected using scanning electron microscope and X-ray for multiple reflow runs using different alloy combinations. Results showed Bismuth-based solder (Bi58/Sn42) to have minimal cracking and improved CTE over other solder alloys. Advantages include reduced costs and improved reliability for applicable devices.
KeywordsSolder alloy material Solder joint quality and reliability Low-temperature reflow Large substrates CTE mismatch
The authors would like to thank FormFactor Inc. management team in manufacturing and operations for providing us continuous support in equipment and material funding.
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