Results of melting behavior, solder joint formation, tensile strength and high-temperature creep tests.
There has always been a latent interest in low-temperature solders, as they can 1) potentially reduce material cost by enabling use of cheaper PCBs and components due to the lower processing temperature, 2) promote long-term reliability by reducing exposure to thermal excursion, 3) reduce labor cost, 4) reduce energy cost, and 5) reduce dynamic warpage in sensitive components.
SnPb alloys have been historically used for making joints. In the case of electronics, eutectic 63/37 SnPb was a very good choice, as solder joints could be soldered at relatively low temperatures, considering its melting point at 183°C. Eutectic SnPb also produced solder joints with very good mechanical reliability. The transition to lead-free was mostly a matter of regulatory compliance, and in the early 2000s various lead-free alloys were considered substitutes for eutectic SnPb, including the eutectic 42Sn58Bi alloy.
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