Abstract:

Solder joints provide critical electrical and mechanical connections in the electronic assemblies. To assure reliability of electronic hardware, it is important to understand the reliability of solder joints under use conditions. The conversion to RoHS-compliant materials has raised concerns about the reliability of lead-free solders used in electronic products. One of the primary mechanisms of solder joint failure is fatigue due to fluctuations in temperature resulting from operational and environmental conditions. Fatigue of solder arises from cyclic strain within the solder joint due to different rates of temperature expansion in the solder and interconnected structures.

To address the solder joint reliability concern of lead-free solder, a systematic set of experiments was conducted to examine the impact of dwell time and mean temperature on solder joint reliability. SAC305, SN100C, and SnPbAg solders were tested and compared with prior test results. The results indicated that lowering the mean cyclic temperature increased the thermal cycling durability of the solders dramatically. Results on the impact of cyclic mean temperature and dwell time revealed that dwell had a larger effect when the mean cyclic temperature was lower. Extended low temperature dwell for a temperature cycle of -25ºC to 75oC was found to be more damaging than expected, particularly for SnPbAg. For a maximum temperature of 125oC, a dwell-time increase from 15 to 75 minutes did not have much effect. Results indicated that SAC305 was slightly less durable than SAC379 but was more reliable than SN100C and SnPbAg solders. SnPbAg was less durable than SnPb solder

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