Low Temperature Vibration Reliability of Lead-free Solder Joints

Work on establishing an experimental setup for isothermal vibration experiments has been recently introduced. The setup enables tests at temperatures from -40 °C to +150 °C and well-defined load conditions to be applied to specially designed specimens. The specimens can be assembled with LCR or FC components for analysis of their solder joint fatigue behaviour. Here, we present the applied experimental procedure, fatigue results and dominant failure modes observed from tests on lead-free LCR solder joints. The tests not only aim for understanding the solder joint behaviour but also to prepare for tests at combined harmonic vibration and temperature cycling conditions.Harmonic vibration tests were performed on SnAg1.0Cu0.5 solder joints under isothermal conditions at -40 °C and room temperature. Experiments were conducted at various solder strain levels between 800 and 2,000 μstrain at both temperatures. Failure events (>20% resistance change) were detected in real-time during the test. Measures of cycles to failure and FEA calculated strain data have then been used to derive and compare S-N-curves: Solder joint durability is seen to significantly decrease at low temperature conditions. Cross sections were examined to determine failure modes at low and room temperature vibration loading: An increased risk of copper trace cracks was found at low temperature conditions in contrast to a higher probability of solder joint cracks at room temperature.