Testing

In order to evaluate Lead-Free solder joint reliability, it is normal to expose suitable assemblies to accelerated testing conditions.

Thermal cycling

Thermal cycling is used to simulate, in an accelerated way, the changes that could occur during in service operation. The exposure of an assembly to continually changing temperatures means that the solder joints are exposed to stresses originating from the differential thermal expansion and contraction of the various materials in the assembly such as the circuit board, the solder alloy and the components. This in turn stresses the solder joints and highlights where solder joint failure is likely to occur. Typical thermal cycling conditions can include thermal shock testing with repeated cycling using conditions such as -25°C to +125°C, with a three minute dwell, -55°C to +125°C with a twenty minute dwell and -40°C to +125°C with a thirty minute dwell.

Widely varying reliability results may be obtained depending on the specific combination of solder, component type tested and the accelerated test conditions chosen. For example, tin-lead alloy has shown less than half the fatigue life of the tin-silver joints when cycled between 0°C and 100°C. However, when the harsher conditions of -55°C to +160°C are used, the tin-lead fatigue life was more than double that of the tin-silver alloy. Great care should be taken when extrapolating accelerated testing data to likely in-service performance.

Vibration testing

This test is used to give a reasonable accelerated simulation of what might be expected in real life operation. Widely varying reliability may be obtained depending on the specific combination of solder, component type tested and the accelerated test conditions chosen.

For example, tin-lead alloy has shown less than half the fatigue life of the tin-silver joints when cycled between 0°C and 100°C. However, when the harsher conditions of -55°C to +160°C are used, the tin-lead fatigue life was more than double that of the tin-silver alloy. Great care should be taken when extrapolating accelerated testing data to likely in-service performance.