Development of life prediction model for lead-free solder at chip resistor

An accelerated thermal cycling test to assess the reliability of lead-free solders at chip resistor has been conducted. Test results indicate that the life of lead-free solder at chip resistor (6432 mm type) could be worse than of SnPb solder in the accelerated thermal cycling condition (125/-50C). Based on the test results and some published data, life prediction model for the solders has been developed. The developed life prediction model consists of stress model and damage model. Stress model, which relates thermal cycling condition to damage at solder, includes FE model with Anand's constitutive equation for solders. Damage model, which relates the damage to life of solder, is based on Darveaux' crack growth approach. Developed life prediction model confirms worse reliability of lead-free solder than leaded solder in the accelerated thermal cycling condition but potentially predicts reverse results in the field condition. To predict the reliability of lead-free solder in the field condition, accelerated factor should be carefully calculated using life prediction model.