Influence of underfill methods on the solder joint fatigue of wafer level packaging

To increase miniaturization, CSWLP (chip size wafer level packaging) has been developed. However, the difficulty to get good solder joint reliability leads to manufacture only small CSWLP modules. Different underfill methods are evaluated here, by measurements and simulations: results prove that underfill is necessary, but a bad choice can also decrease the reliability. An original method called ldquore-enforcementrdquo improves the life time.