Effect of moisture related properties of mold compound on the reliability of power packages

Moisture absorption of epoxy mold compounds (EMC) from IC packages is a serious concern especially for their reliability performance during stress tests. Numerous studies reported the popcorn cracking delamination due to moisture absorption of packaging materials during solder reflow [I]. Though no pop-corn delamination or other EMC to die pad delamination happened at time zero, current leakage may be still observed even if moisture absorption properties changed slightly. This paper reports properties, especially moisture absorption properties, of EMCs that were characterized to identify the failure causes. Also described is a new methodology to detect the moisture absorption amount at EMC to die pad and EMC to leadframe interfaces. To differentiate the moisture absorption amount between EMC and interfaces will give failure analysis a great clue to find the failure root cause. EMCs with same resin type but different resin concentration were selected to build same type of packages with different die sizes. Moisture absorption and desorption tests were conducted to characterize the moisture absorption behaviors of EMC in packages. Scanning Acoustic Tomography (SAT) and Electric test were recorded at Time zero and various stress test durations. Results showed that packages with higher resin content of EMC are prone to current leakage. In order to prevent the moisture absorption related failure, resin contents need to be controlled and monitored carefully. Furthermore, package design, e.g. die size and lead to die pad distance etc. need to be optimized together with acceptable EMC resin specification for production.