Effects of mold compound properties on lead-on-chip (LOC) package reliability during IR reflow

This paper reports the investigation into Lead-On-Chip (LOG) package cracking resistance, the effects of mold compound properties, and the package cracking predication. The vehicle for such investigation was a DRAM LOC package and four mold compounds under two IR reflow processes (220°C and 260°C). As the reliability of the LOC package is strongly dependent on the mechanical properties of the mold compound, great efforts were put into its characterizations. The mold compound characterization was conducted using an Instron Universal Tester with a temperature chamber which regulated the testing temperature from -60 to 260°C. These characterizations included temperature dependence, loading speed effects, moisture effects, creep behaviour, etc. The linear elastic fracture mechanics method was used to predict package cracking resistance. This included obtaining mold compound fracture toughness through 3-point bending test at the IR reflow temperatures, finite element analysis to obtain package stress intensity factors at these conditions, and correlate with the package reliability test results