Substrate opening to increase solder joint reliability and circuit integration

A novel solution to reduce the effect of coefficient of thermal expansion (CTE) mismatch between the package and the circuit board is proposed here. In this solution, the circuit board area directly beneath the package is removed to form a patterned opening. It is believed that the opening provide an additional direction for the circuit board expansion. The simulated result showed that the solder reliability of the substrate opening is better than using underfill. Depending on the requirement, the design of the opening such as the shape and dimension can be optimized. For higher circuit integration density, other package or module can be integrated through the opening. The proposed solution is simple as it only requires to form through opening in the circuit board. It does not require the costly underfill process.