The effect of ball pad designs and substrate materials on the performance of second-level interconnects

The microelectronics industry has been driven to reduce the size of its semiconductors. As packages become smaller with finer ball pad pitches, smaller solder ball and pad sizes will also be needed. This emphasizes the importance of solder joint strength. The purpose of this paper is to understand the effect ball pad designs and substrate materials have on the performance of second-level interconnects. Ball shear testing is used to assess the joint strength in the following areas: soldermask defined (SMD) and non-soldermask defined (NSMD) ball pad designs; the impact of various pad sizes; the different core materials and soldermask materials inclusive of halogen-free materials; the different core material thicknesses. In general, the data shows that an NSMD ball pad design has a higher solder ball shear strength than an SMD with a smaller ball pad size. However, the strength of SMD ball pads exceeds NSMD as the pad size increases or the substrate thickens. The type and thickness of core material all significantly contribute to solder ball shear strength, thus, joint reliability. As a result, the proper choice for ball pad design and substrate materials enhances second-level interconnect reliability for packaging.