Hybrid Laminate Structure for Minimizing Pad Cratering
Authors: Chen Xu, Debbie Fleming, Rose Kopf, Pericles A. Kondos, Ph.D., Yunhu Lin Company: Nokia, AREA Consortium, APL, Universal Instruments, Nokia Shanghai Bell Date Published: 9/17/2017
Abstract: With the mainstream electronic industry now using lead-free assembly, traditional SnPb-compatible laminates have been replaced with lead-free compatible laminates that can withstand the higher reflow temperature required by leadfree solders. Lead-free compatible laminates with improved heat resistance have been developed to meet this challenge but they are typically more brittle than SnPb laminates causing some to be more susceptible to pad cratering. A novel approach for minimizing pad cratering, based on the realization of distinctly different locations of pad cratering (in the external layer) and delamination (in the inner layer), uses pad cratering resistant material (such as traditional SnPb-compatible laminates) in the external layers and leadfree compatible material for the inner layers. In a previous paper , we have demonstrated the much-improved pad cratering resistance of the hybrid structure compared to the PCBs consisting of just lead-free compatible laminates. In this work, we will determine the lead-free compatibility (up to six lead-free reflows) of the hybrid structure consisting of lead-free compatible material for the inner layers and traditional SnPb-compatible laminates in the external layers. ATC, CAF and delamination testing results will be presented in this paper. The advantage of using hybrid structure for minimizing pad cratering without compromising the lead-free compatibility will be demonstrated.