Stability of Solder Bridging for Area Array Type Packaging

As ultra-fine-pitch technologies are adopted to enhance the performance of electronic packaging, solder bridging becomes an urgently serious defect. This work presents a computational model using the Surface Evolver program to analyze the stability of solder bridging for area array type packaging. Several factors that affect the stability of solder bridging spanning two identical circular pads are considered herein, including the pad size, the total volume of solder bumps, the pitch between adjacent pads, the contact angle between the molten solder alloy and the pad, the contact angle between the molten solder alloy and the solder mask and the surface tension of the molten solder alloy, respectively. The critical total volume of solder bumps and the critical pitch between adjacent pads are defined as the corresponding critical values to determine the solder bridging from a stable state to an unstable (vanishing) state. The stability of solder bridging spanning three and four identical circular pads is also discussed. Good agreement between the computed critical total volume of solder bumps for solder bridging and that available in the literature exhibits that the model developed in this work can be practically applied to predict the stability of solder bridging.