EMRS | alumni

Fine pitch area array packages are being developed and researched into, in an effort to concurrently provide a small form factor and ease in handling. The testability of these packages prior to assembly and the elimination of underfills make this technology very attractive in the electronics packaging domain. These packages, which are equal to or slightly larger than the bare dice, offer the benefits of both Ball Grid Arrays (BGAS) and flip chips. The high density requirements of the fine pitch area array packages have imposed significant challenges to board and package manufacturers. These challenges often show up as variations in the board and package related parameters. This research characterized high density boards and fine pitch area array packages, predicted assembly yields that are caused by variations in board and package related parameters, and recommends diameters of the contact pads on the board to achieve a defect free assembly. The impact of the variations in the board related parameters such as variations in the dimensions of the contact pads, the solder mask opening, and the misregistration of the solder mask on the solder bump heights was studied. A discussion of the impact of these variations are presented with the help of case studies. These studies were performed with the aid of 'Surface Evolver', a tool for modeling the shapes of solder bumps and joints. The results show that the variations in the dimensions of the contact pad and the misregistration of solder mask significantly affects the coplanarity of the solder bumps and hence, the assembly yields. Case studies showed that the warpage at reflow is different from the warpage at room temperature before reflow. Mean board pad diameters that would help to achieve zero defects in assembly yields for the observed variations in the board and package related parameters are recommended.


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