Process and design analysis for ultra fine-pitched wiresweep elimination in advanced copper heat spreader BGA package

The semiconductor device trend for increasing functionalities and performances yet with smaller overall feature sizes presents escalating obstacles to the decreasing form factor along with demanding thermal carrying capability required at the package level. To confront this compounding issue, ultra fine pitch wirebond interconnect coupled with thermally enhanced copper heat spreader attached to the package are introduced. But the additional copper heat spreader thickness introduced within the package challenges the design of the package´s wire, its loop height, and the molding process control to prevent wire sweeping occurrences. This study investigates the impact of different ultra fine pitched wire types, wire loop designs, copper heat spreader structures, and mold material types on eliminating device short from occurring due to the wire sweeping phenomena. A full factorial experiment is performed using an active silicon device packaged in a thermally enhanced BGA test vehicle. In addition, test characterization is carried out using X-ray and multi-insertions hot/cold continuity tests. Then, a detailed failure analysis is performed by chemical decapsulation to confirm the experimental findings. In conclusion, the study finds that for an ultra fine pitched thermally enhanced BGA package, wire type is insignificant to reduce wire shorting occurrences. However, mold material and copper heat spreader structure using an optimized wire loop design are significant factors in eliminating wiresweep shorting phenomena. This study concludes,with a Wirebond interconnect and heat slug design recommended along with an improved process parameters and assembly material sets found from the experiment.