Experiment and numerical analysis for edge and corner bonded PoP bottom package assemblies under four-point bending

This paper presents the four-point bend test results for edge and corner bonded 0.5 mm pitch lead-free package stackable very thin fine pitch ball grid arrays (PSvfBGAs) as package-on-package (PoP) bottom packages on a standard IPC/JEDEC bend test board. The tests were carried out based on the above standard with a 30 mm loading span, 90 mm support span and 7.5 mm/s crosshead speed. The daisy chain resistance, strain, crosshead displacement and load of each PSvfBGA were measured and a 20% increase in the resistance was used as the failure criterion. Materials used in this study were a UV-cured acrylic edge bond adhesive, a thermal-cured epoxy edge bond adhesive and a thermal-cured epoxy corner bond adhesive. The test results show that all of them can improve the bend performance significantly: especially the edge bond high module epoxy increased the crosshead displacement, strain and bending force when mechanical damage occurred by 33.46%, 26.74% and 3.05% respectively. Failure analysis indicated that the predominant failure site was PCB pad lift/cratering regardless of with or without adhesives. The 3D quarter finite element model was also built to further study the improvement mechanism of bend performance by these adhesives. (C) 2011 Elsevier Ltd. All rights reserved.