Study on the bend performance of package stackable very thin fine pitch ball grid array assemblies with edge and corner bond adhesives

This paper presents the four-point bend test results for edge and corner bonded 0.5mm 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. Four-point bend tests were carried out based on the above standard with a 30 mm loading span, 90 mm support span and 7.5 mm/sec 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. Tests were conducted on PSvfBGAs with adhesives and PSvfBGAs without bonding. The test results show that all of them can improve the bend performance significantly; especially the edge bond epoxy increased the crosshead displacement, strain and bending force when mechanical damage occurred by 33.46%, 26.74% and 3.05% respectively. The combination of high module adhesive and edge bond dispensing pattern can provide the best improvement. Failure analysis indicated that the most common failure mode was PCB pad lift/crater.