Effects of edge and corner bond adhesives on the drop reliability of package-on-package bottom package assemblies

This paper presents the drop 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 JEDEC drop test board. The test boards were dropped through an 1828.8 mm long, 110.0 mm diameter tube onto a steel plate. The daisy chain resistance of each PSvfBGA was measured by a post-drop resistance measurement system after each drop and a static 10 Ω rise (or more) from initial resistance was considered as the failure criterion. Three 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. Statistics of the number of drops-to-failure for the fifteen component locations on each test board are reported. The test results show that the drop test performance of PSvfBGAs with UV-cured edge bonding, thermal-cured edge bonding and corner bonding are respectively about six, eight and seven times better than the PSvfBGAs without bonding. Failure analysis was performed using dye-and-pry, cross section scanning electron microscope (SEM) and energy dispersive X-ray (EDX) methods. The most common failure mode observed is solder cracking at component side intermetallic compound (IMC)/solder interface.