Systematic studies of second level interconnection reliability of edge and corner bonded lead-free array-based packages under mechanical and thermal loading

Lead-free (LF) solder joints of portable devices are frequently subjected to unintentional drop, bend, shear and thermal cycling loading during transportation, handling, and usage. Various underfills are widely used in the electronics industry to deal with these challenges, however, the above approaches have some intrinsic shortcomings such as high material costs, low manufacturing assembly rate, poor reworkability and so on. To reduce the cycle time and cost of conventional underfill process, two promising polymeric reinforcement technologies for the next generation array-based package (ABP) application, the so-called edge and corner bond adhesives, have been developed. In this paper, the second level interconnection (SLI) reliability of edge and corner bonded LF package stackable very thin fine pitch ball grid arrays (PSvfBGAs) was systematic studied using package to board interconnection shear, monotonic 4-point bend, 90° free-drop, and thermal cycling tests. Three materials used in this study were a UV-cured acrylic edge bond adhesive (EBA), and thermal-cured epoxy EBA, and a thermal-cured epoxy corner bond adhesive (CBA). Moreover, the PSvfBGAs without bonding were also tested for comparison. The test results indicate that all the bonding materials increase the mechanical performance of SLIs, especially for drop reliability. On the contrary, the thermal fatigue lives of PSvfBGAs with edge bond acrylic and epoxy are reduced by 38.42% and 8.34%, respectively. In addition to the comparison of maximum shear and bend forces, crosshead displacement, principle strain, drops and thermal cycles to failure between the four test groups, the failure modes and mechanisms of SLIs under various test conditions were analyzed as well.