Halogen-free and reworkable corner bond adhesive for array-based packages and the impact on board-level solder joint reliability

Capillary flow and no-flow underfill were demonstrated to yield dramatic reliability improvement in the mechanical shock and torsion of most array-base package (ABP) assemblies in portable electronic devices. However, it is very difficult to rework the defective ABPs after the underfill operation. Unfortunately, reworkability of the packages with underfill is needed for printed circuit board assemblies (PCBAs) with ABPs failing either during final test or in the field. Corner bond adhesive (CB A) applying an adhesive only near the corner of an ABP and curing. This adhesive forms a mechanical bridge between the ABP and the PCB, since much less adhesive is used compared to underfill, the area of adhesive in contact with the board and the package is smaller. This should aid in the ability to develop systems that are reworkable without damaging the PCB. In addition, with the improving of life quality and increasing of environmental protection thought, people´s demand for environmentally friendly halogen-free products has become more and more pressing. This investigation provides initial results of an ongoing study aimed at thermo-mechanical reliability of the ABP assemblies with halogen-free and reworkable CBA in portable electronic devices. One halogen-free and reworkable CBA was evaluated in order to get the detail reliability performance for ABP assemblies. Material properties such as coefficient of thermal expansion (CTE), glass transition temperature (Tg), modulus, apparent strengths of adhesion (ASA), etc were obtained. Shear, bend, drop and thermal cycling tests have been conducted with this material. A comparative study of the performance of ABPs with one halogen reworkable CBA materials and no-bonded materials are reported. Results of the above tests shows that the halogen-free CBA has the equivalent or even better performance compared with the halogen CBA.