Underfill and edgebond for enhancing of board level reliability (IMPACT 2014)

With the proliferation of area array packages in consumer, enterprise, automotive, medical, and military electronics, a wide range of board level underfills and edgebond adhesives, reworkable and non-reworkable, have been developed to ruggedize these components. While these materials are used to enhance drop test, bend test, vibration test and Tumbling test performance, their use can affect thermal cycle performance, negatively or positively. The trade-offs between process performance, rework, and reliability, along with advances to overcome the trade-offs are discussed. In this study, we have experiments to compare the drop results between the PCBA with underfill and without underfill. For thermal cycle experiments, one underfill shows positive while another one exhibit negative. There are also the experiment to show the tradeoff between reliability and reworkability. Both thermal cycle experiment and stress calculation illustrated the higher the Tg and the lower the CTE, the longer the thermal cycle life it will be. But too high of Tg, it will be non-reworkable. We also shows a low-CTE, highly crack resistant reworkable underfill encapsulant designed for flexible and bendable application. Finally, the alternative edge bond material is good for the choice of easier rework or reducing the consumption of undefill. The experiment shows that the reworkable edge bond adhesive enhances thermal cycle performance very much.