Impact of Thermal History on Gap Filling Capability of Die Attach Film

摘要

Die attach film(DAF) has being widely applied to various high density packages due to its bleedless,rnconsistent bond line thickness and simple operation without dispensing even skip cure post attachment comparedrnwith traditional liquid-type die attach material . However, void always is one of major concerns, especially for DAFrnapplied between die and substrate in plastic ball grid array packages. In this paper, the thermal history of DAF forrnencapsulated units is analyzed since it is put into assembly and the experiment is designed with different thermalrnhistory to illuminate its impact on void performance. Simultaneously void formation mechanism also is studied byrntracking void status during the whole assembling process. As the result, it was shown that the void issue is caused byrninsufficient gap filling and thermal history play an important role in gap filling capability. Based on thermal historyrnanalysis, heating at wire bond process is a key step due to its long staging time and high temperature. DAF withrnshort thermal history has super gap filling capability. Even voidless result can be achieved if skipping heating atrnwire bonding compared with about 10% void percentage for encapsulated samples under normal building condition.rnIt can be explained that cross-link occurs under thermal condition and gap on the substrate can not filled completelyrnbecause it became rigid. Scenarios for void reduction also are addressed based on this investigation in this paper.