High reliable non-conductive adhesives for flip chip CSP applications

Chip Scale Packages (CSP) have been adapted for mobile phones, DVC, PC cards, PDA's and various other applications due to the robustness, cost effectiveness, and high reliability of CSP packages. For first level interconnection in CSP, wire bonding with encapsulation, Au stud bump by conductive adhesive, and solder bump interconnection with underfill process are mostly used. Non-conductive adhesives (NCA), widely used in display packaging and fine pitch flip chip packaging technology, are recommended as one of the most suitable interconnection materials for flip chip CSPs. NCA interconnection in flip chip assembly have many advantages such as easier processing, good electrical performance, lower cost, and low temperature processing. In this paper, we have developed film type NCA materials for flip chip assembly on organic substrates such as FR-4 printed circuit boards (PCBs) or BT resin. NCAs are generally a mixture of epoxy polymer resin without any fillers, and have high CTE values like conventional underfill materials used to enhance thermal cycling reliability of solder flip chip assembly on FR-4 boards. In order to reduce thermal and mechanical stress and strain induced by CTE mismatch between a chip and organic substrate, the CTE of NCAs was optimized by filler content. The modified NCA interconnection in flip chip CSP showed highly reliable interconnection when exposed to various environmental tests.