High- reliability nonconductive adhesives for flip chip interconnections

Abstract

Non-conductive adhesives (NCA) are one of the interconnection materials widely used in display packaging and flip chip packaging technology, especially for fine-pitch interconnection. NCA interconnection in flip chip assembly has many advantages such as easier processing, good electrical performance, lower cost, and low temperature processing. We have developed new NCA materials, film type, for flip chip assembly on organic substrate such as FR-4 printed circuit boards (PCBs). NCAs are generally mixture of epoxy polymer resin without any fillers. As a result, NCAs have higher CTE values than 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 lowered by filling of nonconductive fillers of diameter below 1 gm. The modified NCA in flip chip interconnection between gold stud bumps of a chip and metal pads of PCB substrates show highly reliable interconnection when exposed to various environmental tests, such as thermal cycling test (-55/spl deg/C/+160/spl deg/C, 1000 cycle), high temperature humidity test (85/spl deg/C/85%RH, 1000 hours) and high temperature storage test (125/spl deg/C, dry condition).