Effect of curing condition of adhesion strength and ACA flip-chip contact resistance

Abstract

There has been steadily increasing interest in using electrically conductive adhesives as interconnecting materials in electronics manufacturing. Simple processing, low processing temperature and fine pitch capability are the major advantages of conducting adhesive technology. A new and innovative connection technology geared towards achieving increased functionality at a lower total system cost is anisotropic conductive adhesive (ACA) interconnection. ACAs provide electrical as well as mechanical interconnections for fine pitch applications when used for flip chip assembly. In the other hand, this new technology still has reliability limitation. One major concern is the poor adhesion strength of adhesive interface, another is the contact resistance shift. The mechanism of adhesion interface and contact resistance shift during elevated temperature and humidity aging had been discussed in previous study. The ultimate goal of this work is to develop conductive adhesive with stable contact resistance and desirable interface adhesion strength. The purpose of this study is to investigate optimum curing degree and curing temperature to achieve the best performance of ACA. The curing reaction of a conductive adhesive was studied with a differential scanning calorimeter (DSC) under isothermal condition and temperature scanning. Adhesion strength was measured by 90 degrees peel test and contact resistance was also studied as a function of curing degree and curing temperature. Microstructural investigations of the fracture surfaces were studied by scanning electron microscopy (SEM). It was shown that the electrical and mechanical performance is dependent on curing conditions. By comparing the dynamic DSC results of the conductive adhesive with different bonding condition, it can be seen that it is not fully correct that high temperature cured sample have higher adhesion strength than low temperature cured sample, peel strength increase proportion with the increase of bonding temperature up to 120/spl deg/C and then decrease when the bonding temperature was above 120/spl deg/C. Contact resistance was found to be strongly dependent on the curing degree, but also revealed no related with curing temperature. In this case, the optimum temperature for bonding with ACA was concluded to be at 120/spl deg/C.