The development and reliability of small pitch flip chip on flex process

In the portable electronics product business, there is a strong trend towards miniaturization. At the same time, when the size and the weight of these products are decreasing, the number of functions and the performance is increasing. This trend towards miniaturization means that the packaging density is increasing significantly. The target of our research was to develop a small pitch flip chip on flex process for electronic module applications. This paper presents the results from the reliability tests of different types of flexible substrates and different types of anisotropically conductive adhesives in high-density flip chip application. The reliability of the samples was tested using thermal shock tests and 85/85 tests. Cross section samples were made to analyze the possible failure mechanism of failed contacts. Two different test devices were used (bump sizes 50×50 μm and 50×90 μm). The effective pitch was 80 μm in both samples and the number of contacts was around 200. The contact resistance was measured with the four-point method and the series resistance with the daisy chain method. The results are part of a European Union supported development project