Development of fine pitch (54 μm) flip chip on flex interconnection process

Lighter, smaller, faster and cheaper are the magic words used to describe the trends in modern electronics. The miniaturization is a must in the market of the portable devices. Beside of the mobile phones there are several other application areas like smart cards, smart cloths, portable minicomputers, cameras, entertainment electronics and so on. The big challenge is to find the most effective technology to produce all those devices with competitive prices. The key factor is the interconnection technology. The environmental factors like lead and halogen free production are other challenges that must be taken into account This paper presents the development of fine pitch (54 μm) flip chip on flex (FCOF) interconnection. There are several factors affecting to the reliability of the high density interconnection like the flex material, the bumping of the test chips, the bonding equipment and the anisotropically conductive adhesive used to make the connection. During the development phase it was noticed that by a careful testing and by making right selections it is possible to find working combination of materials and processes for high density interconnection. To insure the reliability, the samples were tested using thermal shock tests (-40C&rlhar2;+125C) and 85C/85R.H. humidity test. Cross section samples were made to analyze the possible failure mechanism of failed contacts. Two different types of test devices were used. The contact resistance was measured with four-point method and the series resistance with Daisy chain method. The results area part of development project supported by European Union.