Approaches to flip chip technology using electroless nickel-gold bumps

A chemical bumping technology developed and implemented at IZM is presented. The maskless process is based on electroless nickel deposition. Nickel bumps offer a surface which is very suitable for flip chip soldering. They are also appropriate for adhesive interconnections, e.g. with isotropic, anisotropic and non conductive adhesive. The deposition of solder and adhesives can be achieved by different methods on wafer and chip as well on substrates. Therefore, this paper demonstrates the broad spectrum and the high flexibility of these techniques with regard to low cost processes. The interconnections are performed on cost effective ceramic substrates, rigid printed circuit boards (FR-4) and flexible circuit materials. As an example of these approaches, the development of a flip chip interconnection method using dies with Ni/Au bumps and solder printing on ceramic substrates is presented. First reliability results of these joints after thermal cycling are also shown.