Wafer Bumping & Wafer Level Packaging for 300mm Wafer

Summary form only given. 1st the Paper gives a short overview on the history and development of electroless NiAu as low cost bumping technology in industry. The applications in the first phase of production implementation of electroless Ni/Au were focused on wafers with Al-Pads and Ni/Au as UBM or bump material. The second phase of implementation is focusing on low k wafers with copper pad metallization, and the needs of a low cost final pad finish for thermosonic wire bonding. This opens new dimensions for this technology: as alternative to the sputtered Al-layer, electroless Ni/Au can be used. The developed process was implemented in a 300 mm automatic production line. 2nd this paper will give an overview of interconnection technologies in combination with flip chip. The implementation of lead free processes on wafer level has special requirements due to the technologies used in the wafer level bumping processes. On one side, the technical solutions regarding polymeric and adhesive attaches are presented. All the solutions are representing lead free technologies which are in use today and are being implemented in volume products. On the other hand, the technical challenge for bumping is the formation of lead free solder bumps. The paper presents an overview of the solder bumping technologies used today: 1. Electroplating of solder 2. Wafer level stencil printing using solder paste 3. Wafer level solder ball transfer and solder ball reflow. The technological solutions for lead free solder are having certain limitation. Especially, electroplating process is technically limited to SnAg alloys. An overview of the solder alloy compositions in SnAg which are in evaluation today will be given. Wafer level stencil printing is allowing a larger flexibility for the selection of lead free solder alloys. The materials qualified today are based on SnAg and SnAgCu. The results in production qualification of these alloys in reliability tests are presented; data for 150mm, 200mm - and 30mm will be shown. The technology of solder ball transfer and reflow is providing the largest flexibility for solder alloy selection. The results of qualification for different solder alloys are presented. Finally, a comparison of the three technologies -electroplating, wafer level stencil printing and wafer level ball placement is given.