Dry film photo resists and polymers –The low cost option for standard and 3-D wafer level packaging
Driving packaging cost down is essential to make products cheaper. There are several options to reduce costs: One is to switch from one packaging technology to another (cheaper) one. The other is to cut costs for an existing process step by using cheaper material and/or a more cost effective process flow. Dry film materials are well-known from several decades of experience in printed circuit board industry. Lamination of those films guarantees very uniform coating over large panel sizes at low cost. Resolution of dry films has been drastically improved in recent years. Therefore today’s dry films are very attractive for wafer level packaging. This paper is giving an overview about different applications where dry film material can be used for electronic packaging. It also describes additional benefit that is brought by the use of dry film. At several steps of the typical process flow for wafer level packaging dry film materials can be used. First step of the WLP built-up is a polymer coating. Different permanent dry films are available to replace spin-on polymers. Next step is metal lead formation. A subtractive or a semi-additive process can be used here. Dry film photo resists can be used for both type of lead formation. Metal built-up is then covered with another layer of dry film polymer. In case of multi layer redistribution the second polymer layer is followed by a second metal layer and a third polymer layer and so on. After the final polymer passivation (in case of a single layer redistribution the second polymer layer is already the final one) dry film photo resist can be used for electro-plating of UBM (under bump metallization) and solder or Cu-pillar-bumps with or without solder cap. An example of Cu-pillar-bumps with Sn cap is shown in the paper. Instead of electro-plating the complete bump there is also the option of the plating the UBM only and stencil print solder paste into the resist openings. The metal stencil of classical stencil printing is then replaced by the photo resist. After printing the paste the wafers pass through a solder reflow oven with the resist still on the wafer. This requires high thermal stability and good strip ability that cannot be delivered by spin on resists, but only by some special dry films. A cross section after reflow is also shown below. For 3-D-packages dry films can be used as a photo mask for Si dry etching. They do have the capability to bridge over etched cavities or to create 3-D structure. Opportunities provided by the use of dry films will be discussed in the paper.
Tobias Baumgartner Karin Hauck Michael T(o)pper Dion Manessis Oswin Ehrmann Klaus-Dieter Lang Werner Liebsch Mats Ehlin Toshiaki Itabashi
Fraunhofer IZM, Gustav-Meyer-Allee 25, 13355 Berlin, Germany DuPont de Nemours s.a.r.l., Rue General Patton, Contern, L-2984 Luxembourg DuPont Electronic Technologies, Research Triangle Park, NC, USA, DuPont Kabushiki Kaisha, Sanno Park Tower 11-1, Nagata-cho 2-chome Chiyoda-ku, Tokyo 100-6111, Japan
国际会议
西安
英文
50-54
2010-08-16（万方平台首次上网日期，不代表论文的发表时间）