Pan Pacific Symposium Conference Proceedings


LASER PROCESSING OF HIGH DENSITY INTERCONNECTS

Author: Neal Hofmann
Company: Siemens Electronic Assembly
Date Published: 2/13/2001   Conference: Pan Pacific Symposium


Abstract: The rapid miniaturization throughout the electronic industry is driving innovative interconnect technologies. These technologies must be competitive, reliable and allow the manufacturer to build boards or packages that can accommodate the CMOS VLSI circuitry of tomorrow. As a consequence, the packaging and PWB industry are facing the challenging task of finding processes for smaller vias, fine pitch circuitry and soldermask. The use of lasers to produce these interconnect structures is gaining acceptance in the high-end production facilities.

One example is the transition today from mechanical drills to laser via drilling. The bottleneck the mechanical drills pose is they can not facilitate smaller via diameters than 6 mil in production. This means that the pad diameter has to be 14-20 mil, thus taking a large area of the board real estate1 The PWB and Advanced Packaging Industry are making the switch to laser via formation technology to accomplish the smaller pads. This technology is based on the UV Laser and CO2 Laser drilling machines delivered by 12 vendors internationally. Today the CO2 systems compose 70% of the world market share, but as the vias become smaller than 50um (1 mil) the trend is moving from IR laser systems to Green and UV Solid State laser systems. The paper discusses the pros and cons in relation to throughput and quality of these laser processes.

Most imaging processes used in PCB run into roadblocks at 100 um (4 mil) pitch. Alternatives to conventional imaging technology are Laser Direct Imaging (LDI) and Laser Structuring (LS). The LDI technique is an extension of the photoresist process, whereas the laser structuring can be used to create a mask in resists, tin or materials that are not photosensitive. The laser structuring is essentially a micro machining process. The paper will focus on the direct structuring of tin to create masks for etching and the direct structuring of soldermask to accommodate fine pitch packages. Examples for both applications will be discussed in terms of yield, cost and capability.



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