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32 The PCB Magazine • November 2017 MOVING INTO MICROVIAS, PART 2 A concern with via shape as shown in Fig- ure 2 is fluid dynamics as related to the various plating processes. One of the reasons that laser via formation may be preferred over mechani- cal drilling is the via shape. Laser via formation provides a shape that is shaped more like a "V" with a wider opening at the top of the via. This aids in promoting more uniform plating along the via wall and capture pad (Figure 3). The advantage of a smooth transition from traditional drilling to microvia formation on ex- isting equipment is also significant. Transition costs, resulting from downtime while fine-tun- ing upstream and downstream processes (plat- ing, innerlayer alignment, etc.), can be limited. Having the processes under control will make the adoption of other microvia formation tech- nologies much more rapid. So, why consider laser drilling at all and just use mechanical drilling for all microvia produc- tion? Although the capital cost may be very low for mechanical drilling, the operating cost may not be. The costs per via are mainly determined by the drill bit costs that are strongly depen- dent on the bit (i.e., via) diameter. Worn and broken drill bits increase the cost of operation significantly. The cost of drill bits is dependent on the price of tungsten and cobalt. During the last year or so, both metal prices have increased significantly. With advances in laser via forma- tion equipment, one must consider its imple- mentation as via diameters decrease for certain applications. Carefully weigh all costs including capital expense, mechanical drill costs, and via quality and productivity. Summary Moving into microvias and HDI technolo- gy is a critical step for any PCB fabricator. But the market exists and is growing and profitable. Contrary to popular belief, HDI is not just for smartphones. There is an entire market that even small fabricators can exploit and establish a profitable niche. PCB References 1. Holden, Happy, "HDI Handbook," avail- able for free download here. 2. Author discussion with Happy Holden. 3. Burgess, Larry. "Blind Microvia Technolo- gy by Laser," IPC APEX EXPO, 1999. Michael Carano is VP of tech- nology and business development for RBP Chemical Technology. To reach Carano, or read past columns, click here. Figure 3: Blind via formed by UV-YAG laser drill with optimal parameters.