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90 PCB007 MAGAZINE I JULY 2022 In this month's column, I will discuss opti- cal alignment for pinless lamination stackup, a topic that complements the induction lami- nation in my November 2021 column. Exam- ples of this type of equipment are seen in Figure 1. Pin tooling plates have been used for lamina- tion since it first started sometime in the 1960s. I first encountered multilayer stackup when I was assigned to increase capacity for our mul- tilayer output in 1972. is was to accommo- date the growth of our computer business. Unfortunately, the explosive growth of our cal- culator orders in 1973 required that we look for numerous vendors to produce the six-layer logic board in the HP-35 calculator. Hewlett-Packard evolved from using four small holes in our pin lamination to using a four-slot center-line pin with post-etch punch in 1974. Registration experiments on this tran- sition were highlighted by a DOE in Chapter 3, Figure 4 of my book, 24 Essential Skills for Engineers 1 . Optical Alignment/Coupon Welding for Stackups Pin Lamination Although many schemes have been used, the most popular is the four-pin center-line slot approach. Here a high-precision tooling tem- plate with mechanical pins is used for the lay- up and registration. e inner layers must first be prepared with the corresponding registra- tion holes. ese holes are generally drilled or punched post etch. e prepreg must also have holes for the pins. ese holes do not have to be precise, and they can be 1 or 2 mm larger than those of the inner layers. Stainless steel shims and release film are employed between groups of stackups (called books). For the con- ventional vacuum-heated hydraulic multilayer press, numerous tolerances lead to misreg- istration of the various inner layers. Figure 2 illustrates six such tolerances from an excellent paper by Anthony Faraci. 2 Pinless Stacking Around 1999, Faraci, who had been work- ing w ith multilayer tooling for nearly 15 Happy's Tech Talk #10 by Happy Holden, I-CONNECT007 Figure 1: Three suppliers of multilayer stackup alignment and induction bonding of the stackup: a) DIS Technologies; b) InduBond; c) CEDAL. (Source: Product brochures)

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