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60 SMT007 MAGAZINE I NOVEMBER 2020 Parametric Test System The PTS was created by Hewlett Packard's Printed Circuit Division in 1987, based on early HP coupons used in production from 1972 onward. Those early coupons focused on inner layer shifting by using the copper on I/Ls shorting to a plated through-hole (PTH), moire´ patterns, and hole quality cross-sections. Addi- tional influence came from parametric PCBs used as a training and process vehicle for the first NanYa PCB Facility in Taiwan (~1983). This PCB had various design-rule technologies on it and provided feedback on how the pro- cess was improving. The HP PTS was a group of seven coupons that could be placed on production panels or used on a parametric panel to provide a snap- shot of the capability of the process. The initial seven coupons (Figure 1) were designed to test: 1. Outer layer registration 2. Inner layer registration and shifting 3. Conductor/pad opens and shorts 4. Continuity of PTH and I/L conductors 5. Artwork defects 6. Solder mask registration 7. Etch factors The coupons were all designed to be tested by a facility's continuity testers using the bed- of-nails open-short testing machines. In this case, the tester was an ATG2000 grid tester. The tester's fault-file was captured by an HP work- station and stored. Each coupon had a stored perfect response or netlist that was compared to the fault file, and the opens and shorts were translated to dimensional shifts or other para- metric data. The RS/1 statistics program was used to produce control charts and statistical reports, as well as historic data. This system is shown in Figure 2a. Figure 2 (b and c) also demonstrates the small standalone coupon testers that opera- tors had to check the process immediately as a confidence indicator. These home-built mil- liohm meters worked with a simple 1-ampere power brick, a 4-digit digital panel meter, and a machined-Plexiglas coupon holder with eight spring-loaded gold pins wired to a 4-position rotary switch in a four-wire Kelvin measure- ment scheme (Figure 3j). Conductor Analysis Technology CAT is the longest-running commercially available parametric coupon system. Born out Figure 1: The seven coupons designed by HP; (a) Outer layer registration in 0.00025" increments, (b) inner layer registration and shifting in 0.00025" increments, including 0.1-mil X-ray vernier, (c) trace/trace/pad open and short circuit on multiple layers, (d) PTH continuity patterns, including I/L connections at various angles to the PTH, (e) artwork defects analysis in 0.00025" increments, and (f) etch factor analysis in 0.00025" increments.

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