Issue link: https://iconnect007.uberflip.com/i/1511625
NOVEMBER 2023 I PCB007 MAGAZINE 45 e CITC cycles were verified by FEA mod- eling, TMA, and moiré and has been used by IBM for 30 years. e rapid nature of the test and the small size of the coupons has led IBM and I3 Corp., to be able to characterize many important steps in the PCB manufacturing process. PerfecTest came along in 1989 to address the problems in multilayer material movement and drill registration. e coupons (Figure 7a, b) are placed at the outer edges of the multi- layer panel. e coupons work by detecting which plated through-holes have detected the movement of a particular I/L copper wedge. Figure 7b illustrates the 0.002" increments from 1 to 9 mils in the X-Y axis that the coupon will detect. Coupons can be placed on every layer or just specific ones. Although no spe- cific testing equipment is required, Figure 7c shows the PerfecTest unit equipped with anal- ysis and data storage soware. PerfecTest closed in 2013 but many compa- nies around the world continue to use the cou- pons. A simple ET-continuity tester or home- built 4-wire Kelvin probe can be used to test panels aer etching. Hewlett-Packard's PTS-parametric test sys- tem was created by its Printed Circuit Divi- sion in 1987 based on early HP coupons that had been used in production since 1972. It was designed aer HP's parametric dies that had been used in its wafer fabrication. ose early coupons focused on inner layer shiing, by using the copper on I/L's shorting to a plated through-hole, moiré patterns, and hole qual- ity cross-sections. Additional influence came from a parametric printed circuit board used as a training and process vehicle for the first NanYa PCB facility in Taiwan, around 1983. is PCB had various design-rule technologies on it and provided feedback on how the pro- cess was improving. e 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 benchmarked capability of the pro- cess. e initial seven coupons (Figures 7a–f ) were designed to test: 1. Outer layer registration 2. Inner layer registration and shiing 3. Conductors/pads open and shorts 4. Plated through-hole, I/L conductors continuity 5. Artwork defects 6. Solder mask registration 7. Etch factors e 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. e 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 shis or other para- metric data. e RS/1 statistics program was used to produce control charts and statistical reports, as well as historic data. is system can be seen in Figure 7a. Also seen in Figures 7b-c were the small stand-alone coupon testers that operators had to check the process immediately as a confidence indicator. ese home-built milliohm meters worked with a simple one-ampere power brick, a four- digit digital panel meter and a machined-Plexi- glas coupon holder with eight spring-loaded gold pins wired to a four-position rotary switch in a 4-wire Kelvin measurement scheme. e concept was adopted by Foxconn's internal PCB fabrication group as a method of benchmarking its 16 large PCB facilities in China; the number of different coupons was extended to 24 coupons, many that, aer mea- surements, are used for assembly performance benchmarking. Summary For as long as there has been printed circuit production, there have been coupons to test every factor. Many excellent coupons have been designed over the years, too many for me