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20 The PCB Design Magazine • November 2016 C. There is a direct relationship between thickness and uniformity of plated copper in via holes and the ability to consistently form associated plated layer copper features that meet target width, space, diameter and height requirements. PCB designs that contain high aspect ra- tio through vias, sequential lamination, and/ or copper filled microvias can require multiple panel and/or pattern plating steps. Each plat- ing pass adds to the thickness of the resultant copper patterns. Etching of thick plated copper is more difficult than thinner copper base foil or pattern plated foil. The variability in finished conductor width and height can have a direct influence on the ability to meet controlled im- pedance requirements. Shaughnessy: Is there anything else you'd like to add? Wolf: In 2013 CAT began using the OM Thermal Stress System to test both PCQR 2 and HATS TM via reliability coupon designs. The OM system is also capable of testing the AB/R and D cou- pon designs defined in IPC-2221B, Appendix A. CAT developed the OM Thermal Stress Sys- tem as a cost-effective performance based via net reliability test methodology which per- forms both convection reflow assembly simula- tion per IPC TM-650 2.6.27 and air-to-air ther- mal cycling per IPC TM-650 2.6.7.2 in the same test chamber with one set-up. Via net resistance measurements are continuously monitored with one reading taken per net every second. Both the IPC PCQR 2 and the IPC-6012 QML programs utilize the OM system test methodol- ogy. The PCQR 2 program provides strong statisti- cal data that quantifies process capability, quality and reliability while the QML program is a sam- pling plan which verifies conformance to IPC specifications. We offer the OM Thermal Stress Systems for sale or lease, and test services are pro- vided from both CAT and our service partners. Shaughnessy: Thanks for your time, David. Wolf: Thank you. PCBDESIGN If a PCB supplier facility cannot consistently demonstrate excellent via formation capability (via net yields greater than 95%) and plating uniformity as measured by via net resistance (capability potential index or C p equal to or greater than 2.0), those via structures will most likely not meet specified via reliability require- ments after reflow assembly simulation and thermal cycling. B. Not all PCB fabrication facilities can meet the same via registration requirements. For the easiest to register via structures, de- sign with the largest via pad annular ring that the design will allow. The industry benchmark data from PCB supplier facilities participating in the PCQR 2 Database shows that only a limited number of globally based PCB supplier facilities can consistently meet the following registration minimums with yields greater than 95%: • Through and sub-composite via registration requirements of less than +/-0.005 inch [+/-125 mm] • Blind and buried microvia registration requirements of less than +/-0.003 inch [+/-75 mm] CAT'S DAVID WOLF ON VIA RELIABILITY ANALYSIS David Wolf