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104 SMT007 MAGAZINE I SEPTEMBER 2020 this perplexing and currently expensive PCB industry problem. Next, Fritz showed many real examples of microvia failure since microvia challenges and reliability issues have become a great concern to the PCB manufacturing industry. He pro- vided updates on the work of members of the IPC V-TSL-MVIA Weak Interface Microvia Fail- ures Technology Solutions Subcommittee and opportunities to learn about the latest devel- opments in methods to reveal and explain the presence of latent defects, identify causes and cures, and consistently and confidently supply reliable products. The IPC-V-TSL-MVIA Subcommittee is work- ing with IMEC in Europe on its European Space Agency (ESA) microvia reliability study. IPC is using its test vehicle to test stacked microvias on a typical high-Tg laminate, and D-coupons are being fabricated for IPC. James W. Fuller, Jr. The next speaker was James W. Fuller, Jr., VP of engineering and technol- ogy development at San- mina Corporation. He dis- cussed the use of a smartly designed test vehicle, cou- pled with a unique IST test protocol, that provided the company with the tools to improve microvia robustness quickly and definitively. One key challenge included, "How can the technical team evaluate lot-to-lot differences using current test protocols?" Next, the project was to identify and imple- ment an effective combination of a coupon and test that allows for a sig- nificant differentiation of product pro- cesses by making the coupons more sensitive and make the test more aggressive and test to failure. Their IST system was utilized to create a new, more aggressive test coupon at new temperature extremes. The new coupon had 4-, 5-, and 6-mil microvias with these via constructions: 1. L1-14 through via and L2-13 buried via 2. L1-2-3 and L14-13-12 stacked via offset from buried L2-13 3. L1-2 and L14-13 blind via stacked on buried L2-13 4. L1-2-3 and L14-13-12 stacked via on buried L3-12 5. The experimental results for stacked microvias resulted in Table 1. The results of Sanmina's work provides a platform that allows for actionable data from site-to-site, simple evaluations of electroless process control and selections, the evalua- tion of material choices, and the differentia- tion of laser equipment, noting the influence of desmear and glass etch, as well as compari- sons of design considerations. Bill Birch Bill Birch, president of PWB Interconnect Solu- tions Inc., and Hardeep Heer, VP of engineering and CTO of Firan Technol- ogy Group (FTG Corpora- tion), were the next speak- ers. Their presentation, "Reliability of Microvias: Troubleshooting MV Failures," addressed their findings from recent WMI DOEs. They discussed various contribut - ing factors causing microvias to fail and what has been done to make microvias more reliable. Their findings for Type 1 10-layer microvias board are presented in Tables 2 and 3. All the testing was Table 1: Experimental results, stacked microvias, IST cycles to failure.

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