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78 PCB007 MAGAZINE I FEBRUARY 2019 In Part 3 of this column series, I discussed critical aspects of desmear technology related to the preparation of microvias before metal- ization. In this month's column, metalization of the via is presented. It is important to un- derstand that getting the metalization process dialed in is the first step to ensuring long-term reliability. However, in general, just how reli- able are microvias when compared to through- hole reliability? Reliability Extensive reliability testing was performed by IPC—Association Connecting Electronics Industries—and the Interconnection Technol- ogy Research Institute (ITRI) in the late 1990s about the reliability of microvias [1] . Other groups like the High-Density Packaging Users Group (HDPUG) and Jet Propulsion Labora- tory (JPL) have also produced reports on the superior reliability of small-blind vias over through-hole vias [2] . Understanding why is quite simple! The via aspect ratio (AR, or depth-to-diameter ratio) is less than 1:1 compared to a through hole that has an aspect ratio of greater than 6:1 that goes as high as 20:1. This is a result of the thin materials and low Z-axis TCE ma - terials used in HDI. Materials available for high-density interconnect (HDI) designs are numerous. Thus, these materials are covered by IPC-4104A and not IPC-4101B. In addition, industry consortia such as HDPUG have un - dertaken multiple studies on material perfor- mance as related to HDI. There continue to be extensive studies on materials used for the fabrication of printed wiring boards. This includes the HDI market and technology segment of the supply chain. Therefore, thin HDI materials are suited for thermal heat transfer as covered in the IPC HDI design standards (IPC-2226). Moving in Microvias, Part 4 Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY

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