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80 I-CONNECT007 MAGAZINE I SEPTEMBER 2026 T RO U B L E I N YO U R TA N K the technology to create very high-density PCBs and substrates. Of course, this sounds easier than it really is. With increased complexity, yields are chal- lenged. At the end of the day, it is all about yields. Process Controls for Fabricating Reliable Microvias The small blind vias, known as microvias, pose distinct challenges for PCB fabricators. Unlike through-holes, microvias are far more difficult to drill, desmear, metallize, and plate. Laser drilling adds further complexity compared with mechanical through-hole drilling. As shown in Figure 1, there are seven funda- mental quality concerns, all of which can only be verified through microsectioning. Therefore, dedi- cated panel coupons are essential for confirming reliable microvia fabrication. This is more reason for extreme diligence in the via formation opera- tion. With a poorly formed via, even the best plating chemistries will not improve the situation. In a future column, we will address the issues shown in Figure 1 in more detail. The testing of HDI PCB prototypes can be accom- plished with flying probe electrical testers, but volume production is still relegated to bed-of-nails- type custom fixturing. Multiple head flying probe testers do have more throughput, but even those models with 12 heads have only limited production capacity. It is the bed-of-nails fixture that will have to handle the production load. Unfortunately, the very high-density nature of HDI boards makes custom fixtures very expensive. HDI boards have test points that, depending on the application, average 100–2,000+ pins per square inch. As an example, HDI server board may require 150–250 pins per square inch. Semicon- ductor package substrates exceed 1,000 pins per T RO U B L E I N YO U R TA N K Figure 2: Multipurpose test vehicle. (Source: Happy Holden)