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88 PCB007 MAGAZINE I JANUARY 2019 If we have learned anything about moving into HDI manufacturing, it is that it takes a great deal of thought and discipline to be successful. Unfortunately, as the following bullet points delineate, all too often, the fabricator underestimates the scope of HDI and what this manufacturing strategy truly entails. Here are a few common mistakes to avoid: • Bootstrapping it • Designers treating microvia technology like small through-holes • Being afraid to invest in process improvements • Failing to bring the "total package" to the end user • Continuing to do the same things for the last 30+ years • Thinking HDI is only for smartphones These are common mistakes that companies, engineers, and managers make, and are left wondering why they are not participating in the HDI market successfully. These misconceptions lead many firms to miss the HDI opportunity. So, let's frame up the strategic choices, and begin by discussing desmear and metallization. Desmear and Metalization Not a whole lot is different here. It is all about removing drill smear and any laser drill debris from the capture pad, and ensuring that subsequent plating adheres to the resin and copper surfaces. Essentially, you should strive for the quality of the plating (Figure 1). There is no evidence of plating adhesion issues or defects or debris at the capture pad. However, notice the lateral resin removal where the capture pad meets the side wall of the vias. This can be controlled by adjusting the via formation parameters, desmear chemistry concentrations, and operating temperatures. Note the shape of the via. Yes, it is preferred for quality plating purposes to ensure a "V" shape to the blind via. If the via is more or less shaped like a coffee cup, plating is challenged. If the via has a smaller diameter at the top, then widens as the opening leads down to the capture pad, uniform plating will be difficult if not impossible to achieve. Figure 2 shows an excellent guide with respect to via shape. We will discuss more on plating issues related to via shape in a future column. I Moving in Microvias, Part 3 Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY Figure 1: Blind via properly drilled and plated. Figure 2: Preferred shape for blind via formation. Left is optimal, the middle is okay, and Right is not good.

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