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50 PCB007 MAGAZINE I SEPTEMBER 2023 If your HDI or UHDI production process is quality challenged, don't assume your etcher is to blame. Many factors impact the quality of the final product, so assess broadly, and you may find that "the devil is in the details." Generally, the first place most people can get good product specification measurement is at the end of the etching process. It's natural and easy to blame quality shortcomings on the etcher. By all means, look at your etcher and invest some time trying to improve its perfor- mance but don't stop there. Other factors may be affecting the etch uniformity. Each process step prior to etching adds vari- ation to the final product. In most cases, the added variation is small, but as the features on the etched panel get smaller and closer together, they become more important. For example, back in the days when 0.004" (100 µm) lines and spaces were state-of-the-art (yes, I have been around that long), a circuit board manufacturer that had been mostly pro- ducing consumer boards requiring lines and spaces of around 0.008" or more took on a job requiring the then state-of-the-art 0.004" lines and spaces. eir yields went from more than 95% on their 0.008" line-and-space product to less than 50% for the 0.004" space product and they lost money on that job. A lot of time and effort was spent on etcher optimization, which improved yields significantly but not to the point of profitability. In this instance, it was found that a change in procedures in the photoresist exposure step solved their problem. For most of their pro- duction panels, the exposure was made as soon Don't Just Blame the Etcher The Chemical Connection by Don Ball, CHEMCUT

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