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34 I-CONNECT007 MAGAZINE I MARCH 2026 T H E C H E M I CA L C O N N ECT I O N BY D O N BA L L , C H E M C U T T olerances have become increasingly tight as PCBs have grown more complex and reduced in size, weight, and power con- sumption. Even if we maintain a traditional ±10% variation in etched line width, the tolerance in a 50 µm (0.002" or 2 mils) wide etched line is only 5 µm (0.0002" or 0.2 mils). That's not very much and it gets even worse as the line and space re- quirements drop to 25 µm lines and spaces. Lately, I've seen some tolerances as low as ±5% but so far, that's more of a wish than what is acceptable. Unfortunately, it won't be long before that wish becomes a demand. So, what is the best way to manage the cumulative tolerances? Each process step contributes to the total variation in the final product and the variation from Step 2 in the process is added to variation from Step 1 and so on down the line to the final step. To the best Managing Cumulative Process Variations for Fun and Profit