Issue link: https://iconnect007.uberflip.com/i/1540184
OCTOBER 2025 I DESIGN007 MAGAZINE 43 TA RG E T C O N D I T I O N Why This Matters: Tolerance, Testing, and Traceability Take a look at the title block tolerance on your com- pany's PCB drawing format. Do you see a tolerance for "1-ounce" or "2-ounce" copper? Probably not, and that's exactly the problem. Specifying copper weight in ounces disregards any thickness toler- ance. You wouldn't spec a critical mechanical fea- ture without a tolerance, so why would you do it for a critical electrical one, which could directly affect your power distribution solution? Plainly speaking, when a PCB designer simply indicates "1-ounce copper" in a stackup, it causes an instant phone call or engineering query (EQ) because a PCB CAM engineer must know whether the designer made important calculations using base or finished copper thickness values. One-ounce thick- ness might mean 35 µm, or it might not. Depend- ing on plating, etching, and process variation, your finished copper could be thinner—or thicker—than you expected. If your design depends on controlled impedance, thermal management, or precise voltage drops, those variations can cause real-world failures. When you refer to IPC-6012 and specify copper thickness in micrometers or micro-inches, you're not just using more tangible units, you're enabling the entire manufacturing and QA process to work more effectively: P C B t ra c k a n d g a p p ro c e s s i n g g u i d e l i n e s c h a r t . ( S o u rc e : N CA B G ro u p) ▼ • Designers can accurately calculate trace width for current carrying and impedance • Fabricators can measure actual copper thick- ness via micro-section • Inspectors can assess quality to a defined spec with measurable criteria By referring to the IPC-6012 charts and declar- ing base copper in your stackup, a PCB designer can calculate signal integrity and power distribution based upon minimum finished copper thickness: an absolute. The charts take the guesswork out of the equation. Once you know the base and finish expecta- tions, you can help your PCB supplier by spec- ifying manufacturable conductor widths. Work- ing with a supplier or an industry standard is the best way to avoid manufacturing pain points while choosing copper width and spacing values. I've found this NCAB PCB design guideline to be very helpful in indicating trace and space (gap) capa- bility. As in IPC-6012, this chart also leads design- ers in referring to copper base material in ounces, but then shows inner layer (IL) and outer layer (OL) print and etch capabilities. A Call to Designers The industry has done its part by adopting dimen- sional copper specs. It's time for the design commu-