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18 DESIGN007 MAGAZINE I MARCH 2025 Feature Article by Ray Fugitt DownStream Technologies Over the years, I've seen many PCB design- ers make DFM mistakes. At DownStream, I work with design and fabrication, and some- times it feels as if the two segments are speak- ing completely different languages. But once designers learn to speak "fab," many of these DFM challenges disappear. I taught a class at PCB East 2024, "e 21 Most Common Design Errors Caught by Fab- rication (and How to Prevent em)," with my co-presenter Mike Tucker of Millennium Circuits. At PCB West 2024, we presented an updated class, "10 (More) Common Errors in PCB Design and How to Catch em." Is this an evergreen topic? Design007 Editor Andy Shaughnessy and columnist Kelly Dack attended our PCB West class, which was packed with designers and design engineers, and many of them had ques- tions. When Andy asked me to contribute an article on the most common miscommuni- cation errors made by PCB designers, I said, "Sign me up." You Know the Drill Let's start with the drill chart shown in Fig- ure 1. It seems like a normal drill chart at first. But take another look. What is a "finished drill size" anyway? Do they mean hole size? What's the difference? 1. Drill size would be the actual bit used. 2. Hole size [diameter] refers to the size aer plating. Typically, the difference here could be 0.004"- 0.005", which is significant. Not taking the drill size into consideration leads to problems with creating proper padstacks, these include: 1. Annular ring issues 2. Teardropping questions 3. Plane clearance issues (especially in BGA areas) Example: Let's say incoming design inspec- tion discovers that the 0.032" holes have insuf- ficient pads. e fabricator bumps up the pad size, using etch compensation as the reason for not notifying the designer. So much for your note that says, "No changes without approval." Learning to Speak 'Fab' Figure 1