Not every design is practical for every volume.

Not long ago, a customer sent us an 8-layer rigid PCB design for quotation. On the surface, nothing unusual – until we noticed the minimum finished hole size (FHS) was 4 mils. That number might not sound alarming, but in PCB manufacturing, 4 mils is a red flag. Here’s why.

The issue arises when fabricators drill a plated through-hole (PTH) and deposit copper during plating. The remaining diameter after this process becomes the finished hole size. A 4-mil FHS with a tolerance of ±4 mils technically ranges from 0 to 8 mils. That kind of spread becomes nearly impossible to maintain in volume production.

The question not asked may be cause for concern.

It is essential for PCB fabricators to ask their customers engineering questions before production. Clarifying design requirements and expectations ensures they are fully understood, preventing costly errors, avoiding liberties being taken in the fabrication process, resulting in a product that meets both performance and reliability standards.

I write this not only to set clear expectations for customers but to strongly caution that when questions are not asked, there may be cause for concern. Questions must be asked so we can align objectives. The PCB is custom manufactured, and in many cases, the fabricator is either replicating something another manufacturer has built or creating something entirely new. In both scenarios, setting clear expectations is critical. If someone else has built it, we must know what we’re matching. Conversely, if the part number is a first-time build, the customers must understand that we’re doing something that has not been achieved.