Why does drill to copper matter?

When designing flexible circuit board it is crucial to keep drill to copper in mind. That is, the distance between a hole (via or non-plated through hole (NPTH) and a copper feature. The flexible dielectric materials that are used to manufacture flex product are not as dimensionally stable as the standard rigid material (FR4). This material moves, shrinks and contracts during the manufacturing processes which makes drill to copper critical to a successful product.

• Section: The closer the hole (via or NPTH) gets to a copper feature the greater the risk of shorting.
• Section: The minimum recommended distance is 0.005” from a finished hole (via) to a copper feature.
• Section: For board contour routing, the minimum recommended distance from a copper edge to an external corner is 0.010” and .005” for an internal corner.
• Section: If there is not enough room for these distances between your holes, you can request tighter tolerances but will likely have to wait additional time for delivery.
• Takeaway: Keep drill to copper in mind when designing flex circuit boards so that you don't run into manufacturing delays due to tighter tolerances.

Tighter hole to copper is possible, but usually requires a first article to measure the material movement. A longer lead time will be needed.