IPC International Community magazine an association member publication
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24 I-CONNECT007 MAGAZINE I MARCH 2026 ton or pads-only plating can help reduce the impact of this. As copper gets thicker, the ability to control these dimensions diminishes. A realistic tolerance on 35 μm (1-ounce) copper is typically greater than ±25 μm. The tolerances go up from there as copper thickness increases. Holes Drilled holes: Mechanical drill bits are generally available in 25 μm or less increments through the range of common bit sizes of 100 μm to ~ 6.5 mm. Common tolerances for mechanical drill operations are ±25 μm for a non-plated hole and ±75 μm for a plated hole. Remember, any flexible circuit that is two or more layers will typically require plating. Lasered holes: The tolerances on a lasered hole feature are a little tighter and typically fall in the ±12 μm range, but be aware that laser drilling is more expensive than mechanical drilling, Mechanical drilling is typically performed on a stack of materi- als. In some cases, it can be up to 10 or more sheets or panels high. Additionally, today's high-speed drills may have up to six spindles, which can all run simultaneously. Edge or Trim Line • Soft tooling: Chemically milled dies, or steel rule dies. These options typically offer profile tolerances of ~ ±0.4 mm • Laser-trimmed outlines: The actual laser pattern typically is defined to a tolerance of ±50 μm. • Hard tool punch and dies: The tolerances on this method of excising a part are very similar to those of laser-trimmed outlines. Usually in the ±50 μm range. Cover Openings If we lump together both solder mask (photoim- ageable coverlay) and traditional polyimide covers, they can be defined in a few different ways: • Solder mask openings are typically imaged with a laser direct imaging (LDI) system or a high-intensity printer, with LDI becoming in- creasingly common. In both cases, the size of a typical SMT opening is held to ±12 µm. • Drilled cover openings would follow the same guidelines as the drilled holes above: ±12 μm as they come off the drill. Figure 1: A four-spindle drill.