Gloves not Mittens

In this episode Chris and Melissa dig into one of Chris’s favorite PCB design topics: pocket masking vs. gang masking on fine-pitch components.

Chris explains why solder mask slivers matter, how PCB design tools can accidentally create manufacturability problems, and what designers can do to help prevent solder bridging during assembly. The discussion covers solder mask expansion, registration tolerances, stencil printing, pick-and-place placement pressure, and why “gloves, not mittens” is the mental model to remember.

The episode also opens with a few updates, including Chris becoming a Certified Electronics Program Manager and CircuitHub announcing a $28 million raise from Plural Ventures.

TL;DR:

For fine-pitch components, especially 0.5 mm pitch and smaller, pay close attention to your solder mask expansion.

Chris’s rule of thumb:

• Start checking at 0.5 mm pitch or smaller
• Aim for 10 mil spacing between copper pads, edge-to-edge
• Reserve 3 mil for solder mask registration on each side
• Preserve a 4 mil solder mask sliver between pads
• In metric, that means roughly:
  • 0.25 mm copper-to-copper spacing
  • 0.075 mm registration allowance on each side
  • 0.1 mm solder mask sliver

If space is tight, Chris recommends trimming the copper lands slightly rather than sacrificing the solder mask sliver. The sliver is what helps prevent solder from bridging between pads during printing, placement, and reflow.

The short version: protect the solder mask sliver. Gloves, not mittens.

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