6 Common Solder Mask Errors Every PCB Designer Should Know

Solder mask is a critical layer of insulative lacquer applied to a printed circuit board (PCB) that prevents solder from bridging between conductive traces and causing shorts. Here are six common solder mask errors every PCB designer should be aware of:

  1. Inadequate Clearance from SMD Pads:

    • Solder mask should not encroach upon surface mount device (SMD) pads. If the clearance is too small, it can lead to solder mask slivers, which can cause solderability issues and, potentially, shorts.

  2. Excessive Clearance around Through-Hole Pads:

    • While some clearance is necessary, too much clearance around through-hole component pads can allow excessive solder to flow away from the pad during wave soldering, resulting in weak solder joints.

  3. Missing Solder Mask Between Fine-Pitch Components:

    • In designs featuring fine-pitch components, failing to apply solder mask between the closely spaced pins can lead to solder bridging during reflow.

  4. Incorrectly Sized Solder Mask Openings:

    • Both undersized and oversized solder mask openings can create problems. Undersized openings might lead to incomplete curing of the solder mask, while oversized ones could result in unintentional bridging or insufficient solder joints.

  5. Solder Mask on Test Points:

    • When the solder mask inadvertently covers test points or gold fingers, it can prevent proper electrical contact. Make sure test points are free of solder mask to enable consistent test connections.

  6. Incorrect Solder Mask Dam Widths:

    • Solder mask dams between pads help prevent solder bridging, but if they are too narrow, they may not be effective, or worse, they might not be printed at all if below the minimum width that the PCB manufacturer can achieve.

To avoid these errors, PCB designers should always follow the manufacturer's specifications for solder mask application and engage in thorough design reviews before sending the design out for manufacturing. Additionally, designers can utilize automated design rule checks (DRC) that include solder mask rules to catch these issues early in the design process.

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