What to do when solder isn’t penetrating the aperture.

Insufficient fill occurs when the amount of solder paste deposited on a printed circuit board by the printer is much less than the stencil opening design.
Among the potential causes:

Stencil: Paste scooping effect, especially on large pads.
Recommendation: Segment the large opening into smaller apertures.

Screen printer: Paste does not roll into aperture.
Recommendations:

• Reduce print speed.
• Increase print pressure.
• Adopt lower squeegee contact print.
• Ensure paste is not expired or dry.
• Ensure sufficient board support.
• Reduce squeegee pressure.

Paul Lotosky is global director – customer technical support at Cookson Electronics (cooksonelectronics.com); plotosky@cooksonelectronics.com. His column appears monthly.

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