Removing solder mask between pads can mitigate this defect.

Bridging is solder connecting or, in most cases, misconnecting two or more adjacent pads that come into contact to form a conductive path.

Possible PCB causes include:
Surface mount pads will contribute to coplanarity issue, resulting in poor gasketing during printer setup.   

Recommendations:
It is highly recommended to remove solder mask between adjacent pads, especially for fine-pitch components.

Possible stencil causes include:

• Dirty stencil with paste underneath, which will contaminate the bare board on the next print, attributing a potential bridge. Recommendations include verifying zero print gap setup, ensuring minimum print pressure, increasing wipe frequency, and using different cleaning chemicals.
• Stencil tension. Recommendations include ensuring stencil tension is tight. Poor stencil tension will make it impossible to have a good setup for consistent print definition.
• Aperture design. For fine-pitch components, it is highly recommended to have the opening slightly smaller than landing pad size to improve stencil to PCB gasketing.

Paul Lotosky is global director – customer technical support at Cookson Electronics (cooksonelectronics.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it . His column appears monthly.