Component Spacing vs Solder Mask Minimum Width (Insufficient Solder)

[edwardt]

Trying to push the envelope by spacing components tightly such that the pads are separated by 7mils, which allows for 4 mils solder mask webbing.

Questions:

Is there a standard which directly addresses this?

What would be the concern, solder bridging or insufficient solder?

Is the 4mil solder mask webbing sufficient to isolate the two pads solder paste?

Thanks, Ed

 

[edwardt]

The components I am placing close together are 0402 RLCs...

Trying to push the envelope by spacing components tightly such that the pads are separated by 7mils, which allows for 4 mils solder mask webbing.

Questions:

Is there a standard which directly addresses this?

What would be the concern, solder bridging or insufficient solder?

Is the 4mil solder mask webbing sufficient to isolate the two pads solder paste?

Thanks, Ed

 

[marce]

IPC-7351 / Cad Library of the Future / Manufacturers compatibility data.
If the solder paste screen is designed correctly, no concern, only enough solder is deposited for the correct joint formation.
Yes.

 

[FvM]

Many SMD libraries and manufacturer footprint suggestions also define an occupied area or "courtyard" to account for placement tolerances. It usually requires a larger component spacing than minimum solder mask.

 

[edwardt]

IPC-7351 / Cad Library of the Future / Manufacturers compatibility data.
If the solder paste screen is designed correctly, no concern, only enough solder is deposited for the correct joint formation.
Yes.

Thanks for the reply. I am assuming that there could be in increase in risk of solder shorting between LANs across the 4mil solder mask webbing (which in this case wouldn't really matter as the components share the same net between the two pads, but could insufficient solder result as well? Could it somehow pull the solder over the SM webbing onto one of the pads?

 

[marce]

Not if the correct parameters are used to deposit the solder, that means the correct solder paste screen design, the correct squeegee speed and pressure etc.

USE IPC-7351, this is a world standard, well tested and used by most tuned in designers and companies. Unlike manufacturers recommendations and other libraries; IPC-7351 is based on years of tried and tested footprints.