Mask Control

I wonder. Is solder mask difficult to control in most CAD packages? Or do we just not need to control it very often so we forget? Take this little footprint here. Oval pad

It looks like someone just used a little flood fill to create the thermal pad rather than creating a new custom footprint. That would have been fine except that the flood fill area has solder mask on it.

In Eagle, if you want to keep the mask off of an area that would other wise have mask, you draw a polygon in layer 29, tStop (or 30 bStop for the bottom) over the are you want to keep mask off of. Not difficult, but not necessarily obvious either. With Sunstone PCB123, you pretty much do the same thing with the SS Top or SS Bottom layers. I don’t know about any other packages, but I would guess it would be a similar approach.

Of course, just making the footprint with the library package editor would take care of it too, but sometimes it’s just more expedient to take a footprint that’s close and mod it up with a polygon or something similar.

Duane Benson
Is Oregon like a Polygon?
No, because it hasn’t “gone” anywhere

5 thoughts on “Mask Control

  1. Duane,
    In my experience across a number of packages in the last 20 years, a number of those don’t exist any longer, it is pretty similar through most. Custom shapes typically require some manual intervention for soldermask or pastemask issues. Some packages create a custom shaped pad more readily/easily than others but still will usually require manual/custom handling of the mask openings in the land pattern.

    Brad Velander CID
    Senior PCB Designer
    Cobham Avionics, Kelowna

  2. I wouldn’t even say that’s a fill, just a very large trace.

    Altium is the same as you describe, default name is Top Solder/Bottom Solder. 3D view is good way to check for this problem.

  3. To err is human! Goto admit I’ve done similar to that once or twice. The large pad drawn with copper, then you forget to add the corresponding image to the solder resist layer.

  4. Hacking a standard footprint “on the fly” to make a custom like this invites more trouble and gotchas in the long run than making a proper part-specific footprint with the soldermask opening defined. Avoid the trap of “never time to do it right, always time to do it over”.

    Bill Burton, CID
    Blue Sky Electronics

  5. Regardless of how the solder mask on this footprint is fixed…
    The root cause of the error is human.

    Older tools.. make it harder to create custom solution…( new footprint? naw, just a simple tweek here .. and we are done!)

    Older processes (excessive bureaucracy) …. make it slow to verify new footprints…encouraging bad / temp solutions.

    Temp/custom solutions.. generally make a design harder to maintain in the future.

    better training? better processes? better tools?
    all will help…

    Maybe the root cause extends further up the “chain of command”?
    Was there inappropriate levels of urgency being placed on the designer? (I don’t care! get it done now!… forcing bad shortcuts to be made)
    Error is really at the management level?

    so many ways to screw up… so little time…

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