cj at @scalarelectric posts on Twitter about using wedge-shaped solder-paste cutouts in their stencils:
For fine-pitch leaded components, I’m seeing tremendous success with Wedges™ for manual-paste/place reflow.
- Increased gap between paste shapes
- 50% reduction in total paste application
- Occupies same rectangular envelope as default paste shape
- Huge improvement in yield
I can see that it can increase the space between fine pitch pads. cj continues:
To get 50% coverage by way of EAGLE’s (design-wide) pad-shrinking rules would give you what’s shown on the right. Compared with 50% coverage by Wedges™ left. I do use pad-shrink almost everywhere, but for pads with high aspect ratios I think I prefer this bulkier shape.
If there was a way to set pad-shrink on a per-package basis (instead of per-design), I might do exactly that. But once you gotta go in and draw the art manually, the pad-shrink feature goes out the window.
cj continues: I tend not to have much of an issue with leadless packages using simpler paste art. The issue I see with leaded packages is that the high-aspect-ratio recommended footprints result in way too much solder going down, and all that extra solder ends up in undesirable places.
And I came up with the idea after building a proto with the default stencil artwork and getting an outrageous number of bridges.
This is that DF11, .5mm w/ Wedges, no mask between. No bridges, no opens.
cj later says: In my limited use of this technique so far (~150 joints), I’ve had zero shorts or other cause for rework. Compared to a previous attempt at assembling this design with the standard stencil artwork, where 5-10% of joints had issues.
I use it almost everywhere, but EAGLE’s “Perimeter Shave” pad-shrink technique struggles with high-aspect-ratio pads. To get (e.g.) 50% paste coverage you end up with paste apertures that are basically as long as your pad, but ~half as wide. Sometimes *very* narrow.
A final interesting discussion: