Screaming Circuits: Another Land Pattern Mixup


Another Land Pattern Mixup

PCB fab error - L2 pads are not correct Here's an interesting error that doesn't show up very often. Notice that the opening in the solder mask matches about what the copper land pads should be, but the pads themselves are really tiny. To start with, it's not an exact match. It would fit the part a little better if the pads were closer together, but more than that, the pads are just the wrong size. The stencil looks okay and the solder mask opening looks okay (except that it's a little too too wide).

I'm not really sure what went wrong here. Maybe one  person started making a custom library part and PCB Fab error - L2 Pads - Stencil and PCB do not match (stencil correct)someone else finished it, or maybe the component was changed between starting and finishing the library part.

If the stencil photo looks like it's made of cloth - it's not. We just photographed a CRT view of it.

Duane Benson
Need more chocolate.


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It's probably overkill, but to help avoid land pattern problems, I draw every part in Autocad 3D.
Once the layout is finished, I create a DXF file of the top pads and silkscreen, then use the x/y data to place the 3D parts. Of course, this is assuming the parts were drawn in Autocad correctly. This also gives our assembly shop a preview of what they will be building.

I hear you. I hate building library components. Hole size on thru-hole connectors seems to be my most common trip up.

I feel bad for the board designer. I did something similar with a shape on a thermal test board five years ago. The shape was supposed to be etch, but I put it in soldermask. The board wasn't supposed to do anything besides dissipate heat so I didn't put that much thought into to it.

The mistake on the board in the photograph would have been easily spotted in ViewMate if the rest of pads on the board are correct.

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