I've been evolving my stencil for home reflow (modified toaster oven) over some prototype iterations. I've been moving towards smaller holes to avoid bridging. In the future I may follow the advice I was given in this thread
https://www.eevblog.com/forum/manufacture/qfn-bridging-tips/ (thanks btw) for using a supplier who can do soldermask between the pads, and electropolished stencils. But for now I'm just adjusting my current process to what works for me and keeping it cheap.
So I've been specifying the paste layer for some components. The last time I ordered from my current supplier they did it fine. But, with the last order, they based the stencil off of the soldermask layer (GTS) instead of the paste layer (GTP).
I'm assuming this isn't right? I'm going by their naming specifications. I've emailed them asking if they can send me a corrected stencil, but am obviously having to wait for a reply because of CNY. Just wanted to make sure I hadn't done something stupid. Should I have clearly spelled out that the paste layer should have been used? They used it last time so I'm not sure why they're being random.
Thanks, Joe
You should include a README file that spells out what each file is for (top copper, top paste, etc.) and not leave it to chance. They are running through this data really fast, and can miss things like this. Different programs make different file extensions, so if you don't spell it out, it may not be their fault. If you DID spell it out in a documentation file, then for sure it is their fault.
Jon
The last time I ordered from my current supplier they did it fine. But, with the last order, they based the stencil off of the soldermask layer (GTS) instead of the paste layer (GTP).
Quality PCB design software will name the layers in full so there is no confusion.
An example is shown below. Generated in DipTrace (of course).
There is no standard for gerber layer names.
This dates back to the DOS days when you only had 8.3 filenames so a range of 3 letter combinations was used, and unfortunately still persists.
Now that >3 letter extensions are possible, names like <file>.topmask etc. can be useful to make the meaning clear
Paste should be a seperately generated layer, as you don't want paste on through-hole pads, and you may want special paste pad definitions, e.g. on large area pads.
Thanks all, and apologies for the slow reply.
I used their naming convention, but they only specified the extension. So I had .GTP for top paste layer. Next time I'll put something like stencil.gtp and put a note that I want them to use that file.
Anyway, they've re-done the stencil without quibbling, and shown me a picture. All looks good.
Joe
Make sure that it is in a plain txt format, no rtf etc. I have spelled out my layers many times to PCB mfgs. and still they ask which layer is which, even with the included file. Label it PCB layers or something like that...My 2 centavos.
Make sure that it is in a plain txt format, no rtf etc. I have spelled out my layers many times to PCB mfgs. and still they ask which layer is which, even with the included file. Label it PCB layers or something like that...My 2 centavos.
Oh, yes, something else I do is put the layer name ON THE GERBER drawing. My package (Protel 99) does this real easily, I just put special text for board name, print date and layer name outside the board outline. When generating the Gerber files, it puts in drawn text for these fields onto the drawing.
If the drawing boldly says "TOP COPPER" they can't come up with a good excuse for fabricating that layer as the bottom silk screen.
Jon
If it is gerber file, GTP is the file for top side stencil.
