I know this isn’t the right place, but I thought you guys would know the best on this. What is a framed stencil? Also, are there any places to get good stencils?
Does this thread help you?
(And did you try to search the Forum before you posted?)
Thanks, I tried searching and I didn’t see that.
I have purchased good quality stencils from Hackvana (http://www.hackvana.com/store/) and had good results. They offer framed and non-framed.
A framed stencil is one which has a frame. The frame fits a large holder, over the board, so that when paste is applied the assembly doesn’t move.
A stencil without a frame is basically a sheet of polyamide or stainless steel with holes in the material. It’s up to you to figure out how to hold the board and the stencil together while applying paste.
All of the mainline fab houses offer stencils. Some of the quickturn and Chinese places do, too. I just ordered a set of polyamide stencils from OSH Stencils, and I should have them Friday.
Wait, so there’s a cutout for your board so it doesn’t move or is it a big cutout that’s larger than the board?
If you’re not using frame stencil and pasting the board by hand, something like the Stencil8 system is worth considering - http://www.hoektronics.com/2012/10/27/super-simple-smt-stencil8/
(The link actually shows a framed stencil but you can use Stencil8 with a non-framed stencil)
(if you order cheap, you probably get the bottom version)
Applying paste as hobbyist:
There is lots of material and guides out there about this.
Some/most fabs/aggregators that offer stencils also offer some pcb material that will act as alignment help/spacers round the stencil when you put it onto a flat desk and hold the whole thing together with self adhesive tape.
As hobbyist you probably want to get stainless, non-framed and either use some old pcb boards or get the custom spacers from the website that sells the stencils to make your life easier.
Tape everything in place, tape the stencil along one edge (longest is best, avoid bottom edge) to be able to do a couple of boards right after each other.
Also important is the rake/scraper.
I use an old small stencil I don’t need anymore for this.
It needs to have a sharp edge that is clean and straight.
The desk you do this on needs to be flat and firm. You don’t want any flex in there.
The paste should be smooth and not stiff. Try to rake under and angle to not trap air in the pad corners.
The tinier your pads (and thus the holes in your stencil) the better your technique and tools need to be (not to mention paste), to get a successful outcome.
After you got this part mastered there is:
- populating of the pcb with SMD (ideallysome sort of suction pump assembly)
- reflowing the whole thing (ideally some sort of oven that can ramp up to the needed temps in the needed times - see paste manufacturer and SMD datasheets for details)
Soldering paste for SMDs on HASL finished boards
My stencils from OSH arrived yesterday. I think I should have made this one larger. I ordered the $5 plastic jig, and it came with a squeegee to use for applying the paste. Next time I’ll get the 5 mil stencil.