Duel Nature: Time to bake the PCBs! (How to make PCB reflow stencils)
OK so boards came in, and there’s 80-100 to be assembled. They’re pretty simple boards: 1 8-pin micro, 3 resistors, 1 capacitor and 2 4-pin header plugs. Since it takes a long time to solder, I designed the board for mass-manufacture: surface mount parts!
Eventually everyone needs to make a lot of PCBs (at home), the best way to do this is to use solder paste and a reflow oven. Since EYEBEAM has a laser cutter I can use it to make a screening stencil and a registration frame. (You can also buy stencils from your 4pcb.com and probably a bunch of other PCB manufacturers) Then it’s super fast to make tons of PCBs. Just silkscreen on solder paste (available at digikey), place the components, and bake!
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First, cut out a frame from 1/16″ acrylic the same size as the PCB, this will be the registration frame
The PCB should be a perfect fit
Extract the stencil info. I took the stop layer, viewed it in GC-prevue, printed it to a file (ie. PostScript), then opened it in CorelDraw which is set up to print directly to the lasercutter
Cut it out in 2-3 mil Mylar
Register (align) the screen on the frame and tape it down
Now…use a biz card or something similar as a squeegee. Lay down a bead of tasty solder paste…
[gv data="http://video.google.com/googleplayer.swf?docId=6066848196815777770&hl=en"][/gv]
OK now you have a board with solder paste dots
Place the components with your tweezers
[gv data="http://video.google.com/googleplayer.swf?docId=-1907760876743714269&hl=en"][/gv]
Repeat 80 times, and put them into the toaster. 200 degrees for 4 minutes, 300 for 2 and then 450 until the paste melts, then 300 for a minute to cooldown.
Yay you are done! now all thats left is the thru hole parts…
August 3rd, 2006 at 1:20 pm
wowzers — your bake cycle is quite a bit longer than what I use… Although the toasty look on boards can be somewhat endearing…
August 3rd, 2006 at 2:27 pm
Hmm. I just ‘guessed’ what do you use?
August 3rd, 2006 at 2:51 pm
i use 325 for about 3 minutes. I also tend to watch my boards carefully in the last minute to see if things are reflowing. Of course, since I don’t do large batches the way you do its probably easier just to have a recipe and go with that. I’m sure there is a great deal of oven variability though.
I think I started watching so carefully because i didn’t like the smell when I burned my boards…
August 3rd, 2006 at 3:48 pm
Is the solder safe to use (health-wise) in an oven? Is it non-lead? Or do you have an oven dedicated just for that use?
August 5th, 2006 at 9:05 am
Unless it’s RoHS compliant it has lead in it. Personally I love lead based solder because of how nice it flows. The lead free stuff is okay but it’s just not the same. If you use a toaster oven for soldering write “NOT FOR FOOD” on it like I did and never use it for food (RoHS or not). My toaster oven was $15.00 at Walmart and was inexpensive enough to buy a second one for food.
August 5th, 2006 at 9:24 am
I’m sure there are nuances here, but my general answer for the first question is no. Dedicated oven under all circumstances.
November 18th, 2007 at 3:51 pm
How did you cut the stencil?