August 1, 2006 AT 10:57 am

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!

***

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…

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10 Comments

  1. wowzers — your bake cycle is quite a bit longer than what I use… Although the toasty look on boards can be somewhat endearing…

  2. Hmm. I just ‘guessed’ what do you use?

  3. 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…

  4. 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?

  5. 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.

  6. I’m sure there are nuances here, but my general answer for the first question is no. Dedicated oven under all circumstances.

  7. How did you cut the stencil?

  8. Hi,
    I have been trying to bake a board today. After a bit more than 390 degres, the PCB board started to bend and made a weird sound.
    I can notice that you have ordered the PCB through a company to make the layout.
    I wanted to know what PCB do you recommand me as I am doing the layout through a router (milling machine).

    Thanks

  9. this is a really old and not so good version of the project. its being ‘redone’

  10. This is really good,but we want to know when to bake the PCB’s.Can we refer the manufacturing date code.If the thing is like that in which week we can bake the pcb.

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