I have been hand stenciling circuit boards for about 2 years. In that time I stenciled over 1,000 circuit boards by hand. The tools you use will reflect on your work. Meaning, if you use an inexpensive Mylar stencil, then your finished product will reflect that of an inexpensive stencil. I recommend professional metal stencils with a frame (even for hand stenciling). Spreading solder paste is a lot like spreading peanut butter. Fresh out of the fridge it's difficult to spread. Let the solder paste warm to room temperature.
Things You Will Need:
- Printed Circuit Board (PCB)
- Stencil (metal or mylar)
- Solder PasteSqueegee or application tool
- PCB holders (other pcb's with tape work well)
- Scrap Paper
- Paper towels (tissue paper works too)
Step 1: Securing the PCB
Begin by securing your PCB to a flat surface. If you don't have pre-cut holders, you might want to consider using other PCBs. You will want to make sure the holders are the same thickness as your PCB. Typical thickness is 1.64mm.
Step 2: Aligning the PCB
After you fit the PCB snug tight with the holders, you can then align your stencil on top. The key, is to make sure every pad/hole can is aligned.
Step 3: Aligning the PCB (cont.)
You see the stencil is aligned pad for pad, directly on top of the PCB. Sometimes when working with Mylar stencils, they flex after they have been taped to the desk/table. This shouldn't be a big issue, because your squeegee will push the stencil down on the PCB as it runs over the board.
I like to tape only 2 sides of the stencil to ensure the stencil doesn't rotate. The reason I don't tape all 4 sides, is because the Mylar stencil seems to flex too much. And it's a pain when it comes to removing the stencil.
Step 4: Solder Paste
Locate your solder paste and make a blob from the starting side of the PCB.
Step 5: Squeegee
Using your squeegee or applicator, slide from one side of the PCB to the other. Be careful when you attempt to lift up the squeegee, it will attempt to lift up your stencil. If the stencil were to lift and set back down...that could be bad, because the paste may not come out clear. You only want to lift the stencil one time after solder paste has been applied. Make only one pass with the squeegee for best results.I prefer to remove the stencil in one steady fluid move lifting only "one side" of the stencil, and leaving the parallel side to act like a hinge ( < ).
I found the paste comes out crisper, vs. trying to lift the whole entire stencil at one time.
Step 6: You're Done!
You have successfully applied solder paste to your PCB with a stencil. Remember to clean your stencil.
Step 7: Cleaning the Stencil
To clean the stencil, I prefer to set it flat on a piece of scrap paper, and slide my clean squeegee over the stencil to pick up excess solder. Apply a cleaning solution (rubbing alcohol or acetone) to your paper towel, then go over your stencil until it appears clean. Clean each side of the stencil (#1 and #2). It makes for easier application the next time you use your stencil.
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