Creating SMD Stencils for Solder Paste

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Rochey

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Hello folks,

thought I'd post some more details here on making SMD stencils.
I'd let you guys who aren't sure what I'm talking about do a google for them. (for the sake of keeping this post shorter...)

Yes, I could get them laser cut and wait a few days for one to arrive in the post. But I'm too impatient.

Here's the background story

- I have a design for a SMD tool controller that I've recently had PCB's made for.
- I want to make (and sell) these as an assembled board for folks on groupdiy and other forums to use, when assembling future expat audio boards
- I have the design already done in Eagle - and have the ability to export the Solder Paste locations (known as Top Cream in Eagle) as a gerber file, or print to a lazer printer.


Experiments already done.
- I purchased some laminating pouches for ID cards, like these:
s0340469_sc7

- I printed out the image on my lazer printer on to regular paper.
- I removed one side of the pouch (the thinner side that has the adhesive... the other side is clean, thin plastic.
- I taped the paper beneath the plastic, and cut through the plastic to make the apertures with a sharp blade.

This worked, but the holes aren't clean, and solder paste tends to collect and stick to the uneven edges. - annoying.
Pictures to be uploaded soon.

Next Experiment
- Use my CNC machine to drill small holes for each SMD pad.

Questions
- Will a circular deposit of paste be just as effective as a deposit of paste that fits perfectly over the pad?


Cheers
/R
 

Rochey

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Chae,

Thanks for the offer - I'm too impatient though! (and I have a CNC machine here... would prefer to try and get that running first!)

Here's what I'm planning to do for my experiment...

- Generate only the SMD pads:
- Convert to Gerber:
- Load into Cambam, my friendly CNC GCode generator:
- Select all the pads, then press "Drill":
- Update the tool diameter for my 1mm pcb drill:
- Set up the CNC machine, and PRAY! :)
 

Rochey

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I don't say this very often, but everything worked as planned!

I'll post pictures soon, but in the meantime, my feedback is:

It took 2 minutes to set up and drill the stencil.
2 minutes to align the pcb with the stencil
1 minute to squeegee the paste through the stencil!

The result is a very clean pcb with a perfect dot of solder paste on each pad.

Pictures to come!

/R
 

Rochey

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Pictures with proof!

The stencil, after cnc drilling it with my zen toolworks CNC machine.
Notes: The drill will naturally want to pull the plastic up. I had to tape it down on all edges, and hold the plastic down near each cutting point.
Cutting time was less than 2 minutes.
451-031111103128-23161.jpeg



Results: Clean amount of solder paste on each pad.
Notes: I deliberately didn't put paste on every single pad on the TSSOP microcontroller. It would have been a mighty mess as the hole would have been larger than the footprint. Instead, I put two blobs of solder - one at each corner to tack down the device.

451-031111103129-242162.jpeg




Sorry for the poor quality.
 
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