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How does my DIY SMD stencil look? *pictures*

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How does my DIY SMD stencil look? *pictures*

By george graves
-  Thu Feb 17, 2011 6:59 am #120505
So...I made my own SMD stencil - all from thing I found at the hardware store. I'll be doing a full (video)write up once I iron out some kinks - so bear with me.

Pictures are below - but before you forget - please let me know what you think of my joints. It looks like there might be a tad too much solder? Please let me know what you think of it. Too much on the toe?

Some surface mount stuff.
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It's really hard to convey to people how small this stuff is.
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Some test boards - they do nothing. Just testing pad size and the effects of surface tension, pad width and trace location on centering parts during reflow.
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I'm a sneaky little bastard.
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Paste laid up. It came out perfect I think - might need to adjust the stencil for the amount, but looks great.
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ready for reflow
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Finished. Almost perfect. A bit too much solder? My 10 mil traces don't look bad either. That's insane.
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Another look at the heel. How's it look?
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Re: How does my DIY SMD stencil look? *pictures*

By george graves
-  Thu Feb 17, 2011 8:39 pm #120568
@fll-freak - smack your IT guy upside the head. It's just dropbox. ;)

@groggory - I'm planning on a full write up with sources materials, and video soon. Let me work out some details for you.

@TheDirty - Yea, I'm almost thinking that a bit more means higher success rate? (BTW - I think just making the holes smaller and keeping the stencile the same thickness will work. If not, there are two or three other ways you'll be able to fine tune it for yourself when making the stencil)

Also, I get the sense (someone correct me if my thinking is off) that a bit too much solder would be desirable for home/hobby etching. It seems it would ensure success, and have less rejects. No? A dry joint would seem more likely to break, work intermittently, or generally cause havoc.

Does someone know what is the downside to too much paste? What can happen? Why is it bad? (besides bridged pins) Is there a mechanical stress I'm not seeing? Harder to inspect?

Re: How does my DIY SMD stencil look? *pictures*

By TheDirty
-  Thu Feb 17, 2011 8:55 pm #120569
I can get tombstoning with too much paste. That's when the 0805/0402 stands up on one side. Also, too much paste will cause a chip with a thermal pad to 'float' or be raised a little off of the board. Other than bridging, that's the only issues I have.

Generally I use vary little paste.
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Re: How does my DIY SMD stencil look? *pictures*

By lexxmac
-  Thu Feb 17, 2011 10:45 pm #120572
I think the whole thing looks pretty freaking awesome. Your stencil does look pretty thick (compared to the crappy kapton ones I've used), which is going to make the joints have more solder on them (which I personally would prefer).

I'd love to know how you made the stencil.

Re: How does my DIY SMD stencil look? *pictures*

By MichaelN
-  Fri Feb 18, 2011 5:45 am #120584
Looks nice - exactly the same as what I've done in the past :)

I used 0.005" thick brass sheet from the hobby store, with Press'n'peel iron-on transfer sheets and a laser printer to print the design. The design is ironed onto one side, with the other side completely covered in resist - you could use paint etc, but I just ironed on another piece of Press'n'peel at the same time, which was printed all black.

I used ammonium persulphate for etching, mixed a little stronger than usual. You have to watch for over-etching, since it does take much longer than copper PCBs to etch. I guess if you were very careful, you could iron-on a matching pattern on both sides of the brass sheet, which would allow you to etch finer holes.
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