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  • Author Author: modalpdx
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No more paper stencils

modalpdx

I royally botched a GoodFET build today, and at least some of the blame rests with the silly paper solder stencil that I made (shush, it was glossy and it should have worked better. Who doesn't want to save a buck?) I figured it was worth a shot. One fried MSP430 later (I had to use my hot air gun thingamajig to get it off and realign it, and I suspect I cooked its guts in the process) I'm back at square one and I still don't have a GoodFET. Argh?

 

That which does not kill us makes us...something.

 

Oh well. I just ordered replacement chips through Newark/Element14 so round 2 is coming.

 

UPDATE, 6/13: I have replaced the MSP430 2618 chip (torched by my heat gun during Round 1) with a less expensive 2418. This time, I hand-soldered it. No complaints or errors so far. Two things worth noting for others that my be considering building a GoodFET: the 2418 chip seems to be a drop-in replacement for the 2618 (fingers are crossed that the Internet has not let me down on this bit of information) and the monitor self-test ("goodfet.monitor test" at a command prompt) takes a really long time. Don't kill it thinking it's frozen or in an infinite loop, both of which are probably not true.

  • in reply to clem57

    After a certain size, it stops being "a production" and becomes "a sport." image

  • in reply to michaelkellett

    The stencil was made from a page from a glossy magazine that I ran through my laser printer. I believe I printed the tStop layer in Eagle to get the pad blocks. From there, a sharp Xacto knife cut the holes.

     

    I didn't cut out individual pads for the chips; instead, I cut narrow bars out of the paper for each row, trying to make the holes smaller than the pads because I knew this would dump more paste onto the board. I was right: the pads were pasted-over to the point where I couldn't see well enough to place the chip correctly, which is part of what lead me to screwing up the board. All my fault, but still.

     

    When I built a Bus Pirate 4 a few months back, I had a stencil made at OSHStencils that worked beautifully. That thing had around 30 components, most 0603, but everything reflowed correctly the first time around. It was so nice not having to worry so much about placement! A stencil would be too much to pay for on a board as tiny as a GoodFET42, of course. Still, they're nice to have.

     

    I'm considering a paste dispenser. I've seen affordable sets with multiple tips on eBay and elsewhere (haven't tried Aliexpress yet). Until then, toothpicks. image

     

    0402? Yeah, microscopes seem pretty essential at that size. I think my eyes would stay crossed for hours after soldering components that tiny.

  • in reply to michaelkellett

    And I just struggle with headers smaller than normal. WOWimage

  • in reply to modalpdx

    Hello Erik, Thanks for the info.

    How did you make the stencil ?

    I sometimes blob the solder paste on with an el-cheapo Chinese (via Aliexpress) solder paste dispenser and hotplate reflow. Ages ago I bought  a cheap BGA IR machine which I've just started to use - I'll post something when I have  a bit more to report.

    I'm happy with 0603 and I'll do 0402 if I have to (need microscope for them) for hand soldering with an iron.

     

    MK

  • in reply to michaelkellett

    I'm actually hotplate-reflowing, not hand-soldering. I have a kitchen single-burner (1000W) with a 1/4"x6"x6" MIC-6 aluminum plate that I sit on the heating coil and I use a Harbor Freight router speed control to dial in the heat level. Works like a charm.

     

    I've hand soldered chips like this MSP430 in the past (QFP 64) with minimal fuss. If I didn't want to experiment with paper stencils in general, I would have just done the entire build by hand with an iron. There aren't many parts, although other than the chips they are all 0603 which is smaller than I like to hand-solder. After a point, it just gets unpleasant.

     

    Anyway, here's the GoodFET with parts placed but before reflowing on the hotplate. Next time, hand-solder or use less paste.

    image

     

    And, the paper stencil over the GoodFET before applying paste.

    image