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Thread: Custom PCB, Audio Adaptor, afraid of SMD

  1. #1
    Junior Member
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    Custom PCB, Audio Adaptor, afraid of SMD

    Hi,

    I am currently desiging an audio FX module based on Teensy 4.1 + Audio Adaptor board. I built a prototype on perfboard with which I'm quite happy. I would also like to include something like Frank's Memory board: https://github.com/FrankBoesing/memoryboard.

    With the audio adaptor and the memory board, the stack is getting a bit high, so I was thinking about including the SGTL5000 and related circuitry + the additional memory chips on the same PCB; and just plugging the teensy board on top.

    The issue I have is that the SGTL5000 is only available as an SMD. Although I have quite a bit of soldering experience, I have no experience in soldering SMDs, and I only have a temperature-controlled soldering iron. As an additional difficulty, I can only use leadfree solder as I'm located in Europe.

    My question is: is it realistic for a beginner like me to expect to be able to solder SMDs at home ? Which tools would I need at the very least to make the process not too difficult ?

    Or would it be easier to find a substitute for the SGTL5000 which comes in DIP packaging ? From what I've read in this forum, it seems like there aren't any drop-in alternatives.

    Cheers,

    T

  2. #2
    Senior Member houtson's Avatar
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    hi @torché,

    I had a similar issue and concern, I ended up using a different codec (a wm8731) as although still SMD it's an easier package to hand solder.

    Some details in this thread https://forum.pjrc.com/threads/60924...for-Custom-PCB

    cheers Paul

  3. #3
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    The SGTL is 0.5mm pitch TFN - no point risking hand soldering on that. This really requires either an oven or a hot-air rework station,
    and you'll need to use solder paste and a stencil (and a stencil frame of some sort to apply the paste without the stencil moving).
    0.5mm spacing pretty much requires both solder mask on the pcb and stenciling of paste to avoid shorts. Especially for packages without
    long pins

    I made an oven from a cheap toaster oven that I slightly modified (moved the bottom heating element to the top).
    I also made a stencil frame using a steel back plate and strong magnets to clamp the board-holding piece and the
    frame itself - this allows fine adjustment of position yet holds them rigidly for squeegeing the paste.

    I use chipquik SMD291SNL10 lead-free no-clean solder paste and old stencils as squeegees.

    Many PCB houses will do stainless stencils with a pcb order, usually at extra cost - only put SMT components on
    the topside for an easy life(!)

    No new parts are made in through-hole as is much more expensive for industrial manufacture - that's just how it is.

    There is a trick that might avoid need for stencils - pre-tin all the pads with a thin layer of solder and use extra rosin
    to make sure they are not shorting out - then you can hot-air directly down on the tinned pads without needing
    solder paste. If in doubt use less solder and more rosin than you might think - swimming in molten flux is normal for
    SMT rework. The PCB must have solder-mask for fine SMT work BTW.

    With stencil + oven technique is easy to get reliable results like this (ignore the 4 resistors I modded later by hand!):
    Click image for larger version. 

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    All the fiddly work is in the preparation (stencilling, placement of parts) and that's easy to redo if you slip up.
    Last edited by MarkT; 08-01-2021 at 02:19 AM.

  4. #4
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    Thanks a lot for your thread Paul, it looks like we're building the same kind of FX box! I will have a look at the wm8731.

    Mark, thank you for all this information. Regarding the trick you mention about avoiding stencil, how does this work ? Is the surface tension enough to make the solder stay on the pad and avoid shorting them out ?

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