epoxies suitable for electronics

Discussion in 'General Technical Questions and Answers' started by KJ6HZH, Jul 7, 2020.

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  1. KJ6HZH

    KJ6HZH Ham Member QRZ Page

    A couple years ago I replaced the ceramic filters in my Yaesu VX-7 because they went bad because Yaesu didn't put DC-blocking capacitors on them. I added a chip capacitor to each capacitor and secured it with blob of ordinary 5-minute epoxy. Now I'm told that the epoxy might be hygroscopic and change the capacitance of the embedded capacitor. Is this something I need to worry about?
     
  2. K6CLS

    K6CLS Ham Member QRZ Page

    I've used a lot of epoxies,all types, including 5 minute. Never heard that any were hydroscopic. If they wete, thry wouldn't be used on boats.

    So maybe ir is. Maybe it adds a few pF. Oyt of how many nF in your bloxking caps?
     
  3. W6MK

    W6MK Ham Member QRZ Page

    Your source of this information?

    For many uses, two-part epoxy is considered to be a moisture and water vapor barrier.
    The epoxies used in wood-saturated-epoxy composite boat building are used in large measure for that reason alone and are far superior to, for example, typical resins used in fiberglass (resin plus glass fiber) construction.

    My guess is that epoxies used in electronic component construction are external heat-cured rather than chemically-heat-cured using a catalyst.

    A complex topic which is probably not worth trying to understand fully unless you are an
    industrial chemist. Since most two-part epoxies used by hobbyists are sold as waterproof,
    I very much doubt you have anything to worry about. Other than coronavirus.
     
  4. KJ6HZH

    KJ6HZH Ham Member QRZ Page

    The cap I used is 0.1uF. I was told this when I got back a board with a couple chip caps added to take care of a design problem. I proposed adding a blob of epoxy to hold it down and was cautioned against this.
     
  5. W9WQA

    W9WQA Ham Member QRZ Page

    if you soldered chip caps,(pretty small), i doubt they are going to shake loose !!! overkill
     
  6. W6MK

    W6MK Ham Member QRZ Page

    Definitely overkill. I'd add over-worry.

    Many hardware-store 5 minute epoxies (like Devcon) are advertised as "waterproof." This
    suggests that they are NOT hygroscopic.

    I have used hardware-store epoxies for repairing all kinds of things which
    can be exposed to moisture/dampness. Including ceramics like bowls and
    the top of a ceramic coffee pot. Never a problem.

    Epoxies are used in constructing many electronic components including the potting
    of complex circuit assemblies to WATERPROOF them.

    Not to worry. Unless worry is a major source of entertainment. In which case, see
    a shrink.
     
  7. KJ6HZH

    KJ6HZH Ham Member QRZ Page

    The way I mounted the caps was to bend up one lead of the filter, tack one end of the cap to that and a piece of 30ga wire to the other. A delicate arrangement like that called out for a drop of epoxy. The PCB has stuff bodged on by cutting leads, scraping the solder mask off, and tacking the parts to the exposed copper.

    Photos of the VX7 repair are at https://www.flickr.com/photos/32548582@N02/albums/72157667529801877
     
  8. K6CLS

    K6CLS Ham Member QRZ Page

    The rework folks use a dab of hot melt glue.
     
  9. N1OOQ

    N1OOQ Ham Member QRZ Page

    I wouldn't worry about it. Just placing the filter/caps assembly in proximity to the circuit board probably adds a few pF. So what's a few more? The real question is, how well does the filter work now?
     
  10. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    It's hygroscopic before curing. Open tubes will absorb water and weaken the final product (water will be trapped in the matrix), so make sure you keep the tubes well sealed and without excess air.

    73,


    Mark
     

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