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PCB Electrical Testing

Discussion in 'Electronic Design' started by Ian Bell, Oct 2, 2010.

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  1. Ian Bell

    Ian Bell Guest

    I am based in the UK and currently use a UK PCB manufacturer who actually has the PCBs made in
    China. Prices are very good and include electrical testing.

    Another UK company (PCB Train) offers similar prices for PCBs fabricated in the UK except they do
    not include electrical testing - with electrical testing included they are far more expensive than
    my current supplier.

    Now, given that my PCBs are double sided, rather simple tube (valve) based designs, would I be
    making any serious compromise by buying PCBs that have not been electrically tested?

    Cheers

    Ian
     
  2. Gerard Bok

    Gerard Bok Guest

    How much would you save on 'going untested' ?
    What would it cost you if you get, say, 1% faulty boards ?
     
  3. Ian Bell

    Ian Bell Guest

    In the quantities I use it costs and additional 25%.

    Presumably 1%.

    Cheers

    Ian
     
  4. Guest

    Electrical testing itself shouldn't be *that* expensive. It depends on what
    your fallout rate would be and the cost of the assembly. If your board is of
    any complexity at all (large number of traces and vias, fine pitch traces,
    etc.) your fallout rate could be substantial. The added cost could be because
    they know they'll have to eat a lot of boards, rather than the actual cost of
    testing. That would certainly bust your cost curve, considering that you'll
    be throwing away finished product instead of just raw boards (as they would
    be). Find someone else.
     
  5. Guest

    We get a lot more than 1% "x-outs" on even our small boards and we don't see
    completely bad panels.
     
  6. Hi Ian,

    I always specify BBT for production boards, since it costs so much (in
    time and effort) to fix faults. Sometimes you will be lucky and get zero
    failures in a few hundred boards - but sometimes there will be 10% and
    that is a lot of boards to scrap/repair. Depends a bit on the design
    rules and the supplier of course.

    It seems there are two types of board testing. One type ("flying probe")
    costs me ~£60 setup and ~40p per board to test. The other ("bed of
    nails") is ~£200 setup but zero per board.

    For prototypes I don't bother, since I will likely spend so much time on
    them anyway and the quantities are so low that the BBT setup looks very
    expensive as a "per board" cost. I can't remember ever having a problem
    on a "prototype" quantity order (say 1-5 pcs). Perhaps they test these
    anyway, don't know.
     
  7. Ian Bell

    Ian Bell Guest

    I already have someone else who does do electrical test. My only reason for considering changing was
    to support a local company during the current bad times.

    Cheers

    Ian
     
  8. Guest

    Ok, you've fixed the expense of building up from defective boards but you
    still have no idea what your fallout will be. Unless this is an incredibly
    simple board with very relaxed groundrules, I'm sure it will be much greater
    than your 1%. Yeah, if it were only a few dimes it might be good to support
    the local guy, as long as you can make it and your quality doesn't suffer.
     
  9. Guest

    Those costs are *highly* dependant on the complexity of the board. We have
    one where they laughed at us for suggesting bed-of-nails.
    Again, that depends on the complexity. As you note above, troubleshooting and
    repairing boards is *very* expensive, ten times so on an unknown design.
     
  10. Ian Bell

    Ian Bell Guest


    Indeed, if the total cost difference including fallouts was small it would be worth it. I was hoping
    to get some idea of what the typical insdustry fall out rate is.

    Cheers

    Ian
     
  11. Ian Bell

    Ian Bell Guest


    As I mentioned in my origin al post, these boards are really quite simple. All through hole
    components and minimum track size 25 thou/mil. Does that make a significant diffiernce to the fall
    out rate?

    Cheers

    ian
     
  12. Sure, perhaps I should have said that I was talking about two-layer
    boards only (Ians' "rather simple tube designs"). My supplier always
    tests 4+ layer boards anyway as part of their process. Even if they
    didn't I would get them tested since they would likely be always
    impractical to repair, what with the hidden internal planes and all.
     
  13. Rich Grise

    Rich Grise Guest

    If it ain't broke, don't fix it.

    Cheers!
    Rich
     
  14. Those are very "generous" design rules. I normally use 8 thou, my
    supplier will do down to 5 thou without charging extra. However some of
    the defects I have seen on untested boards would still create failures
    even with your rules. For example very occasionally there are things
    that look like "scratches" cutting several parallel tracks. But usually
    it is single track cuts or shorts.

    But yes I think the difference is significant. I think you could risk
    it. I stuck with untested boards for quite a long time before I gave up
    on them and paid the extra, And this was with <8 thou rules and probably
    more complicated boards than yours.
     
  15. Guest

    Correction: laughed at us for suggesting a "flying probe" test. It would
    have taken all day.
    Sure, that's three times the width of a normal trace. You only have a
    two-sided board, another key advantage. Considering that you will do an
    electrical test before populating the board your favored supplier might be a
    good bet.
     
  16. Ian Bell

    Ian Bell Guest


    I remember getting lots of those in 'the old days' (30 years ago) and they were mostly due to human
    hairs introduced in the photographic process. I would have thought with CAD this would no longer occur.

    Cheers

    Ian
     
  17. Ian Bell

    Ian Bell Guest

    Indeed. My only motivation in these hard times was to try to place more work locally.

    Cheers

    ian
     
  18. It only happened a few times, and only on ~one board per batch. I
    guessed they might be scratches on the boards photo resist (rather than
    on the master photoplot).

    But hairs work too :)
     
  19. Nial Stewart

    Nial Stewart Guest

    I am based in the UK and currently use a UK PCB manufacturer who actually has the PCBs made in

    Ian,

    Are you talking about production or prototype quantities?

    All the boards I build are prototypes. I'll always specify electrical test as I
    want to be debugging my design, not boards or the build (I use a good, not cheap
    assembly house).

    I tend to use Kelan (who have recently been bought over) for these boards. They have beaten
    chinese build prices for 10 offs on reasonably complex (6/8 layer) boards
    so it might be worth getting them to quote. They are a 'proper' board house,
    not a pile em high operation like PCB train.

    www.kelan.co.uk

    Hope this helps,


    Nial
     
  20. Uwe Hercksen

    Uwe Hercksen Guest

    Hello,

    if your boards have a low trace density, wide traces and wide isolation
    gaps, few pins and vias with larger hole diameters the probability of
    electrical errors should be low.

    Bye
     
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