Connect with us

PCB manufacture

Discussion in 'CAD' started by rickman, Apr 10, 2008.

Scroll to continue with content
  1. rickman

    rickman Guest

    I had some PCBs made with 22 boards per panel (small boards). I
    wanted a single panel for prototypes, but it turned out I could get 6
    panels for only $500 more. This would get me through the first round
    of production if I didn't need any changes. The day the maker was
    supposed to ship them, I got an email saying they had a poor yield and
    only got 116 good boards out of 7 panels vs the 132 I ordered.

    So now I have a concern about the quality of the boards. I was told
    the failed boards had problems with the plating in the 10 mil holes I
    used for vias. They claim that the "good" boards have no quality
    issues. My concern is that the vias may be marginal and open once
    they are temperature cycled a bit.

    I am not sure how to handle this with the vendor. I guess I could
    just flat out tell them that I am concerned with investing some
    $18,000 building up over 100 boards only to have my customer see
    failures in the field. I don't feel like they have done 100% on this
    since they did not provide the quantity I requested.

    They have offered to rebuild the entire set of panels if I am not
    happy with the result, but that would be a week delay. I also don't
    know if they are willing to let me use one of the current panels and
    remake the rest.

    Anyone have experience with 10 mil via holes and reliability issues?
    If you have a problem with an order like this, is it reasonable to use
    one panel and reject the rest?
     
  2. linnix

    linnix Guest

    Anyone have experience with 10 mil via holes and reliability issues?
    As you have figured-out, pushing the process limit could be
    expensive. We would not go below 16 mil holes, even if we need bigger
    boards. Are you sure you can't use bigger holes?
     
  3. rickman

    rickman Guest

    Sure, I can use bigger holes. But I can't use bigger pads. It was
    hard enough to make the layout work with 10 mil holes and 24 mil
    pads. This board is very small and defined by the customer's
    requirements. It is a daughter card on an existing product so I have
    no flexibility in size except for extending one end which I have
    already done as much as possible. Even that does not do a lot for the
    density issue since the board is over 5 times longer than it is wide.
    Extending the length more just means I have longer lines to try to
    squeeze through the same bottlenecks around the chips and
    connectors.

    I guess I am confused about "process limits". I have seen vendors
    that claim to have capability for hole sizes down to 6 mil. They just
    say that they can't guarantee that the hole will not be plated closed
    which is fine with me. So I don't see where 10 mil holes should be a
    real issue. Did I pick a poor PCB maker? Am I just not grasping the
    realities of PCB manufacturing?
     
  4. DaveN

    DaveN Guest

    Did the vendor you chose give this claim? If not then there's your problem,
    choose a different vendor.
     
  5. DaveN

    DaveN Guest

    Sorry, I meant did your vendor make the claim on 10mil?

    Additionally did you order 132 boards or the yield acheived from the panels?

    The realities with any process is that as you approach its limits, you will
    get higher fallout; edges of the bell curve and all that.

    If your supplier is telling you that parts have failed then it tends to
    suggest that they have a reasonable quality system in place. They know the
    process and its limits and are therefore testing for those failures. It's
    an old but true saying that you can't test in quality, you can only design
    for it.
     
  6. Wingle

    Wingle Guest

    I am looking at a fab right now that is a mix of 10 and 7 mil drilled
    vias. Board has 8 BGA and is 2x7" so your process is not in any way
    pushing the envelope. If you are getting bad plating in 10mil vias
    then the most likely cause is insufficient agitation during the
    plating and air bubbles were trapped in the vias. You will need to
    section (slice & dice) the failing fabs to confirm whether the plating
    is actually thick enough across the whole of the fab. If it is air
    bubbles you are probably okay as that usually is batch related. If it
    is a function of the vendor skimping on the plating, you are screwed.

    That being said, I have no empirical data but there does seem to have
    been an increase in the failure rate of commercial fabs in the last
    year or two. Usually in the plating of the vias. This is across
    several vendors US & Asian.
     
  7. qrk

    qrk Guest

    At least they have a good enough quality control that they can spot
    this problem. You can have them do a cross section of a good board to
    see if the vias look healthy.

    Plating systems have to be top-notch to handle small via sizes. If the
    board house hasn't kept up on updating their equipment, they will have
    problems with small features.

    I routinely use 8mil drill with 15mil pads. The pad size is marginal,
    but the four board houses I have used never had problems with that via
    size for the past 5 to 8 years.

    There is one case back in the early 90s where the plated through holes
    would disconnect when moderate current (apx 1 amp) passed thru the
    plated hole after soldering. Before soldering, the PTH handled 10A,
    after soldering it would blow around 1A. Most of the bypass caps
    disconnected at power up.
     
  8. TheM

    TheM Guest

    I had problems with a vendor once, it was "weak" vias. They were 20mils
    though, done on early ROHS process. And yes, baking boards twice
    for smd and through-hole did create new broken vias, some immediately
    and some later. If I knew about this, I'd toss entire batch right away.
    Caused quite a big of grief. I ask my vendor now to leave them a bit
    longer in the metalization "soup" and he had to compensate for part of the
    damage (tarnished name can't be restored so easily).

    You can try baking boards without components and than passing them
    through tester again, make sure testing current is set to high"ish" level.

    Mark
     
  9. rickman

    rickman Guest

    Thanks for your suggestion. I thought of that, but I don't have a way
    to test the bare boards. Turns out I have four more weeks to order
    the panels, so I have some time to evaluate the boards in the
    prototypes.

    I'm waiting to hear back from the board vendor. But I expect I will
    have to bite the bullet on this one and reorder the production panels
    from a better supplier. The whole reason I bought so many was that
    they were not much more than just buying prototype quantities. So I
    knew it was a bit of a risk. Not a big deal now that I have more time
    to deal with it. I was mainly worried about the schedule.
     
  10. TheM

    TheM Guest

    PCB vendor surely has a machine to check for continuity, even the cheap
    vendors do. Ask them.

    Mark
     
  11. qrk

    qrk Guest

    We have used filled vias for a different reason, to get more space in
    a tight layout. Really strange to see pads with no visible drill hole!
    I normally avoid filled vias due to extra cost. When I put thermal
    vias under a Dpak, I make sure there's enough solder paste to fill the
    via. The pad, or Cu pour, on the opposite side of the board is mostly
    covered with soldermask, but the via drill hole isn't tented so the
    via can burp. I usually use around 50 to 70% pad coverage for
    solderpaste, depending on the part and/or if I use thermal vias in the
    body pad.

    Harry, I've been having fun making switching supplies recently. Made a
    50W forward converter and, something we chatted about briefly a few
    years ago, a SEPIC switcher to charge up a capacitor bank with
    constant current for a pulse amplifier. Both run at 600kHz. The new
    controllers sure make life easy. Both these supplies used the
    technique above for the power components thermal vias.
     
  12. rickman

    rickman Guest

    You are suggesting that I temperature cycle the boards a few times and
    send the blank boards back to the vendor for retest? I guess that is
    an idea. So far they have been a bit difficult to communicate with.
    I shouldn't say "difficult", just very slow getting answers from
    them. I ask a question and it seems to require a lot of research to
    get an answer. Then I hear back after a day or so. It is like they
    don't seem to feel like they screwed up and are not making any real
    effort to help me deal with the resulting repercussions.

    I'll give them until tomorrow (Friday) to get back to me with
    something substantial. If we don't have some sort of dialog going
    that is likely to result in an improvement in my satisfaction, I will
    just cut my losses and move on. I need to keep my customer happy and
    I can't do that with an unresponsive vendor.
     
  13. JosephKK

    JosephKK Guest

    Just be sure that you tell them that. There are a lot of native
    English speaking "Front ends" for Chinese fabs that are several time
    zones away. It could explain the lag and the poor information
    transmission quality.
     
  14. rickman

    rickman Guest

    These guys are in the US. I did finally get someone who could at
    least try to get a little info, but I didn't get a lot. I was told
    they checked the chemistry and didn't find anything out of whack. He
    offered to do a destructive test, but never gave me a RMA. Finally
    someone called as a general follow up and I told her what had
    happened. It was a bit surprising that she didn't know ahead of time
    that there was a problem. She also didn't have access to any
    information on the problem or the contacts I had already had about
    this. She asked me to send her the last email about what they had
    found and promised to get back to me on Monday.

    At this point I am ready to release the test fixture to be made and I
    am looking for someplace else to do it. It is 8" x 10", 4 layers and
    I only need a small number, say 4. Any suggestions?
     
  15. www.pcbcart.com do electrical testing as standard, no additional fee.

    Dave.
     
  16. [Snipped]
    I have had very goods results from http://www.pcbcart.com. They are
    based in china, but I have had no problems with their product. The
    quality is excellent, the price is very good and you can get a direct
    quote on their web site. I normally pay about US$60 to get the boards
    couriered to South Africa, which takes about 36 hours. They have Fedex
    and DHL as an option.
    The only problem I have had is that the status on their web site are
    sometimes not updated. To get the latest status it is best to email
    them.

    Regards
    Anton Erasmus
     
  17. rickman

    rickman Guest

    You got it in one! I ordered from Sunstone. I finally got a proper
    reply from the last person I spoke to and she has given me answers
    that sound like maybe they weren't just pulled out of somebody's...
    well, you know. They said there was a problem with air bubbles and
    that the good boards really should be good. I will be bake cycling
    these boards before I build the production units, but I expect I will
    be able to use them if I don't have to make any changes. They have
    offered to make up the 16 board shortfall or give me credit for the
    missing boards. Plus they are offering 15% off my next order.

    I got electrical testing. Good thing, huh? I assume that otherwise I
    would have gotten untested panels and found the problems myself.

    I can't argue with the price. The reason I ordered from them was that
    they offered 6 panels at the price of one panel from the other shops.
    I think I am going to give them the order for the test fixture. That
    should go out today.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-