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American PCB fabs defaulting to lead-free

Discussion in 'Electronic Design' started by Joerg, May 8, 2007.

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  1. Joerg

    Joerg Guest

    Almost got a black eye here on a prototype. Ordered a bunch of large
    boards at Advanced Circuits and it turns out that the free upgrade to
    lead-free finish is actually a default that cannot easily be changed.
    IOW you can normally not decline this "upgrade". However, they were very
    understanding that we really didn't want lead-free and will now do our
    protos as production runs. No idea why we go RoHS here in the US now
    (this is a company that actually produces in the US).

    Anyhow, just wanted to let you guys know about that before a nasty
    surprise happens to you.
     
  2. I've got some prototypes from them a couple of weeks ago. Looks like regular
    leaded solder to me... I didn't ask for anything specific, they just came
    this way by default. But mine are all thru-hole...
     
  3. John Larkin

    John Larkin Guest

    Some of the coatings are ok, some (like white tin) are awful. The good
    news is that lots of people are now offering gold plating at the same
    price, and that solders beautifully. The bare boards don't tarnish and
    look like jewelry, too.

    John
     
  4. Don McKenzie

    Don McKenzie Guest

    Gold plating I feel is the best approach, but be careful, as some
    companies are asking 25% more. If you can get them at the same price, great!

    I see the future being RoHS, as most companies will eventually gear up
    for world wide sales. Sales don't have country borders these days. :)

    Don...


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  5. Joerg

    Joerg Guest

    I probably could have gotten gold coating but I had to make a
    split-second decision. The Gerber review took their engineers a while
    and it was getting close to 6:30pm in Colorado. Next time I'll try gold.
     
  6. Joerg

    Joerg Guest

    I'll check that out. Sure would look more "blingy". One of the problems
    was that they just didn't offer tin-lead on prototypes anymore.
     
  7. Elect. gold is our new standard. It doesn't look as rich as the old
    gold plated boards, but it's still nice.


    Best regards,
    Spehro Pefhany
     
  8. The reason is that you cannot sell it in the EU unless it's ROHS
     
  9. Joerg

    Joerg Guest

    However, there is a lot of gear that is exempt and many of the parts for
    specialized equipment cannot (yet) be purchased RoHS compliant. Even for
    some on this board that come in RoHS such as data converters I found
    that there was no stock anywhere for the RoHS edition. Had to buy the
    tin-lead versions.
     
  10. Jeff L

    Jeff L Guest

    No surprises - assuming HASL, they work fine using normal leaded solder.
    This includes soldering with irons, wave and reflow methods. It does not
    change the process hardly at all. The leaded solder just dissolves it,
    creating a slightly non eutectic solder (closer to 60/40). It's the same
    with tin plated parts which have been used for quite a few years, other then
    lead free BGA's. The downside is you have a possibility of tin whiskers
    forming in areas that have not been wetted with the leaded solder. The tin
    whisker risk is somewhat dependant on the alloy used for the HASL. Tin
    dendrites are from currents forming in moisture and can be avoided. White
    tin is really bad, as it compresses the surface during plating and causes
    rapid tin whisker growth. We've done many thousands of boards with lead free
    HASL without much issue.

    Gold plating (ENIG) is bad, as it is a flash of electroless gold deposits a
    few atoms thick, over nickel which is plated over the copper traces. The
    gold is sometimes hard to wet (BGA's for one - they are so bad we pre tin
    the pads). The intention of the process is when applying solder it dissolves
    the gold, thus wetting the normally difficult to wet nickel. You now have a
    solder joint with a little gold in it, which if in high enough concentration
    causes the solder to go brittle. The nickel to solder intermetallic layer is
    poor and is prone to cracking (a well known repair problem in the repair
    industry). I think the copper to nickel bond is ok, but I never really
    looked into it in much detail. Other problems that can arise is weird
    thermocouples from all of the dissimilar junctions. This would have been a
    potential problem with some research I did awhile back where were measuring
    temperature from a thermocouple with a resolution of around 1/1000 of a deg
    C. The thermocouple was so sensitive you could peg the graph by breathing
    heavy several feet away!
     
  11. Jeff L

    Jeff L Guest

    This can be bad to solder with small SMT pads, and there are reliability
    concerns - see my other post.
    http://www.speff.com
     
  12. Joerg

    Joerg Guest

    Thanks for sharing your experience, Jeff. Maybe HASL would then be an
    option for us, as long as we wet everything. The latter could be a
    problem in thru-hole areas such as DIN connectors.

    ENIG looked a bit scary to me from the beginning so I politely declined
    when they offered. The nickel-copper is generally good though for
    mechanical stuff, I have used that a lot for shield mounts and the like
    in order to avoid dissimilar metals touching (nickel plating the shield
    studs a well).

    Thermocouples would spell disaster for this circuit as it relies on
    microvolt level DC paths to be stable.
     
  13. The downside is you have a possibility of tin whiskers
    Per the Nasa tin whiskers info collection, it isn't just tin that
    forms whiskers, it is just about every lead-free alloy and metal,
    just some more than others.
     
  14. Jeff L

    Jeff L Guest

    Proper through hole has solder wetting to the top. Problem areas could be
    untented vias, mounting pads and holes, etc. Basically if its not a pad,
    don't leave it exposed to become plated with solder in the HASL process.

    OSP (bare copper with an organic protector) might be another option and it's
    cheap, but comes with it's own problems.
     
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