ken,

Typically  30 micro inches of gold is used only for wire bonding purposes.
I think it is almost impossible to solder to that much gold with out  to much gold
leaching into your solder.

Greg Scott
Cray Inc.

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> Ken,
>
> How very kind of your supplier. I think that thickness of gold would almost
> certainly make your solder joints brittle in the extreme, even if you could
> form any. Or are you talking an overall plating thickness including Nickel
> or Palladium? ENIG (electroless nickel/immersion gold) is a good finish if
> the board is well made, and I've had good results with it so far, but the
> plating over the copper should be between 3 and 6 microns of Nickel and
> about 1/8th micron (5 microinches) of immersion gold. 30 microns as you can
> see is, in comparison, rather hefty.
>
> Regards
>
> Pete Duncan
>
>                     "Chafin, Ken
>                     G."                  To:     [log in to unmask]
>                     <kgchafin@SWI        cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
>                     TCH.COM>             Subject:     [TN] Solder vs Gold Pads on SMT
>                     Sent by:
>                     TechNet
>                     <[log in to unmask]
>                     ORG>
>
>                     08/21/01
>                     02:30 AM
>                     Please
>                     respond to
>                     "TechNet
>                     E-Mail
>                     Forum."
>
> We presently use SMT printed wiring boards with 60/40 tin-lead solder
> finish
> on the pads.
>
> Our PWB supplier has offered to supply our boards with a 30 micron
> electroless gold finish on the pads at the same price.
>
> Does anyone have any views on the relative merits of the two finishes?
> Solderability?  Durability?  Reliability?
>
> We manufacture electronic control and signaling systems for the rail and
> rapid transit industry and our equipment is often in harsh environments.
>
> Thanks for any information on the subject.
>
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