Ken, that is very crafty of your PWB supplier.

It is actually cheaper and easier for them to supply your boards with a 30
micro inches of gold finish.  You see, you already demand the 30 micro
inches of gold for your edge fingers, and getting ENIG (which is different)
on the rest of the board means they would have to do two (count them 2)
different surface finishes.  The extra cost of the gold is practically
nothing compared to the cost of the chemicals that carry the gold and the
process cost of applying it.

Do not worry about gold embrittlement.  You will have to get more than 70
micro inches of gold on the pad before that happens.  Unless, of course, you
are not at reflow temperatures long enough such that the gold does not
homogeneously distribute itself through the joint.

However, the thick gold may cause soldering problems.  Thick gold has been
reported by some to cause voids and/or grainy joints.

If it were me, I would tell them NO WAY, do the board right.

Kind Regards,

Ryan Grant
Advanced Technology Engineer
MCMS

-----Original Message-----
From: Chafin, Ken G.
To: [log in to unmask]
Sent: 8/20/01 12:30 PM
Subject: [TN] Solder vs Gold Pads on SMT

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.

------------------------------------------------------------------------
---------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text
in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases
> E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
------------------------------------------------------------------------
---------

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------