To: Msg to Internet  M2I
 
From: David Estes      DGE1
 
Subj: Re:  TechNet inquiry re:  immersion gold reliability if not soldered
 
Subj:  Reliability of immersion gold if not soldered
 
1. Does anyone have any data or recommendations regarding long-term
reliability of immersion gold that is NOT soldered at assembly?  Please
describe the gold thickness and nickel barrier thickness associated with
your response.
 
2. Are there other alternate solderable finishes that if NOT soldered will
not create an oxidation or corrosion risk?  Looking for an alternative to a
selectively plating a thick layer of electroplated gold.
 
The specific application is a commercial or consumer application whose
typical operating conditions would be standard indoor temperature/humidity
and a average duty of several hours/day for 10 years.
 
The board has a fine pitch device or socket mounted to the board with a
conductive elastomeric adhesive.  Current board design has this land pattern
(selectively) electroplated with nickel-gold with selective HASL for the
rest of the board.  The reliability concern is this:  if a
corrosion-resistant coating is not applied to the land pattern,
corrosion to the base copper or the coating could impact electrical
performance (and system reliability).  Would like to find a single finish
which is solderable and, when not soldered, resists corrosion.  If this is
not possible, would consider an alternate selective finish that is lower
cost than electroplated gold.
 
 
Regards,
David Estes
PCB Commodity Engineer
Texas Instruments, Inc.
e-mail:  [log in to unmask]     Phone:  (214) 995-5238    Fax:  (214) 995-1106