Steve,

This sounds like a problem with nickel passivation, and your
nickel seems a little on the thin side so the copper under-
neath may be oxidizing as well.

When soldering to nickel, a more active flux and/or higher
reflow temperature is frequently required.  Electroless gold
is porous and will not keep the nickel underneath from
oxidizing, especially during thermal excursions.

Regards,
Karl Sauter, Staff Engr.
Sun Microsystems, Inc.
karl.sauter@EBay,Sun.COM


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Date: Fri, 06 Oct 95 10:46:40 EST
From: "ETHIER_SA" <[log in to unmask]>
To: [log in to unmask]
Subject: soldering gold pcb,s
X-Loop: [log in to unmask]

     
     We are having some problems soldering to an electroless gold over 
     nickel card.  specifics are:
     
     5-10 microinches electroless gold over 20 microinches electroless 
     nickel.  .020 thick double sided smt card being soldered in a nitrogen 
     covection reflow oven. components range from 0603-1206 passives, sot 
     23 devices, and a 25 mil ssop. 
     
     Soldering is being done using Alpha 609 water soluble 63/37 paste with 
     a fairly standard profile.
     
     Results thus far are that the joints are granular, cold appearing, 
     with marginal wetting to both card and components.  There are also 
     numerous occurrances of voids/pinholes eminating from the lead pad 
     interface.
     
     Any insights would be helpful in the areas of:
     
                Profiles
                Pastes
                Methods for checking incoming solderability of the cards.
                Any thoughts on optimal gold/nickel characteristics
     
     Thanks for the help.
     
     Steve Ethier
     Mgr. New Product Engineering
     Lockheed Martin Commercial Electronics
     Tel: 603-885-8432


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