Are you hand soldering or possibly have an oven with small number of zones?
I assume the driver here is difficulty of getting the joints to flow because
of the heat sinking effect of the ground plain, and possible concerns for
heat damage through prolonged heating times.
Low melting alloys such as SN/Bi [and its modified variants] may not improve
matters. It's the tin that does the work in solder joint formation and in
these low melting alloys it's relatively dilute so lower to work. In
addition there is less energy due to the lower temperatures so the rate of
joint formation is slow compared to eutectic and SAC types. If you then add
NiPdAu to the mix that is decidedly not going to help. That stuff can be
pretty close to wood in soldering terms.
Flux performance can be similarly impaired. If you are hand soldering by all
means have a go, but you might find it is better to adjust tool performance
so that you get a rapid rise to soldering temperatures before the heat
sinking flattens you and/or to have some background heating to reduce the
burden on local heating.
Don't forget that if choosing a lower MP alloy you are reducing the
operating temperature range of your product and possibly reducing its life
if it sees a lot of temperature cycling in service.

-- 
Regards 
 
Mike Fenner 
Bonding Services & Products
M: +44 [0] 7810 526 317 
T: +44 [0] 1865 522 663
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mumtaz Bora
Sent: Thursday, July 23, 2015 3:46 PM
To: [log in to unmask]
Subject: [TN] Soldering NiPdAu finish components with low melt solder

Dear All, Good Morning,   Looking for some knowledge base  on soldering
NiPdAu finished components with low melt solder such as Sn42.0Bi57.6Ag0.4 to
avoid wetting issues on a heavy copper plane board. Any insight and advise
will be appreciated.

Thank-you
Mumtaz
858-795-0112
Peregrine  Semiconductor


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