Hi Kathy - check to see if the plating on your phos bronze terminals has a
barrier layer or not. If the solder  plating  on the phos bronze terminals
is thin then the copper from the phos bronze alloy will diffuse together
with the tin from the solder plating forming a copper-tin intermetallic
phase. If this copper-tin intermetallic phase reaches the solder plate
surface it will oxidize and become nearly impossible to wet with a solder
using conventional fluxes (i.e. something short of battery acid!). Many
manufacturers use a thin barrier layer such as nickel to prevent the
copper-tin intermetallic formation. Alternatively some manufacturers
intentionally plate a thin layer of  pure copper (over the phos bronze)
and a very thick layer of solder plate - if the solder plate is thick
enough and the components are used in a short period of time the copper-tin
intermetallic never reaches the solder plate surface. There are several
references that discuss this in detail - if you need them let me know. Good
Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]





Kathy Stillings <[log in to unmask]> on 06/15/99 10:49:10 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to Kathy Stillings <[log in to unmask]>

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cc:
Subject:  [TN] Lead solderability




Hi technetters,
Hope all is well.....................  Got a quick question - I am using
Power
chip resistors (manufacturers name with held :) ) that have a "solder
plated
phosphor bronze" terminal.  I am having a bugger of a time soldering these
parts.  I have limited solderability testing capabilites and am forced to
use
the old solder pot test to verify solderability.  I get good solder
adhesion on
some and very poor on others.  I don't have any experience with phosphor
bronze
based terminals.  I am looking for your expertise on how I can wave these
parts.
Note:  leads are very dark in color as if they are contaminated but the
date
codes on the parts is very new. Oh yeah - sodler is 63/37 with no clean
alcohol
base flux spray.

Thanks again in advance for the help!

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