Soldering and brazing are pretty much the same type of process, whereby two [metal]
surfaces are joined by a filler metal using heat and a flux. The two processes are
usually distinguished one from another by the temperature required. Below say 300C
the process is called soldering and above it is brazing. Alloys which melt below 300C
are usually softer than those that go above and this gives us the terms soft
soldering and hard soldering, Alternatively alloys above 300C historically have had a
high silver content so brazing is sometimes referred to as silver soldering.

The usual reason for specifying pins to be brazed is to make a mechanically stronger
connection.
By the rather simplified definition above true bazing would require
fluxes which are far too active for electronics use and temperatures beyond which
certainly a flex circuit would be expected to tolerate. Some alloys straddle the
arbitary 300C marker. A common one for pins which comes easily to mind - in hybrid
thick films anyway - is 80Au/20Sn. With an MP of 280C  this is just in the temp range
for electronic grade fluxes but gives shear strengths many times that of conventional
soft solders such as tin/lead.

Mike Fenner
BSP, OX15 4JQ, England
T: +44 1295 722 992
M: +44 789 999 7715
F: +44 1295 720 937


-----Original Message-----
From: Collins, Graham <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 23 August 1999 20:05
Subject: [TN] brazed connector on flexprint


>Hi TechNet
>Today's question:  A friend outside my company has a RFQ for a job that
>calls for connector pins brazed to a flexprint.  He's not sure what this
>means.  Is this requirement unusual, and is it different from soldering the
>pins to the flexprint?  I know that brazing is joining two metal surfaces
>with a third, different metal, which could include soldering, but I'm
>wondering if something else is meant by this.
>
>regards,
>
>Graham Collins
>Process Engineer,
>Litton Systems Canada, Atlantic Facility
>(902) 873-2000 ext 6215
>
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