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January 2008

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TechNet E-Mail Forum <[log in to unmask]>, Hfjord <[log in to unmask]>
Date:
Mon, 7 Jan 2008 18:56:23 +0100
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To build on Richard's comments, we also make difference between wave
soldering, IR, VP and hand soldering. E.g. with VP, no risk of oxide
formation, no dross, near instant liquidus etc, we use little lower top
temperature, which many components like.

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Stadem, Richard D.
Skickat: den 7 januari 2008 18:14
Till: [log in to unmask]
Ämne: Re: [TN] Reflow profile development - correct starting temperature for
evaluating TAL using non-eutectic solders

To build on Werner's comments, understand that you must be in total
liquidus for wetting dissolution (IMF formation) to take place. No real
wetting takes place in the plastic range between 179 and 189 C. The
difference is somewhat irrelevant, as you should really be above at
least 189 (liquidus) plus 20C as Werner stated. So your TALT should
begin at 209C ramping up and again ramping down. You really do not need
to have this TALT be longer than 15 seconds or so for good wetting on
the coolest solder joint on the assembly, even on ENIG. If this means
having a TALT longer than 120 seconds on the hottest point, then make
sure you use nitrogen else if the solder is held in liquidus for that
long of a time some oxidation begins to occur (just like the dross
formation on your wave solder or tin pot) and you get overheated,
flux-starved solder joints.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Monday, January 07, 2008 10:56 AM
To: [log in to unmask]
Subject: Re: [TN] Reflow profile development - correct starting
temperature for evaluating TAL using non-eutectic solders

Hi Joe,
Unfortunately, a natural outcome of a proper reflow profile has become a
parameter to be aimed at. TAL is NOT a proper reflow parameter, and
assures in and of itself not good wetting and metallurgical bonding.
Adequate solder joint quality is assured with achieving Liquidus+20 C
for 5 seconds at the slowest heating solder joint in the assembly. So
whatever the Liquidus temperature is for your solder alloy +20 for 5
seconds. For eutectic SnPb that means 203C for 5 seconds at the slowest
heating solder joint, which of course means everything else on the
assembly will see higher peak temperatures for longer times [except for
vapor phase, of course]. 

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com



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