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March 2003

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From:
Graham Collins <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 11 Mar 2003 11:57:24 -0500
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Hi Tom
The only flaw in your premise is the second part of number 2 - how are you sure you have removed all washable flux residue?  No flux residue under low clearance components?  None stuck under connectors?   Magic!

It comes down to:
 - how clean is clean enough (end use environment, reliability requirements)
 - what do you have when you mix no-clean with a bit of residue from an OA or other type of flux?

It is easier to sleep nights if you don't mix flux.  You may not have a problem with cleaning and then using no-clean, but it's easier to be sure if you can use no-clean for everything.


regards,

Graham Collins
Process Engineer, 
Northrop Grumman Canada Corporation
Halifax
(902) 873-2000 ext 6215

>>> [log in to unmask] 03/11/03 12:39PM >>>
I've read the recent questions and information concerning mixing of
fluxes.  I agree - do not mix flux types when soldering.  However,
here's one for you that can be looked at from a couple of angles....

1. I build a board - wave solder using washable flux.  Flux is
activated, does it's thing, and board is soldered.
2. Water Wash and Dry the board. All washable flux residue is gone.
3. Add a couple of more components that CANNOT be washed (water will
enter the component and ruin it), using NO-CLEAN.
4. Board is done.

Technically, I have used 2 types of fluxes on one assembly....

Another scenario:
1. Board (described above) is finished.  But, fails test - I find a bad
component...
2. I have to use NO CLEAN to replace the component because I cannot
water wash the board (remember the other components that cannot be
subjected to water wash..)
3. Board is done. Passes test - finished.

Again - Technically, I have mixed fluxes on the same assembly.

In the above description, I do not see a problem - or am I missing
something?


Thanks,
Tom

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