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June 2002

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Subject:
From:
Graham Collins <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 17 Jun 2002 07:18:04 -0400
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Hi Bob
Is it acceptable?  My vote is "NO!".  I assume you are talking about spraying with a hand held spray bottle, or applying with a hand application.  In either case you will likely have a lot of flux added, and it will be very difficult to control the quantity.  This flux will be partially activated, but will not burn off and activate as it is intended to, so you are left with a mystery residue in large quantities.

Two recommendations:
1) check with a bare board to ensure your fluxer is getting flux up through the holes.  The Technet archive has some instructions on doing this.   

2) put thermocouples on the hard to flow areas and make sure that you are properly pre-heating the board.  Kester should be able to advise you on the activation temperature range of the flux.  You may be doing one of two things: either overheating and burning off, or not heating sufficiently to activate the flux that has made it up through the barrel.  Or if you have IR preheaters only, you may not be able to evenly heat everything, so some parts may be too cold and some too hot.  I've got a board that was impossible to solder 'til we retrofitted a convection preheater for the topside, it has some lightly populated areas and some areas with a metal heatsink bonded on to the top side.  



regards

Graham Collins
Process Engineer, 
Northrop Grumman
Atlantic Facility of Litton Systems Canada
(902) 873-2000 ext 6215

>>> [log in to unmask] 06/14/02 03:01PM >>>
We are using Kester 951 no-clean flux. Is it acceptable to either spray the component side of the printed circuit board and/or apply a drop of flux onto the component side hole to increase the amount of vertical fill and fix dewetting.

Thanks Bob 

[log in to unmask]

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