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November 2005

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dehoyos, Ramon
Date:
Mon, 21 Nov 2005 15:19:01 -0500
Content-Type:
text/plain
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text/plain (98 lines)
 

         Hi Guy:
         You are very right. Water soluble flux has acids that remain active after reflow and are corrosive and need to be removed which can be accomplished by and inline cleaner or a batch cleaner and a proven cleaning process.  Acids removal can augmented by adding a 1 to 2% saponifier to the water. The saponifier will reduce the surface tension of the product and allow the water to reach small cavities.
        Regards,
        Ramon

-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Monday, November 21, 2005 11:57 AM
To: Dehoyos, Ramon
Subject: RE: [TN] SV: [TN] Entrapped flux

There were two words in the original post that I think you missed, water soluble. This type flux is not rosin based and is usually H0 or H1 classified (There are a couple of "M" activity level water solubles). But, Ioan's question is not easily answered. Inge may have missed it as well.
When I worked at a lab we did see water soluble flux induce failure in board designs like Ioan described.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
Sent: Monday, November 21, 2005 10:28 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] Entrapped flux


        Hi Ioan:
        I believe that as long as you have a good reflow oven profile that fully activates the acids in the flux and turns them into inert bases that are entrapped by the resins or rosins, they are going no where and cause no problems.
        Regards,
        Ramon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
Sent: Saturday, November 19, 2005 4:29 AM
To: [log in to unmask]
Subject: [TN] SV: [TN] Entrapped flux

We have produced about 500,000 complex RF boards the last years, thousands of vias on each board, never had problem with entrapped flux.
Used in deserts, jungles, mountains, traffic environment, sea, salt, all places.
Such RF boards are impossible to clean 100%, too many pockets. Important
condition: always working or standby, never stored without dessicator bags before mounting.
Inge

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Tempea, Ioan
Skickat: den 18 november 2005 22:26
Till: [log in to unmask]
Ämne: [TN] Entrapped flux

Technos,

I have sort of rookie questions on the following situation:

when reflowing a DPAK, let's say, and the pad thermal pad has vias, the solder will flow inside the via. If the holes are covered with solder mask on the other side, will flux residue build up at the bottom of the hole, like a void between the solder and the solder mask? Or it will rather stay on the surface?

Or, if the DPAK is printed with a nicely shaped stencil, so that no solder goes into the hole, but this time there is no solder mask covering the hole and I fill the vias from the bottom, manually, can I generate a flux pocket somewhere, or the flux only stays on the surface?

And if the flux, water soluble, is entrapped therefore not washable, will it be corrosive?

You must have guessed the application, RF boards, with all these components that have tons of vias under them, vias that must be filled for max thermal transfer, but the solder shall not go on the other side, because the other side is an exposed plane, etc.

Thanks,
Ioan

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