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December 2015

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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 15 Dec 2015 19:30:06 +0000
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I'm going to come right out and make this statement. You can laugh all you want, but the data proves that liquid fluxes are terrible! 

Not only for BGA rework, but pretty much any type of rework! They form particulates in the solder joints, they run all over, and they like to penetrate and boil. Many people do not realize that is one of the main causes of lifted pads.

Let the screaming and moaning and hysterical laughing begin. I really don't care.

I have been training operators in the companies I work for years and years to use only tacky fluxes for touchup, for simple rework, and for hot air or hot gas rework, as well as for molten solder fountain rework. I have qualified the use of tacky fluxes to replace liquid many, many times. The cleanliness results of both water soluble and cleaned RMA tacky fluxes are several times better than for liquid fluxes. The tacky fluxes seem to promote wetting much better than any liquid flux I have ever used, and I think I have used them all.

Because the tacky fluxes are developed for worst-case conditions (hot gas and solder fountain rework) they actually work much better than any liquid flux I have ever tried.

And they typically are much easier to confine to just the solder joint(s) you are trying to touchup or solder.

And they don't evaporate or burn off before you even reach liquidus.

And for about 10,000 other reasons, but one of the biggest is that once the operators try using tacky flux for all rework and touchup, they never go back.

If the REACH folks decreed that there would be no more liquid flux allowed, beginning yesterday, it would not mean a thing to me. I would say, "Good riddance".

Most liquid fluxes on the market today were developed for wave solder or selective solder use; they were never intended to be used as a benchtop flux. People adapted them for compatibility reasons.

My feeling is that they should be limited to wave or selective solder processes. 

Use a good tacky flux of the same chemistry for everything else. Those from one particular solder company have always worked best for me.  God is the ____ and the Omega.

But always qualify, qualify, qualify. 

dean


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann
Sent: Tuesday, December 15, 2015 10:40 AM
To: [log in to unmask]
Subject: [TN] IPC 7095 and Liquid Fluxes for Rework

Dear Technetters:

In reviewing the IPC 7095 BGA guidelines I noticed a mention of liquid based fluxes for BGA rework. Has anyone heard of liquid fluxes being robust enough for Sn63 or lead-free rework processes?


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Thanks

Bob Wettermann/BEST

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