Iain
Brian's response is right on the mark!
Using an active flux masks a lot of solderability problems. While at AT&T I
and several other folks in our component and assembly divisions published a
study looking at the difference in predicted assembly yield based on wetting
balance tests done with both ww rosin and activated flux. I'll look up the
exact reference (published at the Surface Mount International Conference)
and forward it. What we found is that a lot of really awful junk gets passed
as solderable by an active flux: ww rosin is the only way to go.
Greg
-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Friday, May 09, 2003 12:05 AM
To: [log in to unmask]
Subject: Re: [TN] Wetting Balance Testing
Except for when you are doing flux comparisons, wetting balance tests
are used for determining the solderability. To obtain consistent results
you should always use the least active flux so as to reveal all the
faults. If something solders well with this, it will solder with any
flux. Therefore it is normal to use a pure, unactivated WW rosin flux
(usually 25%w/w). That way, you can get reproducible conditions with
your suppliers and/or other plants.
Brian
Braddock, Iain wrote:
> Why # 1, why would you not want to test with the flux you are using on
your
> production?
>
> Iain.
>
> -----Original Message-----
> From: Munie, Gregory [mailto:[log in to unmask]]
> Sent: 08 May 2003 15:11
> To: [log in to unmask]
> Subject: Re: [TN] Wetting Balance Testing
>
>
>
> *** WARNING ***
>
>
>
> This mail has originated outside your organization,
>
> either from an external partner or the Global Internet.
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> Keep this in mind if you answer this message.
> Neil
>
> I've done a lot of wetting balance but I have to add a few comments on
the
> "dip and look." (I agree with all Bev's other comments and suggestions.)
>
> The dip and look as it's traditionally done does deserve to die. But if
done
> correctly it can tell you almost as much as wetting balance.
>
> And I define correctly as:
>
> 1) Use ONLY water white rosin flux. NEVER use any activators in the flux.
>
> 2) Control your immersion (wetting balance is good for this :-)
>
> 3) Coverage criteria means nothing if you don't see active wetting, i.e.
> solder rises ABOVE the surface of the bath to wick UP the part lead.
>
> # 3 is absolutely critical: in a real world soldering situation that is
> exactly what you want to happen for either wave or reflow soldering. It's
> what happens to the section of the lead that's NOT in direct contact with
> the solder that tells you whether the part is solderable.
>
> Greg Munie
>
>
>
>
>
>
>
>
>
>
> Original Message-----
> From: Bev Christian [mailto:[log in to unmask]]
> Sent: Thursday, May 08, 2003 4:25 AM
> To: [log in to unmask]
> Subject: Re: [TN] Wetting Balance Testing
>
>
>
> Neil,
>
> You also need to consider what alloy you are using. Dr. Lee of Indium has
> shown that 62/36/2 Sn/Pb/Ag gives significantly different results. And
then
> there is the work Chris Hunt et al of the British NPL have done on lead
free
> solders. And then are you using a solder globule or solder bath? Don't
> forget temperature, atmosphere (most likely air, unless like Chris you can
> afford a dry box) and preheat (or is that what you mean by hang time?).
If
> you are using a globule block we have also found that how centered your
> component lead is over the solder globule affects your results as well.
>
> I would say it is not so much the length of the lead (unless you are
talking
> about something obscenely long - no comments please), but rather what the
> lead is connected to - like an internal heat sink. And, yes, we have had
> ONE problem with the heat sinking ability of a component affecting the
> results. I gave a short presentation to the J-STD-002 committee at APEX.
I
> will send you a copy. It will not show up for other TechNetters,
> unfortunately. In essence, we found that wrapping the wetting balance
clip
> in polyimide tape allowed the component in question to pass solderability
> testing!
>
> All said, we have had excellent results using a wetting balance and much
> prefer it to the dinosaur "dip and look" test, which I would like to see
DIE
> for SMT components. Now if we can just agree on what pass/fail criteria
> will be....
>
> regards,
> Bev Christian
> Research in Motion
>
> -----Original Message-----
> From: Neil Flatter [mailto:[log in to unmask]]
> Sent: May 8, 2003 1:17 AM
> To: [log in to unmask]
> Subject: [TN] Wetting Balance Testing
>
>
> For those of you doing solderability testing, what sorts of parameters
> should we be concerned about for reliable results? Our tester already
> allows inputs for lead perimeter, cross sectional area, and hang time. My
> company's testing also specifies immersion angle, depth, and speed as well
> as the type of flux. By controlling these factors, can I expect
repeatable
> results?
>
> It has been suggested that we also need to limit the length of the leads
for
> our testing as wall as installing a thermal break between the lead and the
> hanger. Both have been blamed for failing test results. Has anyone
> experienced changes in test results from these variables?
>
> Neil Flatter
> TRW-Automotive
> Process Quality
>
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