David-
Let me try and address the question of how to analyze this (based on
others assessments of what it probably is):
First, you have to ensure your EDX has a "thin window" or a
"windowless" detector and is capable of detecting carbon. Next, you need
to analyze it with the EDX using very low gun voltages, which further
reduce the EDX's sensitivity, but even at 2kV, you should still be able
to see it if the EDX is capable.
Next, I would look for either bromine or chlorine in the
spectra, and 'tune' the EDX for these elements (you can do this by using
a potassium bromide sample (available through suppliers of FTIR
materials) for the calibration sample). These halides are tell-tales of
flux residues. The presence of them is very indicative of flux residue-
their absence however, does not rule out that flux or other organics are
at work here.
I would also submit a sample for FTIR analysis; after running
the FTIR spectra, I would also supply your lab with a sample of the flux
used in assembly, along with the time and temperatures used in the
reflow. The lab, in order to conduct an empirical comparison, will need
to heat up the flux in a similar eviron (time/temp) to flash off any
light weight organics, and get the residue closer to what you're
experiencing.
An alternative method, which is more sensitive than either FTIR
or EDX is that of Gas Chromatography/Mass Spectroscopy (GC/MS). In this
method, a sample is placed into a vial, typically with a solvent
(toluene is typical), and run through a heated, known-length capillary
tube with a quadrapole detector on it. Chemists can then look at the
transition time of the molecules through this column and determine the
molecular makeup of the material.
The latter, if available would be my choice in that it fast,
unambiguous, and very sensitive compared to alternate techniques.
Hope this helps
Bill Davis,
Sr. Scientist
(408)-325-7868
[log in to unmask]
-----Original Message-----
From: David yeh [mailto:[log in to unmask]]
Sent: Friday, May 28, 1999 5:02 AM
To: [log in to unmask]
Subject: Re: [TN] White Residue on solder joints
Tegehall,
Thanks for sharing. I have not ruled out the flux to cause these
residues.
But what puzzled me is why elements of flux are not captured in EDX? I
expect to see some carbon - that is what I thought I should see in flux.
I also thought the water soluble flux would be soluble in DI water- that
is
what my supplier claimed.
The only concern I have over this residue is that it is corrosive in
nature, otherwise it should be harmless like you said.
The residue only showed up after few days and only on some substrate. I
am
in the process of simulating this effect by subjecting in different
temperature profile, storing in different environment, having the
substrate
washed and unwashed. Please share if you have additional input you like
me
to look at.
Thanks once again.
----------
> From: Tegehall Per-Erik <[log in to unmask]>
> To: [log in to unmask]
> Subject: Re: [TN] White Residue on solder joints
> Date: Wednesday, May 26, 1999 10:07 PM
>
> I have seen the type of flux residues you describe a number of times.
In
> most cases, it has turned out to be a lead salt, for example lead
adipinate
> formed when adipic acid in the flux (an activator) react with lead
oxide
on
> the surface to be soldered. My experience is that these salts are very
> difficult to dissolve whatever solvent you use. Since the residues are
so
> difficult to dissolve, they are probably rather harmless for most
> applications (but I have no proof for that statement). However, if you
will
> conformally coat the assemblies, they may cause poor adhesion of the
> coating. What puzzle me is that you say it was manifested a few days
after
> aqueous wash. It should have been there immediately after cleaning.
>
> Per-Erik Tegehall
> IVF
> Sweden
>
> > ----------
> >
> > Has anyone ever come across white residues that looks like snow cap
> > covering the solder joints? The phenomenon only manifested a few
days
> > after Aqueous wash and EDX captured high lead and oxygen. The white
> > residues are so stubborn that they could not be dissolved in DI
water
and
> > IPA. We use a water soluble paste and clean our assembly twice
> >
> > All inputs are welcome and appreciated.
> >
> > ################################################################
> > TechNet E-Mail Forum provided as a free service by IPC using
LISTSERV
1.8c
> > ################################################################
> > To subscribe/unsubscribe, send a message to [log in to unmask] with
> > following text in the body:
> > To subscribe: SUBSCRIBE TechNet <your full name>
> > To unsubscribe: SIGNOFF TechNet
> > ################################################################
> > Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
> > section for additional information.
> > For technical support contact Hugo Scaramuzza at [log in to unmask] or
> > 847-509-9700 ext.312
> > ################################################################
> >
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
following text in the body:
> To subscribe: SUBSCRIBE TechNet <your full name>
> To unsubscribe: SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or
847-509-9700 ext.312
> ################################################################
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with
following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or
847-509-9700 ext.312
################################################################
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
