Brian
This sounds wonderful for the RMA / solvent cleaning technology. I wish we
would have had this on systems at Delco Electronics. What I have found with
the low solids no clean and water soluble fluxes is that the chemical
signature is different by ROSE and that these fluxes show constantly lower readings
in most ROSE automated testers on today's production floor. The ROSE testers
are consider process indicators by the equipment manufacturers that indicate
when large changes have occurred in the process. We still believe that this
is important and if you have a good history and process control then this is
an important process monitoring step. But using a localized non-destructive
extraction method and Ion Chromatography allows Foresite and customers to
understand if the residue is corrosive and what type and level of contamination is
present below a QFN, or on an 0805 cap (dirty from the plating process) or
out of a micro via that has corroded open.
Using the C3 we have been successful at finding high levels of sulfuric
acid in micro via's after being processed through the copper protection system 2
more rework times but pass with levels less than 0.5 ug/cm2. We have also
found that a sensitive filter after cleaning with water only still held a high
level of flux below the ceramic body to cause leakage, but passes the ROSE
testing at less than 1.0 ug/cm2. Hand solder flux that has not been heat
activated or after brush cleaning have both created failures that we have been
able to non-destructively test and identify the contamination source, correct
the process and have great field performance for years after the change and with
regular localized monitoring. Our goal as stated in a newly proposed test
method for localized extraction. Foresite presented (APEX 08) this method to
the Ionic Conductivity / Ion Chromatography task group for peer review and
proposal to the TM 650 as an alternative method for extracting and even
assessing on the production floor if residue from an isolated area is corrosive or
not.
Proposed Test method "Automated Localized Extraction of Electronic Hardware
and Components"
Scope "This test method defines the parameters to non-destructively extract
the ionizable surface contamination from a localized isolated area of an
electronic assembly using heated micro fluids to be used for electrical
assessment and ionic/organic analysis. This localized extraction method is not
designed to remove residues that do not easily ionize or are trapped in a
protective organic film (i.e. rosin) that would not normally be brought into solution
during an elevated temperature humidity event on the electronics. "
We believe that the tools on the floor should allow the engineer to answer
the question "How is my process running and for the incoming boards,
components, SMT 1 and 2, wave solder and selective, hand solder and rework, but if you
have a cleaning process you can look at the systems ability to clean after 12
hours and 3 soldering operations, or do you have to clean after each
soldering process.
Due to increased complexity and increased circuit sensitivity of today's
electronic assemblies, with very little thru hole, and the use of 0201, 01005,
Direct FET's QFN packages, micro via's on many of the assemblies and micro BGA
requiring new tools are being developed for inspection and part placement
then we need to move cleanliness assessment to the digital age and look at the
pockets of contamination that are making a negative impact on field
performance.
Terry Munson
Foresite
765-457-8095
_www.resdiues.com_ (http://www.resdiues.com)
In a message dated 4/21/2008 5:13:11 A.M. Eastern Daylight Time,
[log in to unmask] writes:
Well, yes and no! One contamination tester did indicate a probability of
whether entrapment occurred. You see, by analysing the shape of the
conductivity v. time curve, it can be (and was) done. Any given
non-entrapped contaminant has a given asymptotic curve. Let's say that a
given hypothetical cleaned flux residue reaches 99% of the way to
extrapolated asymptote in 2 minutes. If the same flux is entrapped, it
will not reach 99% of asymptote in 15 minutes, so the curve will look
different. If you have both cases (the normal) the resultant curve will
be the sum of both. By analysing the curve, you can separate them into
the components. The said tester used 9 different curve-fitting
techniques to do the analysis (hellishly more complex than that in
Excel!!!) and compared them to the actual curve, choosing the best fit.
It was able to detect 3 different contamination sources and calculate
the respective quantitative values of each, extrapolating each of the
three curves to quasi-asymptote, even if that were many hours longer
than the test itself. Entrapment tests showed that it worked, with a
reasonable accuracy. However, what it could not do is to differentiate
between entrapment and other slow-leaching sources, such as a poorly
cured solder masks etc. I think the wording on the print-out was
something like, "Very slow dissolving contaminant averaging n µg/cm² eq.
NaCl: may be due to flux residues under components, poorly polymerised
resins or other leaching sources" (I programmed this 19 or 20 years ago,
so my aged brain may be excused if this is not verbatim, but the gist is
there). This technique was appreciated by my clients, because they were
able to judge the proportion of the surface area which was causing
entrapment and thus guestimating the actual entrapped mass.
Brian
Hernefjord Ingemar wrote:
> Well written, Terry! General areas of a board is seldom a contamination
> problem, but ENTRAPMENTS, yes! And one can not be sure the ionic
> contamination test tells you about them.
> /Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Terry L. Munson
> Sent: den 18 april 2008 22:35
> To: [log in to unmask]
> Subject: Re: [TN] Ionic Contamination Question (& added info).
>
> Bill
> As one of the active task group participants during the 90s when we were
> asked to update the equivalence factors table and using low solids
> cleanable and no clean formulations, we found it difficult to assess
> these new types of low solids residues and if you look at the large
> detailed report from the task group (IPC TR 583) we found it difficult
> to correlate between static and dynamic systems. The use of higher
> pass fail criteria were in place for automotive users (one in
> particular used 28 ug/in2 instead of the 14 ug/in2 from
> 1978 to 1991 with no field performance problems related to flux
> residues with mean levels at 21 ug/in2 while using an 18-24% solids RMA
> flux) that did not see problems.
>
> My concern with cleanliness is not the generalized cleanliness of a
> total board but the amount of contamination present between pads, in
> via's or thru-hole devices. The pocket of contamination below an 0805
> capacitor has created drained batteries when the entire assembly tests
> clean by ROSE and by bag extraction Ion Chromatography. It is only when
> we look at the localized pocket of contamination do we see the direct
> correlation to field and reliability performance. Many of the
> localized areas we look at with the C3 tester are clean and show low
> levels of contamination, but when we see the combined processing
> effects of selective wave soldering using a pallet to isolate the area
> we find that the residues that can be trapped between the pallet and
> circuit board (low solids no clean VOC free) are also protected from
> the heat but are very corrosive due to the water carrier and acidic pH
> 2.35. Dendrites are growing in these nearby areas, as well as stray
> voltage problems and intermittent performance issues and No Trouble
> Found (NTF) returns.
>
> It is important to understand the cleanliness of an assembly but it is
> more important to understand the cleanliness of the processing steps
> such as 1st reflow, 2nd reflow, wave soldering bottom and top side, bare
> board unsoldered areas, micro via's that have fabrication residues
> trapped inside causing performance problems and the hand solder / touch
> up residues. This type of cleanliness understanding comes from being
> able to do localized non-destructive residue assessment and ion
> chromatography analysis.
>
>
> Cleanliness testing must predict field performance. Using localized
> testing is the only way I am aware of understanding how much
> contamination is present in the areas of critical circuitry that tends
> to fail earliest.
>
> Terry Munson
> Foresite
> 765-457-8095
> _www.Residues.com_ (http://www.Residues.com)
>
>
>
>
> In a message dated 4/18/2008 1:54:54 P.M. Eastern Daylight Time,
> [log in to unmask] writes:
>
> As perhaps the only person still around that attended the meetings
> resulting
> in the equivalence factors and IPC Cleaning & Contamination Chair at
> that time, perhaps a few points would facilitate the discussion:
>
> 1. The Navy set up the ionic testing development program to solve a
> serious
>
> failure problem in S.E. Asia.
> It worked.
>
> 2. In the timeframe when the test was developed and put in place by
> the
> military, most of the rest of the electronics industry in the US used
> the mil specs since they were free.
>
> 3. As the IPC set up and adopted Classes 1-3 (basically toys up to
> military/high rel), I asked the committee if we used the mil test
> result for Class 3, could we use 1.5x that limit for Class 2 and 2-3x
> for Class 1?
> The response was that with proper cleaning, the mil limit could
> readily be
>
> achieved while serving to monitor daily production. So the industry
> continued to use the (free) mil spec test standard.
>
> 4. The ionic contamination test was a valuable monitoring tool, since
> the SIR tests were done on coupons, not on actual assemblies, and took
> 1-2 weeks to complete. Needless to say, a high volume electronics
> producer could turn out
>
> a significant volume of PWAs during that time, often shipping them
> into the field as soon as assembly was completed.
>
> 5. As noted in my SMT column (offered yesterday) T. O. Duyck of
> Northern
> Telecom was charged with implementing water soluble flux for NT
> electronics
> production. During that time he observed and reported the differences
> in flux residue release rates, pointing out that rosin ca 90% of
> rosin flux residues
> release from the PWA surface during the 10-15 test time for ionic test
>
> equipment, while water soluble flux residues may take up to 2 hrs. to
>
> achieve the same
> level of release. Thus the release rate should be checked to ensure
> the flux used, time test time and the instrument employed provide
> reliable results and guidance to the production engineer.
> (See T. O. Duyck and M. Boulos, "Water Washes Reliability into
> Telephone Circuit Packs", IPC-TR-206, April, 1978)
> Based on this work, I investigated the release rate of SA flux
> residues,
> finding it even faster than rosin fluxes. (See W. G. Kenyon,
> "Synthetic Activated (SA) Flux Technology: Development,
> Commercialization, Benefits and Future Applications", Internepcon
> Japan, 24 Jan. 1986)
>
> 6. In the late 1980's, the materials and acceptance of the no clean or
> low residue or acceptable dirt concept became widely accepted and
> implemented on the designs of the time. Outsourcing to contract
> assemblers (both in the US and
> overseas) became widely practiced, so much of the former 'in-house'
> cleaning
> expertise disappeared.
>
> 7. This was seen at IPC as the number of company sponsored volunteers
>
> dwindled. Could we take on projects today to develop an updated ionic
> test
> for pr
> ocess monitoring? Find enough participants to conduct statistically
> sound
> round
> robin testing?
>
> Bill Kenyon
> Global Centre Consulting
> 3336 Birmingham Drive
> Fort Collins, CO 80526
> Tel: 970.207.9586 Cell: 970.980.6373
>
>
>
>
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