Special feature: Cleaning chemistry vs. mechanical impingement
Galbraith: Yes, the location of large odd- Displacement is really only possible in tomatic for surfactant based products),
form components can limit access to low inline dryers. high disposal costs, operator maintenance
mounted components. Is this something cost, high wear and tear due to scaling, etc.
that designers are aware of when designing
Wack: So I don’t misunderstand Steve.
Taking all costs together and dividing them
boards?
What kind of displacement? Because if you
by the number of boards cleaned provides
distill, meaning evaporate the water, the
the user a cost per cleaned part, which can
Wack: Unfortunately not. I think we all salt residues stay behind…
then easily be compared to any other prod-
wish we could stimulate this discussion
uct in the market (apple to apple). Also, it
with them at the time of the design stage.
Stach: Batch cleaners must use evaporative
has been important for us to think about
drying.
process cost reduction tools, i.e. to reduce
Galbraith: Another common question—Is
evaporation and automated concentration
it necessary to use DI water in the cleaning
Wack: …under the components. No one
monitoring units to keep concentration at
process, and how do you dispose of it?
would be happy with that.
the desired levels. With the introduction
Konrad: Yes. Tap water contains miner-
Stach: So, I believe the purity of rinse
of microphase products in 1996, meaning
als and other non-desirable substances
water depends on the drying method.
products that show a phase separation
not conducive to defluxing. Additionally,
when they are not agitated, the refractive
many defluxing systems are equipped with
Konrad: The use of DI water may be
index method was introduced. Due to the
real-time cleanliness testers that ensure the
avoided if drying was the only concern and
physics of refractive index, we have now
absence of wash solution before ending
one used a displacement drying system
developed an alternative method to show
the rinsing process. This requires the use is
(as in an inline). But DI water has many
even more accurate readings. The main
pure water. DI water measuring at least 5
cleanliness benefits as well.
drawback of refractive index is its inaccu-
MΩ is recommended.
racy, which originates from the 1-3% of dis-
Wack: One could also use an appropriate
solved contamination. This effect can devi-
Wack: Yes, as it introduces little ionic
cleaning agent as the rinsing agent. We
ate the reading by over 10% and therefore
contamination to the process. There are
know that from stencil cleaning processes.
mislead the operator into thinking that
other ways to avoid the use of DI water,
what they read is the actual, right concen-
Galbraith: Gentlemen, I am aware that we
but one has to examine case by case onsite
tration, when its not. Please make sure you
are running out of time. Here is my final
with the engineering support of the vendor
talk to your cleaning service provider about
question: How do you calculate the “Total
before making a general statement. Our
this very important topic.
Cost of Cleaning”?
experience has shown that the use of DI
water has been most beneficial to achieve
Stach: We have developed spreadsheets to
Stach: Many factors. The most overlooked
highest cleanliness levels. We are currently
help. I would be glad to share.
is the cost of not cleaning.
performing a user study on this topic,
Galbraith: Harald, don’t you need to fac-
which we could provide to interested par-
Konrad: Equipment cost, consumables
tor in the capital equipment costs too?
ties once completed.
costs (water, chemical, power, etc), labor,
and most importantly, the cost SAVINGS
Wack: You do. That’s why we devise a total
Konrad: To reply to the earlier question...
associated with a reduction of field failures
process cost comparison, where you can
While I know the phrase “design for
and NTF field returns. In absolute terms,
plug in your current and projected cost.
manufacturability,” I never hear “design
literal pennies per board.
for cleanability.”
Konrad: There goes those chemical guys
Wack: As a global company, we introduced
giving away the equipment again. :)
Wack: Good point.
our products to the US market in 1996, to
encounter only surfactant-based products.
Galbraith: OK, our time is up. I would like
Galbraith: Perhaps this is something IPC
These are very inexpensive, just as dish
to thank each of our panelists for taking
could include in designer guidelines.
soap is. And with it came a long list of
part.
Wack: The earlier designers are included,
process disadvantages. Our products were
the better the overall process will be. It’s
surfactant-free and therefore more costly
Konrad: Thank you everyone!
hard to imagine that there is sufficient
per unit. So we started to define the term
cleanliness knowledge on a designer level.
“cost per cleaned part.” It is defined as the
Stach: Thanks.
overall annual cost of the entire clean-
Wack: Thank you.
Stach: No, it may not be necessary. If
ing process. This includes, for example,
drying is accomplished by displacement
the amount of chemistry that has to be
of rinse water, then no residues are dried.
replenished due to a short bath life (symp-
www.globalsmt.net Global SMT & Packaging – May 2009 – 29
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