Doug
I have in my garden: navel, bitter and and ordinary oranges, lemons, 2
types of grapefruit, mandarines, clementines, 2 types of grape, 2 types
of fig, apricots, peaches and nectarines. Mixed together and allowed to
ferment, these produce a Diet Dew substitute which also makes a good
flux remover. One has to be careful though; 12 seconds too long in the
mixture, it eats away all the solder and copper, as well! At 15 seconds,
it also attacks gold and nickel. At 30 seconds, you're left with a
pristine sheet of perforated epoxy/glass laminate. Wonderful stuff! :-)
Virgil
Sorry, in my earlier post, I hadn't looked too carefully at what you
said and missed out on the batch cleaner. As Doug says, batch cleaners
that use the rotary arm (dishwasher) principle often leave much to be
desired. This is exacerbated when the same arms are used for wash and
rinse, as neither becomes optimised and there is quite a loss of energy
just turning the arms. This is why, when I was making batch cleaners, I
abandoned rotary arms as long ago as 1978 to use motor driven
reciprocating arms, which meant that all the kinetic energy in the fluid
was used to clean the boards with solid jets for cleaning and sprays for
rinsing, in open circuit. Also, it overcame the problem that Doug
mentions: assemblies placed in the corners and edges of the baskets were
as well cleaned as at the centre. Another problem with single-chamber
dishwasher type machines was drying. In the days when we made that type
(1975-1978), we found that three-quarters of the hot air we drove
through the machine was drying the machine itself, not the boards, with
a terrific waste of energy. The result was that the boards that came out
were rarely dry: just think what happens. Rinsing is a series of
dilutions, but there are always contaminants left in the water, even if
your rinse 20 times. When evaporative drying starts, the water starts to
withdraw to the sheltered parts from the air movement (i.e., round the
components), taking the dissolved contaminants with it. As drying
progresses, so the contaminants are laid down round the components,
where you least need them. This is why we developed our batch dryer,
which used rotary air knives to blast off most of the excess water in
the first 20 seconds, taking it and the contaminants up the flue. Only
then did we start to evaporate the residual water with hot air
evaporative drying. Contaminometer tests demonstrated that the residual
ionics were typically only about 20% of what they were with identical
assemblies where the drying was totally evaporative. Good drying is part
of good cleaning. I can now show you what I mean, as this is now
academic, the machines no longer being manufactured, so I have no
commercial interest; there is a 7.5 minute streaming or downloadable
video showing these machines and how they work at
http://www.protonique.com/video. I honestly believe that these machines
were the fastest, most efficient, most economical (and most capital-cost
expensive!) batch machines on the market, up to when my company was
voluntarily liquidated a couple of years ago. The price precluded sales
of vast numbers (I think the total number made was about 65), but many
of our customers habitually obtained Contaminometer readings on SM
assemblies between 0.1 and 0.3 µg/cm2 eq. NaCl with many cleaning
methods. Although the Home Page shows we are no longer an operational
company, we still have a lot of data on batch cleaning (technical as
well as commercial) at http://www.protonique.com/plcom/files/clean.htm
and following pages. You can say that this is residual contamination of
the Internet :-)
[BTW, the most interesting technical paper is not indexed but linked
from the data sheet page - don't ask me why, lost in the mists of time!]
Hope this gives you some extra clues.
Brian
Virgil Lenton wrote:
> We have recently had some cleanliness testing issues.
> We are washing SMT CCA's with RMA solderpaste in a batch washer (AQ400RU)
> with Armakleen E2001A saponifier. The CCA's are being cleanliness Tested
> with an Omega Meter Model 600 SMD without heat.
>
> Cards that easily pass cleanliness testing at the 14uGNaCl/in squared
> acceptance level refered to in MIL-P-28809 have visible traces (under
> magnification) of whitish flux residue under and around many of the SMT
> components.
>
> I do understand that the cleanliness tester is not meant to be an
> analytical tool, but is a tool to be used for process control.
>
> Here are my questions.
> What do others in the industry do to decide when CCA's are clean enough?
> Do you come up with your own acceptable cleanliness test level using SPC
> techniques?
> Any other comments?
>
> Many thanks in advance
> Virgil
>
>
>
> Virgil Lenton - Manufacturing Engineering
> SED Systems - A Division of Calian
> Saskatoon, Saskatchewan
> Canada
>
> ---------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> -----------------------------------------------------
>
>
>
---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
|
