TECHNET Archives

April 2003

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Kane, Joseph" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 18 Apr 2003 11:10:42 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (280 lines)
We have set up our Emulsonators with wash time of 30 minutes and
rinse time of 15, but the rinse cycle will continue for up to 30
minutes if wash sump resistivity does not reach at least 1
megohm-centimeter.  If this level is not met within 30 minutes, the
cycle will abort.

FYI to the group, this is a batch "dishwasher" style machine, with
counter-rotating spray arms at top and bottom, and separate wash
and rinse tanks.  The wash tank contains water with 5 or 10% of wash
chemistry, in our case Bioact EC-7R.  Bioact is not miscible, and
separates, but pumping action creates an emulsion that is pretty
effective at removing RMA flux.

After the wash cycle, the emulsion drains back into the wash tank,
the valves close, and DI water is pumped into the cleaning chamber
from a separate tank and recirculating loop.  In this loop, rinse
water drains from the wash chamber into a decanter, where Bioact
floats to the top, and the water returns to the rinse tank.  Rinse
tank water is pumped through a particle filter, carbon, and
mixed-bed before it flows into the wash chamber.

Since water does not mix with Bioact, the rinse operation uses
water to mechanically remove the solvent, basically "pushing"
the Bioact residue off of the board surfaces.  Any solvent left
on the board will include flux and ionic residues dissolved within.
In our process, boards come out with no visible flux residue, but
we use these systems for gross flux removal, not final ionic
cleanliness.  Before conformal coat, we clean with a separate
dishwasher containing 75% IPA and 25% DI water.


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, April 16, 2003 8:12 PM
To: [log in to unmask]
Subject: Re: [TN] Cleaning Question - Rinse water resistivity?


Hi, Jason,

The resistivity setting will depend on a few factors:

1. The total area (both sides) of boards you have in the machine during any
given cycle.
2. The cleanliness level you're trying to achieve for the boards.
3. The volume of water in your rinse cycle.
4. How good your machine is at correlating actual contamination levels to
what it measures or reads.

If you multiply your total board area by the cleanliness level you require,
you will get the maximum salt equivalent total weight of contamination
allowable.
That amount of contamination divided by the volume of water will have some
direct relationship to the resistivity delta of the water, which I guess
you can either look up in tables or work out for yourself by
experimentation with known volumes of water at known resistivity to which
you add salt in precisely known increments and chart the resistivity drop
against cumulative increments. Look up the total allowable contamination
weight form your first calculation and compare it with your chart - that
should give you an equivalent resistivity.

Personally, I do not trust cleaning machines that give you a "cleanliness"
readout for a couple of reasons:

1. It gives you a very subjective result - the best job it can give you, no
matter how good or how bad, is always "clean". Why? Because it's using the
same water to tell you so that it's been using for rinsing the boards. If
the machine can remove no more contamination, the resistivity will be high
(i.e. board = clean), but you have no idea how much contamination the
machine has not been able to remove. There is no alcohol in the rinse water
to dissolve other contaminants that are trapping remaining ionics.
2. The reading a cleaning machine gives you is an average cleanliness of
all the boards in the machine during that cycle. It's likely that the
machine does not clean entirely evenly - boards in the corners of the
machine probably don't get the same pattern of cleaning water or rinse
water that a board in the middle of the machine does, so cleanliness
results will vary. Although your average reasult may show that your batch
of boards are clean enough, it is only an average. You will thus wind up
with boards that are cleaner than average and others that are dirtier - how
much cleaner and how much dirtier, you cannot tell.

Therefore to again have a better idea on what resistivity figure to set you
machine to, you will need an independant ionic cleanliness tester to test
several batches of boards using an alcohol/DI Water mix. Your tester will
also have to be checked out so that you have a correlation chart for it as
well (actual salt weight vs machine reading). Test each board individually
and map results against the board's position in the machine. Examine the
variance of the results and see how many boards are dirtier than average
and where they are located in the machine. From this analysis, you should
be able to determine what resistivity value you should plug into your
cleaner such that all your boards come out at least as clean as you want.

Hope this doesn't give you a bad weekend.

Peter




Wilson Jason <[log in to unmask]>  16/04/2003 06:34 PM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Wilson Jason

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: Re: [TN] Cleaning Question - Rinse water resistivity?








Hi,

We do use DI water in the rinse.

We use AAT Corp Emulsonator 9700.  It has the feature of monitoring the
rinse cycle's resistivity, and comparing that to a predetermined value.
When the resistivity reaches the predetermined value the rinse stops (if
the time has expired).

Thus I am not sure what to enter for the predetermined rinse restivity
value. Does anyone have a similar machine?  We use an RMA type flux.

Thanks in advance for any help,
Jason


>>> [log in to unmask] 04/15/03 04:31PM >>>
Jason,
I would recommend that you use deionized water in your cleaning for
the
same reason that soft water is better for cleaning clothes.  DI water
is a
hungrier solvent.  I would recommend using 2 megohm-cm resistivity
water
(0.5 uS/cm conductivity) as a minimum.  When you get below 2 megohm,
you
get in RO purity water, better than tap water, but not as good a
cleaner.
I also recommend 140-150F for temperature.

A 10 minute rinse is about normal.

Doug Pauls
Rockwell Collins




                      Jason Wilson
                      <wilson.jason@NORTHROP        To:
[log in to unmask]
                      GRUMMAN.CA>                   cc:
                      Sent by: TechNet              Subject:  [TN]
Cleaning Question - Rinse water resistivity?
                      <[log in to unmask]>


                      04/15/2003 01:39 PM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to Jason
                      Wilson






Hi Everyone,

I am a new member to the list and I have a question on cleaning.
Thanks in
advance for any help you can provide.  It is much appreciated.

What should the value be for rinse water resistivity? The cleaner we
have
is a AAT Corp Emulsonator 9700.

We use an RMA flux (both in wave solder, and in solder paste). The
solvent
we use is EC7R.

Also, we currently rinse for 10 min (+ time to reach resistivity).
Does
this seem low?  We are having trouble with board cleanliness.

Once again, thanks for any help provided.

Jason

---------------------------------------------------
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
-----------------------------------------------------

---------------------------------------------------
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
-----------------------------------------------------




[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]

---------------------------------------------------
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
-----------------------------------------------------

ATOM RSS1 RSS2