Bill,
This is fantastic. My wimpy wooden sword just turned into a light
saber. Now into battle.
Thanks,
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Thursday, August 30, 2007 12:08 AM
To: [log in to unmask]
Subject: Re: [TN] The perils of using Alcohol for cleaning
TESTING: MIL-P-28809, developed by the Navy to remove and measure
ionics
from PWAs, requires the use of 75/25 v/v 2-propanol/deionized water.
One of
their reports contains a page of photographs of 25/75, 50/50 and 75/25
2-propanol/deionized water after use in trying to dissolve WW rosin.
The high level of
2-propanol was needed to dissolve the post-soldering rosin flux matrix,
which released the ionics into the water for proper measurement. This
test method
is still in use today. It can be found in J-STD-001, since MIL-P-28809
has
been canceled. *
The conclusion drawn here is: Alcohol and water are both needed to run
this
TEST, since alcohol (2-propanol) won't do it alone.
CLEANING: Several examples are instructive:
1. Assemblers used alcohol with a q-tip to clean the spot residues from
touch-up operations. This worked since touch-up was usually done with a
very mild
rosin-based flux.
2. British Aerospace built an alcohol cleaning system for use in house,
using a PFC (perfluorocarbon) vapor blanket over the hot alcohol to
minimize any
flammability problems. However, when users tried to run the system to
clean
heavily contaminated parts, especially to remove greases, waxes, etc.
the
alcohol just couldn't carry enough solids to be an effective cleaner. It
did work
satisfactorily to remove dust and some particulate, along with light
oils.
3. Forward Technology commercialized an in-line alcohol cleaning
system,
after inserting a primary tank of the cyclohexane/alcohol azeotrope (ca.
2 parts
cyclohexane plus 1 part alcohol). The azeotrope details are in the IPC
Solvent Cleaning Handbook, SC-60A. Such systems- since hot alcohol is
used-
require explosion- proof wiring & switches, both on the equipment and 4
meters
L/W/H around it. In this case, the alcohol is just used for rinsing and
drying,
while the cyclohexane/alcohol does the cleaning and carries the
contaminant
loading.
*I have a copy of the 1977 Navy report that contains the photograph. Let
me
know off-line if you would like a copy of it. The underlined documents
may be
useful in making your case to management that alcohol alone just won't
remove
the ionics per your in-house/customer requirements. Also, the flux and
paste
formulations of yesteryear were much easier to remove than today's more
complex formulations.
Bill Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO 80526
Tel: 970.207.9586 Cell: 970.980.6373
email: [log in to unmask] (mailto:[log in to unmask])
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