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August 2007

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Thu, 30 Aug 2007 00:08:14 EDT
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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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