Twenty years ago, I had lots of experience with military hardware using 
Type AR, UR, and ER.  As Mike Buetow mentioned in his post earlier today, I 
am sure you aren't looking for a history lesson, but a little background 
might help you understand your situation better.

In those days, Type AR was instantly stripped off using Freon TES in a 
vapor degreaser,  then assemblies were reworked, re-cleaned using the vapor 
degreaser and aqueous equipment, dried, and then re-coated with at least 
two coats of AR (our requirement back then was .001" to .003").

Rework of Type AR in local areas using solvent is easy but left behind a 
myriad of by-products/contaminants. Type AR is soluble in many milder 
solvents but isopropyl alcohol is not one that I would use.

Removal of UR using solvents is not a method I recommended, mainly because 
any solvent that dissolves the urethane can attack the component package 
body and pwb surface as well.
People objecting to Type UR rework should familiarize themselves with the 
"hot knife" method (soldering iron blade tip).

IMHO, conformal coating is for proven assemblies that truly require its 
level of defense in their application.
For example, we used Type AR on Ground ATE that supported the 
airborne/space hardware that was always coated using Type UR.

Hope this helps,

Phil


Ok, so much for being serious.  It is Thursday evening so consider my 
analogy of Conformal Coatings in terms of rain gear as an attempt at Friday 
humor....

Non-users don't care if they get wet,
Type AR's carry an umbrella,
Type UR's wear heavy duty raincoats,
and Type XY's stay dry wearing effective but very expensive Class 100 Tyvek 
bunny suits.



At 07:24 PM 2/15/2007 -0500, - Bogert wrote:
>February 15, 2007
>
>Folks, we have some military OEM'S that are switching from Type UR 
>conformal coating to Type AR.  The main reason for the switch is because 
>it is hard to remove Type UR coating in event of a rework, and certain 
>chemicals sold by the coating manufacturers for UR coating removal are 
>highly conductive and have caused problems since the cleaning process did 
>not adequately remove them.  The other reason is we wanted a coating that 
>could be easily removed in event product failed in the field so we could 
>do ATE to quickly find the source of the problem.  Our product is used in 
>a military application but it is contained in a cabinet that is dust 
>tight.  We have some assemblies that are not coated at all with no known 
>problems.
>
>Do any of you folks use Type AR for military product, and if so, what are 
>your experiences using the coating?  I have heard about problems using 
>alcohol for coating removal since it goes where you do not want it to 
>go.  I have also heard that if a spray process is used, it takes 4 or more 
>passes on each side of the board to achieve the minimum J-STD-001 
>thickness.  At least one source indicated using AR may cause some solder 
>joint reliability issues.
>
>Any info you have would be a help.  Thanks.
>
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