Joseph,
I am not particularly fond of AR type coatings for class 3 products for
the following reasons:
1. Low Tg, from 15 to 40 degrees C
2. As mentioned most forms of hydrocarbon based solvent (and their
fumes) can desolve/liquidfy
the coating.
Depending on the end use environment these items can pose serious problems!
I suggest you get a copy of the IPC-HDBK-830 (Conformal Coating
Handbook) before you decide.
David A. Douthit
Manager
LoCan LLC
Kane, Joseph E wrote:
>We're Class 3, mostly military aircraft electronics.
>Historically, we've used Type UR, but we've recently
>brought in some work from another plant that has
>been using acrylic. We're in the process of switching
>everything over to our UV-curable urethane for the
>following reasons:
>
>1. UV-curing saves a whole lot of cycle time. The
>acrylic must be air-dried or baked.
>
>2. In order to perform any rework at all, you must be
>very careful when removing coating in particular spots,
>and things can look pretty ugly after recoating. More
>often than not, we end up stripping and re-coating the
>whole thing. More lost time.
>
>3. Some of our designs require solvent-resistant coating.
>If we're going to settle on one type of coating, it might
>as well be urethane.
>
>For the record, we haven't noticed any compatibility
>issues with the fluxes and solder masks that we've been
>using.
>
>Of course, YMMV. If you're doing occasional touchup on
>a solder joint or two, Type UR may be preferred. If you
>need to replace a lot of components, it's probably easier
>to strip the coating and start over.
>
>-Joe
>
>-----Original Message-----
>From: - Bogert [mailto:[log in to unmask]]
>Sent: Monday, March 08, 2004 4:55 PM
>To: [log in to unmask]
>Subject: [TN] Pros and Cons on Type UR vice Type AR Conformal Coating
>
>
>As a Class 3 customer we are considering mandating transition from Type UR
>to Type AR conformal coating, to make it easier to replace failed
>components. Are there any Class 3 users of Type AR coating? What is track
>record for using Type AR? Are there any compatibility issues with certain
>types of solder masks? Any input you have would help. Another advantage
>with AR would be for returned equipment. The OEM could remove all the
>coating from an assembly using alcohol, then perform
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