This is a tough question, because most of the cleaners strong enough to remove heavy oils and grime will also begin to damage the conformal coatings.

To my mind, the spray wash is taking the solution in the wrong direction. You're going to use lots of water and water-treatment machinery, lots of electricity to wash and then dry, and quite often have problems with quality of the result. Unless you already have the equipment to use, this is a slow and expensive way to clean these boards.

My suggestion would be to look at a vapor degreasing option, using a milder solvent that will remove the oils but not damage the conformal coatings. You could, if desired, enhance the cleaning with ultrasonics -- the general prohibition on ultrasonics and PCBs has faded into history as the myth it was. The boards will come out clean, dry and with relatively short cycle times (especially when compared to water-cleaning) which will boost through-put.

For solvents, I suggest you check with 3M Novec or DuPont's Vertrel (the
latter of which we sell, so my bias is strong).

For cleaning machinery, Branson Ultrasonics (818) 707-7001, and Ultronics (800) 553-7881, make excellent machines, as does Tiyoda Serec, 502-212-9226.

Acrylic conformal coatings are "thermoplastic" coatings which are used if the coating has to be removed easily or if through-soldering repair should be possible. Acrylic systems can be removed very easy by some solvent especially at higher temperatures as they are thermoplastics. So you have to use a cleaning agent which is not solvent based or which has a very low solvent content and the temperature should be as low as possible. Products that we would recommend would be from the Atron and Vigon product range.

Cleaning of this type can effectively be done with a low pressure (25 PSI) wash system with a weak 1% saponifier (either the Kyzen or EnviroGold saponifier) at 125 F wash and ambient rinse a belt speed of 4-5 ft/min and rinse with DI water at low pressure. By using the weak saponifier the surface tension is lowered and has a bit of cleaning energy but not enough to attack the acrylic coating. By using low pressure in wash and rinse will remove the residue but not ablate the surface of the coating. If you want to run ten test boards through this set up please contact me at Foresite.