We had seen this on our Nordson back when we still used VOC based coatings. If you need to prebake the panels, you have a poor cure oven setup. Try one of these ideas- Adjust the atomization pressure, nozzle size, temperature or viscosity of the coating (thin or thicken it). If any of these are out of the process window, you can get bubbles. Try a controlled experiment and you should find the exact window. Another cause may be your cure cycle. If the surface is allowed to skin over prior to removing solvent from underneath, you will have many bubble issues. We essentially tacked the panels and then elevated the temperature above Tg, in less than 1 minute. No bubbles, no problems, dry to the touch. ______________________________ Reply Separator _________________________________ Subject: RE: Bubbles in Conformal Coating Author: [log in to unmask] at internet Date: 11/8/96 1:40 AM We have experienced serious bubble problems on at least three occasions. In one case, we had applied polyurethane conformal coating to assemblies that had residual moisture on them. Moisture under the coating can cause problems with any chemistry but it was particularly troublesome with this polyurethane because it reacts with moisture to generate carbon dioxide gas. The coating bubbled like 7-Up. Prior to conformal coat, the assemblies had been washed in an aqueous process and then oven dried but the bake cycle was not adequate. The corrective action was to increase the pre-coat bake cycle. I'm not sure if your chemistry is sensitive to moisture. On another occasion, we had lots of bubbles on an assembly that had been cleaned with isopropyl alcohol and then coated shortly after cleaning. The assembly retained solvent and the solvent apparently volatilized during the elevated temperature cure and caused bubbles in the coating. The corrective action was to implement a bake cycle between alcohol cleaning and conformal coat. We use solvent based, heat cure, polyurethane and epoxy conformal coating. We have found that we can cause bubbles in the coating by not allowing enough time for the solvent in the coating to flash off before we start the elevated temperature cure cycle. I hope this information is helpful. Mary Davis Sr. Material & Process Engineer Alliant Techsystems 206-356-3311 [log in to unmask] ---------- From: David.Bruni[SMTP:[log in to unmask]] Sent: Thursday, November 07, 1996 4:57 PM To: technet Subject: Bubbles in Conformal Coating I threw this question out once before but I still cannot determine the source of bubbles in our conformal coating process. We are using an acrylic coating and a Nordson Select Coat System. The bubbles come and go from day to day. We have looked at viscosity, temperature, humidity, pressure, z-height, contamination, micro-adjust, and a few other variables. Has anyone else seen this phenomenon or do you have any insight on it? Any help is very much appreciated. Thank you. ************************************************************************** * * TechNet mail list is provided as a service by IPC using SmartList v3.05 * ************************************************************************** * * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ************************************************************************** * *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************