I have come across this problem at an account in Montreal -but never found out what caused it. we looked into the cure cycles on our LPI -different hold times did a UV bump to fully cross link/cure used different cleaning methods/solutions different finishes -gloss-semi matte matte was not an option tried different mask looked into the method or gun used to apply the conformal coating i felt the wave solder was removing whatever caused the dewetting and that may explain why the solder side was ok We also found there was no dewetting when we sprayed a few sample boards at another location. you could have your supplier do the same afri On Wed, 11 Mar 1998 [log in to unmask] wrote: > Many of you provided useful information to us last year when we were > preparing to change from dry film solder mask to liquid photoimagible (LPI) > mask. I could use some of your expertise again. > > We have now converted to LPI. But recently we had a run of boards on which > there was significant dewetting randomly scattered over the surface--on the > silk screened side only. We have now experimented with a number of test > boards and we get the same phenomenon--dewetting on the silk screened side > only. Cleaning the boards in alcohol before coating helps some. Aqueous > cleaning helps much more (DI water with detergent added per manufacturer's > specifications--our normal board cleaning process). But excessive > dewetting remains. > > In all the tests dry film boards were included as controls and no dewetting > occurred on any of them. (Our supplier can find no change in his process.) > > In addition to the possibility of a contaminant being added in the silk > screening process we question whether there is adequate curing of the mask. > However, there is no dewetting on the non-silk screened side. Moreover, > the silk screen ink is UV cured so that it seems the mask on that side > would be more thoroughly cured if its degree of cure differed at all. (We > use a polyurethane conformal coating). > > Any suggestions would be appreciated. Thanks. > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. > For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 > ################################################################ > > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################