Hi Julie, IF do you have the obligation to conformal coat, AND your experience shows a lack of adhereance (as a main important parameter) THEN this means there is no real qualification (and no awarness of all other propertiers) of the chain: solder resist - fluxer - cleaning (resp. no clean) - conformal coating. Beside the adhereance, this chain influences also the SIR (Surface insulation Resistance) CTI (Comparative Tracking Index) and especially the ability to resist against electromigration (see also IPC-TR-476A). If there there are no defined adhereance/Electromig./SIR/CTI-properties, you could waive the conformal coating, jawohl! May be you haven't defined the solder resist type (or only the resist class. H, T resp. 1, 2, 3) and each pcb supplier is using not specified solder resist. As consequence the electromigration properties will be unknown (as the adhereance). As consequence you should define the solder resist (keyword: purchasing specification, requirement flowdown) and your internal process (solder resist - fluxer - cleaning agents - conformal coating). I've some things: * solder resists secreting substances (unwashable) which decreases the bond in a manner that the conformal coating has been flow away by pressure air (no yoke). * UV-solder resists not abolutely cured. The residual not-cured chemistry has lowered the CTI from CTI600 below 250. * Fluxer containing substances which lowers the bond (of CC) and resists each practicable cleaning process. * Conformal Coating with excellent - and others with miserable bond/adhereance. As consequence you should obtain Appendix D of your bible (J-STD-001B) and consider all implications. regards from Zurich Bernhard > Date: Fri, 19 Nov 1999 09:48:53 +0200 > From: Brian Ellis <[log in to unmask]> > Subject: Re: Adhesion of Conformal Coating > > Julie > > The compatibility of coatings and masks is always a subject of doubt > unless you use similar chemistry for both. In my book, I recommended not > to use a solder mask if you intend to coat, provided you can get away > with it. Certainly, "no-clean" fluxes require compatible masks and this > is a subject for qualification testing: also on the degree of cure of > the mask. As a general rule (but not absolute), the order of quality of > masks are: (worst) dry film, LPI and UV screenable, 1-component > screenable and 2 component screenable (best). BTW I do not recommend > coating on top of "no-clean" residues, except under very specific > circumstances where the residues form part of the polymerisation > reaction chain -- and even then ... > > Brian > > Julie Dixon wrote: > > > > Dear Net, > > > > Has anyone ever heard of a problem with adhesion of conformal coating > being > > caused from UV soldermask? Will no-clean fluxes at assembly plants react > > differently to different types of soldermasks or LPI? > > > > Thanks, > > Julie Dixon > > > > ############################################################## > > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c > > Date: Fri, 19 Nov 1999 11:03:43 -0000 > From: Graham Naisbitt <[log in to unmask]> > Subject: Re: Adhesion of Conformal Coating > > Julie, > > LPI - UV resists can certainly contribute to poor conformal coating > adhesion. > > Reason? Because these materials require de-bubbling and levelling agents > which are either silicone or glycol based surfactants - surface modifiers. > > Naturally silicone based additives will probably leave unconnected > molecules > to which nothing will stick - not even another silicone. Glycol's don't > generally cause this problem, but may contribute to certain board > reliability issues in subsequent process stages - e.g. fluxing. > > The major issue is the way in which flux residues may inter-react with the > solder resist. Most modern fluxes have low solids and high liquid content. > So how do you stop them from dripping off the board when it upside-down? - > Add surface modifiers in the form of wetting agents. > > More liquid = higher preheat = greater surface expansion = greater > absorption of fluid that has low surface energy = reliability problems? > Probably. At least, the conformal coating may not stick very well - but is > this a problem? > > Well, if you expose your finished and coated assembly to full > environmental > testing and it passes, but on subsequent analysis you find that the > coating > adhesion isn't too clever - do you have a problem? In my opinion and > experience, not usually. > > If however, you experience poor reliability test results, then these > unpredictable chemical inter-reactions will very probably be at fault. > This > is why you folks need to seriously consider more effective reliability > testing using new SIR and/or IC measurement techniques. > > Hope this helps. I do have loads more but at this point it gets real > commercial - so I will just ask that if you want more, please ask > off-TechNet and I will send. > > Regards, > Graham Naisbitt > > [log in to unmask] > > WEB: http://www.concoat.co.uk > > CONCOAT Ltd > Alasan House, Albany Park > CAMBERLEY GU15 2PL UK > > Tel: +44 (0) 1276 691100 Fax: +44 (0) 1276 691227 > ----- Original Message ----- > From: Julie Dixon <[log in to unmask]> > To: <[log in to unmask]> > Sent: 18 November 1999 18:04 > Subject: [TN] Adhesion of Conformal Coating > > > > Dear Net, > > > > Has anyone ever heard of a problem with adhesion of conformal coating > being > > caused from UV soldermask? Will no-clean fluxes at assembly plants react > > differently to different types of soldermasks or LPI? > > > > Thanks, > > Julie Dixon > > ------------------------------ > > ############################################################## TechNet Mail List 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://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################