Bev, How about "Water Soluble vs. No-Clean Pastes: The Factors that Affect Performance", Surface Mount Technology, Jan. 93 issue, pp 35-40. Rob Schetty LeaRonal Inc Freeport, NY USA -----Original Message----- From: Bev Christian <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Date: Monday, March 30, 1998 3:24 PM Subject: Re: [TN] Re[2]: [TN] Parts Solderability (2) >Eddie, >I too would like not to see the demarkation but line, but 1) for some >components we were sole-sourced and 2) TI gave us a deal we could not refuse >so... >Secondly, we are using no-clean only in all our plants, so I was referring >to different no-cleans and their efect on d. There is a paper on this >somewhere. Anyone out help us out on a the ref? > >regards, >Bev Christian >Nortel > > >> ---------- >> From: Eddie Brunker[SMTP:[log in to unmask]] >> Sent: Monday, March 30, 1998 5:22 AM >> To: [log in to unmask] >> Subject: Re: [TN] Re[2]: [TN] Parts Solderability (2) >> >> But why should we accept this demarkation line? Let's not lower our >> standards just for TIs convienience. Has anybody done any metalurgical >> research into this? >> >> Bev, >> you said the parts are flux dependant, I agree totally. I have learned to >> live in the realms of higher flux activity, and TI are probably the sole >> reason for this!! Water soluble fluxes will solder almost anything. As BGA >> technology takes over, No clean is the 'order of the day', and this too >> has >> been choosen at the edges of IPC class 3 with healthy residues, to tackle >> the lack of solderability of this finish. >> >> >> Steve, >> > >> > I concur with what you've said. We also had accept/reject issues >> with >> > the palladium solder joints. The demarcation line along the side is >> > unsettling to some inspectors. We answered the great majority of >> > those questions by distributing to QA, a bulletin, with inspection >> > criteria and photographs of acceptable joints. Overall, we get good >> > results with these parts. >> >> Why didn't you take issue with TI for the problem, instead of training QA >> to >> accept "no toe fillets, side fillets, poor wetting angle etc...." >> >> >> >Author: SteveZeva <[log in to unmask]> at 0UTG0ING >> >Date: 3/27/98 12:21 PM >> > >> >> > >> > The biggest difference I've seen between a tin/lead and a palladium >> >coated lead, is solder joint appearance. What I noticed mainly is that >> the >> >solder does not seem to flow as readily to a palladium coated lead as it >> does >> >with a tin/lead coated lead. >> > >> >> Solder flowing to the lead and wetting angle are common indicators of what >> is called solderability. >> >> >> > When you look at a palladium coated lead solder joint under a >> microscope, >> >it will tend to have a very strong demarcation line where the solder >> stops and >> >the lead begins. >> >> Anybody know what the metalurgy of this boundary is? Why should we treat >> this line different to when it is observed on tin/lead terminations? I >> don't >> believe this line is safe!! I think it is a source of weakness, and can >> develop with time into a crack. >> >> Many inspectors see that as the solder appearing to not have >> >wet very good. >> >> Yes!!! >> >> A tin/lead plated lead will have the solder wet and flow over >> >top of the foot making the overall joint look kind of rounded and >> >smooth...many times when you have that kind of variances in solder joint >> >appearance, the inspectors tend to excessively reject the palladium >> joints. In >> >my opinion, when they put a defect arrow on it, and have it reworked, all >> it >> >is accomplishing is making all the solder joints look the same, and >> nothing >> >more. >> >> But why should we accept the difference in the first place???? >> >> > A little higher than normal peak temperature in your profile helps >> things >> >a little, but don't cook your boards! This helps the appearance some, but >> I >> >really don't think it's necessary. I feel the joints are good, the >> plating was >> >designed to be a drop-in replacement for tin/lead. >> >> Maybe your assemblies are simple and uniform, but we have 12 layer, >> complex >> assemblies where with a range of devices which put a wide enough range on >> the delta T already. Again, why should we have to change our profile for >> TI? >> >> > Sure, the joints will look a little different, but that's okay. >> >> How do you know it's ok? Have you performed metalurgical analysis on them? >> The IPC 610 is based on visual characteristics for defects. >> >> From >> >everything that I've been taught and read, the most critical area of a >> solder >> >joint is the interface between the bottom of the foot of a lead and the >> the >> >top surface of the pad, next in importance would be the heel, and I've >> always >> >observed completely acceptable wetting in those two areas on palladium >> coated >> >leads. >> >> What solder between bottom of the foot and the pad? 70% of the strength is >> in the heel fillet! Yes. >> >> Side and toe fillets don't add a whole lot to the joint as far as >> >mechanical strength goes from every stress testing graph I've read. Don't >> get >> >me wrong, they do add a little to the equation, but not as much as you >> might >> >think... >> >> If every other joint on the assembly has a toe fillet but TI devices don't >> why should I accept this? OK so it conforms to IPC, but I would like to >> see >> it there as an indicator that things are going well. The side fillets do >> add >> strength to the joint. >> >> > I spoke with somebody from T.I. back when I first noticed it about >> >5-years ago... (that's right, they've been doing it for 5-years). The >> biggest >> >reason they switched I was told, was that the solder plating operation >> was the >> >messiest, low yielding process that they had. >> >> Yes, we too have been using this finish on devices for a long time. >> >> Once they switched to palladium >> >they saw at least a 50% increase in yields...plus, they eliminated using >> lead >> >completely. >> >> SO WHAT!!!! This is not my problem!!! TI may see the advantages...I don't >> care! >> >> Something that most of us are probably going to have to face >> >sometime in the future. (even though some of us aren't really looking >> forward >> >to it...) >> >> Ah, now I see what you mean by higher profile temperatures! Lead free >> technology with m.p. of 230 deg C. Nice.....very nice...(Electovert, your >> ovens still only have a max. programmable temp. of 280 deg C!) Look, >> California's electronics industry might try to shoot itself in the foot, >> and >> tell the rest of the world how to behave, but first they'll have to >> develop >> a working technology we can all use. Show me someone making complex >> assemblies with lead free solder. >> >> >> > So unless I'm really missing something, from what I see, the only >> problem >> >with palladium coated leads is getting everybody to agree on what the >> >appearance of an acceptable solder joint should be. >> > >> >> ################################################################ >> 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 >################################################################ > > ################################################################ 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. 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