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
################################################################
|
