Sorry, Vladimir, it's an urban myth. Lead pipes are quite safe for
carrying drinking water, after the initial flush-through, because an
ion-exchange mechanism deposits lime on the pipes' insides. The pipes
are effectively calcium hydroxide/carbonate in contact with the water,
not lead. As Werner said, it was lead glaze on ceramics and lead
glassware that caused the damage.
Brian
Vladimir Igoshev wrote:
> Hi Inge,
>
> It does sounds "weird" (the Pb thing) and I spelled it out :-), BUT Pb is dissolved in water and that was why that ancient idea with water pipes made of Pb didn't work out well for the Romans :-)
>
> Regards,
>
> Vladimir
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
> Sent: Wednesday, May 09, 2007 2:04 PM
> To: [log in to unmask]
> Subject: [TN] SV: [TN] SV: [TN] SV: [TN] Metallurgists, need assistance
>
> Dave,
>
> Goofy, agree. No, I have not confirmed the ENIG finish, because my
> client did not send naked boards to me. I will ask for a fresh board so
> that we can check the condition. That's a good thought, to investigate
> the parts before assembly, the board, the solder paste and the FPGAs. My
> client denies there could be anything wrong here, but it can, of course.
> I'll call them tomorrow.
>
> As you could read, one guy pointed out that the voids can be created at
> the polishing process, because of Lead dissolved by the water. Sounds
> goofy too. Suppose that could happen, why don't I get that when
> polishing the good references then. I've seen SnPb cross sections for
> years, but never seen Lead being superseded by voids!
>
> OK, can try oil polishing instead...
>
> Inge
>
> -----Ursprungligt meddelande-----
> Från: TechNet [mailto:[log in to unmask]] För David D. Hillman
> Skickat: den 9 maj 2007 14:12
> Till: [log in to unmask]
> Ämne: Re: [TN] SV: [TN] SV: [TN] Metallurgists, need assistance
>
> Hi folks! I agree with Vlad - I don't see any "B" word characteristics
> in
> the nickel plating. Looking over the SEM photos, something just looks
> goofy. As Vlad pointed out the voids don't seem to be from a flux
> outgassing root cause - they contain rough, jagged features. Inge - have
>
> you run a SEM EDX analysis to get a chemical ID on the structures inside
>
> the voids? My guess is that the cause of the poor solder joint integrity
>
> is linked to the formation of your strange void structures. I was
> thinking
> maybe gold embrittlement but if you are using ENIG then you don't have
> enough gold present. Have you confirmed that the ENIG finish was
> correct?
>
> Dave
>
>
>
> Vladimir Igoshev <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 05/08/2007 08:01 PM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Vladimir Igoshev <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> Re: [TN] SV: [TN] SV: [TN] Metalurgists, need assistance
>
>
>
>
>
>
> Hi Inge,
>
> The images are nice and clearly prove we won't have to use the "B" word
> any more (at least not in that case).
>
> But I got even more confused :-)
>
> My uneducated guess would be that the first two images were taken in
> the
> backscattered electron topo mode. That would explain why there are
> plenty
> of blubs/hillocks (or whatever one'd prefer to call them) on the
> surface.
> That is how surface CAVITIES (not protrusions) can look like in that
> particular mode.
> It's sort of an optical illusion.
>
> Your other pictures are in the secondary electron mode and here the
> cavities do look like cavities.
>
> If I'm right, then I'd have to understand what those black spots are, as
>
> they don't look like voids (voids woud look like protrusions and I'd
> expect voids to be more rounded).
>
> The interface on the board side looks normal on all images (and from my
> understanding that is the interface you are having the problem with).
>
> I don't see any Ni on the lead side and I don't like how the
> intermetallics looks like there (there is kind of a "demarkation" line
> inside the layer, which might bring up a couple of speculations on is
> origin).
>
> The intermrtallics is most probably (Ni-Cu)/Sn, not Ni/Sn as you have a
> huge source of Cu (cut off lead). It even looks like Ni-Cu/Sn, not
> Ni/Sn.
>
> And now we got down to the most "misterious" part :-) - those cavities
> in
> the surface. I might be wrong, but I think I either heard or read
> somewhere that Pb is etched away during polishing (reaction with water).
>
> That would explain why you see the cavities. To prove (or disprove) my
> point, I'd take pictures from the same areas in backscattedred
> COMPOSITIONAL (not topo) mode.
>
> And after all, I'd love to see how a failed joint look like in
> cross-section (with the lifted lead) :-)
>
> BTW, did you see those Sn spheres? :-)
>
> Regards,
>
> Vladimir
>
>
>
> -----Original Message-----
> From: Hfjord
> To: Vladimir Igoshev; 'TechNet E-Mail Forum'
> Sent: Tue May 08 14:44:42 2007
> Subject: SV: [TN] SV: [TN] Metalurgists, need assistance
>
> Vlad & TN gnus,
>
> Hey, curious? I'm still concerned, but at a higher level, as said
> Newton. To begin with, I Xsectioned samples from failed part AND known
> good references. Both finished with 0.1 micron diamond milk. Etched for
> 10 second, 5 seconds, 1 second and no etching at all. Same result: voids
> in the failed parts, absolutely flat with references. I'll send photos
> to Mr Wallman, alias Steve.
>
> Pic new xsections_1 : typical solder joint with void concentrations
> under the lead's foot. Not etched.
>
> Pic new xsections_2 : details from under the lead's foot. Nickel plating
> seen clearly, and a very thin nickel IMC layer. All bright areas are
> predominated by Tin, very little Lead. Black spots are voids that
> contains a little of everything debris from polishing. Not etched.
>
> Pic SEM_3 shows following: from bottom copper pad / solder joint with
> voids / lead with nickel finish. Not etched.
>
> Pic SEM_1 shows upper part of solder joint, with lead copper uppermost.
> Not etched.
>
> Pic SEM_ 2 shows typical solder joint at higher magnification with
> predominating Tin and also little Lead and Copper. Not etched.
>
> As I said earlier, the references show no voids at all like the above.
>
> Preliminary, I have excluded Black pads and Skip plating. Furthermore, I
> don't think there are brittle copper IMCs either, even if there are
> relatively high Cu peaks everywhere. Think Cu peaks come from
> preparation. Nor is it likely with Ni IMCs, they belong to the interface
> parts. So, what is this? Someone mentioned a insufficient soldering
> process, and that is finally what I begin to think too. Against this
> speaks the very experienced and big company that makes these boards (one
> of the big elephants, not Ericsson, not American). On the other hand,
> even the best can fail.
>
> The failure appears randomly around the world, much annoying for the
> customers, and the technicians scratch their heads.
>
> Finally, I remind you all about the fact, that the fractures start close
> to the solder pads and spread to the middle of the solder joints. And
> only on the large FPGAs. No other components are hit.
>
> Inge
>
>
>
> -----Ursprungligt meddelande-----
> Från: Vladimir Igoshev [mailto:[log in to unmask]]
> Skickat: den 8 maj 2007 15:47
> Till: TechNet E-Mail Forum; Hfjord
> Ämne: RE: [TN] SV: [TN] Metalurgists, need assistance
>
> So inge,
>
> What the cross-section looked like? :-)
>
> Vladimir
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
> Sent: Monday, May 07, 2007 4:57 PM
> To: [log in to unmask]
> Subject: [TN] SV: [TN] Metalurgists, need assistance
>
> Diet Coke! Man! Does not remove black pads on your teeth..
> New samples are ordered, will try both oxides on paper and diamond on
> nylon.
> If the customer pays, I may try even FIB or TOFSIMS. Both are superior,
> and even if the time tax is high, I must say that polishing, and
> repolishing and endlessly repeated polishing can be quite expensive as
> well.
> Inge
>
> -----Ursprungligt meddelande-----
> Från: TechNet [mailto:[log in to unmask]] För David D. Hillman
> Skickat: den 7 maj 2007 14:23
> Till: [log in to unmask]
> Ämne: Re: [TN] Metalurgists, need assistance
>
> Hi George! Good comments! It does seem that the industry, at times,
> spends
> more time in describing a phenomena rather than resolving the root cause
>
> so that we can avoid a reoccurrence. As for Inge's Monday dilemma, I
> would
> wait and see what the cross-section results reveal. If the observations
> are that the nickel plating grain boundaries look bad, then I would work
>
> with my pwb fabricator on what went wrong in the plating bath. It the
> observations are that the nickel plating grain boundaries look good, I
> would chase either a poor solderability or a poor soldering process root
>
> cause. As you noted, the plating chemistry suppliers have worked
> extremely
> hard on making the ENIG plating process more robust and "real" black pad
>
> problems are less prevalent today. I have always viewed the solution to
> black pad as one of two choices: don't use ENIG or work very closely
> with
> the pwb fabricator. Here is an article reference which I think really
> does the best job to date, of describing the root cause of black pad
> (one
> of the contributors is our good fried Dick Coyle!).
>
> Zeng, Steirman, Abbott, Murtuza, "The Root Cause of Black Pad Failure of
>
> Solder Joints with Electroless Ni/Immersion Gold Plating", JOM, June
> 2006,
> pp. 75-79
>
> The reality for us may be that no amount of plating bath control will
> completely eliminate the potential of having a black pad situation and
> that a risk assessment on a product basis is the final solution. Ouch,
> way
> too much thinking on a Monday before I have had a Diet Coke!
>
> Dave
>
>
>
> "Wenger, George M." <[log in to unmask]>
> 05/04/2007 07:56 PM
>
> To
> "TechNet E-Mail Forum" <[log in to unmask]>, <[log in to unmask]>
> cc
>
> Subject
> RE: [TN] Metalurgists, need assistance
>
>
>
>
>
>
> David,
>
> I hate the "B" word because it describes an optical appearance rather
> than a failure mechanism. I've heard the "B" word as well as terms like
> "weak Nickel" and "Black Line Nickel" used many times to describe ENIG
> failures. The reason I don't like these terms is because they are
> adjectives to describe what one thinks they see and don't describe the
> failure mechanism that causes the brittle interface failures. We use
> ENIG on an old telecommunications legacy product because it wouldn't be
> profitable to do any engineering evaluations to qualify another surface
> finish. However, since the root cause of the ENIG solder joint failure
> mechanism has never been understood or resolved to the point where one
> can turn it on or off, we avoid the use of ENIG surface finish on all
> new products. Even though the suppliers of ENIG chemistry have done a
> great job of monitoring their chemistry and educating board shops on the
> proper controls to reduce the occurrences of brittle solder joint
> failures they haven't been able to eliminate these type of failure.
> Ingemar is one of the few people I know of on TN that not only has a
> great understanding of solder joints but appreciates the process control
> details one needs to follow in PCB fabrication as well as PCBA to avoid
> un-reliable solder joints. His current problem (i.e., not being able to
> understand the failure mechanism or predict when it is going to happen)
> is the major reason we avoid the use of ENIG surface finish.
>
> Let's just say Ingemar does a cross section and confirms that there is
> "mud flat" nickel grain boundary attack, what does he do on Monday?
> Your advice about having a beer because it is Friday and not worrying
> about this until Monday only will help this weekend but come Monday what
> does he do. I assume that he's already using a "good" board shop and a
> "Good" ENIG chemistry. I know what we did and it worked for us but as
> an engineer I'd really like to what the ENIG failure mechanism is and
> how to avoid it.
>
> Regards,
> George
> George M. Wenger
> Andrew Corporation Wireless Network Solutions
> Senior Principal FMA / Reliability Engineer
> 40 Technology Drive, Warren, NJ 07059
> (908) 546-4531 [Office] (732) 309-8964 [Cell]
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Friday, May 04, 2007 4:45 PM
> To: [log in to unmask]
> Subject: Re: [TN] Metalurgists, need assistance
>
> Hi folks and thank you Steve for being "TechNet Picture Central"! Sorry
>
> but just to warn everyone but I am going to use the "B" word shortly.
> Inge
> - take a close look at picture 4. As Werner pointed out the gold is
> non-wetting the nickel in number of locations. What really jumped out
> at
> me is that "mud flat" appearance on some of the nickel surface regions -
> a
> "mud flat" appearance is a classic indication of black pad! I recommend
> you complete a cross-section to confirm that you have nickel grain
> boundary attack.
>
> But since it is Friday, go have a beer and worry about this on Monday!
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Steve Gregory <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 05/04/2007 01:45 PM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Steve Gregory <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> Re: [TN] Metalurgists, need assistance
>
>
>
>
>
>
> Hi Inge!
>
> Got your pictures posted. Took me a bit, I was swapping our wave
> solderpot from 63/37 to HMP. Done now. I'm getting quicker, I can do it
> in 20-minutes now. Took me about 45-minutes when I first did it...
>
> Anyways, here's the links:
>
> http://stevezeva.homestead.com/files/Pic1.jpg
> http://stevezeva.homestead.com/files/Pic2.jpg
> http://stevezeva.homestead.com/files/Pic3.jpg
> http://stevezeva.homestead.com/files/Pic4.jpg
> http://stevezeva.homestead.com/files/Pic5.jpg
> http://stevezeva.homestead.com/files/Pic6.jpg
>
> -Steve-
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
> Sent: Friday, May 04, 2007 12:22 PM
> To: [log in to unmask]
> Subject: [TN] Metalurgists, need assistance
>
> Have an issue with (randomly) lifted FPGA leads.
> Pic 1: good joint after pull test
> Pic 2: ditto but high magnification
> Pic 3: "rotten" joint after pull test
> Pic 4: ditto but high magnification
> Pic 5: "rotten" cross section
> Pic 6: ditto but high magnification
>
> 60Sn on ENIG, obviously a brittle region. Suspect Kirkendall voids, but
> the pockets with zillions of Tin spheres (0.1 to 2 um in size) points at
> insufficient peak temperature to make 100% melt and good solidifying. If
> these little balls were Lead, I could understand, but they are Tin!
> Never seen like. Any "quickhead" out there, need fast advice.
>
> Note: Pic 2, you can see the underlying board pad nickel as dark areas.
> An experienced analyst will hopefully recognize. No Phosphorous peaks!
>
> My Friday headache.
>
> Inge
>
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