Werner,
if you can mae me understand this a bit better, I'll put a Havanna in your
mouth, and a Margeritha in your hand. The wormlike pattern is a extremly
high concentration of phosphorous. It seems to me as that is what weakens
the IMC structure. I have some other pictures that demonstrat that, I'll
send offline to you. I begin to see how it works, The intermetallic crystals
(grain seems to be a improper description) are very strong in themselves,
but the P-rich stuff in between them makes the total vulnerable to stress.
It's like using a bad cement when building a brick house. So, before the
separation of the layer SnxNix from layer SnyNiy. the cement gives way and
the crystals start separate from each other. Is my anticipation right?
Inge
--------------------------------------------------
From: "Werner Engelmaier" <[log in to unmask]>
Sent: den 3 March 2010 11:37
To: <[log in to unmask]>
Subject: Re: [TN] Hackneyed?
> Hi Inge,
> do not put words in my mouth.
> I suggested that that crater-like ring is the only good solder connection
> with the center of the crater floor having a brittle interfacial
> separation was typical of BP.
> Not those worm-like bands of whatever material—are these bands on top of
> the grain boundaries?
> And no, BP is characterized by 'normal' Sn-Ni IMC development—the
> P-concentration does not, at least initially, inhibit IMC formation; it
> weakens the interfacial bond.
>
> Werner
>
>
>
>
>
>
> -----Original Message-----
> From: Inge <[log in to unmask]>
> To: [log in to unmask]
> Sent: Wed, Mar 3, 2010 12:15 pm
> Subject: Re: [TN] Hackneyed?
>
>
> Hi all,
>
> about 'black pads' . Werner suggested that this was typical BP. However,
> had a visit from a very experienced person who cast an eye on our problem.
> After a few minutes of silence and looking at my images, he scratched his
> head and cleared his throat and said 'Well, this Engelmaier, know
> perfectly who he is and I respect him very much, but I'm not with him.
> IF.. if this is a black pad case, then you can't have such a well
> developed bands (plural) of Tin/Nickel IMCs. The very central thing about
> black pads is that the P-rich surface effectively stops the growth of
> healthy tin/nickel products. In my opinion, you have rather normal such
> IMCs, with the typical variation in strength, and the rupture occured in a
> weak region of these layers'. When you pull or prey off the BGA, the
> thick solder hanging on outside of the periphery of the pad is stronger
> than the inner part of the pad, hence the separation will begin in the
> middle. '
>
> His argument seems to fit better into the story. Furthermore, this new
> explanation seems to coincide with Bunni's theory on hyper Nickel
> boundaries. But before going on his line, I would like to hear your
> meaning. Can you have a very high P%age and still no BP?
>
> Thanks for your valued help
>
> Inge
>
> --------------------------------------------------
> From: "Hernefjord Ingemar" <[log in to unmask]>
> Sent: den 2 March 2010 00:20
> To: <[log in to unmask]>
> Subject: Re: [TN] Hackneyed?
>
>> HiWayne,
>>
>> thanks for your eye on this.--- Correct, no vias under balls. >
>> Non-soldermask defined. Not overbaked. VP soldered, shadowed profile from
>> > Xilinx datasheet. Checked. Question is how the shipped boards will
>> behave > in the future. Some reports have arrived about pressure
>> sensitive boards. > Maybe a consequence of BP?
>>
>> Werner seems rather convinced that these are real BPs, and considering >
>> other's and my own investigations, I've come to the conclusion that this
>> > is to be reported to our staff as being a issue.
>>
>> We have left the ENIG behind, use HASL'd board since a year. I'm going to
>> > do similar investigation on some samples from that production line for
>> > comparison. I really hope that I will see quite different solder joints
>> > with elongation rupture'd Tin/Lead micro joints all over the pad
>> instead > of these 'rotten' ones.
>>
>> I'll let you know what happens.
>>
>> /Inge
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
>> Sent: måndag 1 mars 2010 14:56
>> To: [log in to unmask]
>> Subject: Re: [TN] Hackneyed?
>>
>> Hi Inge-
>>
>> Just completed an emergency FA in another project, so I'm just tuning in.
>> > Others asked about a cross-section. Did I miss your reply? Looking at
>> > the grain structure and elemental analysis for the different zones of
>> the > joint would probably help give us more insight.
>>
>> Also, I haven't seen any theories on the variation in properties across >
>> the joint (periphery looks great, but interior looks rotten). Has Werner
>> > given a theory as to why that is?
>>
>> You haven't suggested dismissing the theory that microvias have anything
>> > to do with this phenomenon, yet I don't see evidence in your pix of any
>> > microvias, so I presume the pix all came from pads which don't have >
>> microvias. Is that correct?
>>
>> I agree with Werner that I've seen overbaked joints do this. In any
>> case, > such joints cause nightmares because they look nice (and are
>> nice) on the > outside.
>>
>> Wayne
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
>> Sent: Saturday, February 27, 2010 11:01 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Hackneyed?
>>
>> Hi Inge,
>> Yes, I have seen this before-not with those absolutely great pictures,
>> but > with very similar elemental distributions.
>> In that case, the assembly saw nine (9!!!) soldering exposures.
>> I looks to me, your assembly was either exposed to soldering temperatures
>> > too often and/or too long.
>> Werner
>>
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
>> Sent: Wednesday, February 24, 2010 2:54 PM
>> To: [log in to unmask]
>> Subject: [TN] Hackneyed?
>>
>> Hi Folks,
>>
>> am asking you to sacrifice a minute on a topic that may make you sick,
>> as > much as it has been discussed. Have a look at the SEM images that
>> (hopefully) will be beamed by our most honorable guy, Dr Gregory. By
>> order:
>>
>> 1. Pic 38 BGA ball after the preying off the 560 ball BGA from the board.
>> SEI mode.
>> http://stevezeva.homestead.com/files/XILINX_Daniel_38.jpg
>>
>> 2. pic 39, same at x 5,000
>> http://stevezeva.homestead.com/files/XILINX_Daniel_39.jpg
>>
>> 3. pic 40,samet at x 10,000
>> http://stevezeva.homestead.com/files/XILINX_Daniel_40.jpg
>>
>> 4.pic, 41 same at x 20,000
>> These four show the face of the pulled-off balls. The package/board was >
>> sectioned into halv by half inch pieces with a thin blade diamond saw and
>> > then each BGA section was separated from the board by means of a steel.
>> http://stevezeva.homestead.com/files/XILINX_Daniel_41.jpg
>>
>> After SEM 1-4 I made EDS, which can be seen below.
>>
>> 5. http://stevezeva.homestead.com/files/XILINX_Backlund_Ball_2.doc
>> As you can see, there is nearly no Lead (!), a high w/% Nickel, a little
>> > Tin
>>
>> and lots of Phosphorous. Clearly, the separation has been in a
>>
>> Now, continue with having a look at the board pads after the preying-off.
>>
>> 6. pic 44, Board pad at low magnification and SEI mode.
>> http://stevezeva.homestead.com/files/XILINX_Daniel_44.jpg
>>
>> 7.pic 46, same at x 5,000
>> http://stevezeva.homestead.com/files/XILINX_Daniel_46.jpg
>>
>> 8.pic 48, same at x 10,000
>> http://stevezeva.homestead.com/files/XILINX_Daniel_48.jpg
>>
>> 9. pic 50, same at x 20,000
>> http://stevezeva.homestead.com/files/XILINX_Daniel_50.jpg
>>
>> 10. pic 51, same but with BS mode
>> http://stevezeva.homestead.com/files/XILINX_Daniel_51.jpg
>>
>> 11. XILINX_backlund_pad_1.doc
>> http://stevezeva.homestead.com/files/XILINX_Backlund_Pad_1.doc
>>
>> As you can see here, there is more Lead, a high w/% Nickell, much more
>> Tin > and still lots of Phosphorous.
>>
>> Discussion:
>> Obviously, real and reliable solder joints are only in the >
>> circumperipheric
>>
>> of the whole (best understood with pic 10). How strong the adhesion was
>> > in the main part of the joint, we don't know. From the function
>> (final) > electrical testing, we have experienced several cases with
>> disturbed > signals. Many a times, we have had to remove the BGA and
>> supersede with a > fresh one. The test engineer told me, that by slightly
>> add pressure to the > BGA, he may get the signal through again. He
>> thinks we have an issue with > the uvias, others think there is a problem
>> with the BGAs, myself I'm > committed to my theory that this has to do
>> with the rotten interface > between
>>
>> the Tin/Lead and the ENIG pads.
>>
>> Question:
>> Is anyone familiar with the said? What is your opinion about the >
>> demonstrated solder joints? Can yoy get cracks and electrical
>> misfunction, > despite that hundreds of balls are holding the BGA close
>> to the board in a > 'iron grip' ?
>>
>> Wayne? Steve? Dave? George W? Vlad?
>>
>> Thanks in advance. You'll have to wait for Steve to fix the exhibition.
>>
>> /Inge
>>
>>
>>
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