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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 17 Sep 2015 14:39:21 +0000
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Joyce, I hate to spoil your fun, but even that Neanderthal Rework Process will not overly extend the IMF by more than 1 or 2 microns.
When the original IMF is formed during reflow, any additional rework is simply soldering solder to the solder already present. The IMF does not increase in thickness appreciably.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Thursday, September 17, 2015 8:00 AM
To: [log in to unmask]
Subject: Re: [TN] BGA Reworked Intermetallic

Hot plate and soaking the part intend to repair in flux and walk away until it was reflowed.  remove the defective part and let the PWA cool down.  put back on the hot plate, with additional flux and clean the site, remove access old solder.  add additional solder to address the pad.  Cool down again by remove from the hot plate.  position the part using microscope that is not near the work station with tacker flux, bring back to the hot plate and reflow again, using tooling to perform minor adjustment to position the part and final cool down... if you check for the IMC after such a repair, you get very thick IMC - the overall time above TL is 5 to 6 x compare to your SMT the least.... (I was told it is not un-common in some places for "repair").  scary.
               jk
> But Vlad - those conditions are so extreme that something is clearly 
> incorrect in the process so focusing on the IMC is the  wrong root 
> cause analysis path. The focus should be on how/why such an extreme 
> amount of IMC is being created in the first place.
>
> Dave
>
> On Thu, Sep 17, 2015 at 7:36 AM, <[log in to unmask]> wrote:
>
>> Hi Dave,
>>
>> That what exactly my point. It does happen under certain conditions, 
>> so I always advise our customers not to start with a very thick layer 
>> of intermetallics.
>>
>> Cheers,
>>
>> Vladimir
>>
>> Sent from my BlackBerry 10 smartphone on the Rogers network.
>> *From: *David Hillman
>> *Sent: *Thursday, September 17, 2015 08:22
>> *To: *Vladimir Igoshev
>> *Cc: *TechNet E-Mail Forum
>> *Subject: *Re: [TN] BGA Reworked Intermetallic
>>
>> Hi Vlad - the growth rates of IMCs are pretty well known as they 
>> follow an Arrhenius equation behavior. The growth of IMCs from 25C 
>> -100C is extremely low so unless you have a product service 
>> environment that has a high temperature such as 150C for long time 
>> periods, you just are not going to "grow" enough IMC thickness to 
>> impact solder joint integrity. Having an IMC of 12 microns (400 
>> uinches) is HUGE and clearly not a normal, typical case found in 
>> standard electronics production. The biggest issue with having an IMC 
>> discussion is that the data doesn't support IMC failure as a typical 
>> root cause for solder joints when we start crunching the numbers.  I 
>> working with one of our industry colleagues and we are pulling 
>> together a paper on industry "myths" where we plan on including the 
>> topic of IMCs.
>> As
>> you can imagine, its a fun paper to work on and we hope to have it 
>> publish in the upcoming year(ish).
>>
>> Dave
>>
>> On Wed, Sep 16, 2015 at 9:52 PM, <[log in to unmask]> wrote:
>>
>>> Hi Dave,
>>>
>>> As far as I remember I said it's a reverie for disaster. As you know 
>>> intermetallics will grow over time and a starting point of 10 or so 
>>> microns doesn't help.
>>>
>>> I had several cases of failure (cracked intermetallics) after it 
>>> grew up to 12-15 microns.
>>>
>>> Does it happen all the time? I don't know  May be not, but the cases 
>>> I had are good enough "argument" , at least for me.
>>>
>>> Regards,
>>>
>>> Vladimir
>>>
>>> Sent from my BlackBerry 10 smartphone on the Rogers network.
>>> *From: *David Hillman
>>> *Sent: *Wednesday, September 16, 2015 22:44
>>> *To: *TechNet E-Mail Forum; Vladimir Igoshev
>>> *Subject: *Re: [TN] BGA Reworked Intermetallic
>>>
>>> Hi Vlad - what data do you have that 10 micron thick layer of IMC 
>>> results in the failure of the BGA? There is TONS of subjective 
>>> comments in the published literature but no hard data of failures. 
>>> As a basic materials engineering principle, IMCs are brittle but 
>>> that specific material characteristic seems to be the only reason 
>>> folks make statements that a "thick" IMC is bad. Should we work to 
>>> keep IMC layers minimized?
>>> Absolutely
>>> but I don't believe, as technologists, we should keep propagating 
>>> the myth about thick IMC layers without having published, reviewable 
>>> data.
>>>
>>> Dave Hillman
>>> Rockwell Collins
>>> [log in to unmask]
>>>
>>> On Wed, Sep 16, 2015 at 9:38 AM, Vladimir Igoshev < 
>>> [log in to unmask]> wrote:
>>>
>>>> 10 microns thick layer is a perfect way for a disaster down the 
>>>> road :-).
>>>>
>>>> There are no parameters for E-Ni, but the appearance of the 
>>>> interface and a P-enriched layer ‎is important.
>>>>
>>>> Vladimir
>>>>
>>>> Sent from my BlackBerry 10 smartphone on the Rogers network.
>>>>   Original Message
>>>> From: Victor Hernandez
>>>> Sent: Wednesday, September 16, 2015 10:11
>>>> To: [log in to unmask]
>>>> Reply To: TechNet E-Mail Forum
>>>> Subject: Re: [TN] BGA Reworked Intermetallic
>>>>
>>>> On ENIG surface I don't see much of an increase in the IMC 
>>>> formation thickness. However, on Cu it is a different story. I have 
>>>> measured IMC formation greater tham 10 microns. Not sure of the 
>>>> below statement about E-NI parameter. Please explain!!!
>>>>
>>>> Victor,
>>>>
>>>> -----Original Message-----
>>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir 
>>>> Igoshev
>>>> Sent: Wednesday, September 16, 2015 8:12 AM
>>>> To: [log in to unmask]
>>>> Subject: Re: [TN] BGA Reworked Intermetallic
>>>>
>>>> The "magic" Number should stay the same 1-3 micron but you'd also 
>>>> have to keep an eye on what happened to the layer of E-Ni underneath.
>>>>
>>>> Regards,
>>>>
>>>> Vladimir
>>>>
>>>> SENTEC
>>>>
>>>> Sent from my BlackBerry 10 smartphone on the Rogers network.
>>>> Original Message
>>>> From: Datacom - Juliano Ribeiro
>>>> Sent: Wednesday, September 16, 2015 09:09
>>>> To: [log in to unmask]
>>>> Reply To: TechNet E-Mail Forum
>>>> Subject: [TN] BGA Reworked Intermetallic
>>>>
>>>> Hi to all,
>>>>
>>>>
>>>>
>>>> When we reworked the BGA, removed the component of the board and 
>>>> replacement another BGA, what's the intermetallic thickness ideal 
>>>> after the rework?
>>>>
>>>>
>>>>
>>>> p.s: Our pcb is ENIG finished and the solder is Tin Lead.
>>>>
>>>>
>>>>
>>>> _____________________________
>>>>
>>>> Juliano Bettim Ribeiro
>>>>
>>>> DATACOM
>>>>
>>>> ENGENHARIA DE PROCESSOS
>>>> Rua América Nº 1000 - Eldorado do Sul - RS CEP: 92990-000
>>>> +55 (51) 8446-2135
>>>>
>>>> +55 (51) 3933-3000
>>>>
>>>> Ramal: 3484
>>>> [log in to unmask] www.datacom.ind.br
>>>>
>>>>
>>>>
>>>>
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>>>
>>>
>>>
>>
>>
>
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