I believe it to be LT 1 um, but I'd ask Paul Vianco at Sandia Laboratories
505-844-3429. Dr. Vianco wrote the "AWS Soldering Handbook, 3rd Edition".
So, he is qualified.
Please let me know the answer.
Dave Fish
----- Original Message -----
From: "Bev Christian" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 26, 2001 8:45 AM
Subject: Re: [TN] AW: [TN] Antw: [TN] exposing intermetallic on BGA pads.. .
> TechNetters,
> Questions of my sex aside.. got your attention now, right?
>
> I will ask again what do people expect for the average thickness of the
> tin/nickel intermetallic. The closest answer I got was the rate of
growth,
> but not what one expects it to start at after a single reflow. I bring it
> up here as it is related to the current discussion.
>
> regards,
> Bev Christian
> Resaerch in Motion
>
> -----Original Message-----
> From: Earl Moon [mailto:[log in to unmask]]
> Sent: October 26, 2001 1:30 PM
> To: [log in to unmask]
> Subject: Re: [TN] AW: [TN] Antw: [TN] exposing intermetallic on BGA
> pads...
>
>
> Guenter,
>
> As you replied to me personally, I respected your not posting on the
> TechNet. So, I said it was someone else but everyone knows it must be you.
> Simply, I didn't/don't want to betray your confidence as I respect your
> privacy.
>
> Earl
>
> ps. I am enjoying this and learning much from this conversation. Still, I
am
> stirring the pot for everyone to benefit. I'm too old to add much but if I
> can elicit responses from real experts, like you, we will all learn more
>
> Earl
>
> ----- Original Message -----
> From: "Guenter Grossmann" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, October 26, 2001 8:46 AM
> Subject: Re: [TN] AW: [TN] Antw: [TN] exposing intermetallic on BGA
pads...
>
>
> Earl
> Well, I think some acceptance criteria is necessary since if there isn't
> even no solder is accepted. However, I agree that in many cases I feel
that
> the acceptance criteria mare more designed in a manner that they can be
> controlled rather than in respect to reliability.
>
> Regarding your comment of IMC and the discussion we had offline I thought
> abut the thing at home:
> - Suppose you do a good job in designing your solder profile. This means,
in
> my understanding, that just enough heat is brought into a PCB that all
> joints are formed and as little heat as possible stresses the components.
As
> an effect the IMC will be very thin.
> - Suppose again that you rework. Again you do a good job in removing the
> remaining tin thoroughly. To do so you need to keep the pad to be cleaned
at
> elevated temperature for quite a while.
>
> The result will be, that
> - Because of thoroughly removing the solder you expose IMC or
> - Because the IMC is thin and the pad is warm for some time the remaining
> little amount of tin that covers the IMC is transformed into IMC.
>
> Hence, one can say that a job too well done leads to a poor solder joint.
> And thus ( just to steer the pot a bit as you like it) if you instruct
> people for repairing solder joints and it works, your instruction wasn't
too
> accurate? ( HeHe)
>
> Have a great weekend
>
> Ps: What do you mean by : you spoke with someone who is also much
respected
> in this field?
>
>
>
> Guenter Grossmann
>
> Swiss Federal Institute for Materials Testing and Research EMPA
> Centre for Reliability
> 8600 Duebendorf
> Switzerland
>
> Phone: xx41 1 823 4279
> Fax : xx41 1823 4054
> mail: [log in to unmask]
>
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