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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