John,
100%...remarkable indeed.
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: den 12 september 2006 21:28
To: [log in to unmask]
Subject: Re: [TN] PbCO3
Very interesting Inge,
So I have a question - are 100% of balls affected or are there some where the effect is "missing"
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Tuesday, September 12, 2006 11:33 AM
To: [log in to unmask]
Subject: Re: [TN] PbCO3
Richard,
thx for your interest. Bev and other specialists seem to be somewhere else.´ According to von Mise's equation, the stress is predominant in the ceramic-to-ball interface, or, in the PWB-to-ball interface, while the equator ought to have the least stress! So, why on earth do the whiskers grow around the circumpherical part of the ball. The balls (nearly pure
Lead) are soldered on the ceramic platform by means of a Lead/Tin alloy.
This alloy wets nearly all the way to the equator. Can the interface between the pure Lead ball and this wetting Lead/Tin alloy cause some stress?
Any hint is welcome. Is there someone from China Lake reading this? Or ERA Welding Institute? Or the Welding Institute in Abington? Holden Happy, who worked with CBGAs earlier at IBM Fishkill ?
Inge
----- Original Message -----
From: "Stadem, Richard D." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, September 12, 2006 3:33 PM
Subject: Re: [TN] PbCO3
Thanks, Reuven
This brings me to the question of PbCO3 lead whiskers. They must be caused by internal stressors. If seen around the widest diameter of the lead balls like in Inge's case where no electro-chemical reaction would be the cause if the balls were actually a Pb90/Sn10 alloy, the whiskers are likely caused by the lateral stresses from the CTE mismatch between the aluminum oxide CBGA substrate and the PWB substrate the components are soldered to. These stresses would thus be concentrated near the widest part of the ball. If the balls are lead plating over some other metal, the lead whiskers would be from stresses due to the plating, and would not be focused on the equator, but distributed evenly over the ball.
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, September 12, 2006 8:17 AM
To: Stadem, Richard D.
Subject: RE: [TN] PbCO3
I don't think so, dendrites caused by electro - chemical reaction and whiskers caused by internal stress and because of metallurgical structure.
Best Regards
Reuven ROKAH
e mail: [log in to unmask]
"Stadem, Richard
D."
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12/09/2006 16:07
Subject
RE: [TN] PbCO3
So is there a relationship between the microcrystalline dendritic growth (size and shape) in metals and whisker formation?
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, September 12, 2006 8:02 AM
To: TechNet E-Mail Forum; Stadem, Richard D.
Subject: Re: [TN] PbCO3
Hi Stadem,
According my best knowledge,
Dendrites phenomenon, look like roots and they are on the surface,
Whiskers phenomenon, look like a needle and grow from the surface / solder joint in different angels.
Best Regards
Reuven ROKAH
"Stadem, Richard
D."
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D-AIS.COM> [log in to unmask]
Sent by: TechNet
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Re: [TN] PbCO3
12/09/2006 15:44
Please respond to
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"Stadem, Richard
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Reuven,
Can you tell us the difference between dendrites and whiskers?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Reuven ROKAH
Sent: Tuesday, September 12, 2006 7:04 AM
To: [log in to unmask]
Subject: Re: [TN] PbCO3
Hi Ingemar,
1. Are you sure its Lead (Pb) Wishers? pls inform how?
2. Dendrites is another phenomenon than whiskers.
3. Can you repeat with this kind of failure? ("whiskers?").
Best Regards
Reuven ROKAH
e mail: [log in to unmask]
"Ingemar
Hernefjord
(KC/EMW)"
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Sent by: TechNet
<[log in to unmask]>
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Re: [TN] PbCO3
12/09/2006 12:56
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"Ingemar
Hernefjord
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<ingemar.hernefjo
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Klein Wassink mentiones a little about Tin Whiskers (dendrites).
One guy here at our company has written a paper about Tin whiskers.
NASA have a lot about Tin whiskers. Et cetera.
But few have anything about Lead whiskers.
Only thread I have is one picture from Klein Wassink. That picture is like a copy of our own photos.
Question is if anyone of you have any idea about the following:
A. Can Lead whiskers grow through Humiseal acrylic? I've heard that Tin whiskers can.
B. Can alcalic saponifier cleaning of BGA high lead balls start whisker formation?
C. Do Lead whiskers burn off easily like Tin whiskers, or are they "stronger" ?
D. What can the reason be that the Lead whiskers grow only around the ball's "equator" ?
E. The CBGA platform is said to come from IBM. Do they differ from others on ball making?
These questions may not be suitable for this forum, but I make a try, well knowing that many of you are extremly experienced.
Thx in advance
Ingemar Hernefjord
Now SAAB Microwave Systems
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