[SI-LIST] Re: Current capacity of a Solder Ball
- From: Pat Diao <Pat_Diao@xxxxxxxx>
- To: "'omism@xxxxxxxxx'" <omism@xxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Wed, 5 Feb 2003 15:18:44 -0800
Solder balls are typically attached to Cu thru: Cu-Ni-Au-Solder system.
None of these metal or intermetallic materials have lower melting point
than solder.
As far as solder ball falling off before it melts, I think there are two
factors involved:
1. Consider a solder ball attached to substrate, the neck has the smallest
cross-section and therefore the highest current density. Often times, there
may be void or imperfect contact between the ball and pad, all these create
additional local electrical resistance, and therefore local heating. Adding
to the fire is the relatively low thermal conductivity of substrate on top
of the solder ball.
2. The geometry of the ball/pad attach area makes it a high stress and weak
area. Compounded with local heating, the neck is likely to reach the meting
temperature slightly before the rest of the solder, and fall off (of course
when not mounted on PCB)
Pat
Pat Diao
ASAT Inc.
Fremont, CA
510-249-1227
-----Original Message-----
From: Ozgur Misman [mailto:omism@xxxxxxxxx]
Sent: Wednesday, February 05, 2003 2:36 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Current capacity of a Solder Ball
Hi All,
I certainly agree with some of the authors that the current carrying
capability of a solderball can not be solely determined by considering the
solderball as a seperate entity.
The current capacity could mainly be influenced by the quality and the
metallurgy of the Solderball/ soderballpad interface.
My question would be whether the ball falls off before it melts?
By the way, I have not come across any technical paper on this issue,
although I have been looking for it for some time.
If anybody has any reference that points out to measured data. PLease
forward a copy to me , I would be very interested.
Regards,
Ozgur Misman
Aubrey_Sparkman@xxxxxxxx@freelists.org on 02/05/2003 02:39:48 PM
Please respond to Aubrey_Sparkman@xxxxxxxx
Sent by: si-list-bounce@xxxxxxxxxxxxx
To: weirsp@xxxxxxxxxx, mchan@xxxxxxxxxxx, BSchieck@xxxxxxxxxx,
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Subject: [SI-LIST] Re: Current capacity of a Solder Ball
Steve,
Let's assume that all your numbers are correct. I had the same conclusion
several years ago at a previous company. We both missed the main point of
Pat's email: You need to re-think what the limiting factor is. It's not
immediately obvious.
Aubrey Sparkman
Signal Integrity
Aubrey_Sparkman@xxxxxxxx
(512) 723-3592
> -----Original Message-----
> From: steve weir [mailto:weirsp@xxxxxxxxxx]
> Sent: Wednesday, February 05, 2003 3:07 PM
> To: mchan@xxxxxxxxxxx; BSchieck@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Current capacity of a Solder Ball
>
>
>
> Moses, and Brian, that current number seems low by orders of
> magnitude. First, the electrical resistance is way off. For the
> resistivity value shown which seems about right at 8X Cu, and
> a rectangular
> section 0.2mm X 0.2mm X 0.6mm yields about 0.002 ohms.
>
> Similarly, the thermal resistance value of 41,000 C/W for a
> metallic object
> 24 thousandths thick cannot be right. Take a small glob of
> solder the size
> of a BGA ball on the bench and connect it to a 10V supply and
> a 100 ohm
> resistor. There is no way, that blob will get warm, much
> less melt. It
> will take multiple amperes to melt the foil leading to or
> away from the
> ball, and the foil will fail long before the ball.
>
> Regards,
>
>
> Steve.
>
> At 11:32 AM 2/5/2003 -0800, Moses Chan wrote:
>
> >Hi Brian,
> >
> >I asked the same question to the list a few months back and got the
> >following answer, below:
> >
> >Solder Ball (63Sn/37Pb) 0.0006 m
> >Ambient Temp. 34 Deg. C
> >Melting Temp. 189 Deg. C
> >Thermal Conductivity 50 W/m-C
> >Electrical Resistivity 0.000000145 ohm-m
> >Thermal Resistance 41026.51161 C/W
> >DC Electrical Resistance 0.297442209 ohm
> >Total Resistance 0.297442209 ohm
> >Power to Melt 0.003778045 W
> >Current to Melt 0.112702164 Amps
> >
> >
> >Moses Chan
> >Vitesse Semiconductor
> >Camarillo, California
> >
> >At 11:13 AM 2/5/03 -0800, Brian Schieck wrote:
> >
> > >Does any one know what the current carrying capacity of a
> solder ball is?
> > >How is the capacity determined?
> > >Is the capacity derated to account for temperature and voids?
> > >
> > >
> > >for a 60 mil solder ball.
> > >
> > >Brian Schieck
> > >NVidia Corporation
> > >2701 San Tomas Expressway MS B22-221
> > >Santa Clara, California 95050
> > >Direct Phone # (408) 486-2697
> > >Corp Phone # (408) 486-2000 x62697
> > >Local Fax # (408) 486-8078
> > >Corp Fax # (408) 486-2200
> > >
> > >Email bschieck@xxxxxxxxxx
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