[SI-LIST] Re: Current capacity of a Solder Ball

Here are some alternative numbers:

>Solder Ball (63Sn/37Pb)
        The original email says 60mils for the solder ball.  That's a pretty big
ball.  Most balls for BGAs are 20-30 mil depending on the pitch
(1.0-1.27mm).  I'll assume 30mil (0.76mm) which is typical for 1.27mm pitch
BGA.  Also assume 20mil final solder joint height and 25mil pad diameters.
>Melting Temp:          183C (183C - not 189C)
>Thermal Conductivity:  50 W/m-C (close enough)
>Electrical Resistivity: 0.000000145 ohm-m (close enough)
>Thermal Resistance:    ~32.2C/W (not 40k C/W)
>DC Electrical Resistance: ~0.24 mohm
>Current to Melt
        We did some experiments that showed that even a small solder ball 
(0.3mm)
can take >3A.  The critical path is almost always the trace connected to the
ball (~2.5A for a 4mil wide trace).  Note: this applies to BGA balls - there
are some different mechanisms that can occur with flipchip solder bumps.

Regards,

Matt

Matt Kaufmann
Principal Engineer - IC Assembly and Packaging Development
Broadcom Corporation
2451 Mission College Blvd.
Santa Clara, CA 95054
408-922-3183(desk)/408-464-9354(cell/pager)/408-922-1023(fax)
mkaufmann@xxxxxxxxxxxx


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
Sent: Wednesday, February 05, 2003 1:07 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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