FreeLists / si-list / [SI-LIST] Re: inductance of a reflowed solder bump

[Raymond Anderson <Raymond.Anderson@xxxxxxx>]

Not sure about the 100um diameter balls , but I've used the number 
816pH/mm for
65um dia. solder balls (actually C4 joints). For a height of 70um this 
would be about
57 pH.  For 100um balls I'd guess the inductance would be somewhat less.

The number was derived from the twin lead transmission line formula 
where the
loop inductance L=0.4*uR*ln(D/a) where D is the distance between conductors
(balls) and a is the radius of the conductor (balls). uR is the relative 
permiability
(1.0 for air). Using this equation assumes the balls can be approximated 
as cylinders.

Note that this will give you an approximation for the partial inductance 
contributed
by the solderball, but says nothing about total loop inductance.

Perhaps someone has some better approximations or formulas.

-Ray Anderson


Firas Azrai wrote:

>Hello everyone,
>Does anyone have a rough estimate or a first order equation that calculates 
>the inductance of a reflowed solderball with a base diameter of 100um and a 
>height of 70um. Can this structure be approximated to a cylindrical one?
>
>I appreciate any response and input.
>
>Firas S. Azrai
>Electrical Engineer
>Integral Wave Technologies
>
>108 Wild Basin Rd.
>Suite 218
>Austin, TX 78746
>
>Tel : 512-416-9700
>Fax: 512-437-2792
>  
>


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