Re: [SI-LIST] : Current flow limit for wire bonding

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From: Doug McKean (dmckean@corp.auspex.com)
Date: Wed Oct 04 2000 - 10:08:09 PDT


Brian Seol wrote:
>
> Dear All,
>
> Does anyone have some approximate numbers for the limit of current that will
> flow through the wire bonding for a power pad of the single chip package?
> If that depends on the number of wire, how many wire do I need to handle
> current of 3A in case of 25 micron diameter gold bond wire? Any comments
> will be appreciated.

I don't know, but I'll try a wing at it. Just so you can
crosscheck, I'm using a Belden wire catalog for my numbers.

Ampacity of wires doubles if the area of the wire doubles.
Every 3 wire gauges (I know you're not using standard wire
gauges but follow me here), the area doubles or halves.
So, ampacity doubles or halves every 3 wire gauges.

Solid 27 awg (area 201.5, diameter 0.0142"/360 microns)
carries twice the current of solid 30 awg (area 100.5,
diameter 0.0100"/254 microns).

If I go the to the Belden wire catalog, there's a degree C rise
table in the back. If you want 10 or 35 degrees C rise with a
certain amount of current, you just read it off the chart.
For this discussion, I'm going to ignore the various factors
for number of conductors in the bundle.

3 amps for 35 degrees C rise looks like 25 AWG or bigger.
3 amps for 10 degrees C rise looks like 21 AWG or bigger.

25 AWG has diameter = 0.0179"/454 microns.
21 AWG has diameter = 0.0285"/723 microns.

So, two wires 28 AWG (dia = 0.0126"/320 microns) are needed
for the one 25 awg @ 35 degrees C rise.

Or, two 24 awg ( dia = 0.0201"/510 microns) are needed for
the one 21 awg @ 10 degrees C rise ... etc ...

25 microns being roughly 1 mil. A wire with the diameter of
1 mil is solid 50 AWG. Looks like you've got a ways to go
get to a bundle of 25 micron diameter wire being able to
carry 3 amps if the rule of doubling is followed.

I.e. for 10 degree C rise, 1 strand 21 AWG, 2 strands 24 AWG,
4 strands 27 AWG, 8 strands of 30 AWG, ...

For 35 degree C rise, just add 4 to the 10 degree C rise series:
1 strand 25 AWG, 2 strands 28 AWG, 4 strands 31 AWG, 8 strands
of 34 AWG, ...

Sounds as if I'm missing something here,
so someone correct me ...

Is this even remotely applicable?

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