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

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From: Bob Lewandowski (Bob.Lewandowski@Vixel.com)
Date: Wed Oct 04 2000 - 18:35:22 PDT


Minor problem, the equation from MIL-M-38510 is I = k*d^(3/2), {three halves
power, not two thirds}

k = 30000 for gold or copper with a bond-to-bond length <= 0.040 in. (0.1 cm).
k = 20500 for gold or copper with a bond-to-bond length >0.040 in. (0.1cm).
(For Al wire k = 22000, and 15200, respectively)
d = wire diameter in inches.
I = DC or rms current.

For a 1 mil gold wire < 0.04" long, I < 0.95A; > 0.04" long I < .65A.

---Bob Lewandowski
    Vixel Corp.

Won Chang wrote:

> Another reference is MIL-M-38510, Military Specification, General Spec for
> Microcircuits. Check section 3.5.5.3 where you can find an equation:
>
> I=kd2/3 (d to the two thirds power)
>
> where: I: maximum allowed current in amperes
> d: bonding wire diameter in inches
> k: a constant (dependening upon wire material and length)
>
> I hope this helps.
>
> Won
>
> -----Original Message-----
> From: jrbarnes@lexmark.com [mailto:jrbarnes@lexmark.com]
> Sent: Wednesday, October 04, 2000 12:12 PM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Current flow limit for wire bonding
>
> Brian,
> In researching the ampacity (current-carrying capacity) of wires and printed
> circuit board (PCB) traces last year, I ran across the Onderdonk equation
> for
> the fusing (opening) current of wires as a function of time. I found three
> sites on the Internet with the identical information on designing fuses
> using
> the Preece Equation and the Onderdonk Equation:
> * http://home.earthlink.net/~jimlux/hv/fuses.htm
> * http://www.2.ozland.net.au/users/egel/fuses.htm
> * http://www2.murray.net.au/users/egel/fuses.htm
>
> Gold isn't listed in the table, but its melting point of 1064C is very
> close to
> that of copper (1083C). The Onderdonk equation suggests that both metals
> thus
> should behave about the same, letting us use the Preece Equation
>
> I = 80.0 * (0.025^1.5) = 316mA
>
> I would not feel comfortable running more than 200mA or so continuous
> through
> each wire, myself.
>
> A. J. Rainal's paper "Current-Carrying Capacity of Fine-Line Printed
> Conductors"
> (Bell System Technical Journal,
> Vol. 60 no. 7, September 1981, p. 1375-1388) pointed out that for printed
> circuit board (PCB) traces there is a
> "runaway" current:
> * Below which the trace's temperature rise will stabilize.
> * But above which, if the current is held constant, the trace's temperature
> will continue to rise until it melts open
> or sets the board on fire.
>
> This is due to the increase in copper's electrical resistance with
> temperature,
> versus conduction/convection/
> radiation carrying the dissipated power away. Since the electrical
> resistance
> of almost all metals increases with
> temperature, I would expect to see a similar behavior for your gold wires.
>
> John Barnes Advisory
> Engineer
> Lexmark International
>
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