[SI-LIST] Re: 0.9 mil,0.8 mil,0.7mil gold wire application for IC packaging
- From: aditya@xxxxxxxxxxxxxxx
- To: heidi.barnes@xxxxxxxxxx
- Date: Tue, 22 Jan 2008 10:11:44 -0700
This is very true. Due to skin effect, at 10 GHz the signal will =20
practically be travelling on the surface of the wire.
So, from this perspective, a typical circular wire is actually the =20
most inefficient. A cylinder has the least perimeter to area ratio.
It's a theoretical statement, but for this reason, an elliptical wire =20
will give much better high frequency characteristics than a circular =20
wire. Maybe someday someone tries it out.
Since the concern mentioned below is cost of gold, it would be easy to =20
see that for the same surface area a 1:2 ratioed ellipse will have =20
more than 33% less area, i.e. more than 33% less gold. Gold prices =20
have hit $ 900 a troy ounce.
Regards
Aditya
Reliant PCB Design Services
Quoting "Barnes, Heidi" <heidi.barnes@xxxxxxxxxx>:
> Hi Davis,
> The smaller Au 0.7 mil wire has been used extensively for micro circuits =
=3D
> in the 10 Ghz range and higher with no problems. The trick is to =3D
> realize that the currents tend to have a bit higher density on the =3D
> outside edges of the microstrip as one goes up in frequency and the =3D
> bigger benefit is to use two wire bonds to go from each edge of the =3D
> microstrip to the pad on the device. The two wires lower the inductance =
=3D
> far more then a wider diameter wire and also provide a better path for =3D
> the signal currents. If the pad is too small.... there have been cases =3D
> of stacked bonds to accommodate the two wires. At even higher =3D
> frequencies, one typically switches to ribbon bonding or strips of wire =
=3D
> mesh cut to a desired shape rather then increasing the wire diameter.
>
> The other issue is current carrying capacity, but again one can double =3D
> up on the bonds if the 0.7mil is not enough. =3D20
>
> As for a rule...it always depends on the application and one should use =
=3D
> a 3DEM simulator to find the electrical properties of the wire bond in =3D
> the environment that it is being used in.
>
> Goodluck on the bonding,
> Heidi
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
=3D
> On Behalf Of Lu, Devis
> Sent: Monday, January 21, 2008 5:11 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] 0.9 mil,0.8 mil,0.7mil gold wire application for IC =3D
> packaging
>
> Dear si-listers:
> As Gold wire price keep increasing in recent year, we are working on
> evaluate 0.9mil,0.8mil, and 0.7 mil gold wire for wirebonding MCP
> package. But we have some SI concerns if we reduce the gold wire
> diameters although our current product speed is only 133MHZ . Does
> anyone have study this before,and come out design rule Gold Wire
> Diameter Vs max wire length?
> Regards
> Davis
>
>
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