An interesting layout

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An interesting layout

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melodyseu

Joined: 22 Jul 2004
Posts: 33

22 Nov 2004 8:53 An interesting layout

I found a interesting layout, but I don't know why
It is the tail current lead of a VCO. The value of the current is very large.
see the attachment...
It uses tow layers of metal in parallel, and the width of the leads are wide enough to allow the big current. But I don't know why is there slots in the leads,and what is more interesting is that the slotted leads are not the same width but from wider to narrow.
What is the reason here?

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nickooeda

Joined: 15 Sep 2004
Posts: 44
Helped: 2

22 Nov 2004 9:31 An interesting layout

u may trace very branch to confirm why not equally divide current

Colbhaidh

Joined: 10 Aug 2004
Posts: 151
Helped: 16

22 Nov 2004 9:53 Re: An interesting layout

In large (long wide) metal traces on an IC, there can be significant movement of the metal with high current densities. To prevent this metal moving about too much and destroying the passivation oxide layers around the metal, stress relief cut outs are employed. This allows an otherwise huge movement of a single metal line to be divided up into smnall components of movement along the track. These stress relief cut outs will be part of the design rule manual for a given technology and is determined by the Fab.
Failure to incorporate stress relief cut outs can lead to early failure of the part in its application. It may not happen immediately, but it will fail.
Most Fabs will either advise what cut outs to use, or will insert them themselves transparent to the designer.

yeewong_su

Joined: 12 Oct 2004
Posts: 126
Helped: 3

23 Nov 2004 6:19 An interesting layout

every wide metal (>10um @ 0.18uM) must sloted

Fom

Joined: 10 Mar 2004
Posts: 759
Helped: 56
Location: Taiwan

23 Nov 2004 7:19 Re: An interesting layout

I don't think it is stress relief cut otherwise they should cut evenly.
I suppose each wire goes to different transistors. These transistors should have different width also. The wire and transistors width are proportional to current flowing trough these transistors. I think it is done to equialize voltage drop across metal wires.

melodyseu

Joined: 22 Jul 2004
Posts: 33

23 Nov 2004 10:16 Re: An interesting layout

Fom wrote:

I don't think it is stress relief cut otherwise they should cut evenly.
I suppose each wire goes to different transistors. These transistors should have different width also. The wire and transistors width are proportional to current flowing trough these transistors. I think it is done to equialize voltage drop across metal wires.

The slotted lead don't go to different transisitors. They converge at the end of the lead.The lead is very long by the way.

mike_bihan

Joined: 21 Mar 2002
Posts: 259

29 Nov 2004 8:05 An interesting layout

do not be too paranoid, it most possibly just some random product of layout guy.

Colbhaidh

Joined: 10 Aug 2004
Posts: 151
Helped: 16

13 Dec 2004 9:54 Re: An interesting layout

Definitely stress relief - even though it is not even, it is a function of contacts to active.

cikyen

Joined: 11 Jun 2003
Posts: 63

17 Dec 2004 4:43 An interesting layout

I think the cuts are metal slot. But no idea why it's not cut evenly

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