What happens when not enough vias area drawn?

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giggs11

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Hi,

What happens when inadequate vias are drawn for inter-layer connection?

We know that if metal line widths are insufficient, metal migration might happen. But I am uncertain if not enough vias are drawn for current conduction from one metal layer to another, does breakage happen or does it merely limit the current transfered betwen the inteconnected layers.

Please specify for both digital and analog cases.

Thanks.
 

hi,

Electromigration problem is more important for Aluminum metalliztion, because it has poor resistance to Electromigration.

Refractory metalls (for ex. W), usualy used for VIA, almost have no problem with Electromigration.
But they have much higher (3-5 times) resistivity.

So, in ur case the problem is a high resistivity of VIA.
 

Usually in the process upport document, there is rule for the VIA's maximum current. I guess you can take that as reference.
 

I think it only affect the current value.
 

First, take into consideration the currnet supported by a single via, and the current you need. Usualy the maximum current through a via is half of max current through a minimum width wire.
Second, if the vias number is not enough, there will probably be a continuous degradation of the contact, finally , say after few months of functioning, the vias will no longer be vias.
Third, place as many contacts and vias as possible. Reliability increses this way.
 

Vias are interconnects and others have addressed the issue significantly.
If inadequate vias are present there is a possibility of ground loop and this difference in potential can cause significant problems esp. in analog / RF syetems. I have seen a significant performance improvement when we used more vias on the same layout. Also the dia of the via matters. Larger dia == lesser inductance and better AC performance.
Hope this helps
 

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