[SI-LIST] Re: How many bond-wires to make a good PDS?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: nemisonic@xxxxxxxxx
- Date: Mon, 03 Dec 2007 12:28:09 -0800
Graham, the answer is probably a lot more than you would like. The bond
wire portion of the inductance loop will depend on factors such as:
proximity to other power bond wires of each polarity, bond wire length
and the shape of the arc. A starting number would be around 10nH for
one pair by the time you get to the PCB. If you are pumping out
100-150ps edges, and have good hf bypass on die, then one power / gnd
wire pair for every four signals should get you in the ballpark.
I caution you to make sure that you make it feasible for your end
customer to package a realizable PDN on their PCB. The cheap package
that you are going into pretty much precludes on-substrate caps, so you
are forcing the bypass problem down to your customer where it is even
harder to solve. If you put too much inductance between your customer's
plane attachment and your die the game is over.
Good luck.
Steve.
Graham Kus wrote:
> Hi everyone,
> So I have a question. When designing a power supply distribution system
> (PDS) for an FBGA bond-wire ASIC package, how many bond-wires are "enough?"
> I understand that 25um(1 mil) diameter bond-wires can accommodate almost 1
> Amp at DC, but I suspect this is completely off base when driving a bus with
> one of these.
>
> The background on my situation involves DDR-2 drivers, and having enough
> bond-wires to prevent SSO. This IC package is an FBGA, 4 layer substrate
> board. The IP vendor supplied pin-based RLC charts for a lead-frame type
> package (although I have yet to see DDR-2 in a TSSOP). These translate well
> to signal routes, but the physics the PDS are different than lead-frame pin
> structures. Also this vendor's numbers for power are based literally on a
> "rule of thumb chart," which to me is code for "open your SI tool and double
> check." We wrestled them into giving us Spice versions of the buffer under
> NDA, so presumably we can simulate this ourselves. Anyhow if you guys have
> advice, I could use it.
>
> Thanks in advance,
>
> -Graham
>
>
> [gmail search terms: bondwire bond-wire wirebond wire-bond]
>
>
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