[SI-LIST] Re: [!! SPAM] Re: 6 layers stackup

Tom,

Well put!


> [Original Message]
> From: Tom Biggs <tbiggs@xxxxxxxxxxxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 2/26/2008 6:16:04 PM
> Subject: [SI-LIST] Re: [!! SPAM]  Re: 6 layers stackup
>
> You can take the bulldozer analogy two ways. It depends on whether you
> care about the weight of the bulldozer with passengers, or just the
> weight of the passengers.
>
> Steve's test fixture was geared toward 'weighing the passengers'. Lee's
> was toward 'weighing the bulldozer'. So they each served their purpose.
> His whole point was that the vias going down 50 mils on a board are
> going to swamp out the advantages of low inductance caps. His test
> fixture, by design, had vias that go down 50mils. I'm sure he'd agree
> that this would be a bad fixture for measuring the cap itself, which was
> not his goal.
>
> The appropriate land pattern to use for the low-inductance caps is a
> separate issue. I'd be curious to see Lee's board with Steve's land
> pattern.
>
>     -tom
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Muranyi, Arpad
> Sent: Tuesday, February 26, 2008 1:31 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: [!! SPAM] Re: 6 layers stackup
>
> Can't resist to illustrate this with an example:
>
> If you want to compare the weight of an ant and a cricket and you put
> them on top of the same bulldozer, you will not see much difference in
> their weight...
>
> Arpad
> ------------------------------------------------------------------------
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Lee Ritchey
> Sent: Tuesday, February 26, 2008 11:16 AM
> To: Charles Grasso; Scott McMorrow
> Cc: Steve Weir; QU Perry; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: [!! SPAM] Re: 6 layers stackup
>
> What does the test vehicle have to do with it?  Both capacitors are
> seeing
> the same stackup.  It's apples and apples.   Why 26 layers?  Lots of
> PCBs
> have 26 layers, pretty much all of them in terabit routers.  This PCB
> was used to test may things besides these two capacitors.
>
> What is being presented is the difference between the two capacitors
> under the same set of test conditions and it is not much.
>
> There are two sets of tests.  One with the capacitors connected to the
> first two planes inside the PCB, which is the lowest added inductance
> and the other is with the capacitors attached to two planes further down
> in the PCB.
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