[SI-LIST] Re: 6 layers stackup
- From: "Peterson, James F (EHCOE)" <james.f.peterson@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 27 Feb 2008 11:04:34 -0500
I just got through watching Dr. Johnson's video "Low Inductance
Capacitor Packages" where he makes what appears to be a pretty fair
comparison of an x2y and a 0402 cap. It does seriously challenge the
results of the paper Lee references. In this video the X2Y equivalent
mounting inductance is almost 1/3 of the 0402 cap...
Regards,
Jim Peterson
Honeywell
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Scott McMorrow
Sent: Wednesday, February 27, 2008 9:43 AM
To: Tom Biggs
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 6 layers stackup
Tom
Well, although Lee pro ports to be measuring the bulldozer (PCB), the=20
article by John Zasio compares two different passengers (capacitors)=20
using a flawed test vehicle. Because of this, the conclusion is dead
wrong.
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed(r) is the registered service mark of
Teraspeed Consulting Group LLC
Tom Biggs wrote:
> 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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