RE: [SI-LIST] : Decoupling capacitors (again!)

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From: Larry Smith (
Date: Thu Aug 17 2000 - 09:41:35 PDT

Martin - The most important thing about Hadco material is the patent.
When it comes right down to it, there is nothing special about the 2
mil FR4 material, except for maybe some handling techniques and room
cleanliness. Somehow, Zycon (bought by Hadco) got a patent on this
concept. Right now, anybody who uses 2 mil FR4 between power planes
must consider their legal position with this patent. ...I am way out
side of my expertise (SI gone to law), so I think I better quit here...

Larry Smith
Sun Microsystems

> Date: Thu, 17 Aug 2000 07:57:41 +0100
> From: "Martin J Thompson" <>
> To: <>
> Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
> Larry, another question on buried capacitance...
> What is it about Hadco's material that allows you to get 2mils separation? Can this not
be achieved with straight FR-4?
> Thanks,
> Martin
> <snipped for context>
> >>> Larry Smith <Larry.Smith@Eng.Sun.COM> 16 August 2000 23:55:52 >>>
> It turns out that the spreading inductance of power planes
> spaced 4 mils apart will give you roughly 20 mOhms at 100 MHz. We are
> using Hadco 'buried capacitance' planes that are 2 mils apart in many
> of our products to get lower impedance.

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