Saw a presentation on it when they were Zycon, of course now they are HADCO
The presentation showed 5 patents:
5079069
5155655
5161086
5261153
As I remember it; it is a sheet capacitance only.  I think there are design
implications as it I believe adds two layers to the board.  Perhaps someone
from  there could give a summary on the TechNet .
 ----------
From: [log in to unmask]
To: [log in to unmask]
Subject: [TN] Buried Capacitance
Date: Friday, July 31, 1998 7:05AM

Buried capacitance material is available from many major laminate, core,
and prepreg suppliers. There is a patent (number unknown to me) assigned
to the process and material. Several Zycon engineering personnel were
responsible for this invention. One is currently with Praegetzer as an
engineering executive (name also unknown to me) and provides technical
information about this material's use.

Simply, the material is a thin laminate with specified dielectric
thicknesses providing the required capacitance in impedance controlled
printed circuitry. At the design level, engineers and designers may
select the desired capacitance and design in the material. No special
considerations are necessary but for unique design needs. This is true
both at the design and fabrication level.

Earl Moon

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following
 text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section
 for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or
 847-509-9700 ext.312
################################################################

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################