[SI-LIST] Re: Buried capacitance materials


All are FR-4 compatible, but only BC-2000 is used in volume.

BC material is very reasonable but the licence to use it is expensive.  The
other have so little use that the cost is not the relavent concern.  Emcap
died as a project with Hadco but 3M is retrying with others.  The
advantange of Emcap is a very high Dk 5X over BC-2000.  The disadvantage is
a 4 mil thickness (higher inductance) and a hard to process Ceramic core.
Dupont's capacitor material is a double screening process but is only
suited for descrete capacitance and inductance needs, so it's area is very
small.  Here are 2 helpful equation in looking at the effects:
C = 225 x Dk x A / t    L = a constant x t / W
C=Capacitance, A=area, t=thickness, L = inductance, W= width

Talk to your PCB supplier about design requirements, assuming us use BC2000
(the "only" available material), you should balance the construction but
keep the BC cores near the components to limit through hole inductance
Layers 2/3 and N-1/N-2 is common.  The more BC planes you get into the
panel the better.  If you have a 12 lyr structure you might have 3 BC
(power/ground) planes.  Area is very important.  Keep the surface
Ground/Power planes as large and full of copper as possible. Copper
thickness is not relavent but 1oz/1oz is easier to transport for your PCB
supplier.

Current carring capability can also be an importance consideration.  The
very thin dielectrics can run into problems at not being able to handle low
current.

Greg Link
Processing Engineering Manager
Topsearch Printed Circuits (HK)




Sunil Kumar <sunilb@xxxxxxxxxxxxxx>@freelists.org on 09/19/2002 05:17:15 PM

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Subject:  [SI-LIST] Buried capacitance materials



Hello everybody,

I am planning to use FR4 compatible buried capacitance (BC) laminates for
power planes in a high speed board. I have come to know about the
following materials:

     1. BC2000 (Hadco)
     2. BC1000 (Hadco)
     3. EmCAP (Hadco)
     4. C-Ply (3M)
     5. HiK (Dupont)

Except BC2000, I could not get much details about these materials. I have
the following questions:

Q1: Are all of them FR4 compatible? (I know that BC2000 is FR4
    compatible.)

Q2: How much costly are these materials?

Q3: What precautions do I have to take in the layout of the board when
    using these materials?

Q4: What are the other BC materials available?



Thanks,

Sunil Kumar
Senior Research Engineer
ATM Group, Switching-B2
Centre for Development of Telematics (C-DOT)
Bangalore-52
INDIA





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