John,

Capacitance (C) calculation for a parallel plated capacitor:

  C in Farads (coulomb^2/Nm) = Er * Eo * A/t

  Where

  Er = relative permittivity of laminate
       (dimensionless and may be equivalent to the dielectric constant Dk)
  Eo = permittivity of a vacuum
       (equal to 8.85 * 10^-12 coulomb^2 / (Nm^2)
  A  = the area of the plates in square meters
  t  = distance between the plates in meters (m)

or in English units:

  C in Farads = Er * Eo * A/t

  Where

  Er = relative permittivity of laminate
       (dimensionless and may be equivalent to the dielectric constant Dk)
  Eo = permittivity of a vacuum
       (equal to 2.247 * 10^-13 coulomb^2 / (N inch^2)
  A  = the area of the plates in square inches
  t  = distance between the plates in inches

So if Er = 3.9 and where t = 0.0035 inches, then

  C = 0.250 nF/SqIn or 250 pF/SqIn or 38 pF/cm^2

  in which case your dielectric thickness between should not
  exceed 3.5 mils


Regards,


  Karl Sauter, Staff Engineer
  VLSI/Advanced Component Engineering
  Sun Microsystems Inc.
  (650) 786-7663


> Date: Thu, 31 Oct 2002 11:39:38 -0800
> From: John Parsons <[log in to unmask]>
> Subject: [TN] FAB - Controlled Capacitance
> X-To: "TechNet E-Mail Forum." <[log in to unmask]>
> To: [log in to unmask]
>
> This is a first for us.  Our customer has specified
>
> "Capacitance between layers 4 and 5, and layers 6 and 7, shall be greater
> than 250pf per square inch, assuming unperforated planes".
>
> Layers 4 5 6 and 7 are all plane layers (ground/voltage pairs each).
>
> Now, I understand the concept of capacitance but I have not come across, nor
> can I seem to source any info telling me how to ensure that we are
> manufacturing to this specification.  I have the IPC-2141 which makes
> reference to controlled capacitance lines (not planes) but does not seem to
> provide any useful info from a manufacturing perspective.
>
> Can anyone help?
>
> Regards
> John Parsons
>
>
> ---------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
> -----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------