RE: [SI-LIST] : Proposal: Rs correlation/collaboration for W-Elem

[email protected]
Fri, 8 Oct 1999 09:40:05 -0400

Here is a partial answer to your question of two months ago. Most printed
circuit boards (PCB's) are made with electrodeposited copper foil. The cathode
side is plated directly on the drum and will be smooth, while the side that
faced the plating bath will be rough, giving it some "tooth" to help it adhere
to the laminate. Flat cables that must withstand many bending cycles, such as
cables to inkjet printer printheads, will be made from wrought copper, which has
been rolled from a copper billet and thus is smooth on both sides. It is a
common practice for PCB and flat cable manufacturers to lightly etch ("treat")
the copper foil before laminating the layers together to provide a better bond
between the foil and laminate/prepreg layers. In a subtractive process the
surface roughness of etched traces should be reasonably close to the surface
roughness of the copper foil that you started with. In an additive or
semi-additive process additional copper is plated onto the starting foil, so the
final surface will be rougher than the starting foil. Deburring drill holes and
some cleaning processes using brushes or mild abrasives can also roughen the

So I would treat the following information from IPC-MF-150F, Metal Foil for
Printed Wiring Applications, as a MINIMUM surface roughness to expect:

3.5.6 Surface Finish
The following requirements for metal foil surface finish shall apply to the
cathode side of electrodeposited foil (if untreated) and to both sides of
wrought foil (if untreated).

The metal foil surface finish shall have a maximum arithmetical average value of
0.43 micrometers [17 micro-inches], as determined by paragraph 4.5.9.

4.5.9 Surface Finish
Surface finish shall be determined in accordance with the requirements of Test
Method 2.2.17 of IPC-TM-650.

For qualification and quality conformance testing, a minimum of one specimen
will be tested for each sample required by the lot inspection plan.

IPC-TM-650, Test Methods Manual, 2.2.17, says:

1.1 The smooth sides of foils shall be evaluated using Ra.

Ra is defined as the arithmetic average value of all absolute distances of the
roughness profile from the center line within the measuring length,

1.2 The treated side of foils shall be evaluated using the parameter Rz (DIN) or
RTM which is defined as the average maximum peak to valley height of five
consecutive sampling lengths within the measurement length. This value is
approximately equivalent to the values of profile determined by microsectioning

John Barnes Advisory
Lexmark International

vadim.heyfitch%[email protected] on 08/03/99 09:58:16 PM

Please respond to si-list%[email protected]

To: si-list%[email protected]
cc: (bcc: John Barnes/Lex/Lexmark)
Subject: RE: [SI-LIST] : Proposal: Rs correlation/collaboration for W-Elem

Such measurements should allow us to nail down the surface roughness
parameter that is required by field solvers. Rs is rather sensitive to this
parameter making it into a good fudge factor. (At 1GHz, skin depth is about
2 micron. Does anyone know how this compares to typical Cu etch roughness?)


-----Original Message-----
From: Mellitz, Richard [mailto:[email protected]]
Sent: Tuesday, August 03, 1999 9:57 AM
To: '[email protected]'
Subject: RE: [SI-LIST] : Proposal: Rs correlation/collaboration for
W-Elem ents


Measurements would be great! Any volunteers? Sounds like a good paper.

I'm not really disputing the accuracy of the W element model. I'm just
trying to figure out how to use them. Especially where I have thin lines and
in frequency ranges where dielectric losses may not be predominate.

I agree that the field solver is not the way to solve the accuracy issues.
However it is the starting point for the W element algorithm. So I really
want too very clearly nail down what I do with the field solver results. I'm
just starting with baby steps.

... Richard Mellitz,

-----Original Message-----
From: Dr. Edward P. Sayre [mailto:[email protected]]
Sent: Tuesday, August 03, 1999 10:15 AM
To: [email protected]
Subject: Re: [SI-LIST] : Proposal: Rs
correlation/collaboration for W-Elements

Dear colleagues:

If we are going to check the accuracy of the .W model, I
wish to make the
suggestion that we use measurements as well for
verification. Most field
solvers do not account for losses in copper or dielectric to
as correct an
extent that I would deem acceptable. Does anybody have a set
of test board
that they would volunteer?

Dr. Dmitri Kuznetsov's comments in a recent si-list
communication see
(7/29/99) are very relevant. The behavior of the skin
effect and
dielectric formulas in the frequency domain, when
transformed back into the
time domain involve functions that have very special

The losses which are proportional to frequency, namely the
losses can be shown to be related to the unit capacitance
and the loss
tangent of the material, Equation (8) for small losses.
See "OC-48/2.5 Gbps Interconnect Design Rules", Sayre, Chen
and Baxter;
DesignCon99 Proceedings. (Available on NESA's web site).
Use of equation
(8) together with the .W model has been found to be very
satisfactory when
the simulation results are compared to measurements.

Lastly, just as recently mentioned by Scott McMorrow, we too
have also seen
small differences with respect to the same problem solved by
two recent
versions of HSPICE. I do not think the way to resolve this
is through the
use of field solver predictions.


ed sayre


At 07:51 AM 8/2/99 -0700, you wrote:
>Apparently the W element model uses a pseudo-propagation
function with the
>following form.
>P(f)= exp{-sqrt[
(G0+f*Gd+j*2*pi*f*C)*(R0+sqrt(f)(1+j)Rs+j*2*pi*f*L) ]*len }
>(From HSPICE application note "Boosting Accuracy of W
>for Transmission Lines with Nonzero Rs or Gd Values")
>Let's assume that this is valid for some conditions. It
would be nice to
>know what the assumptions are.(geometry, frequency, etc.)
We can talk about
>the validity of the above in another thread.
>I would like to make a proposal. I would like to know what
various field
>solvers report in regards to the above propagation
function. Let's start
>with a microstrip first (and only look at skin effect). The
> Height over ground: 0.004"
> Width of conductor: 0.006"
> Thickness of conductor: 0.001"
> Conductivity: 0.58E8 mho/meter
>Let's all use the same units for Rs. Say:
> Ohms/(sqrt(Hz)*meter)
>Now, A colleague of mine has supplied a formula that is
used in microwave
>design. I have attached a PDF file with details. (Too tough
for text, TTFT
>:-)), I remember foobar)
>The answer, using the closed form formula for Rs is:
> 1.806E-03 ohms/(sqrt(Hz)*meter)
>If this is the magnitude of complex Rs, then Re(Rs) would
> 1.277E-03 ohms/(sqrt(Hz)*meter)
>I have received sidebar results from some of you folks, but
I don't want to
>post other people answers. However I will compile a table
of posted
>results. There are issues of complex number involved.
Remember I'm looking
>for the Rs for the above propagation formula.
>Step 2 will be to do same for a strip line geometry where:
> Height over ground: 0.005"
> Width of conductor: 0.0025"
> Thickness of conductor: 0.0005"
> Distance between ground planes: 0.0105
>It would be appreciated if we could find out what "tricks"
people are using
>to get Rs from their field solvers.
>Richard Mellitz
> <<Mathcad - ms_loss_eq.pdf>>
>Attachment Converted: "C:\TEMP\attachments\Mathcad -

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