Re: [PROTEL EDA USERS]: Controlled Impedance Design

["Michael Reagan" <edsi@netstorm.net>]

Hello All,
I spent some down time baselining the controlled impedance tools in 99SE for
accuracy.  Below are the results of my findings:   Several pics are missing
in this email including the stack up and test board, but the stack up info
is listed in the IPC tables at the end.   Conclusion is that the Microstip
controlled impedance tools for top layer routes are fairly accurate.

Mike Reagan
EDSI Frederick



Using PROTEL 99SE  Signal Integrity Tools for Micro Strip Controlled
Impedance Design

OBJECTIVE:  To verify the accuracy of the Signal Integrity /Controlled
Impedance tools supplied with Protel 99SE.

TEST SETUP:

STACK UP:  A four layer board with two internal ground planes  was setup
using Protel's Layer Stack Manager.   Using a recommended stack up from
HADCO (Sanmina), outer layer copper was set to .05 oz.,inner layers were set
to 1 oz copper.  Details of the stack up are shown in  Figure .   (Missing
from this doc to PROTEL USERS GROUP)  A dielectric constant (Dk) of 4.7 for
FR 4 was selected for test purposes.  Regardless of the variation of Dk for
FR4, the purpose of this test setup is to verify Protel's impedance tools
against a known good baseline.

CIRCUIT BOARD DESIGN:  A small design with 6 traces was made using two thru
hole connectors .
All of the traces were 500 mil in length and increased by 5 mils in width
starting at 5 mils and ending at 30 mils.  NET names were assigned to each
trace  500_5T, for 500mil-5 mil width trace, 500_10T for 10 mil trace, etc.

DESIGN RULES:

PROTEL SETUP   Protel signal integrity tools were set up using the following
parameters: Stimulus:    single pulse ( start time = 10 nsec, stop time = 60
nsec, start level = low ).  Since impedance is generally characterized
somewhere between 1 Mhz and 10 Mhz a  mid range value was selected.  Protel
claims its tools are useful to 1 Ghz.

VERIFICATION   Protel SI tools  were compared and verified against results
gained  from IPC  controlled impedance software found  at
http://www.ipc.org/.  Several other impedance calculation software packages
are available online including http://www.hadco.com.  and
http://www.automata.com., however results varied as much as +/- 10 percent
using each of these tools.  IPC is considered as the primary governing
organization for printed circuit board design and  manufacture,  therefore
was chosen as the baseline.


The following assumptions are made:    Solder Mask is one mil thick over the
conductor






FIGURE 1   PROTEL LAYER STACK UP





 Figure 2     PRINTED CIRCUIT BOARD DESIGN

Analysis   PROTEL SI CONTROLLED IMPEDANCE RESULTS

Signal: 500_5T
  Length:              0.0127 inch
  Min. Impedance:      105.307 Ohm
  Max. Impedance:      105.307 Ohm
  Average Impedance:   105.307 Ohm

Signal: 500_10T
  Length:              0.0127 inch
  Min. Impedance:      82.5711 Ohm
  Max. Impedance:      82.5711 Ohm
  Average Impedance:   82.5711 Ohm

Signal: 500_15T
  Length:              0.0127 inch
  Min. Impedance:      69.2669 Ohm
  Max. Impedance:      69.2669 Ohm
  Average Impedance:   69.2669 Ohm

Signal: 500_20T
  Length:              0.0127 inch
  Min. Impedance:      60.0629 Ohm
  Max. Impedance:      60.0629 Ohm
  Average Impedance:   60.0629 Ohm

Signal: 500_25T
  Length:              0.0127 inch
  Min. Impedance:      53.1903 Ohm
  Max. Impedance:      53.1903 Ohm
  Average Impedance:   53.1903 Ohm

Signal: 500_30T
  Length:              0.0127 inch
  Min. Impedance:      47.8179 Ohm
  Max. Impedance:      47.8179 Ohm
  Average Impedance:   47.8179 Ohm


RESULTS FROM IPC  CALCULATOR

4 Layer Stackup
 Layer Material  Dielectric Thickness Trace Width Cu Thickness Dielectric
Constant Impedance Description
1 .   106 ohms MicrostripDielectric  . .  . Core/Pre-preg
2. . 1.4 . PlaneDielectric 20 . . 4.7 . Core/Pre-preg
3. . 1.4 . PlaneDielectric  . .  . Core/Pre-preg
4 e .   . 83 ohms  Microstrip
4 Layer Stackup

 Layer Material Type Dielectric Thickness Trace Width Cu Thickness
Dielectric Constant Impedance Description
1.   70 ohms  MicrostripDielectric  . .  . Core/Pre-preg
2. 1.4 . PlaneDielectric 20 . . 4.7 . Core/Pre-preg
3. 1.4 . PlaneDielectric  . .  . Core/Pre-preg
4 .   . 60  ohms  Microstrip
4 Layer Stackup

 Layer Material Type Dielectric Thickness Trace Width Cu Thickness
Dielectric Constant Impedance Description 1 Conductive .   52   ohms
MicrostripDielectric  . .  . Core/Pre-preg
2 Conductive . . 1.4 . PlaneDielectric 20 . . 4.7 . Core/Pre-preg
3 Conductive . . 1.4 . PlaneDielectric  . .  . Core/Pre-preg
4 Conductive .   . 45 ohms  Microstrip