,
Stack up design for PCBs: Beyond the IPC Recommendations
The Greater Boston Chapter of the IPC Designer's Council will
hold its last meeting of the season Thursday, June 3rd at 6pm.
Eric Bogatin, noted SI and EMC lecturer and consultant, will
speak on the limits of common techniques for predicting board
impedance, and give insight into mediating inevitable cases
where engineer and fabricator disagree.
Abstract:
Controlled impedance circuit boards are the norm. Establishing
the design rules for the PCB stack up is often hit or miss.
Whatever rule of thumb a designer uses, fab vendors have their
own fudge factors to add. Often these are based on empirical
results from building test boards. The IPC tried to assist in
the design process by publishing the IPC-2141 Controlled Impe-
dance Circuit Boards and High-Speed Logic Design guide. They
offer analytic approximations for common PCB stack-ups such as
stripline and microstrip. However, they beg the question, under
what conditions can these equations be accurately used?
In this paper, these recommended approximations are introduced
and compared to results from field solver calculations that have
been verified accurate to better than 1%. For the range of typi-
cal geometries used in circuit board fabrication, the IPC equa-
tions are typically accurate to 5% for the limited range of well
defined cross sections. The predicted delay is accurate to about
20% for some situations. The precise accuracy at various geome-
tries will be reviewed. For simple structures that match the
ideal cross sections, the IPC equations may be used for estab-
lishing the first order design conditions. However, when higher
accuracy is needed or real world structures need to be designed
that these equations do not describe, such as solder mask over
surface traces, asymmetric stripline and coupling between
traces, a field solver is needed. Examples of how simple to use
field solvers can give accurate results for all stack up geome-
tries is presented. These techniques apply to conventional as
well as the new build up multilayer, MCM and hybrid substrates.
Biography:
Dr. Bogatin has been involved with signal integrity and EMI
issues for almost 20 years. After receiving his Ph.D. in Physics,
he has worked at AT&T Bell Labs, Raychem Corp, Sun Microsystems
and Ansoft Corp. Bogatin Enterprises was founded in 1988 to
provide expert consulting assistance in the field of Signal
Integrity and EMI. Activities include training courses, tech-
nology analysis and integration, technical reports, and marketing
assistance for clients offering products for the high speed
industry. Dr. Bogatin's training courses are offered through the
Technical Proficiency Institute. He can be reached by email at
mailto:[log in to unmask] or at www.BogatinEnterprises.com .
Agenda:
Note there is a meeting fee of $10/members $20/non-members.
6:00 pm, Arrivals, Pizza and soft drinks available
6:45 Jeff Seeger - Chapter Update
7:00 Eric Bogatin, Stack up design for PCBs
RSVP:
Non members are welcome at meetings, but expect some pressure
to join...<grin>. Non-members RSVP please, reply/sender-only
mailto:[log in to unmask]
President's Note:
I am very grateful for having attracted Dr. Bogatin to come
from Kansas enlighten us on how to succeed with impedance when
arguments start. Your attendance and meeting fee will help to
defray his travel expense.
Directions:
Lockheed/Martin in Lexington MA. This facility is located off
route 128 at the route 2A/Concord/Hanscom exit. Proceed West
200 yds, turn Left onto Forbes Road. The meeting is in the
first building on the left (after the guard shack).
Mission:
Physical Design in this era is not for the faint-of-heart.
Old assumptions run out of legitimacy as speeds and margins
converge on "need for perfect". Work with us to learn where
perfect might be found.
Your help and participation have made the 1998/1999 meeting
season a great pleasure to organize and host.
Thanks for a great year; we look forward to seeing you at
this meeting and again next fall, where we'll try to prepare
ourselves for the professional side of the next millenium.
--
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
jseeger "at" appliedcad "dot" com 978 649 9800
President, Greater Boston Chapter, IPC Designer's Council
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TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
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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
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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
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