Re: [SI-LIST] : Other materials for GHz application

Paul Franzon (
Tue, 2 Dec 1997 09:45:11 -0500


There are no hard and fast rules for clock rate vs. board technology.
Here are some things to think about, however:

o To operate even point to point connections at this rate will require
careful modeling and analysis, including skin effect and especially
process variations. Everything in a board varies +/- 30%. You will
need a carefully designed termination scheme to suppress reflection
noise. The materials used in a PCB can support very wide frequency
ranges but designing low-latency low-noise nets gets tricky and

o Clock speed by itself is not a driver to MCM over PCB. Common drivers
include size, inter-chip latency, noise control, routability,
and chip I/O count.
However, I will say this. Designing MCM wiring to meet a 200 ps delay
slack spec (to pick a number) is a *lot* easier than designing the same
PCB wiring.

Good luck


On Dec 2, 14:55, wrote:
> Subject: [SI-LIST] : Other materials for GHz application
> Hello,
> Does anyone have information on the following:
> 1. Why and What is the limitation of using FR4 up to 500-700 MHz?
> 2. Beyond this clock freq, what should be recommended for the PCB and
> 3. Under what circumstances, we should migrate MCM and why?
> Thanks in advance.
> Best Regards.
> ******************************************************************************
> Cheah Soo Lan
> SINGAPORE 118 230
>-- End of excerpt from

Paul Franzon, Associate Professor, North Carolina State University
Rm. 443, Engineering Graduate Research Center, Centennial Campus
smail: ECE, Box 7914, NCSU, Raleigh NC 27695-7911
Fedex: Rm. 416, EGRC, 1010 Main Campus Dve, NCSU, Raleigh NC 27606
919 515 7351, fax. 919 515 2285,