90度走线.pdf

90 Degree Corners:
The Final Turn
Doug Brooks, President needs to be fabricated; and then someone with the appro-
UltraCAD Design, Inc. priate equipment and knowledge needs to do the testing
and evaluation. See the acknowledgment at the end of
this article for those who donated their time, effort, and
Only a few topics generate the kind of enthusiastic resources for making this evaluation possible.
discussion that a right angle corner on a trace does. Just Figure 1 illustrates the board that was designed and
the mention of 90o corners --- regardless of whether you fabricated. Six traces provided various configurations for
say that they shouldn’t be used of if you say that they are test. All traces were configured as microstrip, controlled
harmless and can be used without concern--- guarantees impedance traces with identical dimensions ( oz cop-
a response from people with the opposite view. per, 10 mils wide with 7 mils FR4 dielectric thickness
Arguments against 90o corners fall into two cate- between trace and underlying plane, Er = ). Provision
gories: was made at one end of each trace for a 50 Ohm RF
Impedance mismatch: A right angle corner is, neces- connector for mating with test equipment, and for pads at
sarily, wider than the rest of the trace. This results in a the other end of each trace for impedance matching
decrease in Zo, the intrinsic i