width of the trace and printed circuit board

[john]

Hi,

I have following questions

1. How can I determine the size of the trace? What parameters should
be considered before determine the size of the trace?

2. I am using the formula k / ( 1+ (D/H) ^ 2 ) . How can I calculate
the value of "K "?

Thanks
John

 

[Tom Bruhns]

Hi,

I have following questions

1. How can I determine the size of the trace? What parameters should
be considered before determine the size of the trace?

2. I am using the formula k / ( 1+ (D/H) ^ 2 ) . How can I calculate
the value of "K "?

Thanks
John

1. Measure it?? Or do you mean to ask how you can determine what
width trace you should use for a particular application? If it's the
latter, it depends on several things: do you need a particular
impedance? How much current will it carry? What temperature rise can
you tolerate? How much voltage drop can you stand? What is the PC
process you are using capable of?

2. Is K the same as k? If not, what is it? What is k? What are D
and H? What does the formula claim to determine?

You may well find answers to your questions with a Google search about
printed circuit trace width. For example, this was one of the early
hits of such a search: http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/
It may well answer at least your first question.

Cheers,
Tom

 

[Noway2]

1. Measure it?? Or do you mean to ask how you can determine what
width trace you should use for a particular application? If it's the
latter, it depends on several things: do you need a particular
impedance? How much current will it carry? What temperature rise can
you tolerate? How much voltage drop can you stand? What is the PC
process you are using capable of?

2. Is K the same as k? If not, what is it? What is k? What are D
and H? What does the formula claim to determine?

You may well find answers to your questions with a Google search about
printed circuit trace width. For example, this was one of the early
hits of such a search: http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/
It may well answer at least your first question.

Cheers,
Tom

If what you are considering is how wide to make digital traces, you need
to also take into account the ability of the drivers to drive them. The
impedance of the trace and hence the current required by the driver is
a function of the trace geometry: width versus height above the
reference plane.

As a rule of thumb and unless there are other considerations, I try to
keep the digital traces on the order of 75 Ohms though I don't worry too
much about it. I chose 75 Ohms mostly on the advice of another engineer
who's opinion and abilities I respect. When I asked him to review a PCB
layout for me, he commented that my 50 Ohms traces might be a little low
for some drivers to handle, though most modern stuff could, and I might
want to consider going a bit higher. Based on the standard core
thickness used by the PCB vendor I use I typically keep my digital
traces at .008", which gives me an appropriate impedance and is still
reliably producible.

The capabilities of the PCB vendor are another factor to keep in mind,
as is the cost of your design choices.

 

[Robert Baer]

Hi,

I have following questions

1. How can I determine the size of the trace? What parameters should
be considered before determine the size of the trace?

2. I am using the formula k / ( 1+ (D/H) ^ 2 ) . How can I calculate
the value of "K "?

Thanks
John

I normally use a magnifier with a graticule...