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From: aleksa on 17 May 2010 03:35
When I started designing PCBs, I was given an advice
to route GND with 50mils and VCC with 25mils.

But now I read on the net that VCC should be wide, also.

I make two-layer digital boards only.

If I now adjust my VCC tracks to 50mils,
is there any chance of some problems?

And should I adjust? All prior boards work...

Maybe I should note that all my previous boards
were built around discreet chips, GALs, SRAM and Z80,
but am now moving towards 180 MHz ARM and FPGA.


From: Tim Wescott on 17 May 2010 12:36
aleksa wrote:
> When I started designing PCBs, I was given an advice
> to route GND with 50mils and VCC with 25mils.
>
> But now I read on the net that VCC should be wide, also.
>
> I make two-layer digital boards only.
>
> If I now adjust my VCC tracks to 50mils,
> is there any chance of some problems?
>
> And should I adjust? All prior boards work...
>
> Maybe I should note that all my previous boards
> were built around discreet chips, GALs, SRAM and Z80,
> but am now moving towards 180 MHz ARM and FPGA.

I need a rope to hold up a sack containing all my belongings. How thick
should it be?

What? You want to know how many belongings I have, and how much they
weigh, and whether any of them are alive and may make the sack bounce
and jump around? Why oh why would you want to know that, just to tell
me how big a cruddy rope needs to be?

OK: I'll make a deal with you:

_You_ tell _us_ enough about what you're doing (expected current draw,
more about the parts that you're going to use, whether you're running
any analog parts, etc.) Then maybe _we_ will have enough information to
tell _you_ the answer that you need.

And I'll go figure out that damn rope size myself.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: George Herold on 17 May 2010 14:14
On May 17, 3:35 am, "aleksa" <aleks...(a)gmail.com> wrote:
> When I started designing PCBs, I was given an advice
> to route GND with 50mils and VCC with 25mils.
>
> But now I read on the net that VCC should be wide, also.

I don't do much digital stuff, but high speed is high speed. You want
a ground plane. And then make the power traces as wide as possible.
The idea is to keep trace inductance as small as possible. (Which
also implies short traces.)
>
> I make two-layer digital boards only.
That makes it harder. The 'pros' will tell you, four layers with one
inner the ground plane and the other inner for power.

>
> If I now adjust my VCC tracks to 50mils,
> is there any chance of some problems?

Problems, there always seems to be problems. Wider traces may or may
not cure your problems.
>
> And should I adjust? All prior boards work...

If it ain't broke don't fix it.

>
> Maybe I should note that all my previous boards
> were built around discreet chips, GALs, SRAM and Z80,
> but am now moving towards 180 MHz ARM and FPGA.

Good luck and have fun....
George H.
From: aleksa on 17 May 2010 16:14
"George Herold" <ggherold(a)gmail.com> wrote in message news:fa2a60df-7a8a-45b0-943a-d5da4e5b4594(a)s41g2000vba.googlegroups.com...
On May 17, 3:35 am, "aleksa" <aleks...(a)gmail.com> wrote:
>> If I now adjust my VCC tracks to 50mils,
>> is there any chance of some problems?

>Problems, there always seems to be problems. Wider traces may or may
>not cure your problems.

I didn't say I *have* problems, I asked
if widening a VCC *may make* problems.

The guy who suggested I should use 25mil VCC
had an old board, with DIPs, with thick GND
and thick VCC lines (some 100mils), with caps on
all chips, but the board didn't work correctly.
After he had removed the thick VCC line from
one of the chips, and soldered a thin wire,
the board worked correctly.

He also said something like "If VCC lines are
not thick, device will draw spike current from caps,
rather than the VCC line". Something like that.
I'm no expert, and I also have to translate it to English...

Anyway, I'll rephrase the question:
can widening a VCC line make problems?



From: aleksa on 17 May 2010 16:16
"Tim Wescott" <tim(a)seemywebsite.now> wrote in message news:UNmdnem-7tvm7WzWnZ2dnUVZ_tIAAAAA(a)web-ster.com...
> aleksa wrote:
>> When I started designing PCBs, I was given an advice
>> to route GND with 50mils and VCC with 25mils.
>>
>> But now I read on the net that VCC should be wide, also.
>>
>> I make two-layer digital boards only.
>>
>> If I now adjust my VCC tracks to 50mils,
>> is there any chance of some problems?
>>
>> And should I adjust? All prior boards work...
>>
>> Maybe I should note that all my previous boards
>> were built around discreet chips, GALs, SRAM and Z80,
>> but am now moving towards 180 MHz ARM and FPGA.
>
> I need a rope to hold up a sack containing all my belongings. How thick should it be?
>
> What? You want to know how many belongings I have, and how much they weigh, and whether any of them are alive and may make the
> sack bounce and jump around? Why oh why would you want to know that, just to tell me how big a cruddy rope needs to be?
>
> OK: I'll make a deal with you:
>
> _You_ tell _us_ enough about what you're doing (expected current draw, more about the parts that you're going to use, whether
> you're running any analog parts, etc.) Then maybe _we_ will have enough information to tell _you_ the answer that you need.
>
> And I'll go figure out that damn rope size myself.

Perhaps you can hang yourself with it?

>
> --
> Tim Wescott
> Control system and signal processing consulting
> www.wescottdesign.com


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