Hi folks:

Here's a genuinely esoteric question for those among us who design PC
boards. When putting a component pin inside a large metal area, do you use
the option of thermal isolation rings (a narrow gap around the pad, with
traces coming in typically at 3, 6, 9 and 12 o'clock? Or not? If not, why
not?

Peace,
Paul

On Wed, 20 Apr 2005 18:56:40 GMT, Paul Stamler wrote:

Hi folks:

Here's a genuinely esoteric question for those among us who design PC
boards. When putting a component pin inside a large metal area, do you use
the option of thermal isolation rings (a narrow gap around the pad, with
traces coming in typically at 3, 6, 9 and 12 o'clock? Or not? If not, why
not?

Peace,
Paul

I always use thermal relief to inner ground or power planes to ensure good
solder connections. In fact it requires effort not to since this is a basic
design rule in most modern ECAD packages.


Bob

On Wed, 20 Apr 2005 18:56:40 GMT, "Paul Stamler"
wrote:

Hi folks:

Here's a genuinely esoteric question for those among us who design PC
boards. When putting a component pin inside a large metal area, do you use
the option of thermal isolation rings (a narrow gap around the pad, with
traces coming in typically at 3, 6, 9 and 12 o'clock? Or not? If not, why
not?

Peace,
Paul

So you don't have to apply large(er)/longer time amounts of heat when
(de)soldering. This needs to take into consideration the amount of
current (voltage drop and heat generated) to that pin.

Gahd! You just brought back some of my nightmares of Backplane design.

, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

"Steve Urbach" wrote in message
...
On Wed, 20 Apr 2005 18:56:40 GMT, "Paul Stamler"
wrote:

Hi folks:

Here's a genuinely esoteric question for those among us who design PC
boards. When putting a component pin inside a large metal area, do you
use
the option of thermal isolation rings (a narrow gap around the pad, with
traces coming in typically at 3, 6, 9 and 12 o'clock? Or not? If not, why
not?

So you don't have to apply large(er)/longer time amounts of heat when
(de)soldering. This needs to take into consideration the amount of
current (voltage drop and heat generated) to that pin.

That sounds like a "Why you should"; I just wondered if there was any down
side other than slightly greater electrical resistance between the pad and
the metal area, or if the latter was likely to be significant. I'm using
30-mil connectors across the gap.

Peace,
Paul

only down side is in a circuit with very high current like 15 Amps or
more or in a VHF or above RF circuit where the inductance needs to be
very very low like less than 1 nH.

For audio work I can't think of a case where it would be a problem.


Mark

Paul Stamler wrote:
"Steve Urbach" wrote in message
On Wed, 20 Apr 2005 18:56:40 GMT, "Paul Stamler"
wrote:

Hi folks:

Here's a genuinely esoteric question for those among us who design PC
boards. When putting a component pin inside a large metal area, do you
use
the option of thermal isolation rings (a narrow gap around the pad, with
traces coming in typically at 3, 6, 9 and 12 o'clock? Or not? If not, why
not?

So you don't have to apply large(er)/longer time amounts of heat when
(de)soldering. This needs to take into consideration the amount of
current (voltage drop and heat generated) to that pin.

That sounds like a "Why you should"; I just wondered if there was any down
side other than slightly greater electrical resistance between the pad and
the metal area, or if the latter was likely to be significant. I'm using
30-mil connectors across the gap.

For the most part I don't bother with it. In RF design class we were told
it was a bad practice that added more effective lead inductance, and when
you're laying boards out by hand it's a lot of extra work too.

When it would be a big help is when you have very large leads or bussbars
soldered onto the board.... but in those cases you usually want the lowest
possible resistance to the trace (usually the ground plane) that you can get.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."