Ok, folks I got the message on showing resistor "legs" - too risqué for some
folks I guess {:>).

Seriously, I think I will redesign the board to use Surface mount resistors
and capacitors and that will eliminate legs - of course it was sure nice to
use those legs to leap over traces.

Thanks for the input, Finn, Todd, Charlie, et al

Ed


----- Original Message -----
From: "Charlie England" <ceengland@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, February 18, 2005 10:46 PM
Subject: [FlyRotary] Re: Digital Fuel Monitoring System


 

Hey Ed, want a 2nd opinion? What Finn said.

Same reason that 13B through-bolts break.

Charlie


Finn Lassen wrote:

   

Hi Ed.

This of course all only applies to electronics in a vibration exposed
environment.
Good practice, as I was taught it many years ago, is to have hole
spacings to allow components to lie flat on the board.
Of course there are exceptions like power resistors that need airflow
around them, but they should be mounted with "stand-offs" (small tubes
on their legs). The rule used to be that components should not be held
in place by the solder, but by their mechanical mounting. That's why
the pins are typically bent 45 degrees where they stick through the
PCB before being cut off and soldered. Heavy components are
additionally secured with some kind of mechanical fastener or globs of
goo (technical term). Now obviously the weight of the body of the
component in relationship to number of pins/legs is a factor. An
example would be an IC with oodles (another technical term) of pins.

I "grew up" in a company that secialized in sound and vibration. It
was very educational to watch a PCB board mounted on a "shaker"
(basically a loudspeaker where there membrame was replaced with a
mounting place) lit with a strobe light synchronized to the frequency
sweep. Components dancing around and finally falling off if not
properly supported (mounted).

But that was then. Now we have surface mounted components which I know
nothing about...


Finn (Looks like I've been kicked off the list again)


Geez, Finn, I was unaware that there was a "protocol" for resistor
sizes on PC boards.  Seriously, is there some reason (vibration?) for
forcing resistors all the way to the board or is it just "esthetics?".

Ed A