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Date: Fri, 18 Feb 2005 21:46:46 -0600
From: Charlie England <ceengland@bellsouth.net>
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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