ROT PCB Mech Mounting Hole Spacing

[KT77]

Hi. Haven't been by here for awhile.
'Traditionally', I have been using 4in spacing for .063 and 6in spacing for .093 circuit boards (greater than 6"sq, commercial duty). I can't remember where I got these rule of thumb numbers (they were told to me at some time in the 90s), so I decided to research it...and can find nothing, not even for automotive or aerospace.
Are there a specifications or guidelines for service duty, that apply to recommended mounting hole spacing and fastener sizing? What is everybody generally using?
Thanks!

Tracy Norton

 

[itsmoked]

I can't imagine there is a standard. The applications are so vastly different for most boards.

Are there push-buttons? Is the board vertical or horizontally mounted? Are there heavy components? Are large wires terminated to the board? Are there grid array components? Surface mount? Thru hole? Are there stiff terminal blocks? Is there a display? Is the board going into a vibrational setting? Large shocks expected? Can you use large screws or are you constrained to small ones? Does the board have to be mounted close to a surface or far? Are there spade terminals?

There's no way some formula is going handle all this stuff.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[KT77]

There's no way some formula is going handle all this stuff.
I agree.

 

[VEBill]

Consider also plug-in circuit cards such as VMEbus. These cards can be relatively large (some over 300mm) and are only supported around the edges. They're also sometimes used in environments with vibrations and shock. The cards are often equipped with card stiffeners (rigid metal bars).

As above - there's no simple rule.