The best type of "lock washer" I have ever run across is a Schnorr
washer, they are serrated Belleville washers, we have used them in our
military systems, and they held when nothing else would.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Thursday, October 12, 2006 3:02 PM
> To: [log in to unmask]
> Subject: Re: [TN] Compression Limit on FR4?
> 
> Hi, Jack
> I can tell you that typically the torque setting used for hardware on
> pwb assemblies is between 1 to 6 in/lbs. More than that tends to
deform
> the fiberglass over time. Of course, it all depends on the type of
board
> material, layer count, etc.
> It also depends on the application.
> Realize that a lot of relaxation occurs during any type of thermal
> excursion, and the hardware will loosen up. It is always a good idea
to
> use a Bellville washer in conjunction with a serrated or star washer
to
> continue to hold the torque. It is also a good idea to use Glyptol or
> some other threadlocker.
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
> Sent: Thursday, October 12, 2006 1:54 PM
> To: [log in to unmask]
> Subject: [TN] Compression Limit on FR4?
> 
> Does anyone know of any guidelines or recommendations that suggest a
> maximum limit on compressing board material?
> 
> Can any damage occur by over-torque'n screws, for example?
> 
> I've never heard anyone discuss that...
> 
> Jack
> 
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