We have taken similar steps as you have noted for the same reasons.   We
use 222 all over the place in our mechanical assemblies.  Has kept our
loose hardware issues to a  very small     problem.

Randy Bock Sr.
Quality Manager
Pitney Bowes
AddressRight Printers
(p) 203 720-3861
(f)  203 729-5397
(email)  [log in to unmask]




"Croslin, Robert" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
07/01/2004 08:59 AM
Please respond to
"TechNet E-Mail Forum." <[log in to unmask]>; Please respond to
"Croslin, Robert" <[log in to unmask]>


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Subject
Re: [TN] Max. Torque applied to a screw securing a PCB






Marius, I asked my mechanical engineer and he searched through his files
only to find a copy of a post made on 6/11/02 by TechNet's own Phil
Nutting
that contained the information below.  Phil referenced SAE ARP 1928 and
noted plenty of variables like assuming the screw was steel or stainless,
noting that brass should be lower and nylon lower still.

2-56 - 3 inlb
4-40 - 8 inlb
6-32 - 10 inlb
8-32 - 20 inlb
10-32 - 32 inlb
1/4-20 - 60 inlb.

We used to try to lock our boards down using torque specs but stopped.  It
will differ if you're tightening onto a copper surface, HASL surface, or
just plain FR4.  Years ago we went to the use of Loctite 222 (threads
only)
and our problems with loose hardware disappeared. The major problem wasn't
the eventual use of the devices, but the vibrations caused in shipping and
the resonances caused by traveling in trucks like UPS or FedEx. Hope this
helps

Bob Croslin
Nielsen Media Research


-----Original Message-----
From: Marius S [mailto:[log in to unmask]]
Sent: Wednesday, June 30, 2004 8:20 PM
To: [log in to unmask]
Subject: [TN] Max. Torque applied to a screw securing a PCB


Hello All,

I'd like to find out what is the maximum
torque that can be appled to a metal screw that
secures a PCB to a metal chassis. Perhaps someone can
point me to a standards/IPC document on the subject.

With many thanks,
Marius




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