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November 2009

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From:
Reuven Rokah <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Reuven Rokah <[log in to unmask]>
Date:
Mon, 9 Nov 2009 10:13:12 +0200
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You have to keep free space from ceramic components / solder joints, around the PEM hole to prevent cracks





Best Regards



Reuven ROKAH 

e mail: [log in to unmask]

Think green before printing this mail... Thanks



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards

Sent: Saturday, November 07, 2009 4:47 AM

To: [log in to unmask]

Subject: Re: [TN] PEM (rivets) in PCB



Sounds like you have had long history of success using PEM fasteners but you point out a major problem...



Sometimes the designer or customer doesn't analysis the mechanical conditions that the insert fastener is required to perform in...



It is easy to pull off a PCA then it is to pull through a PCA...



Anytimes I have ended up using a rivnut instead of a PEM nut for mechanical reasons...(Field Service personnel)...



Paul





Paul Edwards

Surface Art Engineering





-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of John Goulet

Sent: Friday, November 06, 2009 6:42 PM

To: [log in to unmask]

Subject: Re: [TN] PEM (rivets) in PCB



I've used PEM rivits for 20+ years with excellent results. The standard PEM with the serated edges have great holding power. The design must be compliant to PEM Engineering's specification. The board must be thick enough that the PEM doesn't protrude.



PEMs are normally pressed after all the soldering processes. The keep out area must be sufficient to allow the recommended bottom support tool needed only when the design is a double sided assembly. The bottom anvil supports the PCB so the adjacent components aren't damaged during the press operation.



Crazing and worse can occur if the operator over presses the PEM or the PEM nut is pressed in crooked.



The press should be setup with a mechanical stop or pressure control if using the air driven PEMserter. The PEM product and design is good when the proper assembly process controls are in place.



 PEM has a new type of PEM which uses a collapsable design and is used where a very low extraction force is acceptable. The idea is that when the insert is pressed the compression causes a slight expansion inside and the raised flukes tilt within the mounting hole.



 Our customer did not realize how weak the holding force was. The specifications clearly show that no swaging is required however by swaging the thin protruding part you can greatly increase the holding force. I had this discusion with PEM's engineering staff and they agreed that that was an acceptable fix.



John Goulet



Process Engineer

----- Original Message -----

From: "henry rekers" <[log in to unmask]>

To: [log in to unmask]

Sent: Friday, November 6, 2009 1:54:44 PM GMT -05:00 US/Canada Eastern

Subject: [TN] PEM (rivets) in PCB



Is anybody out there aware of any spec/inspection criteria/documentation on how to specify/design/inspect Pem type fasteners?



We have a design that may require this, but I'm not willing to commit until I have some more background info.  Specifically, is this a normal process for a board shop?  Are there any 'gotcha's'?



Thanks.





      __________________________________________________________________

Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now http://ca.toolbar.yahoo.com.



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