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November 2008

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Subject:
From:
Ioan Tempea <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ioan Tempea <[log in to unmask]>
Date:
Thu, 20 Nov 2008 14:57:29 -0500
Content-Type:
text/plain
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text/plain (129 lines)
I second Steve,

U-shaped for MELF can cause the component to roll all over the place on the PCB, since they simply give less contact between the component and the part, so less tack.

Regards,

Ioan

-----Message d'origine-----
De : TechNet [mailto:[log in to unmask]] De la part de Steve Gregory
Envoyé : 20 novembre 2008 14:53
À : [log in to unmask]
Objet : Re: [TN] MELF pad shape question

Hi Carl & Ben,

I've seen those "U" shaped pads for MELF's as well as just plain ol'
square pads. Personally, I think what might have been a good idea at one
time really isn't necessary for MELF's. The solder paste holds the part
just fine. In fact, I've seen the "U" shaped pads cause the parts to
skew sometimes during reflow. While maybe not a defect, it looks ugly.

Am I the only who has seen that?

Steve 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: Thursday, November 20, 2008 9:26 AM
To: [log in to unmask]
Subject: Re: [TN] MELF pad shape question

Carl,

This notch is used to prevent edge overhang of the component. The pad
shape helps keep the component centered on the pad, otherwise the wider
middle of the component may overhang the pad edge even if the narrower
bottom is on the pad and soldered.

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Thursday, November 20, 2008 10:09 AM
To: [log in to unmask]
Subject: [TN] MELF pad shape question

A customer is using MELF parts on an existing board and is asking us to
add some more parts of a different size.  The new parts are DL-35 and
the manufacturers data sheet shows a rectangular pad as the recommended
size.  All of the MELF parts on their current board have small notches
at the middle-inside of each pad like:

**********                **********
**********                **********
*****                          *****
**********                **********
**********                **********

The customer is requesting that we make pads similar to pads on other
parts, but properly sized for the DL-35 part.

Questions:
1.  Why would pads need to have this notch?
2.  Where can I get recommendations on how to create a notched pad

Thanks,
Carl




Carl Van Wormer, P.E.
Senior Hardware Engineer
Cipher Systems
1800 NW 169th Place, Suite B-100
Beaverton, OR  97006
Cipher Systems (503) 617-7447   
Direct Line (503) 425-5163

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