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1995

DesignerCouncil@IPC.ORG

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Subject:
From:
Dieter Bergman <[log in to unmask]>
Date:
Sat, 30 Dec 1995 07:05:10 -0600 (CST)
Content-Type:
TEXT/PLAIN
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TEXT/PLAIN (52 lines)
Scott,
The land pattern for the MLL34 MELF in the 1993 release of the IPC-SM-782 
is designed to provide a toe fillet of from 0.51 to 0.99 mm [.020 to 
0.39"]. You are right that the optional notch was originally intended to 
prevent rolling of the part during reflow. Some assembly companies have 
found that useful; others say they don't need it. Our European members 
don't seem to feel that it is necessary, in that Phillips makes a bulk 
MELF placement machine which places millions of these parts delivered 
through a hopper system.

The key to prevention of rolling appears to lie in solder volume and 
surface tension of the land as opposed to putting a notch in the land 
pattern. Those who use this concept also put a notch in the solder-paste 
stencil. The most unique method that I have seen to date is a company 
that designs their MELF land pattern using round lands. The center to 
center spacing of the lands matches the length dimension of the MELF (3.3 
to 3.7 mm). The nominal dimension, therefore, is 3.5 mm [.140"].

I'm not sure what diameter land they used. If you follow the 
recommendations for the "X" dimension in the 782 for registered land 
pattern 200, the nominal would be 1.7 mm [.070"]. By the way the "max" 
column of the X dimension is not correct. This will be picked up in the 
addendum. It should be 1.8 (for RLP 200); 2.6 (for RLP 201); 1.6 (for RLP 
202); 2.0 (for RLP 203); 1.8 (for RLP 204); and 2.6 (for RLP 205).

Good luck,

Dieter 

On Thu, 28 Dec 1995, Scott Decker wrote:

> Hi Dieter, I am sorry that I forgot the the designers sig address to post this on but could you sind it out for me? I will write it down this time and stick it to my computer.... I also posted this to another sig and I have edited this one for this group.
> 
> 
> Hi folks... Hope Everyone Had a nice xmas (Even those of you that live where the snow is). Here in Reno, the ground was white but the sun was a shinning....
> This may not be the correct place to post this question but here goes. I am looking for info on the pad design for a MELF LL-34 component. I have looked in IPC-SM-782 for their data and find it to be a little &^%)&^&#$#. The optional pad design has the cutout to keep the part from rolling when assembled, but the cutout looks to me like its under the part so far that the ends still sit on the pad. Maybe I'm not seeing the big picture here but if someone has an idea or picture, I would like to here from you....
> 
> Scott Decker
> AKA: PADMASTERSON
> 
> Hamilton Company
> Reno, NV.
> 
> Voice: (702)-858-3000 Ext. 322
> FAX: (702)-856-7259 For those of you that like to send pictures.
> 
> The above thoughts are mine and mine alone, I'm sure of it?
> 
> 



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