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January 2007

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 2 Jan 2007 08:40:57 -0600
Content-Type:
text/plain
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text/plain (119 lines)
I agree with Bill. Nearly all of the "manufacturer's recommended stencil
aperture layouts" for what we call belly pads on leadless castellated
components are too large by half. An aperture size that provides about
1/2 of the solder paste area for a standard .006" thick stencil provides
just about the right volume of solder to prevent the component from
lifting so high that the perimeter terminations are open. A crosshatched
pattern that provides 50% reduction for the belly pads seems to work
quite well in filling the entire area with solder without lifting the
part off the board.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bill Kunkle
Sent: Thursday, December 28, 2006 10:45 AM
To: [log in to unmask]
Subject: Re: [TN] DRK package

Jim,

Although your attachment does not travel thru Technet, I found that this
package is a QFN style component.

I suggest a stencil opening design as follows:
  perimeter leads: 1 mil width reduction, 100% length, 2 mil corner
radii
  center lug: print 50 - 60% of the the metallized area

Use the area ratio calculation to insure good paste release.

This scheme works well for most QFN/MLF components.

Bill Kunkle
Manager of Stencil Technology
MET Assocs.
140 Mt Holly Bypass  Unit 10
Lumberton, NJ  08048

www.metassocs.com
Ph: 609 261 2670  Fx: 4007



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of West, Jim
Sent: Thursday, December 28, 2006 9:27 AM
To: [log in to unmask]
Subject: [TN] DRK package


Hi,

Looking for some help with the package shown within this email.  The
package virtually sits flush with the PCB, and the pads are directly
under the body of the part.  The pads are exposed on the side, but by a
very small amount.  I have a lot of questions regarding the processes
from the beginning to the end, but wanted to see if anyone else runs
this type of package and what your experiences have been like?  Some
questions would be stencil apertures design guideline, paste height,
after reflow inspection method, and reworking.

Best Regards,



Jim West
Engineering Manager
Nexergy Inc.
www.nexergy.com
tel: (614) 351-6216
fax: (614) 324-1979



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