I calculate the overall volume of the solder paste on a 1-to-1 basis
first. Then I use 75% reduction of that amount, but I distribute this
volume over the whole slug pad in a simple crosshatch pattern in the
stencil. The 75% reduction seems to be a magic number where the solder
will fill out the slug area on the pad, but not so much that the
component will move. The crosshatching helps distribute the solder so
there is some equilibrium of surface tension. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Seymour
Sent: Tuesday, March 28, 2006 9:31 AM
To: [log in to unmask]
Subject: [TN] SO8 with Heatslug

Currently using a Phillips part,

http://www.semiconductors.philips.com/pip/NE57814DD.html

This is a  standard SO8 package with a large "heat slug pad" under the
part.

During reflow the part is floating off center and causing shorts to the
lead pads.
I believe this because of the the volume of paste in the heat slug area
is lifting the part up and surface tensions take over.

I have a call into tech support at Phillips, but I figured I would query
while waiting for a call back.

What is the recommended volume of solder paste under this device ?

What is the recommended solder mask opening(s) under this device?
- Something like 4-6 smaller opening over a continuous top side  ground
plane?

What is the recommended paste printing pattern under this device?
- match the soldermask openings?

Does anyone have experience with such a device?

Thanks,

Dave


--
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560

Direct: (919)653-4249
Main: (919)653-4180
Fax: (919)653-4297

[log in to unmask]

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------