Round pads sometimes work well because during reflow the surface tension of the molten solder will pull more uniformly in every direction. Square pads tend to have the end fillet larger than the side fillets, and because of this and the fact that the paste on one end or the other may go liquidus first, it is easier for the surface tension of the molten solder to lever up the smaller 0402, 0201 and 00105 chips.

Another way to overcome this is to use standard square pads, but purposely set up the pick and place machine program to place the components at about a 30 degree angle. This way the molten solder needs to straighten the part out first before it can lever one end or the other up. By the time it straightens the part out both pads are in liquidus and the movement ensures contact with the molten solder on each end of the chip, and prevents the tombstoning. It may not completely end the issue, but it certainly reduces it.

And horseshoe-shaped paste deposits on square pads have been known to work very well. I don’t know why. Ask your mother.

 

 

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Heidel, Jeff
Sent: Wednesday, June 09, 2010 5:26 PM
To: [log in to unmask]
Subject: Re: [DC] Follow up ~ IPC 0201 land-pattern

 

Is anyone using round pads for their 0201s?  I have seen some artwork recently with round pads and I was wondering what the advantages or disadvantages would be. 

 

 

Fred, I asked around a bit this morning, especially I asked Mike Buetow what he hears from CMs. The verdict I hear is, it depends on the CM.  I’m gonna do some more research and let ya know what I find.

 

p.

 

 

Regard's, Frederick Dark Jr.

Manager Senior PCB Designer

Crestron Electronics, Inc.

22 Link Drive Rockleigh N.J. 07647

P:201.750.7004 ext.11320

F:210.767.5772

[log in to unmask]

 

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________

-------------------------------------------------------------------------------
DesignerCouncil 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 DesignerCouncil
To temporarily stop/(start) delivery of DesignerCouncil for vacation breaks send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings 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
-------------------------------------------------------------------------------

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________

-------------------------------------------------------------------------------
DesignerCouncil 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 DesignerCouncil
To temporarily stop/(start) delivery of DesignerCouncil for vacation breaks send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings 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
-------------------------------------------------------------------------------

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________