Hi Nagaraj -
The paste mask opening is divided in smaller apertures because the squeegee that spreads the paste is flexible and may fold down into the aperture as the paste is screened. This will scoop the paste out of the stencil aperture and leave you with insufficient solder. Subdividing the aperture is a good way of assuring an adequate total solder volume on the pad.

We just had two cases were the paste mask opening of thermal pads were scaled back relative to the copper pad and soldermask opening, but without adding additional apertures in the stencil. The result: insufficient solder volume, no contact to the pad and unstable switching regulators. Make sure you get enough solder on the pad. 

Med vennlig hilsen\Best Regards

HALDOR HUSBY     	
SENIOR DEVELOPMENT ENGINEER
Data Respons Norge AS            	
Kongsberg Næringspark  Tel:    +47 32 29 94 00	
P.O. Box 1022    Dir:    +47 32 29 94 18	
NO-3601 Kongsberg        Fax:    +47 32 29 94 40	
Norway   Mob:    +47 48 04 83 68	
                 	
www.datarespons.no       [log in to unmask]	
 	



-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of ert ert
Sent: 12. juli 2006 06:24
To: [log in to unmask]
Subject: [DC] OFN thermal pad pastemask

 Hi All,

I recently captured on a board, the QFN package has thermal pad whose paste mask is not fully opened but has small square openings as shown below. What the reason to provide this type of pastemask?

 _____________________
|       ___           ____      |
|     |      |          |      |      |
|     |      |          |      |      |
|      ------           ------        |
|                                    |
|       ___           ____      |
 |     |      |          |      |      |
 |     |      |          |      |      |
 |      ------           ------        |
|                                    |
-------------------------------------

Thanks,
Nagaraj C.I.D

---------------------------------
 Find out what India is talking about on  Yahoo! Answers India.

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
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/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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
---------------------------------------------------------------------------------
 So, what's NEW about the NEW Yahoo! Messenger? Find out.

**********************************************************************
This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom
they are addressed. If you have received this email in error please
 notify the [log in to unmask] .

This email message has been virus checked by the anti-virus
programs used by Data Respons .
**********************************************************************

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
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/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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
---------------------------------------------------------------------------------