The dimensions and dimensioning generally follow the JEDEC approved outline and procedures. I am sure specific dimensions could be provided to you from the supplier of the packaged device. Best regards, Leo Director of Applications Engineering ASAT, Inc. 3755 Capital of Texas Highway, Suite 100 Austin, Texas 78704 ph 512-383-4593 fx 512-383-1590 [log in to unmask] www.asat.com The information contained in this electronic message is CUSTOMER/SUPPLIER PRIVILEGED AND CONFIDENTIAL INFORMATION intended only for the use of the individual or entity named above. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution and copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by electronic mail. Thank you. -----Original Message----- From: David Greig [mailto:[log in to unmask]] Sent: Monday, December 06, 2004 11:21 AM To: 'TechNet E-Mail Forum'; 'Leo Higgins' Subject: RE: [TN] Help, Help, I have a QFN Package I don't know what to do ! Hi Leo, One request regarding QFN's (and this is not singularly directed at ASAT) - could the package drawings please dimension the lead terminals relative to the thermal pad? Invariably these are with respect to the outer body, and with LMC/MMC conditions can overlap the thermal pad, or at least leave insufficient clearance. Given the methods of singulation, it would be preferable to use the thermal pad as the reference for the other dimensions. Best Regards David Greig ______________________________ GigaDyne Ltd Buchan House Carnegie Campus Dunfermline KY11 8PL United Kingdom t: +44 (0)1383 624 975 ______________________________ -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leo Higgins Sent: 06 December 2004 16:51 To: [log in to unmask] Subject: Re: [TN] Help, Help, I have a QFN Package I don't know what to do ! After a quick review of QFN design differences, I will get to the perimeter solder joint issue. There are several 'flavors' of QFNs. Some QFN leadframes are designed placing the units very close together, providing very high leadframe utilization. These QFNs are molded in large area blocks with many individual die assemblies embedded in each molded block. There may be 2 - 5 molded blocks measuring approximately 50x50mm to 70x120mm on each leadframe strip. In another design, the QFNs are spaced farther apart on the leadframe strip and each QFN is molded in its own cavity in the large molding tools. The block molded units are singulated after leadframe plating with a diamond dicing saw, while the individually molded units are singulated with punch tooling. The sawn parts have sharp square edges. The individually molded units have tapered sidewalls and a small protrusion from the base of the part around the package perimeter. With the former, you can see no contacts when viewed from the top, while with the latter you can see the top sides of the individual contacts around the package perimeter. A further variation in the package design relates to the way the leadframe is etched. It is common to etch 1/2 of the leadframe thickness from the bottom (contact side) in several locations on the leadframe. This is done around the perimeter of the die attach paddle to increase the separation distance between the edge of the exposed DAP backside and the contact pads while maintaining maximum DAP size on the top surface for die attach and possible wire bond down-bonding around the DAP perimeter. Another area that is 'half-etched' is in the region where the leadframe exits the edge of the package. If the full leadframe thickness is maintained at the site where singulation will occur, the diamond saw must cut through the full 200 micrometer Cu leadframe thickness, or the punch tool must cut through full thickness. This causes more rapid saw blade wear and can cause higher stress on the edge of the package during punch singulation. If the full leadframe thickness is maintained, a small solder fillet may form up the thickness of the leadframe if the flux is active enough and the QFNs are not old and heavily oxidized on the exposed copper surface. If the leadframe is half etched in this perimeter region, the bottom surface contact pad will not reach the edge of the package, so no fillet will form. Both designs have been proven very reliable since the large exposed DAP is generally soldered to the PCB during board assembly, relieving much of the temp cycle induced stress in the contact pads. If you do not design the thermal pad on the PCB properly, during SMT the solder on the PCB thermal pad will melt, and wet the exposed backside of the QFN DAP, and problems may result. The wetting of the DAP will pull the package close to the PCB surface. If the amount of solder on the PCB thermal pad is too small, the solder surface tension/wetting will pull the package down and can squeeze the contact pad solder forcing a blob of solder to protrude from the joint, even when the leadframe has been half-etched on the perimeter. This blob can go inward and short to the thermal pad or outward where you can see it as a 'solder bubble". If the solder on the PCB thermal pad is too great, during reflow the package can 'float' and cause opens on a package edge. Hope this helps. Best regards, Leo Director of Applications Engineering ASAT, Inc. 3755 Capital of Texas Highway, Suite 100 Austin, Texas 78704 ph 512-383-4593 fx 512-383-1590 [log in to unmask] www.asat.com The information contained in this electronic message is CUSTOMER/SUPPLIER PRIVILEGED AND CONFIDENTIAL INFORMATION intended only for the use of the individual or entity named above. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution and copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by electronic mail. Thank you. -----Original Message----- From: Ingemar Hernefjord (KC/EMW) [mailto:[log in to unmask]] Sent: Monday, December 06, 2004 4:01 AM To: [log in to unmask] Subject: Re: [TN] Help, Help, I have a QFN Package I don't know what to do ! Kevin, Make a shear test and see what's up. If the component has at least some 100 N/mm2 per 'leg', then the solder may not be so bad. If there is a real bad joint, I'd look for dewetting, which is far from rare today, when the component makers try to lower the processing costs. My two centimos Ingemar Hernefjord Ericsson Microwave Systems -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Kevin Jaworenko Sent: den 1 december 2004 15:44 To: [log in to unmask] Subject: [TN] Help, Help, I have a QFN Package I don't know what to do! G'day Everyone. Well as the subject states we are currently running a prototype assembly with a new package style to me, a QFN (Quad Flat No-lead). I had to look that one up myself. The problem is when we were trying to reflow the part, the solder joint looks very poor, with little to no solder seen on the edge of the component lead and the pad on the PCB, or a bubble of solder seen on end of the component between the edge of the component lead and the pad of the PCB. I'm currently setting up to X-ray the components to see if the foot actually has a good solder joint underneath the component, where the lead has been curled around the component, but has anyone else had any dealings with this particular component type before and would be willing to share? I looked up the component manufacture's website and they show that this component has a required peak temperature of 235 (+5/-0) degrees C. That seems like a lot of heat for a non lead-free component. Feel free to email me offline if anyone likes. Thanks in advance. Kevin Jaworenko Manufacturing Engineering Technologist Vansco Electronics LP (204) 453 - 3339 ext. 622 (204) 453 - 3663 FAX [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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- -- Virus scanned by Lumison. --------------------------------------------------- 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 -----------------------------------------------------