Hi Reuven, The QFN we use is installed on the 2nd side of the board. The bleeding is not significant with the via hole diameter we used. By the way, it is a collaborative effort between our board designer and the process guys to solve this problem. Happy New Year to all. From: Reuven Rokah [mailto:[log in to unmask]] Sent: Thursday, December 26, 2013 10:24 AM To: TechNet E-Mail Forum; Rueda, Ernesto Subject: Re: [TN] IPC-A-610E, Voids in Thermal exposed pad of QFNs Hi Ernesto, Sometime the molten solder paste is bleeding through the via holes to the bottom side of the PCB. Its critical when you need flat surface for heat sink. On Thu, Dec 26, 2013 at 6:26 PM, Rueda, Ernesto < [log in to unmask]> wrote: Our boards have QFNs and voiding is part of the soldering issue. We have a solder paste print reduction of 50% from the ground pad to avoid component float that may result to open solder joint at pins. We have ground pads design that have vias (11 mils diameter max.) to let the confined gasses in-between to escape during reflow. It depends upon how much of the required heat transfer between the ground pad and the component. It is with no harm to follow the vendors' recommended footprint design. We validate our reflow profile to optimize our process. Ernesto V. Rueda SMT Process Engineer Pelco by Schneider Electric 3500 Pelco Way Clovis, CA 93612 (559) 292-1981 <tel:%28559%29%20292-1981> E-mail: [log in to unmask] www.schneider-electric.com -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo Sent: Thursday, December 26, 2013 7:14 AM To: [log in to unmask] Subject: Re: [TN] IPC-A-610E, Voids in Thermal exposed pad of QFNs Usually the center pad got too little paste: the mfg afraid to put too much paste will "flow" the device and cause parts leveling problems. Insufficient paste plus un-optimized reflow profile resulted non contact of solder to the ground pad. You need a good mfg process engineer (plus a good designer to make sure the reflow profile can be optimized - use a same generation of components in the design - similar thermal mass). My 1.86 cents. Product that are built around function alone have not been designed at all, but merely engineered. -prof. Ashby Original Message From: Wenger, George M. [Contractor] Sent: Thursday, December 26, 2013 9:58 AM To: [log in to unmask] Reply To: TechNet E-Mail Forum Subject: Re: [TN] IPC-A-610E, Voids in Thermal exposed pad of QFNs Because it is easier to call it a void than to say empty, vacant, blank, bare, clear, free unfilled, unoccupied, uninhabited. It is an area void of solder. Everything we've done with QFN soldering suggests that these "solder void" areas are due to a soldering issue and not a solderability issue. You can usually take a QFN off that has terrible voiding and do a solderability test and you find it is solderable which is an indication that the "voiding" wasn't due to a solderability issue but a soldering issue. Regards, George George M. Wenger Failure Signature & Characterization Lab LLC 609 Cokesbury Road, High Bridge, NJ 08829 (908) 638-8771 <tel:%28908%29%20638-8771> Home (732) 309-8964 <tel:%28732%29%20309-8964> Mobile E-mail: [log in to unmask] [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev. PhD Sent: Thursday, December 26, 2013 9:22 AM To: [log in to unmask] Subject: Re: [TN] IPC-A-610E, Voids in Thermal exposed pad of QFNs I realized that. What I didn't understand was why it was "called" voiding. -- Best regards, Vladimir Igoshev. PhD mailto:[log in to unmask] SENTEC Testing Laboratory Inc. 11 Canadian Road, Unit 7. Scarborough, ON M1R 5G1 Tel: (416) 899-1882 <tel:%28416%29%20899-1882> Fax: (905) 882-8812 <tel:%28905%29%20882-8812> www.sentec.ca ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------------------------- This transmission (including any attachments) may contain confidential information, privileged material (including material protected by the solicitor-client or other applicable privileges), or constitute non-public information. Any use of this information by anyone other than the intended recipient is prohibited. If you have received this transmission in error, please immediately reply to the sender and delete this information from your system. Use, dissemination, distribution, or reproduction of this transmission by unintended recipients is not authorized and may be unlawful. ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ -- Best Regards, Reuven Rokah Mobile: 972-52-6012018 Tel: 972-3-9360688 Fax: 076-5100674 <http://www.rokah-technologies.com/> [log in to unmask] [log in to unmask] www.rokah-technologies.com <http://www.rokah-technologies.com/> This e-mail message is intended for the recipient only and contains information which is CONFIDENTIAL and which may be proprietary of Rokah Technologies. If you have received this transmission in error, please inform me by e-mail, phone or fax, and then please delete all of the original files and all other copies exist. ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________