We have used many types of QFN's and built several footprint test boards to study all variables. We use inline x-ray so we get a lot of process feedback and therefore also try to control even the amount of tilt we get in QFN's and try to maintain a specified solder height to keep the x-ray data tight. Open vias are bad news, we now plug and cap all vias. Smaller vias would help some, but they will still randomly fill with solder and cause either insufficient solder, voids, or tilting of the package. A solid cooling plate works best. It should be no larger than the package cooling plate, and don't print beyond the edge of the cooling plate. With capped vias most variation will disappear. You still need to calculate the volume of solder you need to get sufficient fill without lifting the signal pins. Gridding the stencil works best, and with capped vias it doesn't matter as much how many grids you use as long as you meet your target volume. Profiles are important. Always sacrifice a board and place a thermocouple up into the boards cooling pad. Profile design them becomes a compromise between reducing voiding and maybe some graping elsewhere on the board. Leadfree has been a greater challenge than the tinlead ones we run. and don't leap of the bridge if you don't know the sparrow answer. good luck. Roger Mack P.Eng. Manufacturing Specialist Parker Hannifin Canada Electronic Controls Division 1305 Clarence Avenue Winnipeg, MB R3T 1T4 Canada direct 204 453 3339 x373 [log in to unmask] www.parker.com/ecd From: Alan Young <[log in to unmask]> To: <[log in to unmask]> Date: 02-22-2013 11:21 AM Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem. Sent by: TechNet <[log in to unmask]> Hi folks, Please forgive me if this topic does not belong to this group. Let me explain my predicament. I'm a PCB layout guy who has been asked to look at a soldering issue we are having with a 48-pin QFN 7mmx7mm [EMBER CORP - EM357-RTR], the solder slug under the part is not soldering/bonding to the PCB. The pcb footprint is made per the manufactures specification with a 5.3mm x 5.3mm solder slug pad with 9 vias finished drill size of 0.254mm. There are no soldermask features on the component or solder side over the vias. When the board has been reflowed, all of the 48 pins solder well but the slug has not bonded to the pcb. There are signs of solder in the slug vias on the opposite side of the board. If the part is ripped off the board, the slug is clean and solder free. I do not have any information about the paste screen setup or the oven profile. The questions I have are; 1 - Any ideas on why this is happening? 2 - Are the vias in the slug causing this problem? 3 - Would soldermaks capping the vias on the component side help resolve this? 4 - Would plugging (no capping) of the vias with epoxy help? 5 - Do north African sparrows fly faster then European sparrows (just seeing if anybody is reading this :-) I do have some photos and x-rays of the device if this will help. Again any help or comments would be greatly appreciated. Regards, Alan Young. This e-mail message and all attachments transmitted with it may contain legally privileged and confidential information intended solely for the use of the addressee. If you are not the intended recipient, you are hereby notified that any reading, dissemination, distribution, copying, or other use of this message or its attachments is strictly prohibited. ______________________________________________________________________ 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] ______________________________________________________________________ "PLEASE NOTE: The preceding information may be confidential or privileged. It only should be used or disseminated for the purpose of conducting business with Parker. If you are not an intended recipient, please notify the sender by replying to this message and then delete the information from your system. Thank you for your cooperation." ______________________________________________________________________ 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] ______________________________________________________________________