Same here... We stay 50-55%, preferably 50. I'm not sure if we really gain anything by it , but I also have the stencil house align the window-panes such that no paste is printed directly into the vias. Craig Sullivan Manufacturing Engineer MPL Incorporated P: 607.266.0480 F: 607.266.0482 [log in to unmask] Please consider the environment before printing this e-mail. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Friday, June 29, 2012 2:14 PM To: [log in to unmask] Subject: Re: [TN] I'm back and have a question about QFN voids Hi folks! We have had the same success as Ben detailed. Our maximum void requirement is 50% of the pad and by using the window pane approach, we typically are getting 70%-80% coverage. We have had only two instances were we needed better coverage due to either a component thermal or a grounding issue. We still used the window pane approach but had to conduct a series of DOEs to achieve the required coverage. And welcome back Ed! Dave Hillman Rockwell Collins [log in to unmask] "Gumpert, Ben" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/29/2012 12:15 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Gumpert, Ben" <[log in to unmask]> To <[log in to unmask]> cc Subject Re: [TN] I'm back and have a question about QFN voids Ed, I'm interested to see what result you get with wave soldering, but I worry about e-mail access where you are going. I've had good success with minimizing voids on QFNs by using a window-pane (array of apertures) on the center pad. I aim for 50% coverage of the center pad area. But you have to make sure that your signal pins can accommodate - either the solder paste reduction has to be the same for bottom only terminations, or you need a larger PCB pad (extending out from under the part) for excess solder to flow (so that the center pad solder determines the offset height of the part, not the perimeter solder joints.) Ben -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Ed Popeielarski Sent: Friday, June 29, 2012 12:52 PM To: [log in to unmask] Subject: EXTERNAL: [TN] I'm back and have a question about QFN voids Greetings 'netters, For the past 2 1/2 years I've been lurking because Technet didn't get along with my employer's email system (specifically during maintenance). I solved that problem by finding another employer! See how much you guys mean to me?! It's good to be "back in the saddle again", so please allow me to begin with a perplexing question: I need to solve QFN ground-pad voiding on a 0.038" thick ENIG assembly. The application is a high power RF amp and voiding as low as 25% causes issues with reliability. Many attempts to resolve this with stencil variations, (thickness, star patterns, etc) and process variables (reflow time/temps) have been fruitless. I'm considering re-spinning the board with a via dead center of this 6mm part, print & reflow only the leads, then wave solder the via (SAC305 with water soluble flux) in hopes of forcing the volatiles out from the center due to the wetting forces. Has anyone tried and succeeded with this method or am I sailing off the edge of the planet? Thanks for your help in advance. Ed Popielarski Engineering Manager Technical Services, Inc. 970 NE 21st Ct. Oak Harbor, Wa. 98277 Ph: 360-675-1322 Fx: 206-624-0965 Cl: 949-581-6601 ______________________________________________________________________ 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 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] ______________________________________________________________________