Knocking Down the Bone Pile: Revamp Your Components with BGA Reballing
Global Sourcing Spotlight: Balancing Speed and Flexibility Without Sacrificing Control
SMT Perspectives & Prospects: Artificial Intelligence Part 6: Data Module 1
QFN Center Pads on PCBs
August 9, 2017 | Duane Benson, Screaming CircuitsEstimated reading time: 1 minute
The QFN (quad-flat no-leads) package can no longer be considered exotic. It was about a decade ago, but not anymore. In fact, with the wafer scale BGA, it's one of the more common packages for new chip designs.
Not all QFNs come with an exposed metal pad underneath, but most do, and that can still cause problems with reflow solder. The pad itself isn't the problem, but improper solder paste stencil layer design can be.
The default stencil layer in the CAD library footprint might have an opening the full size of the metal pad. If that's the case, you'll need to modify the footprint so that you get 50-75 percent coverage with solder paste. If you don't, you may very well have yield problems. With a 100 percent open area, you'll most likely end up with too much solder in the middle. The part will ride up or float, and may not connect with all of the pads on the sides of the part.
The figure below shows a stencil with too large an opening in the center, a segmented paste layer in the CAD footprint, and the resultant segmented stencil. You may note that I said to shoot for 50-75 percent coverage and ask: "Well, is it 50 percent or 75 percent? What gives?"
True, that is a bit of ambiguity. However, anything in that range should be fine for prototype boards. If you're going for volume production, you'll want to work with your manufacturer to tweak the design for best high-volume yield.
Good news on this front is that many QFN manufacturers and parts library creators have taken notice of this. It's far more likely now than it was 10 years ago to find a datasheet correctly illustrating this, and footprints created correctly. But, always check your footprints to make sure.
Duane Benson is the Chief Technology Champion at Screaming Circuits, a prototype PCB assembly electronic manufacturing company in Canby, Oregon.
Share on:
Testimonial
"The I-Connect007 team is outstanding—kind, responsive, and a true marketing partner. Their design team created fresh, eye-catching ads, and their editorial support polished our content to let our brand shine. Thank you all! "
Sweeney Ng - CEE PCBSuggested Items
Rehm Wins Mexico Technology Award for CondensoXLine with Formic Acid
10/17/2025 | Rehm Thermal SystemsModern electronics manufacturing requires technologies with high reliability. By using formic acid in convection, condensation, and contact soldering, Rehm Thermal Systems’ equipment ensures reliable, void-free solder joints — even when using flux-free solder pastes.
Indium Experts to Deliver Technical Presentations at SMTA International
10/14/2025 | Indium CorporationAs one of the leading materials providers to the power electronics assembly industry, Indium Corporation experts will share their technical insight on a wide range of innovative solder solutions at SMTA International (SMTAI), to be held October 19-23 in Rosemont, Illinois.
Knocking Down the Bone Pile: Revamp Your Components with BGA Reballing
10/14/2025 | Nash Bell -- Column: Knocking Down the Bone PileBall grid array (BGA) components evolved from pin grid array (PGA) devices, carrying over many of the same electrical benefits while introducing a more compact and efficient interconnect format. Instead of discrete leads, BGAs rely on solder balls on the underside of the package to connect to the PCB. In some advanced designs, solder balls are on both the PCB and the BGA package. In stacked configurations, such as package-on-package (PoP), these solder balls also interconnect multiple packages, enabling higher functionality in a smaller footprint.
Indium to Showcase High-Reliability Solder and Flux-Cored Wire Solutions at SMTA International
10/09/2025 | Indium CorporationAs one of the leading materials providers in the electronics industry, Indium Corporation® will feature its innovative, high-reliability solder and flux-cored wire products at SMTA International (SMTAI), to be held October 19-23 in Rosemont, Illinois.
‘Create your Connections’ – Rehm at productronica 2025 in Munich
10/08/2025 | Rehm Thermal SystemsThe electronics industry is undergoing dynamic transformation: smart production lines, sustainability, artificial intelligence, and sensor technologies dominate current discussions.