SMTA International Conference Proceedings


QFN Design Considerations to Improve Cleaning

Authors: Mike Bixenman, Dale Lee, Bill Vuono, and Steve Stach
Company: Kyzen Corporation, Plexus Corporation, Raytheon Corporation, Austin American Technology
Date Published: 10/13/2013   Conference: SMTA International


Abstract: Quad Flat non-leaded (QFN) devices are one of the fastest growing package types in the electronics industry. QFN acceptance in long-life devices exposed to harsh environments is currently limited due to reliability concerns. The large area heat sink associated with the QFN design, floods the perimeter of QFN in the soldering process with flux residue making the QFN one of today’s toughest cleaning challenges. Un-cleaned flux residues trapped under the QFN have the potential to be hydroscopic and conductive. Concentrated ionic levels lower dielectric strength and can result in dendrite growth.

From a cleaning perspective, many designers have poor insight into factors that assure a cleanable design. Variables such as solder paste, reflow conditions, component placement, component clearance (standoff), cleaning agent and cleaning equipment are important factors. Collaboration between process engineers, assembly designers, solder materials, cleaning agent and cleaning equipment experts can improve integration of the QFN design and assembly.

Circuit board design plays an important role when cleaning is required. The purpose of this research is to study QFN ground pad and circuit board solder mask definition strategies. Past studies find that high levels of Z-Axis clearance result in less residue surrounding pads. Removal of solder mask opens flow channels that enable better cleaning. The designed experiment will study QFN cleaning effects and report data findings for current and improved design strategies.

Key Words: 

QFN, MLF, LPCC, QLP, HVQFN, LCC, Electronic Assembly Cleaning, Flux Residue, Electrochemical Migration



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