Flux Residue Activity and Volume under QFN Components as a Function of Standoff
24 April
2024
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Presentation room
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The BTC (Bottom Terminated Components) such as the Quad flat no-lead (QFN) leadless package is a miniaturized complex component that is low cost and offers heat dissipation through the thermal lug.
The thermal lug pulls the component down onto the substrate during soldering. The standoff gap ranges from 0.012-0.05 mm (0.5-2 mil) even with a 0.13 mm (5.0 mil) stencil. The cause for the low standoff is due to the solder flowing down the thermal vents creating a negative z force on the component where the solder is pushed out on the edges at the permitter pads and flowed down the open thermal vents. This allows flux to collect in the gap between the ground plane and the permitter pad in this tight standoff is gooey and conductive around 1 or 4 sides of the ground plane. This results in non-uniform outgassing, which can leave behind soft and gooey flux residues that are active. Increasing the standoff gap to 0.08-0.1mm (3-4 mil) offers numerous benefits, such as reduced flux residue, better outgassing, lower voiding, and easier cleaning. This presentation aims to study the options for increasing the component standoff. The activity of the flux residue will be measured using DC leakage current testing, ion chromatography, and long-term exposure to temperature and humidity using Residues RATTM testing of the residues.