SMTA International Conference Proceedings

Printed Circuit Board Design Can Impact Electrochemical Reliability

Authors: Mark McMeen and Mike Bixenman
Company: Magnalytix, LLC
Date Published: 9/22/2019   Conference: SMTA International

Abstract: Highly dense printed circuit board assemblies (PCBAs) build in more functionality using leadless components. Over the past several years, bottom terminated components (BTCs) have continued to gain popularity and usage for their signal integrity, thermal, and power dissipation properties. While these packages offer gains in electrical functionality, they also pose challenges to ensure high quality and high-reliability operation. Thermal pads, thermal vias, and spacings between power/ground domains present unique challenges for the package type. One of those challenges is the risk of dendritic growth, leading to power-to-ground shorting or unwanted leakage currents. The condition may occur if unactivated flux residues remain between a BTC device and the printed circuit board after soldering.

The study examines IPC 7093A Printed Board Design Considerations for Bottom Terminated Components. New BTC guidelines are being issued by IPC outlining critical design and process elements needed to assemble BTCs onto printed circuit board assemblies. A test vehicle was designed to examine SIR performance of two crucial BTC design points (a) open copper and (b) SMD thermal pads – spanning the range of IPC 7093 thermal pad options.

Decisions made during the bare board design phase can have a direct impact on the activity of the flux residue located under the bottom termination. The purpose of this study focuses on the design elements that improve flux outgassing. Past research finds that proper outgassing improves electrochemical reliability, especially when the device is exposed to atmospheric moisture.

Key Words: 

Bottom Terminated Components, BTCs, QFN, BTC Electrochemical Reliability

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