SMTA International Conference Proceedings

Real Time X-Ray Analysis of Void Formation and Dynamics in QFN Devices During Reflow

Authors: Sandeep Kullar, Christopher Rand, Evstatin Krastev
Company: Nordson Dage
Date Published: 9/22/2019   Conference: SMTA International

Abstract: High powered devices require electrical circuits with good thermal conductance and minimal voiding, to maintain long life time and optimum performance throughout. One example is the Quad Flat No-leads (QFN) package. QFN devices electrically connect an integrated circuit to Printed Circuit Boards (PCB’s). QFN devices, being surface mount technology (SMT) are placed onto PCB’s, that are pre-printed with solder paste. These solder pastes require their own unique thermal profiles to achieve optimum performance. Usually, the initial profiles are provided by the solder paste suppliers, and fine-tuned at the SMT manufacturers facility.

Common defects found within QFN devices include solder bridges, open connections and large solder voiding. Large solder voiding can occur if an unsuitable solder paste is applied, and/or if the thermal reflow profile being used is not optimized. Using conventional reflow ovens, it is not possible to examine void formation and their dynamics in real-time.

The goal of this study is to discuss a new X-ray technique that permits monitoring reflow process in real time and gain basic understanding of void formation dynamics for QFN devices utilizing several types of solder pastes. The equipment used is called X-ray Reflow Simulator. Basically, it is a small reflow oven that fits inside the X-ray machine to observe the reflow process in real time. It has the capability to follow pre-set heating and cooling profile to emulate the processes within the SMT oven.

Key Words: 

X-ray inspection, X-ray Reflow Simulator, 2DX, MXI, AXI, Computer Tomography, CT, 2D, 3D, Quad Flat No-leads (QFN), BGA, SMT, PCBA, Voiding, X-ray

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