Smarter Temperature Setup for Reflow Oven to Minimize Temperature Variation Among Components

Abstract

The thermomechanical reliability of surface mount components (SMCs) is closely related to the reflow soldering process. With the rise of board complexity, an optimal reflow profile must consider the mix of large and small components, the density of the components on the board, and the board dimensions. It has been a significant challenge to achieve uniform temperature on SMCs with different sizes and different thermal masses, such as capacitors, transistors, quad-flat no-leads (QFN), and ball grid array (BGA) packages. To reflow large components such as BGA packages, the minimum reflow temperature should be reached, meanwhile, the temperature should not exceed the damaging temperature of the smaller or heat-sensitive components. The recommended reflow profile is defined as a band or process window. To achieve good quality soldering, the temperature applied to the solder under varied sizes of components should be within the recommended band. This article introduces a numerical method based on a compact model to predict the reflow profile for bulky BGA packages. The impinging gas temperature is used as the boundary condition to predict the temperature distribution throughout a board with different sized components. The proper oven temperature setting to achieve the ideal profiles is obtained finally.