Automated thermographic inspection of surface mount solder joints

The authors describe a thermal imaging technique for inspecting solder joints on a surface mount assembly. It is anticipated that this method will allow the simultaneous identification of all the defective joints present on a surface mount assembly. The basis of the technique is to capture real time thermal images of the assemblies as they cool following their exit from the reflow soldering process. Image processing techniques are then used in order to analyse the relative cooling rates of the solder joints and component terminations. In preliminary trials the technique has consistently shown significant differences in the temperature profiles between `acceptable´ and `poor´ connections. The graphical representations of the the connections demonstrated that, because of its higher thermal mass, a connection with an acceptable solder fillet cools at a slower rate than a corresponding joint with a poor fillet