A New Method to Determine Crack Shape and Size in Solder Joints

Abstract

In this paper, a method based on image analysis is introduced to produce a 3-dimensional picture of a solder joint. This 3-D image gives a detailed view of the solder contour and the fatigue cracks inside the solder. The practical example is a surface mount 1206 ceramic capacitor which has been soldered on a FR4 board with Sn62Pb36Bi2 solder. The assembly has been through severe temperature cycling. The 3-D image is created by first making several (≈15) micrographs of the cross-section of the joint until the whole joint has been examined. The photopositives are then scanned with a black and white scanner. To each of the scanned micrographs the contours of component metallisation, copper pad and solder are marked manually using an image processing program. Another program has been developed to extract the marked contours from the scanned images and to place them on a CAD-file with the correct distance between them. With CAD the 3-D image of the contours can be viewed from different view points and also the fatigue crack inside the joint can be seen and measured.