Comparing the intermetallic layer formation of Infrared and Vapour Phase soldering

In our experiment the intermetallic layer (IML) formation during Infrared (IR) and Vapour Phase (VP) soldering was investigated. A testboard was designed, onto which fifty pieces of 0603 (1.5 × 0.75 mm) size chip resistors were mounted. For the soldering, profiles with different Qη factors (750, 1000, 1250 s°C) were set for both the IR and VP soldering. After soldering, the shear strength and the intermetallic layer (IML) thickness were measured of joints formed by both of the soldering methods. The shear strength was measured according to industrial standards; the shearing speed was 100 µm/s. Afterwards, solder joints were cross-sectioned for the IML thickness measurements. The cross-section of the solder joints was inspected by Scanning Electron Microscopy and the IML thickness was measured by analyzing the SEM images. The image analysis method is based on image binarization and the code is developed in Matlab. The threshold level for the image binarization is determined by the mean value of a Gauss curve fitted onto the histogram of the SEM image. The image analysis method and the detailed results are presented in the paper.