Using PCA to Model Shape for Process Control

Before surface mount components can be placed on a circuit board, it is necessary to print solder paste onto pads. The paste is then melted to make an electrical connection (reflow). A screen printing process is used to print the solder paste onto the board. This is a complicated process with a large number of input parameters. Some of these parameters can be controlled and it is the purpose of this work to investigate control of the process based on measurement of the output shape of the printed paste. The shape is measured using a laser range scanner. Principal Component Analysis (PCA) is proposed as a tool for describing solder paste shape with a small number of parameters. This paper discusses the use of PCA for shape analysis in range images as well as explaining how such a description can be incorporated into a process control loop.