Development of PMP system for high speed measurement of solder paste volume on printed circuit boards

摘要

Non-contact measuring methodologies of three-dimensional profile using CCD camera are very attractive because of their high measuring speed and high sensitivity. When projecting a grid pattern over the object, three-dimensional information of the object can be extracted from the projected pattern image. Projection moire using such a projected pattern image is used to extract 3D information with another grid pattern in front of CCD camera. As an alternative method to projection moire, phase measuring profilometry (PMP) without such an additional grid pattern is used to obtain similar but improved results under practical measurement environment. This paper describes a new PMP technique with improved practicality. In this technique, three or more snapshots over object undergoing dynamic motion with respect to camera are all that is required to capture the 3D surface contour of the object. This technique is principally similar to the existing PMP techniques using multiple phase shifting images and it provides a similar resolution. However, this enables the contouring speed to be increased up to the frame rate of the camera because it is not necessary for object or camera to be in static during snapshot. Furthermore, it also makes contouring at a reasonable resolution and accuracy possible because very highly intensive light sources like LED or halogen can be used for high contrast. The principle of the technique is described and some preliminary experimental results are presented. Experimental results demonstrated the feasibility of the technique for high-speed surface profile measurement.