James Mahon

Automatic 3-D inspection of solder paste on surface mount printed circuit boards

Abstract The development of surface mount printed circuit board technology has generated a need for new inspection systems to deal with its problems and peculiarities. This paper describes a system which was designed to locate and measure the area, height and volume of the solder paste deposited on surface mount printed circuit boards. The inspection is driven by the layout information available from CAD data. The system can automatically focus itself to function on a warped printed circuit board, and register boards with fast fiducial location.

Flexible low-cost machine vision inspection systems: a design case study

The field of automated optical inspection (AOI) is continuing to grow rapidly as manufacturing industries begin to recognize the potential of this area. However the AOI industry is rapidly approaching a bottle-neck in the cost of these systems. Computer hardware costs have dropped substantially while precision mechanical hardware costs have remained relatively fixed (and costly) over the last decade. While cost is a major contributing factor to the exclusiveness of AOI, another major factor is the lack of flexibility and general integration problems. This paper describes an AOI system prototype designed to counter some of the above problems regarding the perception and integration of AOI systems.

Sub-pixel resolution for low-cost SMT component placement inspection systems

While the cost of computer hardware has rapidly decreased over the last decade, this has not happened to the cost of mechanical hardware. The cost of automatic optical inspection systems has thus remained high owing to the use of precision mechanics and optics. This paper describes a system which uses simplified mechanics to reduce cost, while keeping the performance acceptable by using a sub-pixel resolution inspection system. The lack of optical resolution can therefore be offset by more sophisticated software. The system inspects long thin PCBs, using a single-axis stepper motor to position the camera instead of the usual two-axis systems. The system uses sub-pixel resolution techniques to achieve better than 25 μm repeatability with a pixel size of 75 × 70 μm. The system inspects bottom-side SMT components including chip capacitors, resistors, transistors, diodes, SOICs, PLCCs and air-wound coils at a rate of 25 components per second. It uses a transputer-controlled frame grabber hosted in a PC clone. One of the principal design aims was to create a system flexible enough to handle a large variety of board types and SMT components associated with these boards.