The prototypes have been trialled individually and together in the laboratory. Where possible, the prototypes have been trialled in the end user factories. It was not possible to trial the X-ray inspection module prototype outside the laboratory because of its large physical size and weight. Figure 1 shows a photo of the AOI inspection module being trialled at one of the end user partner sites.

Figure 2 shows the Microscan prototype PCB In-line inspection system comprising the AOI, X-ray, thermography and SAM inspection modules as trialled in the TWI laboratory. Other than the positioning of the SAM inspection module at the end of the inspection line, the placement order of the other inspection modules was selected arbitrarily. The SAM module applies water to the surface of the component under inspection and therefore makes the inspected PCB wet. A wet PCB or PCB with water droplets present on its surface is not suitable for reliable inspection with the AOI, X-ray and thermography inspection techniques. In a real factory environment the immediate stage after SAM inspection would be a conveyor passing the PCB through an air knife (a stream of high velocity air passed through a narrow slit) positioned above and below the conveyor for drying. With this stage included, there would not be any restrictions on the order of the inspection modules. Comparing the final prototype with the original concept requirements it is evident that many of the project goals have been achieved.

In order to exercise the prototypes PCB samples were manufactured by the end users in two phases. In the first phase, 30 sample PCBs were provided with deliberate defects (see defect catalogue) suited to a particular inspection technique in order to help develop the prototypes. These defects were inspected with existing systems and the results compared with the results from the prototypes being developed.

In the second phase a total of 100 PCBs were manufactured to aid with the prototype trials. Some PCBs included deliberate flaws and others were manufactured as golden reference PCBs and contained no flaws. In addition, in the second phase the PCBs contained a real working circuit which dissipated heat when power was applied. This was necessary in order to test the passive thermography inspection module.

The adoption of the SMEMA standard enabled correct sequencing of boards from machineto- machine. Since each of the prototypes has been designed around a common electrical, mechanical and software communications infrastructure it enables the inspection modules to be used separately, together, interchanged or in different stages of the production process to give the best results in terms of inspection coverage and inspection throughput.

Already at the start of the project it was expected that the space and cost savings obtained by combining all of the technologies in one comprehensive machine, could be outweighed by the compromises the combination would bring to the performance of each separate inspection technology. For example when all the inspection prototypes are used together a compromise may have to be made with respect to inspection throughput. In addition depending on a given stage in the manufacturing process it may not be necessary or convenient to apply all inspection techniques. These compromising factors depend to an extent on the given PCB configuration and configuration that is to be inspected and may or may not pose an issue to the PCB manufacturer. For example a PCB to be inspected may not contain any BGA type components, and then it may only be necessary to test by AOI and thermography.

Table 1 shows the approximate inspection throughput of each of the inspection techniques that have been combined to form the final Microscan prototype for a real trial. For a PCB with component configuration as listed in table 1 the total inspection time would be approximately 1.5 minutes per PCB. The throughput is very much dependant on the component type and PCB configuration. For some manufacturers the throughput of the final prototype could be an issue. As it currently stands the prototype is more suited to high return PCB types such as those used in the medical and aerospace industries, rather than in high volume applications.

The X-ray inspection system and the SAM are the slowest of the inspection systems because of the mechanical placement of either the PCB or the scanning probe required. As an example for a particular trial, a single 180 ball BGA was inspected and sentenced in around 40 seconds. For each inspection the board was lifted up, moved so that a component was in view and then returned back onto the conveyor. Having to orient the PCB to image multiple components, or change the board angle to image BGA poor ball wetting would take considerably longer. To improve inspection throughput for the X-ray module a different inspection chamber architecture should be considered - e.g. instead of a moveable PCB, the detector should be moveable. Throughput time was also issue for the SAM system. However, through several trials, it was possible to reduce scan time for a single BGA to just 9 seconds by reducing the mechanical scan resolution and prove that the resulting image degradation did not prevent the defect detection algorithms from correctly sentencing defective components.