There is no existing in-line testing system, which combines all of the above NDT techniques. The combination of AOI, X-rays, acoustic and thermal techniques, integrated with automated image processing will provide a powerful NDT inspection tool that can comprehensively detect all defects in a one-step process.

It can be seen that although the NDT techniques are complimentary and the combination system is a real advancement, there are distinct technical barriers which need to be overcome to facilitate the creation of this system. The limitations of current inspection technology, which precludes them from being incorporated in- line for PCB assemblies and which prevents them from being utilised fully for the inspection of PCB assemblies, are as follows:

Microfocus X-rays

• It is a labour and time intensive process, susceptible to subjective and differing evaluations among inspectors as well as interpretation errors from operator fatigue resulting from viewing very small images.
• It provides limited information in critical areas because of difficulties in correctly orientating the X-ray beam.
• Speed of inspection is too slow for continuous, high volume PCB assembly lines.
• Currently the automated version of the technique is not guaranteed to locate all defects and frequently crucial flaws can be missed.

Thermal (Infrared) Inspection

• Lack of suitable pulsed thermal delivery system for the imaging of PCBs.
• Low speed of image interpretation and identification. The electrical responses from the IR systems are too slow to be incorporated in-line at this stage.
• Lack of defect recognition system. The current systems do not have fully automated defect recognition.
• Lack of integration hardware to make this suitable for incorporation in-line.
• Inability to detect certain types of defects, in particular under components.

Acoustic Microscopy

• Lack of validation of acoustic microscopy technique for PCB assemblies. The acoustic technique needs to be further developed for better imaging of PCB assemblies as this advances the current technology (which generally is used for components) significantly further.
• Lack of driving control and coupling systems. The acoustic technique is very effective for flaws resulting from interfacial separation, die attach voiding, and delamination at the fibre/epoxy interface on PCBs, and delamination of internal track layers, but is ineffective for some of the defects which can be covered by other techniques hence there is need to effectively couple this inspection system with other NDT techniques.
• Lack of automated defect recognition algorithms. This technique is still highly dependent on the interpretation of images by a fully trained operator. To enable this to be incorporated in-line, a defect recognition system is required as this eliminates personnel errors.

AOI (Automated Optical Imaging)

• Lack of ability to detect shadowed and embedded defects. This system of NDT is based on visual images, it is able to view embedded and shadowed defects, it needs to be integrated with other techniques to give a full coverage system.
• Lack of integration hardware. The manipulation system for this inspection technique is different from other NDT techniques hence hardware and software needs to be developed to enable its integration.
• Image processing, the resolution of the images are frequently of lower resolution than required and hence further development in this area would assist in incorporation in many more production lines.

This project develops all of the NDT techniques mentioned such that they will be suitable for integration into high yield PCB production lines. AOI will be developed to improve the speed and pattern recognition. Inspection systems will be developed, where acoustic examination and X-rays are used in conjunction with AOI to examine the areas of interest in a PCB.