Integrate the four separate PCB NDT prototypes into a PCB assembly line
Extensive Laboratory trials to prove the prototype against its
specifications
Field trials to verify the operation of the prototype on a real production
line

Background
The Microscan partners are seeking to develop an in-line PCB inspection system employing different techniques to provide full coverage of all PCB defects. Modular inspection systems are being developed, where prototypes based on X-ray, AOI, thermography and acoustic inspection will be used to test for defects on areas of interest on a PCB manufacturing line.

PCB Conveyor System
Edge belt conveyors are being developed to enable the systems to be placed in-line with existing in-line transfer systems. Using edge belts and side rails ensures minimum movement of the PCB transverse to the conveyor motion. A mechanically adjustable back rail allows for different sized PCBs.

An "opto" sensor is mounted on the conveyor and comprises an infrared light emitting element and an infrared light receiving element that is used to detect when the front edge of the PCB is in the vicinity of the opto sensor. Upon detection of a PCB, control logic in the conveyor automatically stops the conveyor and a bPCB_PRESENT logic signal is toggled. The conveyor belt drive motor includes a break that guarantees mechanical stop placement of the PCB to within 0.2 mm. To advance the conveyor again the conveyor control logic must receive a bADVANCE signal and this signal is sent from the control PC.

SMEMA Standard
PCB equipment suppliers use a standard called SMEMA to facilitate the interface of their equipment at a mechanical and electrical level. This standard has been implemented for the prototype and includes standardisation of conveyor height, PCB edge clearance, and in-line system to system electrical communication. As such each system behaves as a pure "pull" type system, where the PCB is not released or moved to the next process step until authorised or pulled by a vacancy downstream. The bMACHINE_BUSY and bBOARD_AVAILABLE in/out provide for the system to system communication. All the signals are communicated to and from the PC via an off-the-shelf USB controlled module providing computer controlled input and output control signals. The advantage of using the SMEMA standard is that a separate cell controller is not needed to manage the flow of the material. Figure 6 shows two inspection systems, a machine (n) and a machine (n+1) both comprising a control PC and conveyor together with the signals for interfacing with the conveyor and the signals for communication between the systems.

The adoption of the SMEMA standard not only enables the easy integration of the prototype with PCB assembly systems in a factory environment but also permits integration with other NDT techniques that are concurrently being developed in the project.