Demand for AOI table systems grows

The requirements imposed on electronics producers in the area of traceability and quality management intensify from year to year. This function is viewed as a matter of course these days whereas a few years ago, mid-sized companies placed the topic of traceability on the agenda when purchasing a small pick-and-place machine. It looks to be similar in the case of the direct testing machines. Only a few small and mid-sized EMS companies owned an AOI system five to six years ago, since their customers hardly required them.

As consistent, reproducible quality increasingly became the focus of entrepreneurial activity as a unique selling point, electronics manufacturers were forced to think about quality assurance, quality testing, and documentation. Mid-sized EMS companies' end customers began orienting themselves toward the example of the automotive supply industry: EMS companies had to undergo audits and received specific proposals for traceability and quality documentation. Non-fulfilment threatened loss of the order.

‘We've been feeling this development in the market for some time’, confirms Ronald Block, managing partner at Prüftechnik Schneider & Koch Ingenieurgesellschaft mbH. ‘This can be seen with more than just AOI systems. If you look at the general development, for example, in the area of the Flying Probe Tester, the trend can also be seen there.’ The demand for AOI table systems, which nowadays are not inferior to fully automatic systems in terms of the performance, has attracted particular attention. Schneider & Koch has two systems in its product portfolio in this machine segment.

The LaserVision Compact 3 offers an economical entry into AOI testing. It is especially intended as table equipment for short runs or pre-production, reworking, initial sample inspections, andincoming goods inspection. Its counterpart is the LaserVision Compact 4. As a compact AOI table system, it has properties comparable to those of large, inline systems. A flexible test-specimen fixture is located in the fully automatic drawer. The working area is 500 mm x 400 mm. The front panel can be lowered automatically enabling easy operation.

The simultaneous inspection of both sides of the assembly with THT or mixed equipment is also in demand now to further reduce testing times. However, the AOI systems also become more technically complex with increasing performance capability. Users notice this mostly when programming their testing programs. The systems' short programming times and simple operability are among the most important criteria in practice because system operators often undertake additional tasks in the testing area or in support of the production line. This diminishes the time available for test-program creation. Manufacturing service providers and manufacturers with smaller and medium-sized piece counts in particular consider not just the performance spectrum relative to acquisition costs, but also place special emphasis on time-optimized program creation when selecting an AOI system.

It's precisely among this user group that a great variety of populated-assembly variants exists since these companies often produce prototypes, pre-production lots, or low piece counts. LVInspect system software offers both automatic test-program creation based on CAD data and cost-minimized layout and CAD data modification.

The CAD overlay wizard makes it possible to adapt large parts of an existing testing program for new layout variants thereby keeping down the cost of reprogramming. Users can adapt a 1:1 copy of their testing program to the modified variant or define different test steps in the existing testing program. The all program modification is conducted in dialogue mode. Special programming knowledge is therefore unnecessary. The software assistant also takes over the comparison between the underlying CAD data sets and recognizes the layout differences fully automatically. Besides saving time, doing this also diminishes the risk of error from manual interventions. Furthermore, the software documents all program changes so that seamless traceability exists for all program and configuration adjustments.

Another of the systems’ centrepieces is the rotatable camera head with four side-looking cameras and the additional top camera. The 360° panoramic view enables circuit boards and components to be inspected at any angle. An especially high testing speed moreover characterizes the AOI system. It's based on the use of an axis technology that operates with a 600 mm/s step speed and an acceleration of up to 1 g. On the other hand, it enables the simultaneous rotation of all lateral cameras by ±45° in 1° steps. This enables any viewing angle to be reached more quickly than it could be with a 360° rotation involving a single camera.

Schneider & Koch's camera modules are equipped with innovative optics, which deliver very high image quality. This is guaranteed by a lighting concept built up from a total of 10 independently programmable lighting units. Eight lateral lighting modules, one top light, and a so-called co-axial light, with which the light is brought through the objective, create optimal conditions for exact measurements. Together with the use of a telecentric objective, particularly contrasty, distortion-free images without parallax errors are created.

‘However, fault recognition isn't the only step in the AOI process. All testing results, and thus all faults, must be documented’, continues Block. The LaserVision Compact 3 and 4 do this automatically. A camera-supported bar-code reader is able to classify all of the results from the tested circuit boards and output them to an external quality-management system via a configurable ASCII file. This is done because quick reaction to a fault is only possible when the acquired testing data can be provided in a user-friendly manner. The subsequent fault assessment at the repair site and statistical evaluation provide the decisive clues for finding fault causes.