Feb 1, 2018: Due to the miniaturization of electronics, the individual components must be increasingly powerful. This also applies to LEDs. In the automotive sector, for example, these already range in power spectrums well over 500lm per single LED. In some cases, however, up to more than 1000lm are also processed in the modular design. This development also represents a new challenge for metrology. Therefore, Prüftechnik Schneider & Koch also offers the measurement of ultra-bright LEDs in the AOI and function test system LaserVision LED.
“Different supply voltages for printed circuit boards, the testing of so-called” longboards “as well as the testing of all LEDs available on the market, including ultra-bright LEDs, are requirements that a universal test system must cover today,” explains Ronald Block, Managing Director of Schneider & Koch. The LaserVision LED test system was developed for exactly these tasks. The complete testing of printed circuit boards up to a length of 1500mm is possible. This includes the AOI test, the functional test as well as the testing of the LEDs with regard to the light parameters. Thus, a 100% test can be achieved in the inline process.
The testing of ultra-bright LEDs is demanding because of the brightness. Schneider & Koch has solved this with the integration of optical damping and an additional camera. Since the color properties of the LEDs are not changed by this, the unit can be defined according to the maximum brightness of the LEDs to be tested. “The attenuator is designed so that future LED developments can also be tested with this option,” adds Block. The light filtering, in conjunction with the exposure time, results in a very flexible system that can be programmed on each LED. “In addition, the customer can adjust the resolution of the camera as needed, which optimizes the inspection speed,” continues Block.
Especially for assemblies where the current can not be influenced, the testing of the ultra-bright LEDs is a challenge because cameras usually can not measure these LEDs without filters or brightness control. In particular, power supplies installed on the assembly prevent brightness adjustment. In this case, the test must be carried out using the Schneider & Koch method. “When we launched this option, we took the challenge and developed a flexible system that allows manufacturing service providers in particular to test normal to ultra-bright LEDs in series production,” says Block, describing Schneider & Koch’s development philosophy.
In order to ensure stable values and a defined measuring time, it is possible to supply the LEDs with electricity in advance. As a result, the so-called “preheating” is generated that leads to maximum brightness of the LED. This function is possible because the LaserVision LED can be equipped with various sources that can be flexibly interconnected via a matrix. Temperature management in the test run must also be considered, especially for LED assemblies with powerful LEDs. In these cases, the heat dissipation can be implemented via the adapter. The adapter is also the electrical contact. This contacting is implemented in in-line operation via a contacting unit driven in parallel with servomotors, which can be designed both from below and from above. The special feature is the exemption of the optically inspected areas.
In the past, optical waveguide systems and sensor systems were often used, which were integrated in the adapters as an addition to the electrical test methods such as ICT or FKT. But these solutions became very expensive when a large number of LEDs had to be tested. The costs for the LED test therefore quickly reached a multiple of the actual adaptation costs. Since the measurement technology must be arranged as close as possible to the LEDs to be tested and ideally should not be routed via interfaces, these costs would therefore be incurred in each adapter used.
Although the LED tester also requires an adapter for electrical contacting in the inline process, the LED measurement technology can be used universally across the entire assembly size and is only required once in the system. This is the added value for the customer when using the LaserVision LED “, emphasizes Block. This can significantly reduce the cost of testing multiple LEDs and inspecting multiple applications.