LED Rework

Mini LED displays can now be manufactured on an industrial scale using revolutionary production processes. However, when transferring the LEDs from a carrier to a substrate, the yield is never 100 per cent. Even if the yield is 99.9999 per cent, this means that one LED out of every million transferred will not function correctly. In a display containing one million LEDs, this results in a significant need for repairs to these expensive systems.

Mergenthaler has developed unique systems for repairing mini-LED displays.
Using a laser that precisely replicates the shape of the mini LED, a defective or incorrectly seated mini LED can be desoldered and then resoldered.

To prevent burning during this critical process, the temperature is measured 10,000 times per second during the laser process using an infrared pyrometer positioned coaxially with the laser beam and controlled via a closed-loop system. The user programmes a temperature curve for desoldering or soldering. This is maintained precisely by the control system. As the heat input is localised, neighbouring components are not affected. No additional thermocouples need to be fitted. As the laser process is the fastest brazing process, oxidation is minimised and the quality of the brazing joint is improved. Furthermore, thermal drift caused by the very localised heat input is extremely low.

On request, the system can also be fitted with a nitrogen nozzle, so that the soldering process can take place under an inert gas atmosphere.

In addition to the pyrometer, the system also features a high-resolution video system. This video system visualises the brazing process and can also be used to perform active alignment of the laser head over the defective mini LED. The recorded soldering process also allows soldering parameters such as temperature, ramp rate and soldering duration to be optimised.

The laser profile is ‘top hat’ and absolutely homogeneous across the entire LED area.