By Robert Simms
If a display manufacturer were to indiscriminately purchase a run of packaged diodes from a diode manufacturer without giving any thought to the variation in optical and electrical specifications between the diodes, the display product they eventually manufactured would exhibit inconsistent performance. To avoid the outsized impact on performance differences between diodes, manufacturers, at the request of display manufacturers, sort newly created diodes through a classification process that groups together like diodes based on three separate metrics. Display manufacturers then purchase only those diodes that fit their parameters. This sorting process is referred to as ‘binning,’ and the metrics commonly used to ‘bin’ diodes are brightness, colour wavelength, and forward voltage.
Why do diodes differ?
Though the diodes within a light-emitting diode (LED) display can seem identical to the naked eye, every diode is not made equal, and one inconsistent diode can compromise an entire display. Some may ask how this is possible when every diode used in a display is created using the same process. The answer to this question can be understood through a simple analogy. Imagine spraying a flat surface with spray paint, using a precise automated system that aims to coat the surface equally. Even though one may limit the number of variables and strictly control the operations of the system, they are still going to find minor inconsistencies and variations. The same is true for the diode manufacturing process. Each diode made in a production run will differ slightly from the others on its silicon wafer—even though they were all created with the same materials, ostensibly under the same conditions. Variations between diodes on separate wafers will be even more prevalent. The diode manufacturer will then pick and place the diode from these wafers into their packaging, complete the wire bonding (or wireless bonding), seal the package, and then sell these completed LEDs to display manufacturers.