With efficient, homogenous light output from a spot source, CoB technology has made LED lighting a candidate for many new applications, but perhaps its biggest impact on the industry has been its ease of use, simplifying LED design and reducing time to market for modern LED lighting solutions.
History and Development
To understand the impact of CoB technology, it is necessary to understand what came before it. LEDs were invented in the ‘60s and started out in a dual in-line package
(DIP) format. These translucent epoxy enclosed devices are still used today, but mainly for signage purposes. The relatively bulky packaging of DIPs and their low lumen output make them unsuitable for the small form factors of most modern electronics.
Surface mount technology changed the face of LEDs as we know them, shrinking the dimensions of individual chips down to the order of millimetres. Designed for mass production by the same equipment used to create printed circuit boards, surface mounted device (SMD) LEDs come in a vast variety of types, lumen outputs, and colours, but generally just a few standard sizes ranging from 1.1 mm to 5.7 mm square are the most popular.
Seeing an opportunity in the deficiencies of SMD technology, LED manufacturers in recent years have come out with chip-on-board (CoB) LED technology. CoB LEDs forego the standardized packaging of SMD LEDs in pursuit of superior thermal efficiency and lumen density. Just as SMD technology shrunk LEDs, CoB LEDs shrink them even further to where they’re often less than a millimetre thick and just barely visible to the naked eye. Anywhere from just a dozen, to dozens, or even hundreds of these tiny chips will popular a single array. These LED dies are directly attached to the PCB substrate and wire bonded. Instead of individual phosphor coatings for each diode, a single large phosphor coating covers the entire array for creating a uniform spread of light.
CoB LEDs are generally larger than SMDs and range from a few millimetres to a few centimetres square. Instead of being soldered onto a PCB like SMD modules, they are attached directly to a heatsink, creating better thermal performance. Wiring is very simple with just two contacts on each CoB array.