Chiponboard

Chip-on-board (COB) is a method of mounting one or more semiconductor dies directly onto a printed circuit board or substrate, with wire bonds connecting each die to the substrate traces, and the assembly encapsulated in an epoxy or silicone potting compound. This packaging approach eliminates individual package enclosures for each die, allowing multiple chips to form a single, compact unit.

The process typically involves attaching bare dies to a substrate, bonding the die pads with fine wires, and applying a protective encapsulant. The resulting device can feature a flat, highly integrated surface with many connections underneath or around a dense array of chips. Substrates may be made of materials such as ceramic or metal-core boards, chosen for thermal management and mechanical stability. Clip or lid structures may be used in some variants.

Advantages of COB include reduced packaging steps and parasitics, higher circuit density, and often lower material costs in high-volume production. It can also improve thermal performance when paired with an appropriate substrate and provides a relatively compact footprint, which is particularly valued in lighting and compact electronics.

Disadvantages include challenges in rework and testing after encapsulation, potential reliability concerns from wire bonds under thermal cycling, and limited suitability for high-speed or high-reliability requirements where packaged ICs are preferred. COB is widely used in LED lighting, where COB LEDs assemble many diodes on a single substrate to produce bright, uniform light, as well as in some low-profile electronic assemblies and sensing applications.