What does cob mean?

COB Chip On Board (COB) technology firstly covers the silicon wafer attachment point with thermal conductive epoxy resin (generally epoxy resin mixed with silver particles) on the substrate surface, then directly attaches the silicon wafer to the substrate surface, and carries out heat treatment until the silicon wafer is firmly fixed on the substrate, and then directly establishes the electrical connection between the silicon wafer and the substrate through wire bonding. There are two main forms of bare chip technology: one is COB technology, and the other is flip chip technology. Chip on board package (COB), in which a semiconductor chip is attached to a printed circuit board, and the electrical connection between the chip and the substrate is realized by wire stitching, and the electrical connection between the chip and the substrate is realized by wire stitching, and covered with resin to ensure reliability. Although COB is the simplest die mounting technology, its packaging density is far less than TAB and flip-chip bonding technology. The main welding method of COB: (1) Hot pressing welding is to press the metal wire and the welding area together by heating and pressure. The principle is that the welding area (such as AI) is plastically deformed by heating and pressurizing, and the oxide layer on the bonding interface is destroyed at the same time, so that the attraction between atoms can achieve the purpose of "bonding". In addition, when the interface between the two metals is uneven, the upper and lower metals can be embedded with each other by heating and pressurizing. This technology is usually used as the on-board glass chip COG. (2) Ultrasonic welding Ultrasonic welding utilizes the energy generated by an ultrasonic generator, and the transducer rapidly expands and contracts under the induction of an ultra-high frequency magnetic field to generate elastic vibration, so that the cutting knife vibrates correspondingly, and at the same time, a certain pressure is exerted on the cutting knife, so that the cutting knife, under the combined action of these two forces, drives the aluminum wire to quickly rub on the surface of the metallization layer (aluminum film) in the welding area, so that the surfaces of the aluminum wire and the aluminum film are plastically deformed, and this deformation is also destroyed. The main welding material is aluminum wire welding head, which is generally wedge-shaped. (3) Gold wire ball bonding is the most representative welding technology in wire bonding, because the current semiconductor package and triode package adopt AU wire ball bonding. Moreover, the operation is convenient and flexible, the solder joint is firm (the welding strength of gold wire with a diameter of 25UM is generally 0.07 ~ 0.09n/ point), and the welding speed is as high as 15 points/second. Gold wire welding is also called thermal (pressure) (ultrasonic) welding. The main bonding material is gold (AU) wire bonding head, so it is ball bonding.