Chip-on-Board (COB) process: First, the substrate surface is covered with thermally conductive epoxy resin (usually silver-doped epoxy resin), then the wafer is placed directly on the surface of the substrate and heat-treated until the wafer is firmly fixed on the substrate and then the electrical connection is established directly between the wafer and the substrate using wire welding.

Bare chip technology mainly has two forms: one is COE technology, and the other is flip-chip technology. In chip-on-board packaging (COB), the semiconductor chip is hand-attached and mounted on the printed Qianhu circuit board. The electrical connection between the chip and the substrate is realized by wire stitching, and the resin is covered to ensure its reliability. Although COB is a very simple bare chip mounting technology, its packaging density is far inferior to TAB and flip-chip bonding technology.

COB welding method

1. Thermocompression Welding

Use its heat and pressure to make the wire and the welding area pressure-welded together. The principle is to cause plastic deformation of the welding zone (such as AI) by heating and applying pressure, and at the same time destroy the oxide layer on the welding interface, thereby creating an attractive force between atoms and achieving the purpose of "bonding". Well, the unevenness of the interface between the two metals can make the upper and lower metals embedded in each other when heated and pressed. This technique is generally used for COG of chips on glass.

2. Ultrasonic Welding

Ultrasonic welding uses the energy generated by the ultrasonic generator, and then through the transducer under the induction of the ultra-high frequency political field, the rapid expansion and contraction produces elastic vibration, so that the riving knife vibrates correspondingly, and at the same time the riving knife a certain pressure is applied on it, so the rivet will, under the combined action of these two forces, drive the Al wire to rub against the metallized layer of the welded area, such as the surface of the (AI film) rapidly, so that the Al wire and the AI film plastic deformation occurs on the surface, and this deformation will also damage the oxide layer at the interface of the Al layer, so that the two pure metal surfaces are in close contact to achieve the bonding between atoms, thereby forming a weld. The main welding material is aluminum wire welding head, which is generally wedge-shaped.

3. Gold Wire Welding

Ball bonding is the most representative welding technology in wire bond bonding, because the current semiconductor diode and triode packages are all using AU wire ball bonding. Moreover, its operation is more convenient and flexible, and the solder joints are relatively firm (the welding strength of AUE with a diameter of 25UM is generally 0.07~0.09N points), and it has no directionality, and the welding speed can reach up to 15 points per second. Gold wire welding is also called thermal (pressure) (ultrasound) acoustic welding, and the main bonding material is gold (AU) wire welding head, which is spherical, so it is also called ball welding.