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Chip On Board COB


COB chip-on-board (Chip On Board COB) process is first covered the surface of the substrate with a thermally conductive epoxy resin (epoxy resin is generally doped with silver particles) the wafer placed point, the wafer is then placed directly on the surface of the substrate,heat treatment to the wafer is firmly fixed to the substrate so far, and then reuse the wire bonding method to establish electrical connection between the wafer and the substrate directly.

The bare chip technology mainly in two forms: one is the COB technology, the other is a flip chip technology (Flip Chip). Chip-on-board package (COB), the transfer of semiconductor chip mounting on a printed circuit board, the chip and the substrate electrical connection leads stapling method to achieve electrical connection of the chip and the substrate with a lead stapling method, and covered with resin to ensure reliability . COB is the easiest bare chip mounting technology, but it’s far less packing density the TAB and rewind welding technology.

COB soldering method:

(1) thermo-compression bonding
The use of heat and pressure to the wire and the weld zone welded pressure. Its principle is that through heat and pressure, so that the welding area (such as AI) plastic deformation occurs at the same time destroy the oxide layer on the bonding interface, thereby to produce attractive achieve the purpose of the “bonding” between the atoms, in addition, the two-metal interface does not formation of heat and pressure can make the upper and lower metal inlaid with each other. This technology is generally used for the glass chips COG.

(2) The ultrasonic welding
The ultrasonic welding is the use of energy generated by the ultrasonic generator, the transducer in the ultra high frequency magnetic field induction, the rapid expansion and contraction of the elastic vibration, the respective vibration chopper, exert a certain pressure on the chopper at the same time, so the chopper in the combined effect of these two forces, driven by AI wire weld metal layer (AI film) rapidly on the surface friction, so that the AI wire and AI membrane surface plastic deformation, this deformation also undermines the AI layer interface oxide layer, so that the two pure metal surface into close contact to achieve bonding between the atoms, to form a weld. The welding material for aluminum welding head, generally wedge-shaped.

(3) gold solder
The ball bonding wire bonding, welding technology, is the most representative because the semiconductor package, transistor package AU wire ball bonding. And it is convenient, flexible, solid solder joint (the diameter for the the 25UM AU wire welding strength is generally 0.07 to 0.09N /), nor directional, welding speed can be as high as more than 15 points / sec. Gold wire bonding, also known as thermal sonic welding the bonding material (pressure) (hyper) gold (AU) wire welding head is spherical and therefore the ball bond.

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