Chip On Board, COB
process is First using a thermal conductivity covering the wafer placed on surface of substrate (usually with the epoxy resin mixed with silver particles). Then the silicon wafer directly placed on the surface of the substrate, a silicon wafer is firmly fixed to the base with heat treatmen Final, create a electrization connection between the surface of substrate and silicon wafer with way of wire welding. Bare chip technology mainly has two forms: one is the COB technology, the other is the flip chip technology (Flip Chip).The board chip packaging (COB), a semiconductor chip connection mounted on the circuit print board, electrical connects in surface of substrate and chip whit suture method for lead. covered with resin to ensure reliability. Although COB is the most simple chip mounting technology, but the packaging desity if not as good as than TAB and a welding technology.
COB mainly welding method: (1) hot pressure welding
The metal wire and the welding pressure welding together by heat and pressure. Its principle is to add pressure and add heating, makes the welding zone to produce plastic deformation and destroy the oxidation layer of pressure welding on the interface,so that the inter atomic appeal to “bond” purposes, in addition, two metal uneven interface to add heating and add pressure can make mutually embedded compression and incrustation for the the top and bottom metal.This technique is generally used for chip on glass plate COG.
(2) for ultrasonic welding
Ultrasonic welding can be generated energy by ultrasonic generator,through the transducer in the ultra high frequency magnetic field induction,rapid expansion to generate elastic vibration, make a corresponding vibration for the chopper, driven the AI metal layer as the pad (AI film) rapid surface friction. Then the AI wire and AI membrane surface of the plastic deformation, the deformation and failure of the oxide layer, make the two pure metal surface in close contact to interatomic bonding, and come into being wedge. The main welding material for aluminum wire bonding.
(3) wire welding
Ball welding technology is the most representative welding technology in wire bonding. Because the semiconductor packaging and triode package use wire ball bonding welding. And it is convenient in operation, flexible, solid solid solder joint(AU wire diameter 25UM of weld strength is generally 0.07 ~ 0.09N / point) and no direction, the welding speed can be up to 15 point / sec. Wire bonding is also called thermal (pressure) sonic welding main bonding materials for gold (AU) wire welding, Having the shape of a sphere, also called the solder ball
The first step: expanding crystal。 Expansion machine will uniform expand the whole LED wafer thin film.the attachment of LED grains are closely arranged in a thin film on the surface opened, easy thorn crystal.
Step two: gum. The expansion of good crystal crystal ring put in gum machine(gum machine has been scraping silver layer), back silver paste. Point Silver. LED chip is suitable for bulk.(Dispenser)using the appropriate amount of silver paste on the PCB printed circuit board.
third step: the expanding ready Silver Crystal Ring crystal planes into the thorns,the operator used the microscope LED wafer crystal pen with barbed spines are on
The printed circuit board PCBunder the microscope the
fourth step: Put the thorn good crystal of PCB circuit print board into heat cycling constant temperature oven for a period of time. Wait for the silver slurry is solidified out(not for a long time, otherwise LED chip coating will be roasted yellow, oxidizing, difficult to bonding ). LED chip bonding is necessary above step, the IC chip bonding is not necessary above step.
fifth step: sticking chip. using the (Dispenser) place amount of Red glue on PCB the circuit print board IC position。Then put the IC into correct on red plastic or vinyl with anti-static devices (vacuum suction pen or sub).
The sixth step:drying. The good die stick need to constant temperature for a period of time on hot circulating oven big plane. Can also to naturally cure (but time is longer).
The seventh step: bonding(wire).connect of wire between the wafer (LED grain or IC chip) and PCB board corresponding to pad via aluminum wire bonder machine. This is wire of welding for COB.
eighth step: Pretest。 Using profession test tools(according to difference purpose to choice difference tools )to check out the COB board, will not be qualified to repair。
ninety step: dispensing。The dispenser will deploy a good amount of A B venue to the LED grain bonding, IC with black plastic package, then base on the require of customer will package.
tenth step: curing. The sealed plastic PCB printed circuit board placed in an oven heated to stand the heat cycle, the requirements can be set according to different drying times.
eleventh step: after the test. The packaged PCB printed circuit board with special tool for the detection of electrical performance test, to distinguish good or bad. compare of other technology of package, The COB technology price is low cost(just only for the same chip about 1/3), space saving, technology maturity However, any new technology can not be perfect at first appear,