COB packaging process
In the first part, we talked about the welding method of COB, and then we will talk about the packaging process of COB.
The first step: expand the crystal. The expansion machine is used to uniformly expand the entire LED chip film provided by the manufacturer, so that the tightly arranged LED chips attached to the surface of the film are pulled apart, which is conducive to the thorn crystal.
Step 2: Adhesive. Place the expanded crystal ring on the surface of the adhesive machine where the silver paste layer has been scraped, and apply the silver paste. Suitable for bulk LED chips. Use a dispenser to dot the appropriate amount of silver paste on the printed circuit board of the PCB.
The third step: Put the crystal expansion ring prepared with silver paste into the thorn crystal holder, and then the operator will pierce the LED chip onto the PCB printed circuit board with a crystal pen under the microscope.
Step 4: Put the pierced PCB printed circuit board in a thermal cycle oven at a constant temperature for a period of time, and wait for the silver paste to be taken out after curing (do not leave it for a long time, otherwise the LED chip coating will be baked yellow, that is : Oxidation will cause difficulties for bonding). If there is LED chip bonding, you need to do the above steps; if you only have IC chip bonding, you can cancel the above steps.
The fifth step: stick the chip. Use a dispenser to place an appropriate amount of red glue (or black glue) on the IC position on the PCB printed circuit board, and then use an anti-static device (vacuum suction pen) to correctly place the IC die on the red glue or black glue.
The sixth step: drying. Put the glued die into a thermal cycle oven, and place it on a large flat heating plate at a constant temperature for a period of time, which can also allow it to solidify naturally (for a long time).
The seventh step: Bonding (ie: wire bonding). The aluminum wire bonding machine is used to bridge the chip (LED die or IC chip) with the corresponding pad aluminum wire on the PCB board, that is, the inner lead welding on the COB.
The eighth step: pre-test. Use special testing tools (different testing equipment for COB for different purposes, the simplest is a high-precision regulated power supply) to test COB, and re-repair some unqualified boards.
The ninth step: dispensing. Use a dispenser to apply an appropriate amount of prepared AB glue to the already bonded LED die, and the IC is packaged with vinyl, and then packaged according to the customer's requirements.
The tenth step: curing. Put the sealed PCB printed circuit board into a thermal cycle oven and let it stand at a constant temperature, and different drying times can be set according to requirements.
The eleventh step: post-test. The already-packaged PCB printed circuit board is then tested for electrical performance using a special inspection tool to distinguish between good and bad and good and bad.
Compared with other packaging technologies, COB technology is cheaper (only about 1/3 of the same chip), more space-saving, and more mature. However, it is impossible for any emerging technology to be perfect when it first appeared. COB technology will also require additional welding machines and packaging machines, sometimes the speed will not keep up, and PCB placement requirements for the environment are more stringent and impossible. Disadvantages such as maintenance.
The chip on board (COB) layout of certain boards can improve the performance of IC signals, because they have now removed a large part or all of the package, which means that most or all of the parasitic components have been removed. However, along with these technologies, there may also be some performance problems. In all these designs, due to the lead frame chip or BGA logo, the substrate may not be well connected to VCC or ground. Possible problems include coefficient of thermal expansion (CTE) issues and poor substrate connections.
