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Step 1: Crystal expansion. Use an expansion machine to evenly expand the entire LED chip film provided by the manufacturer, so that the LED grains closely arranged on the surface of the film are pulled apart for easy crystal piercing.
Step 2: Back glue. Place the expanded crystal ring on the back glue machine surface with the silver paste layer scraped, and apply silver paste on the back. Apply silver paste. Applicable to bulk LED chips. Use a glue dispenser to apply an appropriate amount of silver paste on the PCB printed circuit board.
Step 3: Place the expanded crystal ring with silver paste in the crystal piercing rack, and the operator will pierce the LED chip on the PCB printed circuit board with a crystal piercing pen under a microscope.
Step 4: Put the pierced PCB printed circuit board into a heat cycle oven at a constant temperature for a period of time, and take it out after the silver paste solidifies (do not leave it for a long time, otherwise the LED chip coating will be baked yellow, that is, oxidized, causing difficulties in bonding). If there is LED chip bonding, the above steps are required: If only IC chip bonding is required, cancel the above steps
Step 5: Glue the chip. Use a glue dispenser to apply an appropriate amount of red glue (or black glue) to the IC position of the PCB printed circuit board, and then use anti-static equipment (vacuum suction pen or sub) to correctly place the IC bare chip on the red glue or black glue.
Step 6: Drying. Put the glued bare chip into a thermal cycle oven and place it on a large flat heating plate at a constant temperature for a period of time, or it can be cured naturally (for a longer time).
Step 7: Bonding (wire bonding). Use an aluminum wire bonding machine to bridge the chip (LED crystal or IC chip) with the corresponding pad aluminum wire on the PCB board, that is, the inner lead welding of COB
Step 8: Pre-test. Use special detection tools (different equipment for COBs with different uses, the simple one is a high-precision voltage-stabilized power supply) to detect the COB board and rework the unqualified boards.
Step 9: Glue dispensing. Use a glue dispensing machine to apply an appropriate amount of the prepared AB glue to the bonded LED crystal, and the IC is encapsulated with black glue, and then the appearance is encapsulated according to customer requirements.
Step 10: Curing. Place the sealed PCB printed circuit board in a thermal cycle oven and keep it at a constant temperature. Different drying times can be set according to requirements.
Step 11: Post-test. Use a dedicated detection tool to test the electrical performance of the packaged PCB printed circuit board to distinguish between good and bad.
Compared with other packaging technologies, COB technology is cheap (only about 113 of the same chip), saves space, and has mature technology. However, any new technology cannot be perfect when it first appears. COB technology also has the disadvantages of requiring additional welding machines and packaging machines, sometimes not keeping up with the speed, and PCB patch has more stringent environmental requirements and cannot be repaired.
Some chip-on-board (CoB) layouts can improve IC signal performance because they remove most or all of the packaging, that is, most or all of the parasitic devices. However, there may be some performance issues with these technologies. In all these designs, the substrate may not be well connected to VCC or ground due to the lead frame sheet or BGA logo. Possible problems include coefficient of thermal expansion (CTE) problems and poor substrate connections.