LED Chip on Board (COB) Packaging Process

The LED chip on board (COB) packaging process first covers the silicon wafer placement point on the substrate surface with thermally conductive epoxy resin (usually epoxy resin doped with silver particles), then directly places the silicon wafer on the substrate surface, heat treats until the silicon wafer is firmly fixed on the substrate, and then uses wire bonding to indirectly establish electrical connections between the silicon wafer and the substrate. The packaging process is as follows:

Step 1: Crystal expansion Use a crystal expansion machine to evenly expand the zero-crystal LED chip film provided by the manufacturer, so that the LED grains that are closely arranged on the surface of the film are pulled apart to facilitate crystal piercing.

Step 2: Back glue Place the expanded crystal ring on the back glue machine surface where the silver paste layer has not been scraped, and apply silver paste. Apply silver paste. Applicable to disassembling LED chips. Use a glue dispenser to apply a proper amount of silver paste on the PCB printed circuit board.

Step 3: Put the expanded crystal ring with prepared silver paste into the crystal piercing frame, and the operator will pierce the LED chip onto the PCB printed circuit board with a crystal piercing pen under a microscope.

Step 4: Place in a thermal cycle oven Place the PCB printed circuit board with the pierced crystal in a thermal cycle oven and place it at a constant temperature for a period of time. Take it out after the silver paste solidifies (do not place it for a long time, otherwise the LED chip coating will turn yellow, that is, oxidize, making bonding difficult). If there is no LED chip bonding, the above steps are required; if only IC chip bonding is required, the above steps can be omitted.

Step 5: Stick the chip. Use a glue dispenser to put an appropriate amount of red glue (or black glue) on the IC position of the PCB printed circuit board, and then use an anti-static device (empty suction pen or female) to place the IC bare chip accurately on the red glue or black glue.

Step 6: Drying: Put the bonded die 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 (it takes a long 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 of the COB is welded.

Step 8: Pre-test: Use special testing tools (there are different equipment for COBs with different uses, the simplest one is high-precision voltage and current regulator) to test the COB board, and send the unqualified boards back for repair.

Step 9: Glue dispensing: Use a glue dispensing machine to apply an appropriate amount of the prepared AB glue to the bonded LED die, seal the IC with black glue, and then perform appearance sealing according to customer requirements.

Step 10: Curing: Place the sealed PCB printed circuit board in a heat circulation oven and place it at a constant temperature. Different drying times can be set according to requirements.

Step 11: Post-test: Use common testing tools to test the electrical performance of the packaged PCB printed circuit board to distinguish good from bad. With the advancement of technology, the packaging includes aluminum substrate COB packaging, COB ceramic COB packaging, aluminum substrate MCOB packaging and other forms.