COB,is chip-on-board LED technology,is to adhere the bare chip to the interconnection substrate with conductive or non-conductive adhesive,and then conduct wire bonding to realize its electrical connection.COB LED is also called COB LED source,COB LED module.There are many packaging forms:long strip,square,round or special custom shape.
COB LED area light source firstly covers the silicon wafer mounting point with thermal conductive epoxy resin (usually epoxy resin mixed with silver particles) on the surface of the substrate,and then directly places the silicon wafer on the surface of the substrate,heat treatment until the silicon wafer is firmly fixed on the substrate,and then directly establishes the electrical connection between the silicon wafer and the substrate by wire welding.There are two main forms of bare chip technology: one is COB LED technology, and the other is flip chip technology.chip on board packaging (COB),semiconductor chips are connected and pasted on the printed circuit board,the electrical connection between the chip and the substrate is realized by the lead suture method,the electrical connection between the chip and the substrate is realized by the lead suture method, and is covered with resin to ensure reliability.
Step 1: Crystal expansion.The whole LED chip film provided by the manufacturer is evenly expanded by the expansion machine,so that the closely arranged LED grains attached to the film surface are pulled apart, which is convenient for crystal pricking.
Step 2: back glue.Place the crystal expanding ring with the expanded crystal on the back glue machine surface with the silver paste layer scraped, and back the silver paste.Point silver paste. Suitable for bulk LED chips. Apply a proper amount of silver paste onto PCB printed circuit board with glue dispenser.
Step 3: put the crystal expanding ring prepared with silver paste into the spinel frame,and the operator stabs the LED chip on the PCB printed circuit board with a spinel pen under the microscope.
Step 4: put the pricked PCB into the thermal circulation oven and let it stand at a constant temperature for a period of time,and take it out after the silver paste is cured (do not leave it for a long time, otherwise the LED chip coating will be baked yellow,that is, oxidized, causing difficulties to bonding). If there is led chip bonding, the above steps are required; If there is only IC chip binding, cancel the above steps.
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 the anti-static equipment (vacuum pen or sub) to correctly place the IC bare chip on the red glue or black glue.
Step 6: drying.Put the bonded bare sheet into a thermal circulation oven and place it on a large flat heating plate for a period of time at constant temperature, or it can be cured naturally (for a long time).
Step 7: bonding.An aluminum wire bonder is used to bridge the chip (LED grain or IC chip) with the aluminum wire of the corresponding pad on the PCB, that is, the inner lead of the cob is welded.
Step 8: pre test.Use special testing tools (COB has different equipment according to different purposes, simply high-precision regulated power supply) to test cob boards, and repair unqualified boards again.
Step 9: dispensing.The dispensing machine is used to place an appropriate amount of the prepared AB glue on the bonded LED grains, the IC is encapsulated with black glue, and then the appearance is encapsulated according to the customer’s requirements.
Step 10: curing. Put the sealed PCB printed circuit board into the thermal circulation oven and let it stand at a constant temperature. Different drying times can be set according to requirements.
Step 11: post test. Test the electrical performance of the packaged PCB with a special testing tool to distinguish the good from the bad.
Therefore, compared with traditional LED technology, COB LED technology saves more space, has better heat dissipation and higher luminous efficiency.