LED COB PCB packaging process

  LED COB (Chip on Board) packaging process, first is covering the surface of the silicon wafer of substrate with a thermally conductive epoxy (generally use epoxy resin mixed with silver particles), and then place the silicon wafer to the right surface of the substrate indirectly, heat treatment firmly fixed to the silicon substrate is OK. Then build electrical connection between the silicon wafer and the substrate indirectly by re-wire welding methods. Its packaging process is as follows:

The first step is expanding chip.

Expanding LED chip film provided by manufacturer smoothly by chip expanding machine, make LED die closely attached to the film surface expanding for thorn crystal.

The Second step is gum.
Put the expansion chip ring to the surface of scraping gum machine with no silver layer, cover silver paste, place silver paste. It is suitable for bulk demolition LED chips. Using the dispenser place right amount paste on the printed circuit board.　

The third step is putting thorn crystal frame.
Put the r the expansion chip ring with silver paste into the thorn crystal frame. Thorn LED chips to circuit board under microscope by crystal pen.

The fourth step is putting thermal cycle oven.
Put circuit board placed with chip thorn to thermal cycle oven with thermostat for some time, and get out after silver paste curing ( not be too long, or the coating of LED chips will be roasted yellow, namely oxidization, which will bring problem to bonding). If there is no LED chip bonding, the above few steps is needed; If there is IC chip bonding, the above steps could be cancelled.

The fifth step is sticking chip.
Put the right amount red plastic (or vinyl) to the IC of PCB circuit board by dispenser, and then use the anti-static equipment (real suction pen or female) to put the IC die accurate on red plastic or vinyl.

The sixth step is drying.
Put chip die stick to the large flat heating plate outside the thermal cycle oven for some time, and also can cure naturally which may be longer.

The seventh step is bonding wire.
Uses aluminum wire bonders place chip (LED grains or IC chips) on to the PCB pads for aluminum wire bridging connection, which is Cob’s inner lead bonding.

 

The eighth step is pretesting.
Use public inspection tools (Choose different devices for COB different purposes, simple is the high-precision current regulator) detecting COB board, repair the board failed.

The ninth step is dispensing.
Use dispenser to deploy AB glue to bonding the LED die, IC is with vinyl. It could be packaged according to customer requirements.

The tenth step is Curing
Put the PCB circuit board sealed with paste outside the thermal cycle oven in thermostat. Drying time could set upon request.　　

The eleventh step is after- test.
Use the public test tool to test the electrical performance of sealed PCB circuit board again and then split the good and not good.

With the development of technology, there are aluminum PCB circuit board COB packaging, ceramic PCB circuit board COB packaging, and copper PCB circuit board MCOB package and so on.

  Compared with other packaging technology, COB technology cost is affordable (only with 1/3 of the chip), space is saving, and process technology is mature. But there is also some problem with COB technology. It needs allocated with welding machines and packaging machines sometimes couldn’t keep pace, with strict environmental requirements for PCB soldering and can’t be repaired and other shortcomings.

   Some chip on board design could improve the IC signal performance because they remove most or all of the parasitic parts. However, there may be also some performance issues with these techniques. In all these designs, because there are the lead frame sheets or BGA signs, it may not be well connected to VCC or ground. Problems may include a coefficient of thermal expansion (CTE) of the substrate and the poor connection problems.