PCB Tech - COB requirements for PCB circuit board design

This article is an introduction to the PCB circuit board design requirements of COB in the PCB circuit board process

Because COB does not have a lead frame for IC packaging, it is replaced by a PCB circuit board, so the design of the solder pad of the PCB circuit board is very important, and the fish can only use electroplated gold or ENIG, otherwise gold wire or aluminum Cable, even the latest copper cable will have the problem of not being able to connect.

COB PCB circuit board design requirements

1. The finished surface treatment of the PCB circuit board must be electroplated gold or ENIG, and it must be thicker than the gold-plated layer of the general PCB circuit board to provide the energy required for Die Bonding to form gold-aluminum or gold-gold Total gold.

2. In the wiring position of the solder pads outside the COB Die Pad, try to make sure that the length of each solder wire has a fixed length, that is to say, the distance between the solder joints from the wafer to the solder pad of the PCB circuit board should be as consistent as possible. In this way, the position of each welding wire can be controlled, and the problem of short-circuiting of the welding wires can be reduced. Therefore, the diagonal pad design does not meet the requirements. It is recommended to shorten the solder pad spacing of the PCB circuit board to eliminate the appearance of diagonal solder pads. It is also possible to design elliptical pad positions to evenly disperse the relative positions between the welding wires.

3. It is recommended that a COB wafer has at least two positioning points. The positioning points should not use the traditional SMT circular positioning points, but use the cross-shaped positioning points, because the Wire Bonding machine is doing automatic Basically, the positioning will be done by grasping a straight line. I think this is because there is no circular positioning point on the traditional lead frame, but only a straight outer frame. Some Wire Bonding machines may be different. It is recommended to design with reference to the performance of the machine first.

Fourth, the Die Pad size of the PCB circuit board should be slightly larger than the actual wafer. One can limit the deviation when placing the wafer, and it can also prevent the wafer from rotating too much in the die pad. It is recommended that the wafer pads on each side are 0.25~0.3mm larger than the actual wafer.

5. It is best not to have through holes in the area where COB needs to be filled with glue. If it is unavoidable, then the PCB circuit board factory is required to completely plug these through holes 100%, in order to avoid the penetration of the through holes during Epoxy dispensing. To the other side of the PCB circuit board, causing unnecessary problems.

Sixth, it is recommended to print the Silkscreen logo on the area that needs glue, which can facilitate the dispensing operation and the control of the dispensing shape.

The above is an introduction to the PCB circuit board design requirements of COB in the PCB circuit board process