Because COB does not have IC sealed Leadframe (Guide frame), but uses the PCB to replace, so the PCB welding mattress design Handy is very important, and fihish can only use electricity plated gold or enig (isotopes leaching gold), whether the Gold line or aluminum line, Even the latest brass lines have problems that can't be beaten up.
PCB Design requirements for COB
- The finished surface of PC board must be electric plated gold or enig, and it is thicker than normal PC board plated gold layer, can provide die bonding energy need, form gold aluminum or Ginkin of co-gold.
- Solder Mattress Line routing position (layout) outside the COB's Die Pad, to measure the length of each welding line has a fixed length, that is, the solder point from the wafer (die) to the PCB solder mattress from the distance to the same amount, so as to control the position of each weld line, reduce the welding line intersection short-circuit problems. Therefore, there is a mattress for the welding of the angle line design does not meet the requirements. The suggestion can shorten the PCB welding mattress distance to cancel the mattress of the angle welding. It is also possible to design the elliptical orbits circular weld mattress position to evenly disperse the opposite position of the weld line.
- Recommend a cob wafer to have at least two or more positioning points, the positioning point is best not to use the traditional SMT circular positioning point, and instead of using the 10-glyph positioning point, because the wire Bonding (welding wire) machine in the self-positioning will basically grasp the straight line to do the positioning, I think this is because there is no circular anchor on the conventional wire frame, only the straight frame. Maybe some wire Bonding machine is not quite the same. Recommend that you take a look at the machine performance to do the design.
- The size of the PCB (die Pad) should be a little bit more than the actual wafer (die), which can limit the drift of the wafer, and can also avoid the rotation of the wafer in the die Pad too heavy. It is suggested that each side of the wafer welding mattress than the actual crystal Circle big 0.25~0.3mm.
- Cob need to fill the area of the best not to have a guide through the hole (vias), if not avoided, that requires the PCB factory to the guide through the hole 100% complete plug hole, the purpose is to avoid the epoxy point of penetration through the hole to the other side of the PCB, causing unnecessary problems.
- Suggestions can be printed in the area where the need to glue the silkscreen logo, you can easily paste into the industry and the point of the shape of the control tube.
COB Requirements for PCB design
