People quote a sensor part number and think they bought a camera. The die still has to sit in a package, on a board, under a holder, under glass. COM (chip on module) puts the chip on the optical assembly side so the lens and the die share a more honest seat. COB is the older cousin: die on the PCB, holder glued, more chances for tilt and FPC warp.
What COM is trying to buy
- Less tilt from a holder that was glued in a bad mood.
- A thinner gold-wire stack, so the FPC can flex without lifting the image plane.
- A thermal path that is not only 'hope the flex is short'.
- A chance at better MTF because the lens is looking at a flatter world.
What it does not buy
COM does not fix a lens that cannot cover the format. It does not fix a CRA fight. It does not replace black PCBs. Packaging is one costume of the die. The custom camera module flow still has to pick the stack as a system.
When a drawing says COB or COM, treat it as a mechanical and optical spec. Ask for height, keep-out, and a sample that has been through heat. Two 'IMX335 cameras' with different seats are not the same part.