Thermal pad for Hdmi chip and Scei chip

A thermal pad alone won't do anything.

A thermal pad is simply a pad made out of a material that conducts heat very well. However, that heat still needs somewhere to go. If all you do is put the thermal pad on and do nothing, then you may as well not bother.

What you can do is apply a heat sink on top of the thermal pad. This will allow the air (which is colder than the chip) to touch a much larger surface area, thus heating up more and thus transporting more heat off the chip.

Whether or not this is really necessary is up to you to decide, but if you are set on modifying your PS4, then a thermal pad and a heat sink are certainly an option.