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Hi! The i5-5257u Processor in my MacBook Pro 13" Retina (early 2015) has 2 chip dies on the CHU chip carrier. The thermal paste is only applied on larger CPU die. The Platform Controller Hub chip die (PCH) on the other hand is not covered by radiator and it also does not have any thermal paste! You could cover the PCH using a thermal pad and it will contact with copper tube. What do you think? I think it will be better way to cool my MacBook Pro. P.S. Sorry for my bad english.
The i5-5257u does not require its PCH cooled unlike older versions. In fact I suspect you would cause heat issues as the heat from the CPU will sink to the PCH making it run hotter! From what I’ve read Apple does not want you to apply paste on the PCH in the Haswell chip series. Besides, the added pressure of the thermal pad sandwiched here onto the die could damage it. I would not do it! What I would do is make sure I was using the correct thermal paste and make sure the fan and the cooling fins where clean. I would also recommend getting a good thermal sensor & fan monitoring app like: TG Pro.
