It just depends on the pads, some are not very pliable. For example, the high-performance Kerafol pads.
People don't realize how much aluminum it can take to get a 0.1
C/W difference (say from 0.3 C/W to 0.2 C/W) however, getting a 0.1 C/W difference from seeking out high performance heat transfer solution at the pad level is a lot easier. Unfortunately, this level of performance will not allow the use of goo (unless you start looking at the phase transition stuff, what's I'm a huge fan of). My point is, asking a bunch of headphone amplifier builders you will get different answers, because they don't need to really eek out the last bit of performance from a large TO-247 or TO-3P package device. Ask people that are building large power amplifiers and you'll get a different answer.
One other possibility, that hasn't been mentioned (probably due to the fact that it has it's own share of risks) is just using an "bare" anodized heat sink with phase change compound mentioned above (for example, Aavid's Ultrastick) or a high performance goo, like the blue Aavid stuff. You have to really trust the thickness of the anodizing material though in this case
People don't realize how much aluminum it can take to get a 0.1
C/W difference (say from 0.3 C/W to 0.2 C/W) however, getting a 0.1 C/W difference from seeking out high performance heat transfer solution at the pad level is a lot easier. Unfortunately, this level of performance will not allow the use of goo (unless you start looking at the phase transition stuff, what's I'm a huge fan of). My point is, asking a bunch of headphone amplifier builders you will get different answers, because they don't need to really eek out the last bit of performance from a large TO-247 or TO-3P package device. Ask people that are building large power amplifiers and you'll get a different answer.
One other possibility, that hasn't been mentioned (probably due to the fact that it has it's own share of risks) is just using an "bare" anodized heat sink with phase change compound mentioned above (for example, Aavid's Ultrastick) or a high performance goo, like the blue Aavid stuff. You have to really trust the thickness of the anodizing material though in this case
