:: puts on materials scientist hat ::
Everybody is talking WAY too generally here. In general, for a heatsink you want high thermal conductivity and high heat capacity. You want both. Like anything else in the world though, you can't have both, so you have to make an engineering decision: higher heat capacity, or higher thermal conductivity.
No, you are making it harder than it is - there are only a few metals that we really have the option of using. All we have to do is look at the options and determine the best of those metals and then decide if the cost is worth the performance.
It almost certainly boils down to aluminum or copper, but there are a few other materials worth looking into. RHD brought up some good points and asked some thought provoking questions that were worth looking in to for those of us building lasers and trying to get the maximum duty cycles that we can out of them.
When you are toasting $45-$55 (or more) diodes it makes sense to invest some time and perhaps even money into making sure your design is good. Especially if you plan on selling your builds.
And that decision will change in every application. Heat load, geometry, environment, it all changes the calculus, and you'll have to calculate it or measure it for YOUR application to find the best one. You can wave your hands around and say "heat capacity is more important" all you want, but until you either calculate it or measure it, then you're just blowing hot air.
Well, that is the goal. But no, we aren't blowing hot air. We are talking it out, putting lots of eyes and brains on the problem and making sure that we have the right answers.
By defining the problem, then finding materials that can solve the problem, we are able to improve the design.
You say the situation changes with every application but that is the whole point of this discussion, to determine the needs of our application.
But as of now, this is a thread full of hand-waving arguments with no real data, because every application is different.
I strongly disagree. First of all, a lot of this work has been done before. It is out there and researchable. There is a good reason that most sinks are made from Aluminum and Copper.
By looking at their properties and determining why they make good sink material we can look at other materials with similar specs and try to see if they might be better.
Your attitude seems to be that it is too tough to solve so we are wasting our time talking about it.
Don't forget to include another factor...time.
How much of a difference in final operating temperature is your time worth? If I told you that you could lower your diode's operating temperature by 10C if you spend several hours doing all of this analysis, is that worth it to you?
I think most of us participating in this thread find the mental exercise stimulating. It's fun. If it isn't fun to you, that's fine.
