I looked on heatsinkusa and could only see a $12.35 option for 4" wide cut to 4" length. I guess I didn't find the right one. Can you give me a link to the $5 one? I'd like to see and if it's right then I'll just tell people they could order those, though I think even cheaper options could turn up.
I see they have a 4" wide option with 2" high fins for $12. Maybe that is large if we want to stack them close together.
They also have 3.5 and 4.2" inch sizes with .75" high fins for about $4 and $5 respectively. If 3.5x4" is big enough, $4.36 is pretty cheap.
Those 2" high heatsinks are quite beefy. The site claims a thermal resistance of 1.4 degrees C/watt for a 3"x4" section (presumably with natural convection). With such a thermal resistance, it looks like you can dissippate the heat of 16 chips with a slow/quiet fan, or perhaps no fan at all.
I think that one is very good but a bit expensive. They actually rate it at 1.4deg/W for a 3" section. So if it were 4" it should be a bit better at 1.05. With 35C air and 32W we'd be looking at 1.05*32 + 35 = 66C. Even with a small fan it would be good. However, I'd prefer to see something cheaper than $12.35. It's crazy that the most costly single part involved is a chunk of metal. When I have time I'll do some extensive searching but if other want to scour the web for something suitable I'd welcome suggestions. We're looking for something 1.05C/W or less for about $5 or less.
BkkCoins ,
Do not forget that heatsinks are heavy (with big volume weight also). As long as we are 100% sure about board size 10x10 i will look forward to alibaba and i will try to find a heatsink supplier having in mind 1+ month for delivery (to cut delivery costs as much as possible). If we need them fast it may turn out that delivery cost alone will be more than heatsinks
I will share my findings about hetsinks here also.
PS: that is why i am still considering mineral oil as an option. It is bit messy but it is just nonesence for me to pay 10+USd for a pice of metal