I want copper copper copper! (well... maybe not)

[piferal]

Well, typical 6061 aircraft grade aluminum that I use for my heatsinks (it's the best aluminum for machining, I am sure that's what most of us machinists use) has a better thermal conductivity of, at worst, like 150 W/(m-K), so it's still better than zinc. Copper, on the other hand, is pretty easy to get "pure," i.e. in most cases, when you buy copper stock, it should be pretty close to pure copper and not be alloyed.

Another beter exampple of a Aluminium alloys is the 1050A grade, this has one of the higher
thermal conductivity values at 222-229 W/m•K (appox) and one density of 2.71 kg/m3

Has an excellent corrosion resistance and high ductility.

Well yeah, except radiation is very small in this case.

Well, maybe but the facts are these.

 

[piferal]

I think you are both right. FP makes great heatsinks, but they almost always are intended to add the mass of the body to the thermal mass, and not to radiate directly. Whereas, normally when I think of a heatsink, I think of a device meant to pull heat from a source, and generally dissipate it into the air.

If you ask me, I think a bigger issue is doing away with aixiz modules. Theoretically, you only have a small line of contact between the aixiz module and the host. Try to make two perfect circles of differing diameters touch in more than one point, it is not possible. You will see that the area between the two circles is exponentially proportional to the difference in their diameters. This is not feasible, though, because aixiz aren't perfectly round, and not all of us have tools that can produce enough pressure to press something like that.

Yes, now that you mention it, maybe F.P talk about of heat conductivity, and me of the heat radiation.

I think Wolfman29 also referred to that.

If so, sorry F.P for the misunderstanding :beer:

 

[Sigurthr]

I still say it comes down to the HOST's heatsinking, radiating, or convection ability. When your host is thin, light weight, low contact area to the heatsink, and of low surface area having a highly conducting but low heat capacity heatsink will not help very much. All that will do is get your host warm very quickly and the heat reaches a "brick wall" and can't go anywhere so it starts to build up inside.

 

[tsteele93]

Material HAS to be a factor. Take it to the extreme. Suppose you were using plastic or wood... Even in a small host, copper or aluminum sinks are going to help vs a crappy material.

So even in a small host, better sinking materials are advantageous, no?

Here is an interesting wrinkle. Diamond is a great heat sink material except cost and machinability. So it makes sense that graphite might be good too.

Graphite Heatsinks: Like Copper Without the Weight - graphite heatsinks

 

[Sigurthr]

Yes, material is a factor.

Take your example of a wood host. Ok, now you have a copper module and a copper heatsink of the normal size, say C6 size. That copper has no where to send it's heat at all, the wood is an insulator. Yes, it will stay cool longer than aluminium. Why? because it has a higher heat capacity (specific heat) than aluminium. Know what has a higher heat capacity than copper? Steel or Nickel. As RHD said, nickel would be best. So in that wooden host the diode would stay cool longest and thus give the longest duty cycle in a nickel heatsink, not a copper or aluminium one.

It's normally all about transfering heat from the diode to the environment, but when you stop heat from getting to the environment it is then about holding as much heat as you can.

 

[tsteele93]

Yes, material is a factor.

Take your example of a wood host. Ok, now you have a copper module and a copper heatsink of the normal size, say C6 size. That copper has no where to send it's heat at all, the wood is an insulator. Yes, it will stay cool longer than aluminium. Why? because it has a higher heat capacity (specific heat) than aluminium. Know what has a higher heat capacity than copper? Steel or Nickel. As RHD said, nickel would be best. So in that wooden host the diode would stay cool longest and thus give the longest duty cycle in a nickel heatsink, not a copper or aluminium one.

It's normally all about transfering heat from the diode to the environment, but when you stop heat from getting to the environment it is then about holding as much heat as you can.

BUT, you also have to spread the heat THROUGH the sink material. So nickel or stainless may heat up very high where it makes contact with the diode but not flow that heat equally to all parts of the sink.

Copper will not heat up very high at the contact point and keep the heat there, it will spread the heat very uniformly throughout the entire sink because it has good thermal conductivity.

SS or Ni may not use the whole sink because it isn't flowing the heat from the diode to the outer parts of the sink.

EDIT: Another problem that I have with all this Nickel and Stainless Steel talk is practical in nature. If you go on a heavy duty heat sink materials search, you just DON'T find any talk of nickel or stainless steel. You just don't. Aluminum, Copper and Silver as an aside are mentioned and that is pretty much it.

Nickel and stainless steel aren't cost prohibitive so that is no excuse, they just don't transfer heat away from a source very well compared to readily available alloys of copper and aluminum.

Here is another source... http://www.acousticpc.com/re_metals_that_transfer_heat.html

 

[Sigurthr]

You have to keep in mind that it is very rare to have an application where you don't have airflow over the heatsink. That's the case with handheld nonfinned laser hosts.

 

[rhd]

EDIT: Another problem that I have with all this Nickel and Stainless Steel talk is practical in nature. If you go on a heavy duty heat sink materials search, you just DON'T find any talk of nickel or stainless steel. You just don't. Aluminum, Copper and Silver as an aside are mentioned and that is pretty much it.

Nickel and stainless steel aren't cost prohibitive so that is no excuse, they just don't transfer heat away from a source very well compared to readily available alloys of copper and aluminum.

Are you kidding me? Have you taken a look at the price of Nickel?

The cost of Nickel IS cost prohibitive. The cost of steel is not.

Sure, if you search here for machinists using steel, you won't find any. Why? Because this thread was posted yesterday, and until now, nobody has seriously suggested it. But if you actually search for rod stock at the sources our machinists use, you'll find tons of it (generally more if it than aluminum in fact).

I understand what you're hinting at re: specific heat capacity doesn't help if you can't move the heat throughout that entire heatsink anyway. But that's not the reality of how much impact heat conductivity has. You would never have the center of a steel heatsink getting hot, while the edges didn't.

When you're talking about 5 to 10 mm of thickness to the "ring" of a typical heatsink, and 1 minute or longer duty cycles, you WILL get the heat spreading through that heatsink, regardless of the metal. In a scenario (as has been discussed ad nauseum here) where you can't transfer the heat to the outside environment efficiently, your best bet is to be able to absorb as much heat as possible. That gives you a longer duty cycle, period.

- Picture a room with a fire in the middle of it.
- The room's only escape is via a single hallway.
- At the end of the hallway is a single revolving door to the outside world.
- That revolving door to the outside world can move 5 people through it every minute.

Now imagine that there are hundreds of people in this room that is on fire. What's more important, that people can run down the hallway quickly, or that the hallway is able to hold lots and lots of people?

 

[sinner]

All that reading and a brilliant example from rhd, i would like to finalize the thought in one sentence..

"Copper Core Heatsink with finned aluminium"

Why?
1. First off we have to decide the priority here, Which is and will always be the heatsinking of the LD.. now that said, Main problem here is the basic understanding of the term heatsinking, which we infact are mixing with terms which doesnot prove anything without the mathematical answers for the geeky thermodynamics equations and God knows what constants..

2. To summarize and support my argument, the 5.6mm size of the LD is too small, and it gets hot..
So to Increase that MASS, Cu with its faster absorption of heat from the source LD is BETTER.. Now At this point only Cu is not sufficient..
Aluminium fins WILL DISSIPATE HEAT FASTER.. So to say the thermal equillibrium will occur faster.. Heat absorbed from the source LD will be equal to Heat dissipated in less time... As we all must know after that there is no rise in the temperature lets say the terminal increase in temperatures is about 10C and is established at 180sec.

 

[lasersbee]

- Picture a room with a fire in the middle of it.
- The room's only escape is via a single hallway.
- At the end of the hallway is a single revolving door to the outside world.
- That revolving door to the outside world can move 5 people through it every minute.

Now imagine that there are hundreds of people in this room that is on fire. What's more important, that people can run down the hallway quickly, or that the hallway is able to hold lots and lots of people?

You've explained the hallway as Copper... (quick movement of heat)
The revolving door is your ability to move the heat to the air..
I would get rid of the revolving door for better heat dissipation
into the air...

Now place obstacles in the hallway and you have Steel... (slow
movement of heat)

The idea of a heatsink is to move the heat generated by a Laser
Diode away from IT as quickly as possible so IT does not overheat.


Jerry

 

[rhd]

Yep,

And those obstacles are just fine if the hallway can fit more people in it, slowly walking towards the door that can let out 5 people per minute.

 

[RyanElectro]

All that reading and a brilliant example from rhd, i would like to finalize the thought in one sentence..

"Copper Core Heatsink with finned aluminium"

Why?
1. First off we have to decide the priority here, Which is and will always be the heatsinking of the LD.. now that said, Main problem here is the basic understanding of the term heatsinking, which we infact are mixing with terms which doesnot prove anything without the mathematical answers for the geeky thermodynamics equations and God knows what constants..

2. To summarize and support my argument, the 5.6mm size of the LD is too small, and it gets hot..
So to Increase that MASS, Cu with its faster absorption of heat from the source LD is BETTER.. Now At this point only Cu is not sufficient..
Aluminium fins WILL DISSIPATE HEAT FASTER.. So to say the thermal equillibrium will occur faster.. Heat absorbed from the source LD will be equal to Heat dissipated in less time... As we all must know after that there is no rise in the temperature lets say the terminal increase in temperatures is about 10C and is established at 180sec.

100% agree. So true.
First contact = Copper
Heat dissipation = Aluminum

 

[benmwv]

While having a 5.6mm LD mounted directly into steel wouldn't be a great idea, steel does have a higher specific heat than copper and aluminum so it can hold more heat. You have to find the balance between: 1. having enough surface area between the initial copper heatsink and the secondary steel heatsink that you can transfer heat to the secondary heatsink without causing the primary heatsink to rise in temperature due to the thermal resistance 2. having enough steel to provide an adequate amount of heat-holding capability.

If the steel is too big (making the copper too small) you wont be able to transfer heat between them well. If the copper is too big (and steel too small) there will be very little benefit to going through the trouble of a secondary steel heatsink.

Regardless of ^that^ though, I would still stick with copper as the metal of choice because it still has a high specific heat, and has very good thermal conductivity too.

 

[Wolfman29]

I like rhd's example. However, I think the issue is that we want to get heat away from the diode as quickly as possible. While steel can hold a BUNCH of people walking slowly towards the door, there is still a big back up of people in the hallway. However, if everyone runs towards the door and its thinner, assuming that all of the people can fit in the hallway (i.e. the amount of heat generated by the LD *can* be transferred throughout the heatsink faster than it can generate heat), then there will still be very few people near the burning room. However, even if its really wide, for a significant amount of time, there will still be people NEAR the room (heat near the diode, and thus it will be hotter near the diode).

Basically, what I am saying is that, because copper is sufficient to absorb the heat from a heatsink (it certainly if if SS is - it's heat capacity is only slightly lower), then what we want is the highest conductivity to get the heat away from the diode quickly. Of course it will fit up faster, but that's not our concern. We're okay with a filled heatsink, as long as its the diode that fills up last (i.e. there will be a traffic jam near the door BEFORE a traffic jam near the room/hallway entrance). However, if more people are trying to go into the steel hallway than they can exit (i.e. if its not wide enough to hold everyone), then we will have a traffic jam near the fire (diode) and the heatsink won't be doing its job.

 

[Tech_Junkie]

Damn. You guys need to get laid. Geez. :na:

 

[tsteele93]

Are you kidding me? Have you taken a look at the price of Nickel?

The cost of Nickel IS cost prohibitive. The cost of steel is not.

No, but since we are also discussing silver in small amounts that we would need for sinking lasers and the fact that most Canadian nickels up to 1982 were made from 99% pure nickel leads me to believe it wouldn't be astronomical.

Sure, if you search here for machinists using steel, you won't find any. Why? Because this thread was posted yesterday, and until now, nobody has seriously suggested it. But if you actually search for rod stock at the sources our machinists use, you'll find tons of it (generally more if it than aluminum in fact).

Whoah, I'm not searching HERE. I'm talking about massive hunts on google for heat sinking materials. Nickel just isn't there except as a plating, mostly for looks.

I understand that sinking a laser isn't exactly the same as sinking a processor, or likely many other sinking situations, but many of the important parts are the same. You've got to move heat away from the diode.

In our situation, much of the time you are going to simply take the diode's heat and spread it throughout a hunk of metal surrounding the diode and that will be the end of it for all practical purposes. Some heat transfer might take place from the outer shell of the host into the air or your hand, but most is going to sit in the sink, slowly getting warmer. UNLESS you have a sink big enough and with a reserve able to hold all of the heat generated at a steady level.

As someone else mentioned, we aren't talking about a LOT of heat here, so we likely don't need fins and air cooling for MANY of the builds anyway.

In many cases, a nice hunk of copper can do all you need.

I understand what you're hinting at re: specific heat capacity doesn't help if you can't move the heat throughout that entire heatsink anyway. But that's not the reality of how much impact heat conductivity has. You would never have the center of a steel heatsink getting hot, while the edges didn't.

But you could have a metal that was poor enough in conducting heat that the area near the diode is hotter than the area near the outer body of the laser.

My point is that thermal conductivity DOES matter a LOT.

I think Stainless could be a metal that doesn't spread the heat evenly enough and fast enough to be a great sink material. I also suspect it is hard to machine, worse than copper or aluminum, but I'll leave that to the guys with lathes to speak up.

I also have a source at NASA who does exactly this stuff (KSC prototype lab - machining metals and such, not specifically heat sinking), so I am going to try and drag him into this discussion if I can.

When you're talking about 5 to 10 mm of thickness to the "ring" of a typical heatsink, and 1 minute or longer duty cycles, you WILL get the heat spreading through that heatsink, regardless of the metal. In a scenario (as has been discussed ad nauseum here) where you can't transfer the heat to the outside environment efficiently, your best bet is to be able to absorb as much heat as possible. That gives you a longer duty cycle, period.

Again, I think there may be metals that don't spread the heat evenly enough or quickly enough and would leave the area near the diode hotter. I might be wrong on that, but I know good alloys of copper and aluminum take every bit of heat thrown at them and VERY quickly spread it out evenly over the entire sink.

As long as they can hold enough heat to stabilize at a safe working temp then they will work well and we don't have to worry about whether the heat has been spread evenly and away from the diode.

For instance, if you have a theoretical sink made from copper and another from SS and you fire up your diodes, the SS sink may feel cool to the touch on the outside for some time as the heat works it's way through the sink and during that time, the SS near the diode is hotter than the areas that haven't had the heat "arrive" yet.

The copper would very quickly begin spreading that heat evenly throughout the sink, resulting in lower temps at the diode.

- Picture a room with a fire in the middle of it.
- The room's only escape is via a single hallway.
- At the end of the hallway is a single revolving door to the outside world.
- That revolving door to the outside world can move 5 people through it every minute.

Now imagine that there are hundreds of people in this room that is on fire. What's more important, that people can run down the hallway quickly, or that the hallway is able to hold lots and lots of people?

With copper, everyone gets farther from the fire quicker so no one gets burned. With stainless, the people have to mingle around near the fire longer before they get to enter the hall and they are hotter when they get there. Plus, everyone may not get away from the fire, while copper moves them to a safe distance faster.