EEVblog #1196 - Custom Heat Sink Design

[EEVblog]

Designing your own custom heat sink is cheaper and easier than you might think.
At look at why you might want to design your own heat sink, the costs, the advantages and disadvantages, design considerations for surface mount PCB's, air convection, and mechanical DRC, and die-cast vs machining.

[nctnico]

That seems very cool! I'm going to keep this in mind for a project I'm working on. Still I have a few questions...
1) where can you have these made?
2) what are the ballpark startup costs?
3) what are the volume production costs?

Another thing I'd like to point out: the cast aluminium is likely ZAMAK. In the past I have had problems with cases made from ZAMAK. For some reason it may act as an antenna and cause EMC problems for radiated emissions. A plastic or pure aluminium housing where not a problem but the same board in a ZAMAK casing suddenly brought out a huge spike which was below the noise floor when using the other casings or no casing.

[langwadt]

will be interesting to know how well the top heat-sink works. I suspect the horisontal spreading resistance of the copper area is pretty bad compared to the vertical resistance though vias directly under the tap. But with the pockets cut out to fit on he top the bottom heatsink can't take advantage of that 

[EEVblog]

That seems very cool! I'm going to keep this in mind for a project I'm working on. Still I have a few questions...
1) where can you have these made?
2) what are the ballpark startup costs?
3) what are the volume production costs?

I address that in the video, any CNC house will machine it. For casting just search for any aluminium casting place on Alibaba or locally.
Exact volume production cost not 100% sure yet, but should be cheaper than commercial heatsinks.

[EEVblog]

will be interesting to know how well the top heat-sink works.

There is no top heat sink in this case, I just mentioned it was possible because the of the design symmetry.

[Razor512]

I wonder, for a low volume product, would it be possible to just get access to probably older CPU heatsinks that would be decently effective on a mobile device?

For example, would it be possible to get a company to check if they have any old unsold stock of a heatsink, and then design the case to hold the repurposed heatsink in place?

e.g., Some of the older Scythe branded heatsinks did not sell very well, especially since at the time not all cases were well suited to handle the odd shape, but if it can be repurposed, for lower thermal loads (e.g., from a portable device), you may be able to get away without needing a fan.

[orion242]

Where does sintered metal parts fit in the cost/volume matrix?

Forgive me if that's not the exact term.  Powered metal compound molded and heated under pressure to form the finish part type process.

[johnlsenchak]

That heat  sink design is  very similar to what  computer  laptop  manufactures  do  with   thermal connections   between the CPU and the  fan  heat exchangers   which goes across    the  motherboard  space  Would  love to see  how Dave #2  did  the CAD  design  of that heat sink , along with   the type of SIL pads  that you are going to use to interface  the surface  mount  transistors  to the  metal  surface.

[helius]

For those who may not be aware, there are compact heat spreaders that can move much more heat compared to solid heat sinks, using vapor phase technology. It is an extension of the sealed heat pipes used in laptops.
http://www.wakefield-vette.com/products/fluid-phase-change/standard-vapor-chambers.aspx

[mariush]

May be a bad example, but if you change the fin direction it looks like a heatsink that could be extruded in long bars then cut heatsinks to desired widths.

Then just use one of those wire saws to cut that curve and drill two holes for the screws (use one big drill to remove fins around screw hole, then small drill for actual hole).

[Barny]

It would be nice to see the mechanical approach of an electronic guy.
Is there an reason to manufacture these prototypes in china and not locally?

May be a bad example, but if you change the fin direction it looks like a heatsink that could be extruded in long bars then cut heatsinks to desired widths.

That would be much more expensive.

Depending of the casting method the only machining needed is the contact-surface.
(Using a steel-mold or fine casting in lost ceramic molds.)
Using sand-castings the holes need to be drilled too.

For an extruded part you have to make the extruding-form, pay the setup-costs for extruding, pay the extruding, pay the set up costs of the saw which cut them in length, pay the cut, pay the setup costs of the mill, pay the mill costs.
All together this will cost nearly the same than milling the whole heat sink out of an solid block

Then just use one of those wire saws to cut that curve and drill two holes for the screws (use one big drill to remove fins around screw hole, then small drill for actual hole).

That would be two settings.
First drill the two holes with an stepped drill.
Stop the machine or let the machine work on another part.
Take the part out of the vice or holding device and turn it 180°
Put the part back & machine the second side.

Thats an quite labour intendsive work.

Thats why casting is the cheaper solution in this case.

[mariush]

see below.. and then..
Would be interesting to know what would be the difference when it comes to heat transfer between having both "legs" the same width, or the one on the left being wider... does it really help that much with that circuit board?
If die casting is so cheap, what would be the point of using extrusion anymore? Tooling costs for extrusion vs casting? 

I was thinking of something like this

Flip the fins, lose the fins above and below the screw holes (so you use only one drill)
Make both sides with the screws same width so you have symmetrical layout (less aluminum lossess when you cut the rectangles from a long extruded bar).. or no losses if you can live with 90 degree instead of that curve shape
Maybe make the vertical height of the "legs" smaller so that you could add on one side a wider strip of aluminum to cover that wider pad on the circuit board. IF just adding a bit of thick thermal pad won't do basically the same thing.
I imagine extruding would also help if you later decide to make the heatsink smaller in length (as you'd just drill the holes closer together and adjust the cuts)

[Barny]

The best manufacturing method depends on the requirements.

If you only need to cut the part lo length or put one hole in it at maximum, extrusion is the way to go.
But if you need to cut the pattern like you have shown in the picture & need pockets for the parts like shown in the video, the production costs shoot up quite substantial.

To get an non linear cut in an industrial way, you have to mill or use a water-jet cutter.
Both way add their part to the costs.
Its possible to cut the parts with a band saw.
But only a small number and with low accuracy.
To cut 1000 to 10000 parts with a band saw is not practicable.

The tooling costs for casting depends on the methode.
Sand casting and fine casting with ceramic have low tooling costs but higher running costs.
Casting with steel molds have similar tooling-costs like extrusion but next to no running costs.
(Except the needed aluminium and the heating to melt the material.)

The main cost factor in this case is the amount of chipping needet.

Thats why I wrote that casting is the cheapest solution in this case.
There is no "best way" to produce parts.

[rx8pilot]

I have done piles of custom heat sinks for very low-volume stuff. It can be fun making them look cool.

[rx8pilot]

A fun RasPi project that needed to operate in high ambient temps - only needed a few of them.

[wilfred]

I have done piles of custom heat sinks for very low-volume stuff. It can be fun making them look cool.

Nice work, First class pun that. 

[Brumby]

Nice work.

[ali_asadzadeh]

Dave, that's cool. please show us how it's done in the CAD

[rx8pilot]

Im no expert, but I think instead of custom heatsink, which is so expensive, it makes more sense to probably redesign the pcb

in a recent gamers nexus video, they talked about using dummy plastic jigs to play where the heatsink should go game? I dont know, maybe the entire circuit should need a rethink from perspective of heat first. but that will lilkely create the messiest ratsnest in the world

If there is an option for an off the shelf heat sink....TAKE IT.
Not all designs have the option. In my experience, the high-density projects usually end up needing a custom solution. If I have a bunch of room, there are all sorts of options available that are way cheaper and easier.