RAMBo Motor Driver Heatsink Upgrade

[teoman]

I found these for a good price and I installed them. These heatsinks were originally designed for raspberry PI's and similar higher performance small computer cards.

As I was installing them, i started thinking, did I do something stupid.

Obviously they will help with cooling the drivers, but are the drivers in need any cooling? (I will be installing the whole printer inside a chamber, and we can get close to 40 degrees here in the summer).

In my imagination, they cannot do any harm while they work, however if they were to detach themselves from the chips that would not end well.
From what i can read from the labeling on the adhesive tape on their back side (it was a double sided black tape), it is manufactured by a company called "Dexterials Materials Corporation".


NOTE TO PEOPLE WHO WILL DO THIS MOD: Install or print a temporary spacer between the chips and the sockets for the motors. This will enable you to have all of the heatsinks aligned. If not, you can install them according to fengshui as I did.

[rpress]

Those chips can certainly be helped with additional cooling.

They are the "QFN" type package like these:
[img]http://media.digikey.com/Renders/Texas% ... 20-QFN.jpg[/img]

You see the large pad in the center? That's the part attached to the silicon die inside, and that's how the heat is drawn out of the chip. The circuit board is soldered to that square pad, and a bunch of small vias draw the heat out and into the board. So really the most effective way to cool those chips is to cool the board down. You can do this by putting the heat sink on the back of the board. In addition the fan blows onto the back of the board so the additional surface area of the heat sinks will have the greatest benefit there. Having one on the top won't hurt, but really the back is where you want it.

I suspect your heat sinks are too tall for the stock board spacers so you may need taller spacers. In my thread I show the heat sinks that I use. Note that I put these heat sinks on top and bottom because they came 20 to a pack.
http://forum.seemecnc.com/viewtopic.php ... 539#p51042

[Eaglezsoar]

rpress, thanks for the excellent tip!

[Jimustanguitar]

There's some conjecture on this... Some will tell you that certain chips are designed to shed heat through their connection legs into the circuit board and that you draw heat through the cooler parts of the chip by putting a heat sync on top of them...

I can understand the argument, but I didn't buy it. I've got the little adhesive heat sinks from ultimachine on mine.

[Eaglezsoar]

There's some conjecture on this... Some will tell you that certain chips are designed to shed heat through their connection legs into the circuit board and that you draw heat through the cooler parts of the chip by putting a heat sync on top of them...

I can understand the argument, but I didn't buy it. I've got the little adhesive heat sinks from ultimachine on mine.

I also use the heatsinks on top, I do believe that the bottom would be better but placing them on top also dissipates a lot of heat.
Mine work fine being on top so I am not about to change it.

[rpress]

The metric here is thermal resistance. A heat sink on top will have to conduct through the plastic of the package. A heat sink on the bottom will conduct through the thermal pad, through the solder, through the copper vias, and finally through the solder mask. While this seems like a more torturous path, the thermal resistance is lower (better).

A heat sink can dissapate more power with a higher temperature difference to ambient. This is why you want the heat sink on the hottest part of the chip.

[geneb]

That type of chip is _designed_ to be cooled the way that rpress describes.

g.

[JFettig]

Keep in mind, the PCB is quite a good insulator, having a heatsink on the front will help, even though it might be minor.

[teoman]

Yes. But I would liketo imagine that the designers of the rambo board took that in to consideration and made under the chips dense in metal.

[enggmaug]

I would have learnt something today. Thanks...

I'll keep my heatsinks on the top, as they are already there, and satisfactory until now... My board did not freeze anytime since I have them installed.

But well, that is good to know.

[teoman]

If the drivers overheat, the RAMBo should not freeze. From what i understand, if they overheat they will miss a step, but the microprocessor/software will be unaware of it.

If the rambo does freeze due to heat you should install a heatsink on to the Atmel microprocessor.

[enggmaug]

It used to freeze on long prints. I read somewhere on the net it was from the drivers overheating.
I installed heatsinks, nad try to keep the printer door open while printing... since that, hours, days, weeks, months of printing without a single freeze.

You may be right that it could be from the processor, since I open the door, it does help it to cool down a bit... but well... I don't really want to investigate more, as it would imply vonluntarily fail some prints.

[teoman]

Well, today i had to open up my board and apparently the adhesive is not up to it. The heatsinks had shifted down. I suspect they are either lower quality or they were intended to be attached to boards that lay flat.

[Jimustanguitar]

Well, today i had to open up my board and apparently the adhesive is not up to it. The heatsinks had shifted down. I suspect they are either lower quality or they were intended to be attached to boards that lay flat.

Hope you don't short anything!


My post earlier in the thread sounded snarky, yikes. I wasn't trying to call the experts naysayers, I was just saying that some cooling, regardless of the type, has got to be better than none Hopefully I didn't make anybody bang their head into the wall.

[teoman]

I did not perceive any snarkyness.

I removed them before a problem occurred.

[RocketMagnet]

Then Rambo Manual here covers this issue on page 9:
http://reprapelectro.com/wp-content/upl ... Manual.pdf

"The design of the RAMBo also allows it to act as a heat dissipater for the stepper motor drivers, which means that there is no need to install a heatsink on the stepper driver chips as was often the case with the RAMPS."

However I agree you can never have enough cooling and keeping those chips cooler will be a useful addition.