This heatbed is an etched, single sided 220x250mm big PCB, ~1,5mm thick in total with 35ym coppper thickness.Mounting it
The PCB itself is not flat, but can be bent slightly. Similar to Prusajr's design, I utilized magnets to keep the sides down.
The Magnets I use are 9mm in diameter and 5mm thick NdFeB ones. They have a catch: The ones I use can only withstand temperatures up to 80°C. Because of that, I didn't glue them onto the PCB, but I glued some strips of steel tape onto it with temperature resistant glue.
I made a pile of 2 magnets each on four sides of an MDF board hoping to keep the temperature down a bit. The magnets are glued to the MDF using some expoy glue. So far, this works nicely.After a couple hours of operation, the glue on the middle piece failed. The ones on the side don't get that hot and are still working.
As it turns out, magnets are not the most elegant way to mount it but probably the easiest non-permanent "do-it-yourself" way.
Electrical issues
The heatbed needs a lot of power. It draws 11A @ 12V when cold. Using this kind of power from a ATX PSU requires to use two plugs and probably a very good PSU. I had problems that the voltage on the +12V rail dropped too much on my 400W PSU (which is appearantly rated for 16A on the +12V rail). Currently I'm using an external power supply for the heatbed.
Heating up & Polyimide Tape
To stick ABS onto the heatbed, I use Polyimide tape. Those can be ordered in the same size as the PCB is. Large strips of Polyimide tape are a bit tricky to get on to the PCB without air bubbles. The factory actually suggested a machine to roll it onto, but from $350 a bit pricey.
Anyone else use large tape and have different experience?
Printing quality
Apart from some air bubbles I had, the parts come out perfectly flat. A bit of warping still appears on the sides of the heatbed. Nophead wrote about this and has a nice solution for his Mendel.
The bigger problem I still see is in adjusting the heatbed. If the nozzle height is not set correctly, it can easily snap traces on the PCB. Once snapped, they can be repaired with solder and some sanding, but the results are far from perfect.
I was thinking of putting a thin sheet of aluminium on top of the heatbed to protect it. But this would need a better way of mounting it.
Posts
Why not use a double sided PCB with solid copper on the top side?
ReplyDeleteThat way it be flatter as the copper is balanced.
Hi Nophead,
ReplyDeleteI spoke to a couple of manufacturers. On single sided PCBs some of them do additive process, some of them subtractive process (normal etching) to reach the desired copper amount. On doubles sided PCBs they all do additive process.
When they manufacture it with additive process the copper amount will be 35µm +-8µm. On subtractive process it will be base material tolerances (which I don't know yet) -5µm.
I think the difference in tolerances of the different manufacturing processes will make a big difference.
I think that additive process on double-sided PCB is neccesary only when plated holes/vias are used. So there should be no problem to use substractive process on both sides (can check easily with my pcb house).
ReplyDeleteI would be also concerned with temperature coefficient of copper. Hotter areas will have higher trace resistance, thus consuming more power a heating even more. Thermal resistance to ambient should compensate this to some degree, but bed temperature MAY be quite uneven.
Petr,
ReplyDeletewith rising temperature the resistance goes down, so does the power consumption. A double sided etched PCB would be perfect. Note that you should ask at least for FR4-TG150 material.
Where can we buy the polyimide-Tape in the proper size? Can you please give information about your distributor or add the polyimide tape as a Product in your Shop?
ReplyDeleteI just bought the heated platform and some material and I'll need some polyimide tape also...
Cheers Ijon
Even i was already working on this project and very soon i published it.. Thanks for share this great post and it also help me to get some more better ideas. Keep moving on ..Nice blog.
ReplyDeleteprinted circuit board manufacturers
PCB prototype plays a very important role in the creation and design of PCB. It gives you the opportunity to check your product before production. These are checked in all critical conditions as everything must be checked and every problem must be solved before the production. Thanks a lot.
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