Custom made heated bed.
My bed size is 275*220mm and got tired of cheap aluminium heated beds. I have not found any good options given my bed size so I have decided to build my own one.
1) Bought a 10mm thick rectified aluminium plate;
2) Designed a custom PCB heater made out of 4 double sided PCB's (at www.jlcpcb.com anyhow you need to order a minimum of 5 pieces so instead of designing one big PCB I designed for 4 smaller ones). The heated side is towards the aluminium plate for best heat transfer.
3) Stick the 4 PCB plates on the bottom of the plate using a high temperature resistant PCB glue (I tried with gap-filler material + screws - no success the PCB bent more than the gap-filler elasticity).
4) Test - turned out that the cooper thickness on the Chinese PCB is closer to the lower limit, therefore I ended up at about 310W @ 25 deg instead of the intended 360W total. 80W intended power / module at 60 deg Celsius.
5) attached a frosted sticker on the top.
Overall I'm satisfied with the result it work pretty well, this is a pretty cheap way to build your own heated bed, no need a bit of layout design knowledge. The price of the 5 PCB's was 5$ and another 30$ for the aluminium plate.
This heated bed works without any issues up to 100 deg Celsius.
P.S. The infra-red pictures are not done in a proper environment, the heated bed temperature is seemingly not completely uniform, this is only because I've done the picture in an open space near the window this causes additional reflections from outside IR radiation. Nevertheless my aim was to check for hot-spots which may be caused by gaps in the PCB glue.