RepRap PCB Heatbed MK2 - Improved heated bed for Prusa & Mendel

Description from http://www.reprap.org/wiki/PCB_Heatbed_MK2

MK2 Heatbed - Minor changes by Tony Lock

I liked Josef's original design but wanted to be able to use through hole components, have the thermistor poke through the middle and for it to look good on the 'back' with the silkscreen that Josef designed on that side as well.

Printing

Although you can print directly to the bed covered in Kapton/polyamide tape, no PCB is perfectly flat. It is recommended that you follow the directions in mounting, below, for better results.

Mounting

MK2

The MK2 board can be mounted either side up and is designed to be mounted as Josef describes:

http://josefprusa.cz/pcb-heatbed-final-mounting-and-wiring-solutio

The holes in the 4 corners to attach the heated bed MK2 to the top print plate are not suitable for M3 bolts though! Use M2.5 instead.

The glass protects the tracks from a head crash and is easily swapped out.

The board dimensions are identical to the MK1 design.

Insulation between the board and the thick plate should improve heat-up times and reduce energy consumption. An example is here:

http://reprap.org/wiki/Mendel_heated_bed#Thermal_Insulation

Caution, I have not tried this with the temperatures that the PCB bed can reach!

Sides

MK2

The PCB still has a side with the traces on and a side without but now the silkscreen is on both the top and bottom, this makes it look good even when 'upside down' under a layer of glass. The LED, resistor and power wires can be mounted on either side of the board, with either surface mount or through hole components. If you are using through hole be careful when soldering to not have overhang on the other side of the board that could interfere with the glass and introduce a gap between the glass and the PCB.

There is a central hole in the board (similar to this one http://wiki.makerbot.com/cchb1). It is sized so a small thermistor (for example the EPCOS one: http://uk.farnell.com/jsp/search/productdetail.jsp?CMP=i-ddd7-00001003&sku=3878697 ) will fit though it allowing contact directly with the glass.

Connection

Polarity doesn't affect the PCB, however the LEDs have a polarity.

MK2

There are pads and plated through holes for connecting the power wires, ensure that the wire you use is thick enough for 10A. It is a good idea to think about strain relief so your moving build platform does not flex the joint, this can lead to failure of the joint over time. I recommend routing the wire from the heated bed to strain relief on the thick sheet before routing it to your controller/power supply.

Optional LEDs

MK2

The LEDs are optional, but if you choose to use the LEDs you MUST install the resistor.

'Parts' (Not included)

2 x Surface Mount LEDs (traditional wired LEDs may also be used)

1 x 1K ohm Surface Mount Resistor

With the MK2 traditional wired parts can be substituted for the Surface Mount parts.