This was the first upgrade made on my K8200. The heater bed tends to buckle and in that case you cannot achieve a exact print. The reason is the PCB heatbed does not heat up evenly and often it is braced by the mounting screws. Additionally, the back side is not reliable enough to hold a object. So i decide to use a glass plate. I decide further to turn around the PCB down side up because the board is a FR4- or FR5- PCB and thus has bad heat transfer rate. Now, the prints are better fixed on the plate and the warm up phase is shorter. I changed the heatbed supply voltage from 12V to 24V like eytec described on http://www.thingiverse.com/thing:153877. This all brought a imense improvement. Warm up from 20°C to 65°C in less than 4 minutes. Max. temperature: 97°C. Once printed object (PLA) is not removable till temperature falls down under 35°C You need a standard glass as it is used in cheap picture frames. The size should be at least most 20 x 20 cm an 2mm thick. To turn around the PCB and use that glass plate you have to replace the thermal resistor first. To fix the glass plate use these well known metall paper clips, but it ist recommended to upgrade these clips like i did here: http://www.thingiverse.com/thing:270482 Further, i add a second cardboard to improve thermal isolation. Cutting of free areas (see image) to have more air (better isolation) between the PCB and the second cardboard.