An ink cartridge for a pen includes a cartridge having a writing tip. The method also includes distributing a soldering paste on the at least one first and one second pad, so as to form a first and a second contact conductive bump with electric connection contacts of the micro module, and distributing, along the whole perimeter of the micro module or of the recess, a layer of non conductive glue. A resistive element is formed on the quartz chip. The coating comprisesa first, innermost layer of TiCxNyOz and a total thickness from about 0. A ferning index is also defined and calculated based on the percentage of area coverage of line segments which are exceeding the threshold line length. A further heat transfer interface is formed between the heat sink plate and the top panel in the assembled light bar.