gallery into which filtered air can flow and exhaust through the nozzle guard 24 the flex pcb 17 carries all data and power connections from the main pcb not shown to each u201c memjet u201d printhead module 11 the flex pcb 17 has a series of gold plated domed contacts 69 fig2 which interface with contact pads 41 42 and 43 on the fine pitch flex pcb 26 of each u201c memjet u201d printhead module 11 two copper busbar strips 19 and 20 typically of 200 micron thickness are jigged and soldered into place on the flex pcb 17 the busbars 19 and 20 connect to a flex termination which also carries data the flex pcb 17 is approximately 340 mm in length and is formed from a 14 mm wide strip it is bonded into the metal channel 16 during assembly and exits from one end of the printhead assembly only the metal u channel 16 into which the main components are place is of a special alloy called u201c invar 36 u201d it is a 36 nickel iron alloy possessing a coefficient of thermal expansion of 1 10 th that of carbon steel at temperatures up to 400 u00b0 f the invar is annealed for optimal dimensional stability additionally the invar is nickel.