Four major components comprise an inkjet cartridge (Fig.lA): (1) the pen body which contains the ink and positions the cartridge in the printer; (2) an ink delivery system which supplies ink at the correct backpressure and flow rate; (3) a flex circuit which provides the electrical interconnect to the printer; and (4) the printhead which generates and directs the drops. Because of its complexity and small critical dimensions, the printhead poses the greatest analytical challenge for many failure analysis problems. Each printhead may contain as many as 300 firing chambers (Fig. IB). Each chamber consists of a resistor surrounded by a polymer-based barrier material which forms a cavity into which ink flows from the ink delivery system. The chamber is capped by a metal or polymer orifice-containing plate. Printing occurs when the resistor is heated to form an ink vapor bubble which subsequently ejects a droplet of ink though the orifice onto the paper.