February 28, 2018

HP DeskJet 840c thermal inkjet printing head : weekend die-shot

This chip was used in monochrome ink cartridge of HP DeskJet 840c thermal inkjet printer. Die has a "power" transistor to control heating element near each nozzle. External heaters are connected on top and bottom parts of the chip. "Heaters" are printed on a Kapton film using conductive ink, and this film is glued to the face of the die to directly connect printed heaters to the die pads. When heater is enabled - it forms small bubble of vapor which ejects small droplet of ink through the nozzle.

Die size 15.12x4.39 mm.

Inkjet nozzles on a Kapton tape are likely ion-etched, laser drilled holes should have been much less perfect. On the other hand positions of nozzles are slightly not regular.

Nozzle diameter is 25µm, nozzle pitch is 75µm.