Anatomy of a 7900/9900 Ink Cartridge

If you've never wondered what's inside an ink cartridge (besides ink), that's probably because you have a normal brain and worthwhile things to do with your life. I, on the other hand.... Sometimes it's useful to know how or why things work. Sometimes not. Either way, it's often interesting. I can't resist taking things apart.

What follows is a series of photos of the parts inside my spent, 90ml "starter" cartridge of light magenta ink. While I have some hunches about the purpose of the various pieces, I've no direct knowledge from Epson. Best I can do is guess what some of these things do.

This view shows the cartridge after I snapped off the cover. The front "handle" end of the cartridge is at the bottom of the picture. There's a transparent film seal (which I removed before taking this picture) covering the compartment housing the ink bladder (the silver bag with the bar code). That seal allows the cartridge to be pressurized by the printer through the nipple at the bottom-rear of the cartridge. I replaced this cartridge when the 7900 stopped printing and required a new one. It's clear the machine squeezed every last bit of ink from the bag. It's completely flat, with no pockets of wasted ink. Nice!

The rear of the cartridge. The CSIC chip (Customer-Specified Integrated Circuit, a micro-controller made to Epson's specifications) is at the top. Below that is a component with a small ink reservoir, the valve through which ink exits the cartridge, and a pair of conductors that make contact with pads on the underside of the CSIC chip. The nine gold pads on top of the CSIC chip communicate cartridge status to the printer.

 This complex gadget includes a small reservoir through which ink flows from the bag to the exit valve that mates with the nipples in the back of the printer's ink bays. The nipple at far left fits into the ink bag in the cartridge.

There's a chip, or perhaps a piezo element, between the two metal tabs behind the small reservoir. My guess is that this either counts pulses from the small, spring-loaded "paddle" that covers the reservoir (not shown), or directly measures or senses the presence of ink in the reservoir. In any case, the count or sensed input is communicated via the metal tabs to the CSIC chip shown in the next image.

The CSIC chip, showing the chip-on-board construction. The two gold pads, showing slight wear marks in their centers, make contact with the metal conductors running to the top of the part in the previous two pictures. This board has nine gold pads on the opposite side. I assume there are matching contacts for at least some of those pads in the printer's ink bays, so information from the chip can be communicated to the printer.

That's the best I can do with my technical guess-work. Perhaps someone more knowledgeable can chime in with descriptions of what these parts really do, and perhaps provide proper names for the various components.

Clearly, when one buys a cartridge (currently I'm paying about $85 for 150ml carts) one is getting much more than ink.

  --Jay