Principles of Pneumatic Inking

Pneumatic inkers work on the principle of constant air pressure and varying the amount of time that the valves are open (pulse duration). Ink dots are deposited via pneumatic actuation of a shuttle mechanism and a simultaneous pulse of air into the cartridge reservoir.

The air pulse into the cartridge reservoir causes the ink to be displaced through a Teflon tube, forming a small droplet of ink at the end of the tube. At the same time, the shuttle (cartridge holder) moves downward via a pulse of air compressed into a cylinder. When the shuttle reaches its fullest travel (the cartridge tip is 1-2 mils from the wafer surface), the ink droplet is deposited. After 22.5 milliseconds, the shuttle air valve closes and the shuttle retracts.

When the cartridge air pulse is complete, the valve closes and the ink flow is stopped. This causes a small vacuum to develop, pulling excess ink back into the cartridge reservoir. This prevents ink dripping. After 10 seconds without actuation, the air valve is opened for 10-20 milliseconds (depending on dot size setting). This displaces a small amount of ink back into the Teflon tube and aids in maintaining proper dot size after a long delay between dots.

One cartridge configuration can produce a range of dot sizes. The dot size in a standard cartridge (or conventional inker) is determined by the filament diameter and inside diameter of the needle (which control ink flow). Different dot sizes require different cartridges/inkers. In a pneumatic system, dot size is controlled by changing the duration of the air pulse into the cartridge reservoir. This determines how much ink is forced through the Teflon tube and thus the size of the ink droplet. Therefore, a given cartridge configuration may offer a dot size range of 20-30 mils or 30-40 mils (depending on the controller setting).  

Pneumatic inking addresses the problem of inking large dots with conventional inkers; the flow volume required for large dots (and typically long test times) can often result in inconsistent inking. When there is a long wait between bad die, excess ink easily builds up at the end of a filament, resulting in dripping or the deposition of ink "blobs." However, at higher speeds the ink flow is insufficient to keep up with filament travel — resulting in undersized dots. This problem becomes severe at off-line speeds of up to 15 dots per second.  

In a pneumatic system the automatic vacuum pulse discussed previously eliminates the problem of ink dripping. Undersized dots do not occur because the ink flow is not dependent on filament travel for deposition — it is a function of the air pulse duration and pre-set shuttle travel. Ink viscosity and tube size are matched in the cartridge and characterized for a specific range of dot sizes at different air pressure and controller settings.  

Controller Specifications (Except Auto-Z and Motorized-Z)

Pneumatic Ink Cartridges