| 摘要 |
A dispensing pump for dispensing liquid, particularly suitable for dispensing two-part epoxy for encapsulation of integrated circuits, includes a pumping chamber in communication with a nozzle via a three way valve, the pumping chamber including an outlet, an internal volume, a pair of spaced directional seals located away from the outlet, an open volume reciting between the seals and an external port opening the open volume to atmosphere. A stepped plunger extends axially within the pumping chamber, with a first portion sized to be received and aligned through the first directional seal, the plunger being movable to move the first portion toward the outlet to close off the internal volume at the second seal. The second portion of the plunger is relatively smaller in transverse cross-sectional dimension than the inside diameter of the second seal, to cooperate with the port to promote fluid removal from the internal volume during initial filling and priming of the pumping chamber. Once filled and primed, the plunger causes positive volume displacement of liquid from the pumping chamber and out of the nozzle, with very good repeatability and high fluid flow rates, independent of material viscosity, and/or temperature or viscosity changes. For refilling, the plunger is retracted from a volume which corresponds to the volume of material refilled into the internal volume. |
