Dispensing – Motor operated outlet element
Reexamination Certificate
1999-10-29
2001-06-26
Bomberg, Kenneth (Department: 3754)
Dispensing
Motor operated outlet element
C222S509000, C222S518000, C251S065000
Reexamination Certificate
active
06250515
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to liquid dispensers and, more particularly, to dispensers utilizing reciprocating valve stems to selectively dispense liquid through an outlet.
BACKGROUND OF THE INVENTION
Various liquid dispensers, such as positive displacement piston pumps, are used to accurately dispense viscous liquids. These pumps may be used, for example, during the manufacture of semiconductor chip packages to dispense encapsulant material around a silicone die after the silicon die has been electrically connected to a substrate, such as a PC board. For many applications, it is desirable to dispense these viscous liquids in near vacuum conditions. Vacuum encapsulation has been developed to better obtain void-free encapsulation of the silicon dies. Typically, capillary action pulls the encapsulant material beneath the die to encapsulate all of the wire bonded leads and electric contacts between the die and the substrate. Void-free encapsulation ensures that the delicate wire bonded leads are protected from moisture, chemical attack and mechanical stresses.
The pumps normally used to dispense such materials rely on atmospheric pressure to keep the liquid from dripping out of the outlet between dispensing cycles. Essentially, these pumps operate similar to syringes and dispense liquid only when a piston or plunger displaces the liquid from a supply chamber or passage through an outlet. When the piston or plunger is stopped, atmospheric pressure will keep the liquid from dripping out of the outlet. However, under near vacuum conditions these types of pumps or dispensers will drip upon shut-off and, as a result, the liquid will fall on unintended areas of the substrate or surrounding components.
During the vacuum encapsulation of semiconductor chip packages, accurate repeatability of the dispensed encapsulant material is also very important. Therefore, any valve structure used in conjunction with the dispensing pump must not have characteristics which adversely affect this accuracy and repeatability. Conventional pneumatically or electrically-actuated valves will typically have internal seals and other components that break or modify the fluid path such that highly accurate, minute amounts of liquid may be dispensed from the outlet. In these applications, it is therefore preferable that the liquid enters the valve and flows through a constant fluid path which will not change in volume, such as due to the presence of various compressible seals, even under very high pressures on the order of 500 psi to 1,000 psi and above. With specific regard to electrically-actuated valves, these valves will generate heat which is very difficult to dissipate in a near vacuum environment. Therefore, the life of any electrically-actuated valve would be significantly shortened in a near vacuum environment.
For at least the various reasons discussed above, it would be desirable to provide a highly accurate liquid dispenser which prevents dripping in near vacuum conditions but does not have other drawbacks associated with prior dispensing valves.
SUMMARY OF THE INVENTION
The present invention generally provides a dispensing apparatus using at least one magnetic element for reciprocating a needle within a valve body between open and closed positions. Generally, the apparatus includes a valve body with a liquid passage containing a valve seat and communicating with an outlet. A needle is mounted for reciprocating movement between open and closed positions in the liquid passage and with respect to the valve seat to dispense liquid from the outlet. An armature is connected for reciprocating movement with the needle and an actuatable magnetic element is mounted outside the liquid passage and, preferably, outside the valve body. The magnetic element moves between a first position that magnetically maintains the armature and the needle in the open position against the force of a return spring and a second position in which the armature and the needle are moved to the closed position by the return spring. An actuator is operatively connected to the magnetic element to facilitate its movement between the first and second positions. In the preferred embodiment, this actuator is a pneumatic actuator, specifically in the form of an air cylinder having a reciprocating piston, but other actuators may be used as well.
As a more specific feature of the invention, the magnetic element may further comprise opposed permanent magnets mounted on opposite sides of the armature. The armature preferably comprises a member carried by the needle and formed from a ferrous metal. The armature may be an integral portion of the needle or a portion separately affixed to the needle. In the preferred embodiment, a carrier is mounted for movement between the first and second positions in a direction transverse to the movement of the needle. The carrier includes magnet mounting portions disposed adjacent opposite sides of the valve body. The permanent magnets are respectively mounted to the magnet mounting portions. The magnets at least substantially align with the armature when the needle is in the open position and are substantially out of alignment with the armature when the needle is in the closed position.
In operation, pressurized liquid is introduced into the liquid passage within the valve body with the needle initially disposed in the closed position under the force of the return spring. The permanent magnets disposed outside the valve body are moved by the actuator to a position facilitating a magnetic attraction between the armature and the magnets. The magnetic attraction causes the needle to move away from the valve seat against the force of the return spring and allows liquid to move through the outlet. When the magnets are moved to the second position, the magnetic force or attraction between the magnets and the armature is less than the spring force and, therefore, the spring forces the needle to the closed position to stop the flow of liquid.
Various objectives, features and advantages of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3348543 (1967-10-01), Stafford
patent: 3609425 (1971-09-01), Sheridan
patent: 5685459 (1997-11-01), Wardle
patent: 5904300 (1999-05-01), Augustin
patent: 6003734 (1999-12-01), Oh
patent: 6053425 (2000-04-01), Stringfellow
Newbold John
Verrilli Brian
Bomberg Kenneth
Nordson Corporation
Wood Herron & Evans L.L.P.
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