Patent Description:
The present invention generally relates to non-contact, jetting dispensers for depositing small droplets of a viscous fluid onto a substrate, and more specifically, to dispensers of this type that are actuated by one or more piezoelectric elements.

Non-contact viscous material dispensers are often used to apply minute amounts of viscous materials, e.g., those with a viscosity exceeding fifty centipoise, onto substrates. For example, non-contact viscous material dispensers are used to apply various viscous materials onto electronic substrates like printed circuit boards. Viscous materials applied to electronic substrates include, by way of example and not by limitation, general purpose adhesives, ultraviolet curable adhesives, solder paste, solder flux, solder mask, thermal grease, lid sealant, oil, encapsulants, potting compounds, epoxies, die attach fluids, silicones, RTV, and cyanoacrylates.

Specific applications abound for dispensing viscous materials from a non-contact jetting dispenser onto a substrate. In semiconductor package assembly, applications exist for underfilling, solder ball reinforcement in ball grid arrays, dam and fill operations, chip encapsulation, underfilling chip scale packages, cavity fill dispensing, die attach dispensing, lid seal dispensing, no flow underfilling, flux jetting, and dispensing thermal compounds, among other uses. For surface-mount technology (SMT) printed circuit board (PCB) production, surface mount adhesives, solder paste, conductive adhesives, and solder mask materials may be dispensed from non-contact dispensers, as well as selective flux jetting. Conformal coatings may also be applied selectively using a non-contact dispenser. Generally, the cured viscous materials protect printed circuit boards and mounted devices thereupon from harm originating from environmental stresses like moisture, fungus, dust, corrosion, and abrasion. The cured viscous materials may also preserve electrical and/or heat conduction properties on specific uncoated areas. Applications also exist in the disk drive industry, in life sciences applications for medical electronics, and in general industrial applications for bonding, sealing, forming gaskets, painting, and lubrication. Document <CIT> discloses an adhesive applicator head that includes a piezoelectric drive, a lever arm, and a movable needle.

Jetting dispensers generally may have pneumatic or electric actuators for moving a shaft or tappet repeatedly toward a seat while jetting a droplet of viscous material from an outlet orifice of the dispenser. The electrically actuated jetting dispensers can, more specifically, use a piezoelectric actuator. Piezo stacks are very accurate and extremely fast reacting ceramic devices. A property of the piezo stack is that when a voltage is applied the ceramic material will perform a displacement in one direction. A jetting dispenser comprising an actuator including a piezoelectric unit that lengthens by a predetermined distance in response to an applied voltage is known from <CIT>. In an embodiment, the jetting dispenser of <CIT> further comprises a pair of springs arranged on opposite sides of the piezoelectric unit and adapted to maintan the piezoelectric unit under compression at all times. One main drawback is that the piezo stack produces a very small displacement. For example, a <NUM> x <NUM> x <NUM> long stack produces about <NUM> microns of movement. This displacement is not enough for proper jetting of fluids. It is known to form an actuator with a piezo stack and an amplification mechanism. Space limitations and life expectancy are also considerations when designing an actuator that includes a piezo material. Life expectancy is severely shortened when the stack is placed in a tension condition. The piezo stack needs to be able to operate at a frequency of <NUM> continuous, and needs to apply sufficient force to reliably and accurately jet a small amount of fluid. There are a wide variety of methods of achieving the amplification that is necessary for this application, however achieving long life cycles <NUM> can be challenging. The two main methods of rocker arm or lever amplification are pivot and flexural. The pivot method is susceptible to wear which will reduce the overall displacement, and the flexural method is prone to breakage around areas of high stress.

A piezo stack produces a significant amount of heat during operation. The amount of heat generated by the actuator is dependent on several factors such as heater body temperature, piezo frequency, and duty cycle. This heat is transferred to the surrounding metal in the actuator. This results in a change in the position of the lever or rocker arm and can negatively affect the intended stroke of the jetting device.

For at least these reasons, it would be desirable to provide a jetting system and method that addresses these and other issues.

In a first illustrative embodiment the invention provides a jetting dispenser including an actuator and a fluid body. The jetting dispenser comprises an actuator including a piezoelectric unit that lengthens by a first distance in response to an applied voltage, an armature adapted to be operatively coupled for movement with the piezoelectric unit, an upper actuator portion containing the piezoelectric unit, and a lower actuator portion including the armature and an amplifier in the form of a lever having a first end and a second end, the first end of the lever moving through the first distance under the applied voltage and the second end of the lever moving through a second distance, larger than the first distance, under the applied voltage; a movable shaft operatively coupled with the second end of the lever; and a fluid body including a fluid bore and an outlet orifice, whereby the amplifier includes a flexural portion coupled to the first end of the lever, positioned between the first end of the lever and the armature, and coupling the first end of the lever to the armature, and in that the flexural portion flexes when voltage is applied to the piezoelectric unit so as to move the lever to oppose a resilient bias applied by the flexural portion, thereby moving the movable shaft to jet an amount of fluid from the fluid bore through the outlet orifice.

Referring to <FIG>, a jetting system <NUM> in accordance with an embodiment of the invention generally comprises a jetting dispenser <NUM> coupled with a main electronic control <NUM>. The jetting dispenser <NUM> includes a fluid body <NUM> coupled to an actuator housing <NUM>. More specifically, the fluid body <NUM> is held within a fluid body housing <NUM>, which may include one or more heaters (not shown), depending on the needs of the application. The fluid body <NUM> receives fluid under pressure from a suitable fluid supply <NUM>, such as a syringe barrel (not shown). A tappet or valve assembly <NUM> is coupled to the housing <NUM> and extends into the fluid body <NUM>. A mechanical amplifier (e.g., a lever <NUM>) is coupled between a piezoelectric actuator <NUM> and the tappet or valve assembly <NUM>, as will be described further below.

For purposes of cooling the piezoelectric actuator <NUM>, air may be introduced from a source <NUM> into an inlet port <NUM> and out from an exhaust port <NUM>. Alternatively, depending on the cooling needs, both of the ports <NUM>, <NUM> may receive cooling air from the source <NUM> as shown in <FIG>. In such a case, one or more other exhaust ports (not shown) would be provided in the housing <NUM>. A temperature and cycle control <NUM> is provided for cycling the actuator <NUM> during a jetting operation, and for controlling one or more heaters (not shown) carried by the dispenser <NUM> for maintaining the dispensed fluids to a required temperature. As another option, this control <NUM>, or another control, may control the cooling needs of the actuator <NUM> in a closed loop manner. As further shown in <FIG>, the piezoelectric actuator <NUM> further comprises a stack <NUM> of piezoelectric elements. This stack <NUM> is maintained in compression by respective flat, compression spring elements <NUM>, <NUM> coupled on opposite sides of the stack <NUM>. More specifically, upper and lower pins <NUM>, <NUM> are provided and hold the flat spring elements <NUM>, <NUM> to one another with the stack <NUM> of piezoelectric elements therebetween. The upper pin <NUM> is held within an upper actuator portion 26a of the actuator <NUM>, while a lower pin <NUM> directly or indirectly engages a lower end of the stack <NUM>. The upper actuator portion 26a securely contains the stack <NUM> of piezoelectric elements so that the stack <NUM> is stabilized against any sideward motion. In this embodiment, the lower pin <NUM> is coupled to a lower actuator portion 26b and, more specifically, to a mechanical armature <NUM> (<FIG>).

An upper surface 50a of the mechanical armature <NUM> bears against the lower end of the piezoelectric stack <NUM>. The spring elements <NUM>, <NUM> are stretched between the pins <NUM>, <NUM> such that the spring elements <NUM>, <NUM> apply constant compression to the stack <NUM> as shown by the arrows <NUM> in <FIG>. The flat spring elements <NUM>, <NUM> may, more specifically, be formed from a wire EDM process. The upper end of the piezoelectric element stack <NUM> is retained against an internal surface of the upper actuator portion 26a. The upper pin <NUM> is therefore stationary while the lower pin <NUM> floats or moves with the spring elements <NUM>, <NUM> and with the mechanical armature <NUM> as will be described.

When voltage is applied to the piezoelectric stack <NUM>, the stack <NUM> expands or lengthens and this moves the armature <NUM> downward against the force of the spring elements <NUM>, <NUM>. The stack <NUM> will change length proportional to the amount of applied voltage.

As further shown in <FIG>, the mechanical armature <NUM> is operatively coupled with a mechanical amplifier which, in this illustrative embodiment, is formed as the lever <NUM> coupled to the armature <NUM> generally near a first end 24a and coupled to a push rod <NUM> at a second end 24b. The lever <NUM> may be integrally formed from the lower actuator portion 26b through, for example, an EDM process that also forms a series of slots <NUM> between the mechanical armature <NUM> and the lever <NUM>. As will be further discussed below, the lever <NUM> or other mechanical amplifier amplifies the distance that the stack <NUM> expands or lengthens by a desired amount. For example, in this embodiment, downward movement of the stack <NUM> and the mechanical armature <NUM> is amplified by about eight times at the second end 24b of the lever <NUM>.

Now referring more specifically to <FIG>, <FIG>, <FIG> and <FIG>, a flexural portion <NUM> couples the lever <NUM> to the mechanical armature <NUM>. As shown best in <FIG>, the lever <NUM> pivots about a pivot point <NUM> that is approximately at the same horizontal level as the second end 24b of the lever <NUM>. This position of the pivot point <NUM> serves to minimize the effect of the arc through which the lever <NUM> rotates. The series of slots <NUM> is formed in the lower actuator portion 26b form the flexural portion <NUM>. When the piezoelectric stack <NUM> lengthens under the application of a voltage by the main control <NUM> as shown by the arrow <NUM> in <FIG>, the lever <NUM> rotates clockwise generally about the pivot point <NUM> as the stack <NUM> pushes downward on the mechanical armature <NUM>. The slight rotation of the lever <NUM> takes place against a resilient bias applied by the flexural portion <NUM>. As the second end 24b is rotating slightly clockwise about the pivot point <NUM>, it moves downward and likewise moves an attached push rod <NUM> downward (<FIG>) as indicated by the arrow <NUM> in <FIG>.

The second end 24b of the lever <NUM> is fixed to the push rod <NUM> using suitable threaded fasteners <NUM>, <NUM>. The push rod <NUM> has a lower head portion 68a that travels within a guide bushings <NUM> and bears against an upper head portion 76a of a tappet or valve element <NUM> associated with the tappet or valve assembly <NUM>. The guide bushing <NUM> is held in the housing <NUM> by a pressfit with a pin <NUM> as best seen in <FIG>. The assembly of the push rod <NUM>, guide bushing <NUM> and pin <NUM> allows for some "give" to ensure proper movement of the push rod <NUM> during operation. In addition, the push rod <NUM> is made of a material that will slightly bend sideward, in an elastic manner, during its reciprocating movement with the tappet or valve element <NUM> and lever <NUM>. The tappet assembly further comprises a coil spring <NUM> which is mounted within a lower portion of the housing <NUM> using an annular element <NUM>. The tappet or valve assembly <NUM> further comprises an insert <NUM> retained in the fluid body <NUM> by an O-ring <NUM>. The annular element <NUM> and the insert <NUM> comprise an integral element, i.e., a cartridge body in this embodiment. A cross-drilled weep hole <NUM> is approximately in line with the lower end of the spring <NUM> to allow any liquid that leaks past the O-ring <NUM> to escape. An additional O-ring <NUM> seals the tappet or valve element <NUM> such that pressurized fluid contained in a fluid bore <NUM> of the fluid body <NUM> does not leak out. Fluid is supplied to the fluid bore <NUM> from the fluid supply <NUM> through an inlet <NUM> of the fluid body <NUM> and passages <NUM>, <NUM>. The O-ring <NUM> seals the outside of the cartridge body formed by the annular element <NUM> and insert <NUM> from the pressurized liquid in bore <NUM> and passage <NUM>. The fluid passages <NUM>, <NUM> are sealed by a plug member <NUM> threaded into the fluid body <NUM>. The plug member <NUM> may be removed to allow access for cleaning the internal passage <NUM>.

The operation of the system <NUM> to jet droplets or small amounts of fluid will be best understood by reviewing <FIG> in conjunction with <FIG> illustrates the tappet or valve element <NUM> raised to an open condition when the voltage to the piezoelectric stack <NUM> has been sufficiently removed. This causes the stack <NUM> to contract. As the stack <NUM> contracts, the flat spring elements <NUM>, <NUM> pull the armature <NUM> upward and this raises the second end 24b of the lever <NUM>, and also raises the push rod <NUM>. Thus, the coil spring <NUM> of the tappet or valve assembly <NUM> can then push upward on the upper head portion 76a of the tappet or valve element <NUM> and raise a distal end 76b of the tappet or valve element <NUM> off a valve seat <NUM> affixed to the fluid body <NUM>. In this position, the fluid bore <NUM> and the area beneath the distal end 76b of the tappet or valve element <NUM> fills with additional fluid to "charge" the jetting dispenser <NUM> and prepare the jetting dispenser <NUM> for the next jetting cycle.

When the piezoelectric stack <NUM> is activated, i.e., when voltage is applied to the piezoelectric stack <NUM> by the main electronic control <NUM> (<FIG>), the stack <NUM> expands and pushes against the mechanical armature <NUM>. This rotates the lever <NUM> clockwise and moves the second end 24b downward, also moving the push rod <NUM> downward. The lower head portion 68a of the push rod <NUM> pushes down on the upper head portion 76a of the tappet or valve element <NUM> as shown in <FIG> and the valve element <NUM> moves quickly downward against the force of the coil spring <NUM> until the distal end 76b engages against the valve seat <NUM>. In the process of movement, the distal end 76b of the valve element <NUM> forces a droplet <NUM> of fluid from a discharge outlet <NUM>. Voltage is then removed from the piezoelectric stack <NUM> and this reverses the movements of each of these components to raise the tappet or valve element <NUM> for the next jetting cycle.

It will be appreciated that the piezoelectric actuator <NUM> may be utilized in reverse to jet droplets. In this case, the various mechanical actuation structure including the lever <NUM> would be designed differently such that when the voltage is removed from the piezoelectric stack <NUM>, the resulting contraction of the stack <NUM> will cause movement of the valve element <NUM> toward the valve seat <NUM> and the discharge outlet <NUM> to discharge a droplet <NUM> of fluid. Then, upon application of the voltage to the stack <NUM>, the amplification system and other actuation components would raise the valve element <NUM> in order to charge the fluid bore <NUM> with additional fluid for the next jetting operation. In this embodiment, the tappet or valve element <NUM> would be normally closed, that is, it would be engaging the valve seat <NUM> when there is no voltage applied to the piezoelectric stack <NUM>.

Claim 1:
A jetting dispenser (<NUM>), comprising:
an actuator (<NUM>) including a piezoelectric unit that lengthens by a first distance in response to an applied voltage, an armature (<NUM>) adapted to be operatively coupled for movement with the piezoelectric unit, an upper actuator portion (26a) containing the piezoelectric unit, and a lower actuator portion (26b) including the armature (<NUM>) and an amplifier in the form of a lever (<NUM>) having a first end (24a) and a second end (24b), the first end (24a) of the lever (24a) moving through the first distance under the applied voltage and the second end (24b) of the lever (<NUM>) moving through a second distance, larger than the first distance, under the applied voltage;
a movable shaft operatively coupled with the second end (24b) of the lever (<NUM>); and
a fluid body (<NUM>) including a fluid bore (<NUM>) and an outlet orifice, characterized in that the amplifier includes a flexural portion (<NUM>) coupled to the first end (24a) of the lever (<NUM>), positioned between the first end (24a) of the lever (<NUM>) and the armature (<NUM>), and coupling the first end (24a) of the lever (<NUM>) to the armature (<NUM>),
and in that the flexural portion (<NUM>) flexes when voltage is applied to the piezoelectric unit so as to move the lever (<NUM>) to oppose a resilient bias applied by the flexural portion (<NUM>), thereby moving the movable shaft to jet an amount of fluid from the fluid bore (<NUM>) through the outlet orifice.