Abstract:
A precision dispensing pump for dispensing fluids and method of dispensing for use in semiconductor packaging and/or semiconductor assembly. The precision dispensing pump employs a working fluid displacement drive for volumetric displacement of a working fluid, a dispensing reservoir for containment of dispensing fluid and a isolation diaphragm for isolating the working fluid from dispensing fluid in the dispensing reservoir. Volumetric displacement of dispensing fluid in the dispensing reservoir is proportional to volumetric displacement of working fluid in the working fluid displacement drive.

Description:
BACKGROUND OF THE INVENTION 
     It is well known to use pumps for dispensing of adhesives, encapsulates, pastes and other high through low viscosity liquids and pastes. Recent developments in the processing of semiconductors include the introduction of packaging techniques which require high speed precision dispensing of epoxies, solder pastes encapsulates and underfill materials. In the past, augering screw type pumps like those disclosed in U.S. Pat. Nos. 5,819,983 and 5,795,390 have been employed in such applications; however with the advent of higher precision dispensing requirements, these pumps have reached their limit in terms of performance and accuracy. In order to overcome accuracy limitations of augering screw type pumps, a series of piston based positive displacement pumps like those manufactured by Asymtek, a Nordson Company have evolved. While exceeding accuracy of augering screw type pumps, these piston based pumps have suffered limitations in terms of the ability to service and clean parts of the pump exposed to the various fluids. 
     The apparatus of the present invention relates generally to positive displacement pumps. The invention further relates to positive displacement pumps for dispensing of adhesives, encapsulates, pastes and other high through low viscosity liquids and pastes. 
     One object of the present invention is to provide a precision dispensing pump for high accuracy dispensing of liquids such as adhesives, encapsulates, pastes and other high through low viscosity liquids and pastes. 
     Another object of the present invention is to provide a positive displacement pump for high accuracy dispensing of liquids such as adhesives, encapsulates, pastes and other high through low viscosity liquids and pastes. 
     Another object of the present invention is to provide a precision dispensing pump which has simplified cleaning of parts exposed to dispensing fluids in order to minimize down time for service. 
     Another object of the present invention is to provide a precision dispensing pump which has disposable parts exposed to dispensing fluids in order to minimize down time for service. 
     Another object of the present invention is to provide a precision dispensing pump which has repeatable calibration. 
     SUMMARY OF THE INVENTION 
     The invention resides in a precision dispensing pump for dispensing fluids for use in semiconductor packaging and/or semiconductor assembly. The precision dispensing pump comprises a working fluid displacement drive for volumetric displacement of a working fluid, a dispensing reservoir for containment of dispensing fluid and a isolation diaphragm for isolating the working fluid from dispensing fluid in the dispensing reservoir. Volumetric displacement of dispensing fluid in the dispensing reservoir is proportional to volumetric displacement of working fluid in the working fluid displacement drive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a isometric view of a precision dispensing pump according to one embodiment of the present invention; 
     FIG. 2 is a side view of the precision dispensing pump according to FIG. 1; 
     FIG. 3 is a cross section view of the precision dispensing pump according to FIG. 1; 
     FIG. 4 is a cross section view of the precision dispensing pump according to FIG. 1 also showing an inlet and outlet valve; 
     FIG. 5 is the inlet or outlet valve according to FIG. 4 shown in the closed state; 
     FIG. 6 is the inlet or outlet valve according to FIG. 4 shown in the open state; 
     FIG. 7 is a cross section view of the precision dispensing pump according to FIG. 1 also showing a switching valve; 
     FIG. 8 is the switching valve according to FIG. 7 shown in the dispensing state; 
     FIG. 9 is the switching valve according to FIG. 7 shown in the charging state; 
     FIG. 10 is a diagram showing the dispensing sequence of a precision dispensing pump according to one embodiment of the present invention; 
     FIG. 11 is a diagram showing a precision dispensing pump with a portion of the working fluid displacement drive remotely operable; 
     FIG. 12 is a cross section view of a portion of the isolation diaphragm of one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A precision dispensing pump for dispensing a dispensing fluid according to one embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
     Referring now to FIG. 1 there is shown is an isometric view of a precision dispensing pump  10 . Precision dispensing pump  10  includes a pump body  15 , a dispensing fluid container  20 , a dispensing needle  25 , inlet valve  30  and outlet valve  35 . Dispensing fluid such as adhesives or encapsulates are stored in dispensing fluid container  20  which may be a syringe or other suitable container and may or may not be under pressure from pressure source  40 . Inlet valve  30  and outlet valve  35  each have two states; either opened or closed. Dispensing fluid enters pump body  15  through inlet valve  30  and exits pump body  15  through outlet valve  35 . Dispensing needle  25  is connected to outlet valve  35  and dispensing fluid is ultimately dispensed through dispensing needle  25 . Precision dispensing pump  10  is typically mounted to a programmable gantry well known in the art which is capable of movement in directions x, y and z. Pump body  15  alternately draws dispensing fluid from dispensing fluid container  20  and then exhausts dispensing fluid through dispensing needle  25 . Controller  27  is used to coordinate the pump motor  29  of pump body  10 , inlet valve  30 , outlet valve valve  35 , pressure source  40  and other pump related functions well known in the art. Controller  27  can be a micro controller, computer, programmable logic controller or other controller well known in the art. 
     Referring now to FIG. 2 there is shown a side view of pump body  15  of the precision dispensing pump  10  according to FIG.  1 . Pump body  15  includes a working fluid displacement drive  40 , a dispensing reservoir  45  and isolation diaphragm  50 . Working fluid displacement drive  40  acts as a drive or pump for s the volumetric displacement of a working fluid. The working fluid can be oil, hydraulic fluid, air, any liquid or gas, but is ideally a substantially incompressible fluid. Working fluid displacement drive  40  can be a piston driven, bellows driven, diaphragm driven, or any other type of positive displacement or displacement pump. Working fluid displacement drive  40  can be driven by a lead screw combined with a stepper motor or servo motor plus encoder which can be dc or ac driven. Alternately, working fluid displacement drive  40  can be driven by a linear motor plus encoder, piezoelectric motor, linear stepper, can be a screw to belt to motor, rotary to linear reciprocating drive, or any other drive known in the art with accurate motion. Working fluid displacement drive  40  can be mounted with precision dispensing pump  10  as shown or can be divided and a portion remotely mounted with the working fluid piped to the remaining portion of precision dispensing pump  10 . Dispensing reservoir  45  in combination with isolation diaphragm  50  creates a dispensing volume through which dispensing fluid passes. Dispensing fluid is drawn into dispensing reservoir  45  from dispensing fluid container  20  by expanding the dispensing volume with isolation diaphragm  50 . Dispensing fluid is exhausted from dispensing reservoir  45  into dispensing needle  25  by contracting the dispensing volume with isolation diaphragm  50 . Isolation diaphragm  50  serves to isolate working fluid from dispensing fluid. Isolation diaphragm  50  is deflected by volumetric displacement of working fluid from working fluid displacement drive  40 . Volumetric displacement of working fluid is, as a result, proportional to volumetric displacement of dispensing fluid. Isolation diaphragm  50  can be a single diaphragm or a plurality of diaphragms in contact with each other. Isolation diaphragm  50  can be flat, curved, a bellows shape or other applicable diaphragm shapes and can be made out of metal, plastic or other polymers or materials appropriate for diaphragms. Dispensing reservoir  45  can be made out of metal or plastic or other material that is compatible with dispensing fluid. Dispensing reservoir  45  may be disposable and may have a secondary diaphragm attached to dispensing reservoir  45  which follows a primary diaphragm attached to working fluid displacement drive  40 . Dispensing reservoir  45  may be attached to working fluid displacement drive  40  by means of a clamp or quick disconnect clamp collar or other fast release devices known in the art in order to allow simplified cleaning or replacement of parts exposed to dispensing fluid for ease of service with minimum down time for service. 
     Referring now to FIG. 3 there is shown a cross section view  3 — 3  of FIG. 2 of pump body  15  of the precision dispensing pump according to FIG.  1 . Pump body  15  includes a working fluid displacement drive  40 , a dispensing reservoir  45  and isolation diaphragm  50 . Working fluid displacement drive  40  includes a motor driven lead screw assembly  55 , a housing assembly  60  and bellows assembly  65 . Motor driven lead screw  55  includes a lead screw  56  and stepping motor  57 . Stepping motor  57  is fastened to housing assembly  60 . Lead Screw  56  is fastened to bellows assembly  65  with fasteners  58 . When stepping motor  57  is energized, lead screw  56  moves axially in direction z′ causing compression or extension of bellows assembly  65 . A bellows assembly is preferred construction. As an alternative to bellows assembly  65 , a piston may be used. A bellows has advantages over a piston as a bellows does not have moving parts such as dynamic seals which can wear and leak over time and also a bellows can be designed for longer fatigue life beyond that of dynamic seals minimizing or eliminating maintenance. Bellows assembly  65  includes shaft  66 , bellows  67  and flange  68 . Both flange  68  and shaft  66  are welded to bellows  67 . Shaft  66 , bellows  67  and flange  68  are typically made out of steel or stainless steel. Shaft  66  is fastened to lead screw  56  with fasteners  58 . Flange  68  is fastened to housing assembly  60 . Housing assembly  60  includes housing  80  and bushing  82 . Bushing  82  is fixed to housing  80  and provides guidance and stability for shaft  66 . Isolation diaphragm  50  includes a primary diaphragm  70 , a secondary diaphragm  72  and a clamp ring  75 . Alternately, isolation diaphragm  50  could include only a single diaphragm. The primary shape of Isolation diaphragm  50  is shown to be flat and round but may alternately be flat and rectangular, concave and round, concave and rectangular or other suitable shape generally for diaphragms known in the art. Clamp ring  75  clamps primary diaphragm  70  to bellows assembly  65 . Secondary diaphragm  72  remains in contact with primary diaphragm  70  by a temporary adhesive or thin liquid film. Alternately, secondary diaphragm  72  can simply remain in contact with primary diaphragm  70  due to the pressure applied to or by the dispensing fluid or to or by the working fluid with out need for a temporary adhesive or thin liquid film. Secondary diaphragm  72  can be fastened to dispensing reservoir  45  or alternately be clamped between reservoir  45  and primary diaphragm  70 . Dispensing reservoir  45  has an interior surface  102  which is preferably shown generally in the shape of a round vortex. This preferred shape allows the contact area between diaphragm  50  and dispense reservoir  45  to progress and close in on outlet  90  when diaphragm  50  is expanded toward interior surface  102 . Alternately, any combination of shapes may be applied to diaphragm  50  and interior surface  102  which allows the contact area between diaphragm  50  and dispense reservoir  45  to progress and close in on outlet  90  when diaphragm  50  is expanded toward interior surface  102 . Alternately, dispensing reservoir  45  can have an interior surface generally in a concave shape and also can either be round, rectangular or other suitable shape. Dispensing reservoir  45  has inlet  88  and outlet  90 . Alternately, outlet  90  may operate as both an inlet and an outlet to dispense reservoir  45  thus eliminating inlet  88 . Inlet  88  is preferably located in close proximity to the interface between dispense reservoir  45  and diaphragm  50  when diaphragm  50  comprises a single diaphragm. Inlet  88  is preferably located in close proximity to the interface between dispense reservoir  45  and secondary diaphragm  72  when diaphragm  50  comprises a primary diaphragm  70  and secondary diaphragm  72 . When inlet  88  is located as preferred, the filling and gas purging cycle is minimized as dispensing fluid enters dispensing volume  100  at its outer edge when diaphragm  50  is contracted away from interior surface  102  and exits dispensing volume  100  at outlet  90  when the contact area between diaphragm  50  and dispense reservoir  45  progresses and closes in on outlet  90  when diaphragm  50  is expanded toward interior surface  102 . When inlet  88  is located as preferred, any gas remaining in dispensing volume  100  during a purge, fill or dispense cycle will be minimized as it can not re-enter dispensing volume  100  such as in the case where outlet  90  operates as both an inlet and an outlet to dispense reservoir  45  thus eliminating inlet  88 . Dispensing reservoir  45  is clamped to bellows assembly  65  using pump clamp  86 . Pump clamp  86  can be a clamp or quick disconnect clamp collar such as a KF type vacuum clamp or other fast release clamping devices known in the art in order to allow simplified cleaning or replacement for ease of service with minimum down time for service. Working fluid is contained in interior region  95  of the bellows assembly  65  and isolation diaphragm  50 . Dispensing fluid is contained and dispensed via dispensing volume  100  of dispensing reservoir  45  and isolation diaphragm  50 . Removal of pump clamp  86  allows quick removal and replacement or cleaning of dispensing reservoir  45  and a portion of isolation diaphragm  50  if applicable. 
     Referring now to FIG. 4 is a cross section view of the precision dispensing pump according to FIG. 3 also showing inlet valve  104  and outlet valve  108 . Inlet valve  104  has a supply port  112  and a inlet port  110 . Outlet valve  108  has an outlet port  114  and a dispense port  116 . Supply port  112  is connected to dispensing fluid container  20 . Inlet port  110  is connected to inlet  88  of dispense reservoir  45 . Outlet port  114  is connected to outlet  90  of dispense reservoir  45 . Dispense port  116  is connected to dispensing needle  25 . 
     Referring now to FIG. 5 is inlet valve  104  or outlet valve  108  according to FIG. 4 shown in the closed state where dispensing fluid will not flow. 
     Referring now to FIG. 6 is inlet valve  104  or outlet valve  108  according to FIG. 4 shown in the open state where dispensing fluid may flow. 
     Referring now to FIG. 7 is a cross section view of the precision dispensing pump according to FIG. 3 also showing switching valve  120 . Switching valve  120  has a supply port  122 , a reservoir port  126  and dispense port  124 . Supply port  122  is connected to dispensing fluid container  20 . Reservoir port  126  is connected to port  130  of dispense reservoir  45 . Dispense port  124  is connected to dispensing needle  25 . 
     Referring now to FIG. 8 is switching valve  120  according to FIG. 7 shown in the dispensing position where dispensing fluid may flow from dispense reservoir  45  to dispensing needle  25 . 
     Referring now to FIG. 9 is switching valve  120  according to FIG. 7 shown in the charging position where dispensing fluid may flow from dispensing fluid container  20  to dispense reservoir  45 . Switching valve  120  may also be placed in an intermediate position between the charging position of FIG.  9  and the dispensing position of FIG. 8 in order to effectuate a stoppage of flow. 
     Referring now to FIG. 10 is a diagram showing the dispensing sequence of a precision dispensing pump according to one embodiment of the present invention. Referring to steps one through four of FIG. 10, precision dispensing pump  135  includes piston  138 , isolation diaphragm  142 , dispense reservoir  144 , and switching valve  146 . Switching valve  146  has ports A, B and C. Port A is connected to dispensing fluid container  148 , port B is connected to dispense reservoir  144  and port C is connected to dispensing needle  152 . When switching valve  146  is in a charging position, port A communicates with port B and port C is closed. When switching valve  146  is in a dispensing position, port B communicates with port C and port A is closed. Working fluid  155  is isolated from dispensing fluid  160  by isolation diaphragm  142 . In step 1, dispensing fluid  160  is drawn from dispensing fluid container  148  into dispense reservoir  144  by drawing piston  138  in direction z″. In step 2, switching valve  146  is changed from the charging position state to the dispensing position state. In step 3, dispensing fluid is exhausted from dispense reservoir  144  to dispensing needle  152  by drawing piston  138  in direction z″′. In step 4, switching valve  146  is changed from the dispensing position state to the charging position state. Steps 1 through 4 are then repeated to continue the dispense cycle until dispensing fluid has been exhausted. Alternately, the dispense sequence recited may be accomplished using an inlet valve and outlet valve as previously described instead of a switching valve to achieve the same functional result. For the charging state, this may be achieved by having the inlet valve open and the outlet valve closed. For the dispensing state this may be achieved by having the inlet valve closed and the outlet valve open. The intermediate position of the switching valve where none of ports A,B or C communicate with each other corresponds to the state where both the inlet valve and outlet valve are closed in the alternate embodiment. 
     While the present invention has been particularly described with respect to certain elements in its preferred embodiments, it will be understood that the invention is not limited to those particular methods and/or apparatus&#39; described in the preferred embodiments, the process steps, the sequence or the final structures depicted in the drawings. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the the spirit and scope of the invention defined by the appended claims. In addition, other methods and/or devices may be employed in the apparatus of the instant invention. 
     Referring to FIG. 11 is a diagram showing a precision dispensing pump with a portion of the working fluid displacement drive remotely operable. Pump  160  includes a working fluid displacement drive  165 , a dispensing reservoir  170  and isolation diaphragm  175 . Working fluid displacement drive  165  includes bellows assembly  180 , motor driven lead screw  185 , tubing  190  and interface  195 . Working fluid  200  is pumped between bellows assembly  200  and interface  195  via tubing  190 . 
     Referring now to FIG. 12 is a cross section view of a portion of the isolation diaphragm of one alternative embodiment of the present invention. Isolation diaphragm  205  isolates working fluid  210  from dispensing fluid  215 . Isolation diaphragm  205  comprises primary diaphragm  220  and secondary diaphragm(s)  225 . Secondary diaphragm(s)  225  are adhered adjacent to primary diaphragm  220  temporarily and may be a plurality of thin stacked membranes which are compatible with dispensing fluid  215 . Dispensing reservoir  230  is removable for cleaning or disposal after use for dispensing. To clean and remove dispensing to fluid from Isolation diaphragm  205 , one of the thin membranes of secondary diaphragm(s)  225  is peeled away and disposed.