Information
-
Patent Grant
-
6270019
-
Patent Number
6,270,019
-
Date Filed
Friday, October 29, 199924 years ago
-
Date Issued
Tuesday, August 7, 200122 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Wood, Herron & Evans, LLP
-
CPC
-
US Classifications
Field of Search
US
- 239 105
- 239 290
- 239 291
- 239 294
- 239 418
- 239 423
- 239 1
- 222 504
- 222 509
- 118 300
- 118 303
- 118 308
- 118 63
- 118 600
-
International Classifications
-
Abstract
A liquid material dispensing system includes a nozzle assembly that is adapted to dispense a droplet of liquid or viscous material, such as solder flux or adhesive, onto a substrate. The nozzle assembly includes a liquid discharge passageway for dispensing the droplet, and an air discharge orifice for discharging a sheath of pressurized air. The sheath of pressurized air substantially surrounds the dispensed droplet and any satellite portions associated therewith during flight toward the substrate. The sheath of pressurized air advantageously contains the satellite portions within the discharged sheath to prevent them from falling onto areas of the substrate where it is undesirable to have a coating of liquid or viscous material. Methods for dispensing a droplet of liquid or viscous material onto a substrate are also disclosed.
Description
FIELD OF THE INVENTION
The present invention generally relates to apparatus for dispensing liquid or viscous materials and, more particularly, to an apparatus and method for dispensing droplets of liquid or viscous material onto a surface of a substrate.
BACKGROUND OF THE INVENTION
Liquid dispensing systems have become an integral part of the electronics manufacturing process for depositing underfill, encapsulants, solder fluxes, surface mount adhesives, conformal coatings and other materials onto a substrate, such as a printed circuit board. Each liquid dispensing system used in the electronics manufacturing process has a particular dispensing characteristic that is determined in large measure by the desired liquid dispense pattern on the substrate, the liquid flow rate and/or liquid viscosity of the dispensed material, and the desired electronic component assembly throughput through the dispensing system.
For example, in the assembly of ball gate arrays (BGA's) and other electronic components onto a ceramic or FR-4 substrate, the component must be soldered onto the substrate to form the necessary electrical interconnections. As each component occupies a predetermined area on the substrate, the liquid dispensing system must have the capability to dispense liquid or viscous material in a controlled manner within the selected component areas. Typically, the liquid dispenser is mounted on a movable platform to provide automated and accurate movement of the liquid dispenser in three dimensions relative to the substrate with the aid of a machine vision system.
Prior to the component soldering process for establishing the electrical interconnections, it is often necessary or at least desirable to dispense a layer of solder flux onto a substrate within rectangular areas associated with each component. To provide this capability, liquid material dispensers have been developed in the past that use filled syringes or reservoirs of solder flux, and dispensing valves to dispense droplets of flux material onto the substrate in a controlled manner with up to 25,000 to 40,000 dots of fluid per hour for a typical dispenser platform. These liquid dispensers, known as “dot jetting” dispensers, are programmed to dispense an array of liquid or viscous material droplets within each selected rectangular area which are then allowed to flow into contact with each other to form a generally rectangular thin layer of flux within the component area. “Dot jetting” dispensers are also used to dispense multiple droplets of adhesive onto a substrate to adhesively bond an electronic component to the substrate at a desired location.
In the “dot jet” process, each droplet of material is formed by rapidly closing a valve against a valve seat to impart kinetic energy to the fluid material within the dispenser. Closing of the valve causes the material to break off from the nozzle of the dispenser from which it is being dispensed and propel toward the substrate and onto the substrate as a droplet. Due to the high velocity imparted to form the jet or droplet of viscous material, the jet's tail may break into smaller droplets forming satellite portions associated with the main droplet. These satellite portions have a tendency to stray or deviate from the dispensing axis and cause problems when they hit the substrate outside of the area of the main droplet. The satellite portions may fall within areas of the substrate where it is undesirable to have a coating of viscous or liquid material, and may adversely affect the uniformity of the material coating applied to the substrate. As a result, the outlet of the “dot jetting” dispenser must typically be positioned relatively close to the substrate, such as in a range of about 1.5 mm to about 2.0 mm, to limit how far the satellite portions may deviate from the dispensing axis.
However, it will be appreciated that any reduction in the height of the nozzle tip relative to the substrate has a tendency to also reduce the size of droplet that may be dispensed onto the substrate since the droplet's ability to expand in flight toward the substrate is affected. This results in the need for more droplets of material to be dispensed to cover a given area of the substrate, and also results in increased dispense cycle times and reduced throughput of components through the dispenser.
Thus, there is a need for a liquid dispensing system that dispenses droplets of liquid or viscous material in a more accurate and repeatable manner. There is also a need for a liquid dispensing system that improves control of the dot shape and application of the dots toward a substrate. There is also a need for a liquid dispensing system that reduces dispense cycle times and improves throughput of components through the dispenser over known dispensing systems.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing and other shortcomings and drawbacks of liquid dispensing systems and methods heretofore known for forming and dispensing droplets of liquid or viscous material onto a substrate. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The liquid dispensing system of the present invention is particularly adapted for dispensing a droplet of liquid or viscous material, such as solder flux or adhesive, onto a substrate. The dispensing system includes a nozzle assembly that is configured and adapted to dispense a droplet of liquid material, and also to discharge a sheath of pressurized air that substantially surrounds the dispensed droplet and any satellite portions associated therewith during flight toward the substrate. The sheath of pressurized air is operable to contain the satellite portions within the discharged sheath to prevent them from falling onto areas of the substrate where it is undesirable to have a coating of liquid or viscous material. In this way, the height of the dispenser outlet can be increased, such as to about 2.00 mm or greater, without adversely affecting the dispensed pattern of dots.
More particularly, the nozzle assembly includes a liquid dispensing nozzle body that is adapted to be connected to a dispenser body of a liquid dispenser. The liquid dispensing nozzle body includes a liquid discharge passageway in fluid communication with the liquid dispenser for dispensing the droplet of liquid or viscous material toward the substrate. An air discharge body is operatively connected to the liquid dispensing nozzle body and includes an air discharge orifice for discharging the sheath of pressurized air. The air discharge orifice is configured and located relative to the liquid discharge passageway to discharge the sheath of pressurized air so that the sheath substantially surrounds the dispensed droplet and any satellite portions associated therewith during flight toward the substrate to contain the satellite portions within the discharged sheath.
In one aspect of the present invention, the liquid discharge passageway and the air discharge orifice are co-axially aligned with one another. The air discharge orifice may be an annular orifice that surrounds the liquid discharge passageway. The air discharge body includes a plenum connected to the air discharge orifice. The air discharge body may have multiple radially directed vanes disposed in the plenum for guiding pressurized air flow through the plenum.
The present invention also contemplates a method for dispensing a droplet of liquid or viscous material onto a substrate. The method generally involves dispensing a droplet of material from a liquid discharge passageway that tends to separate into a droplet and at least one satellite portion during flight toward a substrate. Pressurized air is discharged as a sheath from an air discharge passageway so that the droplet and the satellite portion associated therewith are substantially surrounded by the discharged sheath during flight toward the substrate. The discharged sheath of pressurized air is operable to contain the satellite portion within the sheath.
Accordingly, the present invention provides an apparatus and method for accurately and reliably dispensing a droplet of liquid or viscous material onto a substrate. With the sheath of pressurized air surrounding the droplet and its associated satellite portions during flight toward the substrate, better control of the dot shape and application of the dots toward the substrate is achieved. Further, the method and dispensing apparatus of the present invention permit higher dispense heights than previously achieved by known material dispensing systems, thereby allowing greater material coverage on the substrate with fewer dots.
Various additional advantages, objects and features of the invention will become more readily apparent to those of ordinary skill in the art upon consideration of the following detailed description of the presently preferred embodiment taken in conjunction with the accompanying drawings.
DETAILED DESCRIPTION OF DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
FIG. 1
is a side elevational view of a liquid dispensing system in accordance with the principles of the present invention for dispensing a droplet of viscous material toward a substrate;
FIG. 2
is an enlarged partial cross sectional view of a nozzle assembly attached to the end of the liquid dispenser, taken along line
2
—
2
of
FIG. 1
;
FIG. 3
is a top view taken along line
3
—
3
of the disk of
FIG. 2
; and
FIGS. 4A and 4B
are diagrammatic views illustrating the liquid dispensing system of
FIG. 1
dispensing a droplet of liquid material onto a substrate.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
With reference to the figures, a liquid dispensing system
10
for dispensing a droplet
12
of liquid or viscous material onto a substrate
14
(
FIGS. 4A-4B
) such as a printed circuit board is shown in accordance with the principles of the present invention. Liquid dispensing system
10
includes a standard, commercially available syringe
16
filled with liquid or viscous material, such as solder flux, surface mount adhesive, epoxy or other material, that is fluidly connected to a housing
18
of the dispensing system
10
. While not shown, it will be appreciated that syringe
16
could be replaced with a typical fluid material reservoir as known in the art. As will be appreciated by those skilled in the art, housing
18
includes an elongated flow bore
20
(
FIG. 2
) that forms a flow passage
22
generally aligned with a longitudinal axis of the dispensing system
10
. Flow passage
22
fluidly communicates at one end with an output of syringe
16
, and at the other end with an outlet end
24
of the dispensing system
10
from which the pressurized liquid or viscous material is dispensed as will be described in detail below.
An air tube (not shown) is connected to a pressure regulator (not shown) and a source of low pressure air (not shown). The air tube (not shown) has one end connected to an inlet (not shown) of syringe
16
to force the liquid or viscous material, typically having a viscosity of between about 20 and about 3,000,000 centipoise, into flow passage
22
of dispensing system
10
at a constant pressure between about 4 PSI and about 30 PSI. While not shown, it will be appreciated that liquid dispensing system
10
is mounted on a movable platform for moving the dispensing system
10
in a controlled manner relative to the substrate
12
. For a more detailed description of the structure and operation of liquid dispensing system
10
, the reader is referred to U.S. Pat. No. 5,747,102, assigned to the common assignee, which is hereby incorporated by reference herein in its entirety.
Briefly, liquid dispensing system
10
includes a cup-shaped valve seat assembly
26
(
FIG. 3
) that is press fit, soldered or otherwise mounted within a lower end of flow bore
20
adjacent to the outlet end
24
of dispensing system
10
. Valve seat assembly
26
has a flow passage
28
that fluidly communicates with the flow passage
22
extending through housing
18
. An outlet opening
30
and associated valve seat
32
are formed on the lower end of valve seat assembly
26
for cooperation in known manner with a vertically reciprocal valve stem
34
.
More particularly, valve stem
34
has a lower valve head
36
adapted for sealing engagement with valve seat
32
to normally close outlet opening
30
. An opposite upper end (not shown) of valve stem
34
is engaged with a control mechanism
38
of dispensing system
10
for controlled, reciprocal movement of valve head
36
into and out of engagement with valve seat
32
. With valve head
36
positioned in a retracted position away from valve seat
32
by operation of control mechanism
38
, liquid or viscous material is permitted to flow through the outlet opening
30
of valve seat assembly
26
and through the outlet end
24
of dispensing system
10
. While valve stem
34
is illustrated with a spherical valve head
36
, it will be appreciated that other valve head shapes are possible without departing from the spirit and scope of the present invention. Also, while not shown, it will be appreciated that a heating element may be disposed adjacent valve seat assembly
26
for heating a small volume of liquid or viscous material in the valve seat assembly
26
as described in detail in U.S. Pat. No. 5,747,102 which is incorporated herein by reference.
A principle feature of the present invention relates to nozzle assembly
39
which is mounted in fluid communication with the outlet end
24
of liquid dispensing system
10
. As shown in
FIG. 2
, nozzle assembly
39
includes a liquid dispensing nozzle body
40
having internal threads
42
for connection with external threads
44
of a dispenser body
46
associated with the dispensing system
10
. Nozzle assembly
39
further includes an air discharge body
48
connected in surrounding relation to the liquid dispensing nozzle body
40
through conventional means such as epoxy adhesive or welding. While liquid dispensing nozzle body
40
and air discharge body
48
are shown as separate pieces, they may also be integrated into a single piece.
Still referring to
FIG. 2
, liquid dispensing nozzle body
40
has an internal liquid discharge passageway
50
which is in fluid communication with the flow passage
22
of dispensing system
10
through the outlet opening
30
of valve seat assembly
26
. Liquid discharge passageway
50
extends through a nozzle tip
52
that extends away from the outlet end
24
of dispensing system
10
and is aligned along the longitudinal axis of dispenser body
46
.
The air discharge body
48
has a plenum
54
disposed bout the liquid dispensing nozzle body
40
and an air discharge orifice
56
. Plenum
54
and air discharge orifice
56
are in fluid communication with an air inlet passageway
58
that is operatively connected to a regulated supply of pressurized air
60
.
Advantageously, the plenum
54
and air discharge orifice
56
are co-axially aligned with the liquid discharge passageway
50
extending through the nozzle tip
52
of liquid dispensing nozzle body
40
. Preferably, the liquid discharge passageway
50
is disposed within and surrounded by the air discharge orifice
56
so that the air discharge orifice
56
is an annular orifice that surrounds the liquid discharge passageway
50
. The annular air discharge orifice
56
may be continuous or uninterrupted about liquid discharge passageway
50
or, alternatively, it may include one or more interruptions.
As shown in
FIGS. 2 and 3
, a disk
62
may be inserted into the plenum
54
of air discharge body
48
that includes multiple radially extending vanes
64
that are circumferentially spaced equidistantly within the plenum
54
. The vanes
64
extend from a planar wall
66
of disk
62
to substantially engage a planar shoulder
68
of the liquid dispensing nozzle body
40
. The vanes
64
function to straighten and develop a streamlined flow of pressurized air through the plenum
54
prior to being discharged through the air discharge orifice
56
as described in detail below.
As best understood with reference to
FIGS. 4A-4B
, operation of liquid dispensing system
10
will now be described for forming droplets
12
of liquid or viscous material onto substrate
14
. Droplets
12
may be solder flux, surface mount adhesive, chip underfill, epoxy or other liquid or viscous material used in the assembly or packaging of electronic components.
The dispensing method and dispensing apparatus contemplated by the present invention begins by positioning the liquid dispensing system
10
to a predetermined X-Y position relative to substrate
14
, and setting the nozzle tip
52
to a predetermined Z position above substrate
14
. For dispensing adhesives, the nozzle tip
52
may be set at about 2.0 mm or more above a top surface of the substrate
14
. Prior to a dispensing cycle, a regulated supply of pressurized air from air supply
60
is provided to plenum
54
of air discharge body
48
. The pressurized air is then discharged through the annular air discharge orifice
56
as a sheath
70
(
FIGS. 4A-4B
) of pressurized air that extends generally to the top surface of the substrate
14
. The sheath
70
of pressurized air may be continuous or uninterrupted about its circumference or, alternatively when the air discharge orifice is interrupted, the sheath may include discontinuous or bands of pressurized air streams that are arranged circumferentially to form the sheath
70
.
During a dispense cycle for forming a single liquid material droplet
12
as shown in
FIGS. 4A-4B
, the valve stem
34
is retracted from valve seat
32
to allow a small amount of liquid material to flow through liquid discharge passageway
50
for a pre-selected amount of time. After the pre-selected amount of time of fluid flow has expired, valve stem
34
is returned to the closed position to dispense the droplet
12
of liquid material from the nozzle tip
52
predominantly by the pressure exerted by valve head
36
returning into sealing engagement with valve seat
32
. As the droplet
12
exits the nozzle tip
52
, one or more satellites portions
72
associated with the droplet
12
may be formed. While the droplet
12
generally travels in flight toward the substrate
14
in a direction, indicated generally by arrows
74
, that is generally aligned with dispensing axis of the dispensing system
10
, the satellite portions
72
have a tendency to stray or deviate from the dispensing axis, as indicated generally by arrows
76
. It will be appreciated that the stray satellite portions
72
can become problematic when they hit the substrate outside of the area of the dispensed droplet
12
. These satellite portions
72
may fall within areas of the substrate
14
where it is undesirable to have a coating of viscous or liquid material. Further, the satellite portions
72
may adversely affect the uniformity of the material coating applied to the substrate
14
.
In accordance with the method and dispensing apparatus of the present invention, as shown in
FIG. 4B
, the sheath
70
of pressurized air is discharged to substantially surround the droplet
12
and its associated satellite portions
72
during their flight toward the substrate
14
. In this way, the satellite portions
72
that have a tendency to stray from the dispensing axis are contained within the sheath and prevented from contacting the substrate
14
in undesirable areas. The sheath
70
of pressurized air may cause the satellite portions
72
to merge with the dispensed droplet
12
as shown in FIG.
48
. With the sheath
70
of pressurized air containing the satellite portions
72
, the dispense height of nozzle tip
52
may be set at or above 2.00 mm, while still achieving accurate and repeatable dot formations on the substrate.
Thus, those skilled in the art will readily appreciate that the liquid dispensing system
10
of the present invention is particularly adapted for forming droplets of material and dispensing those droplets onto a substrate in an accurate and repeatable manner. With the sheath of pressurized air surrounding the droplet and its associated satellite portions during flight toward the substrate, better control of the dot shape and application of the dots toward the substrate is achieved. Further, the method and dispensing apparatus of the present invention permit higher dispense heights than previously achieved by known material dispensing systems, thereby allowing greater material coverage on the substrate with fewer dots.
While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in considerable detail in order to describe the best mode of practicing the invention, it is not the intention of applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the spirit and scope of the invention will readily appear to those skilled in the art. The invention itself should only be defined by the appended claims, wherein I claim:
Claims
- 1. A method for dispensing a plurality of droplets of viscous liquid material in sequence with each droplet tending to separate into a droplet and at least one satellite portion during flight toward a substrate using a dispenser having a liquid discharge passageway in fluid communication with a source of viscous liquid and an air discharge passage in fluid communication with a source of pressurized air, comprising:dispensing the plurality of droplets of viscous liquid in sequence from the liquid discharge passageway in a travel path substantially transverse to the substrate; discharging pressurized air as a sheath from the air discharge passage in a direction substantially parallel to the travel path of the droplets; and substantially surrounding each dispensed droplet and the satellite portion associated therewith with the discharged sheath of pressurized air during flight toward the substrate so that the satellite portion is contained within the sheath of pressurized air.
- 2. Apparatus for dispensing a plurality of droplets of viscous liquid material in sequence with each droplet tending to separate into a droplet and at least one satellite portion during flight toward a substrate, comprising:a dispenser body having a liquid supply passageway adapted to connect to a source of the viscous liquid; and a nozzle assembly connected to said dispenser body and having a liquid discharge passageway in fluid communication with said liquid supply passageway of said dispenser body for dispensing the plurality of droplets of viscous liquid material in sequence in a travel oath substantially transverse to the substrate, and an air discharge orifice adapted to connect to a source of pressurized air and being configured and located with respect to said liquid discharge passageway to discharge pressurized air as a sheath in a direction substantially parallel to the travel path of the droplets that substantially surrounds each dispensed droplet and the satellite portion associated therewith during flight toward the substrate so that the satellite portion is contained within said discharged sheath of pressurized air.
- 3. The apparatus of claim 2, wherein said liquid discharge passageway and said air discharge orifice are co-axially aligned with one another, and further wherein said air discharge orifice is an annular orifice surrounding said liquid discharge passageway.
- 4. The apparatus of claim 3, wherein said annular orifice is uninterrupted surrounding said liquid discharge passageway.
- 5. The apparatus of claim 2, wherein said nozzle assembly includes a liquid dispensing nozzle body having said liquid discharge passageway, and an air discharge body operatively connected to said liquid dispensing nozzle body and having said air discharge orifice.
- 6. The apparatus of claim 5 wherein said air discharge body has a plenum connected to said air discharge orifice.
- 7. The apparatus of claim 6 wherein said air discharge body has a plurality of radially directed vanes disposed in said plenum for guiding pressurized air flow through said plenum.
- 8. The apparatus of claim 4, wherein said liquid dispensing nozzle body and said air discharge body are integral.
- 9. A nozzle assembly for dispensing a plurality of droplets of viscous liquid in sequence with each droplet tending to separate into a droplet and at least one satellite portion during flight toward a substrate, comprising:a liquid discharge passageway adapted to connect to a source of viscous liquid for dispensing the plurality of droplets of viscous liquid in sequence in a travel path substantially transverse to the substrate; and an air discharge orifice adapted to connect to a source of pressurized air and being configured and located with respect to said liquid discharge passageway to discharge pressurized air as a sheath in a direction substantially parallel to the travel path of the droplets that substantially surrounds each dispensed droplet and the satellite portion associated therewith during flight toward the substrate so that the satellite portion is contained within said discharged sheath.
- 10. The nozzle assembly of claim 9, wherein said liquid discharge passageway and said air discharge orifice are co-axially aligned with one another, and further wherein said air discharge orifice is an annular orifice surrounding said liquid discharge passageway.
- 11. The nozzle assembly of claim 10, wherein said annular orifice is uninterrupted surrounding said liquid discharge passageway.
- 12. The nozzle assembly of claim 9, wherein said nozzle assembly includes a liquid dispensing nozzle body having said liquid discharge passageway, and an air discharge body operatively connected to said liquid dispensing nozzle body and having said air discharge orifice.
- 13. The nozzle assembly of claim 12 wherein said air discharge body has a plenum connected to said air discharge orifice.
- 14. The nozzle assembly of claim 13 wherein said air discharge body has a plurality of radially directed vanes disposed in said plenum for guiding pressurized air flow through said plenum.
- 15. The nozzle assembly of claim 12, wherein said liquid dispensing nozzle body and said air discharge body are integral.
US Referenced Citations (6)