U.S. patent application number 09/358981 was filed with the patent office on 2001-12-27 for method and apparatus for dispensing viscous material.
Invention is credited to HA, VINH VAN, LIN, JEFF JIN HER, TRUBLOWSKI, JOHN.
Application Number | 20010054627 09/358981 |
Document ID | / |
Family ID | 46203651 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054627 |
Kind Code |
A1 |
LIN, JEFF JIN HER ; et
al. |
December 27, 2001 |
METHOD AND APPARATUS FOR DISPENSING VISCOUS MATERIAL
Abstract
A novel apparatus for compressing viscous material through
openings in a stencil is disclosed. The novel apparatus has a
compression head cap which provides a contained environment to
direct and to aid the flow of pressurized viscous material through
the openings in the stencil. The apparatus further includes a
selectively expandable diaphragm which selectively and expandably
allows the viscous material to be dispensed into the compression
head cap.
Inventors: |
LIN, JEFF JIN HER; (CANTON,
MI) ; TRUBLOWSKI, JOHN; (TROY, MI) ; HA, VINH
VAN; (SOUTHFIELD, MI) |
Correspondence
Address: |
VISTEON GLOBAL TECHNOLOGIES INC
1 PARKLANE BLVD
SUITE 728 PARKLANE TOWERS EAST
DEARBORN
MI
48126
US
|
Family ID: |
46203651 |
Appl. No.: |
09/358981 |
Filed: |
July 22, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09358981 |
Jul 22, 1999 |
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08716037 |
Sep 19, 1996 |
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08716037 |
Sep 19, 1996 |
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08363806 |
Dec 27, 1994 |
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Current U.S.
Class: |
222/386.5 ;
222/399 |
Current CPC
Class: |
H05K 3/1233 20130101;
B41F 15/42 20130101; H05K 2203/0126 20130101 |
Class at
Publication: |
222/386.5 ;
222/399 |
International
Class: |
G01F 011/00 |
Claims
What is claimed is:
1. An apparatus for selectively dispensing viscous a container
which receives viscous material, said apparatus comprising: a
container which receives viscous material; and a selectively
expandable diaphragm which selectively and expandably causes said
contained viscous material to be dispensed.
2. The apparatus of claim 1 further comprising a pressurized source
of air which is coupled to said selectively expandable diaphragm
and which causes said diaphragm to selectively expand.
3. The apparatus of claim 1 wherein said diaphragm includes a
plurality of pleated portions.
4. The apparatus of claim 1 wherein said diaphragm includes a
plurality of telescoping tubular portions,
5. The apparatus of claim 1 wherein said diaphragm has a
substantially uniform thickness.
6. An apparatus for selectively dispensing viscous material, said
apparatus comprising: a reservoir containing viscous material; a
plunger which is movably disposed within said reservoir; an
selectively expandable diaphragm which is secured within said
housing and which abuts said plunger; and a pressurized air source
which is communicatively coupled to the selectively expandable
diaphragm and which selectively causes the diaphragm to expand,
thereby selectively causing said plunger to dispense at least a
portion of said viscous material from said apparatus.
7. The apparatus of claim 6 wherein said expandable diaphragm is
manufactured from a flexible material.
8. The apparatus of claim 6 wherein said expandable diaphragm is
manufactured from rubber.
9. The apparatus of claim 6 wherein said expandable diaphragm
includes a plurality of selectively expandable pleats.
10. The apparatus of claim 6 wherein said expandable diaphragm
further comprises a plurality of concentric telescoping tubular
segments.
11. A method to selectively dispense viscous material comprising
the steps of: providing viscous material; placing said provided
viscous material within a container having a dispensing aperture;
placing a member over said contained viscous material; providing a
selectively inflatable diaphragm in close proximity to said member;
and selectively inflating said diaphragm effective to selectively
move said member within said container, thereby causing said member
to force at least a portion of said contained viscous material
through dispensing aperture.
Description
[0001] This application is a continuation in part from pending U.S.
patent application Ser. No. 08/716,037 (filed Sep. 19, 1996), which
is a continuation of U.S. patent application Ser. No. 08/363,806
(filed Dec. 27, 1994, and now abandoned).
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention relate generally to
methods and devices for depositing viscous materials onto a printed
wiring board. In one aspect, the present invention relates to
methods and devices for compressing viscous materials, such as
solder paste, through openings in a perforated substrate, such as a
patterned screen or stencil.
[0004] 2. Description of Related Art
[0005] Surface Mount Technology (SMT) involves placing circuit
components onto circuit paths embedded on the upper surface of a
printed wiring board and then soldering the components in place by
a process called "reflow soldering". Before the circuit component
is placed on the printed wiring board, however, it is desirable to
apply solder paste to the area on the printed wiring board where
the component is to be soldered into place.
[0006] Conventional methods do exist to deposit ("print") solder
paste onto desired areas of a printed wiring board by forcing the
paste through openings in a substrate (e.g., a stencil) placed in
intimate contact with the printed wiring board.
[0007] U.S. Pat. No. 4,622,239 describes such a method and device
for dispensing viscous materials. The method includes forcing a
viscous material from a housing through an opening and depositing
it onto a stencil between a pair of flexible members (parallel
squeegee blades) which depend from the housing on either side of
the opening and are in contact with the stencil. The ends of the
flexible members are not connected and remain open ended. The
viscous material, accordingly, is not contained within an enclosed
area when it is deposited on the surface of the stencil. Movement
of the housing and the flexible members horizontally across the
stencil causes the trailing flexible member to force the viscous
material through the openings in the stencil. U.S. Pat. No.
4,720,402 describes a similar method and device except that the
leading flexible member is raised off of the stencil during
movement of the housing.
[0008] U.S. Pat. Nos. 5,133,120 and 5,191,709 describe methods for
filling through-holes of a printed wiring board via a mask with
pressurized conductive filler material by means of a nozzle
assembly unit having a nozzle tip member. The nozzle tip member,
however, is designed only to dispense the pressurized conductive
filler material through the mask to a single through-hole. The
nozzle tip member then "scans" the printed wiring board for a
second through-hole to fill. The nozzle tip member has a blunt end
section which rests on the mask and a circular exit, the diameter
of which may be increased or decreased by changing the nozzle tip
member. The nozzle tip member dispenses the filler material without
controlling unwanted flow of "excessive" filler material back
through the stencil. Additionally, the nozzle tip member does not
define a contained environment where "compression" of the filler
material takes place through the mask followed by the immediate
shearing off of the filler material within that contained
environment from the surface of the stencil. In fact, the nozzle
tip member itself provides no effective means for shearing off
filler material from the top of the stencil, rather, after the
through hole is filled and filler material "backs up" through the
stencil, the nozzle tip member moves forward whereupon the
"excessive" filler material is then wiped off by a separate,
single, flexible squeegee member which is designed for
unidirectional use only.
[0009] Unfortunately, these conventional efforts do not provide a
contained environment for compression of viscous material through
holes in a stencil and shearing of viscous material within the
contained environment from the upper surface of the stencil.
Reliance upon squeegee movement to force the viscous material, such
as solder paste, through the stencil openings can lead to damage
and eventual failure of both the squeegee blades and the stencil
due to repeated friction. Since conventional efforts do not provide
a contained environment in which compression and shearing is
accomplished, waste of the viscous material is frequently
encountered.
[0010] Conventional efforts, therefore, (1) fail to maximize the
efficiency of printing solder paste onto a desired area of a
printed wiring board and (2) fail to minimize waste of the solder
paste during the printing process. A need therefore exists to
develop a method for printing solder paste onto a printed wiring
board and a device suitable for use therewith which overcomes the
deficiencies of the conventional efforts.
[0011] Other methods which utilize a pneumatically driven piston,
or a direct injection or application of air or other gasses, to
force viscous material from a syringe, have several drawbacks. For
example, air or other gases which are used to directly expel the
paste or viscous material from the container, or which are used to
selectively move a piston, oftentimes cause undesirable voids in
material. Moreover, in order to selectively expel the entire
contained quantity of the viscous material from the syringe, the
stroke of the pneumatically driven piston must be substantially as
long as the syringe. The use of relatively small and inexpensive
conventional pistons therefore requires the concomitant use of many
short syringes which must be frequently replaced and/or refilled,
thereby undesirably increasing production time and concomitantly
decreasing production efficiency. The use of longer more expensive
pistons allows for the use of larger syringes containing more
viscous material and requiring less frequent replacement and/or
re-filling. However, these large pistons are relatively heavy,
thereby requiring costly and undesirable structural modifications
to the compression head, are difficult to package, and/or are
difficult and/or awkward to replace.
[0012] The present invention is directed at eliminating the need
for a pneumatically driven piston while allowing for the selective
distribution of a relatively large amount of viscous material.
SUMMARY OF THE INVENTION
[0013] The present invention includes a novel apparatus and method
for dispensing viscous material through openings in a stencil.
Embodiments of the present invention include a process herein
referred to as "compression printing" wherein pressure is applied
to a viscous material within a contained environment defined by a
compression head cap so as to compress it through openings in a
stencil.
[0014] The apparatus of the present invention includes a reservoir
containing viscous material which is operably connected to a
pressure source. The reservoir is in fluid communication with a
housing which terminates in a substantially uniform opening defined
by a compression head cap formed from contiguous walls. During
operation of the apparatus, the compression head cap is placed in
contact with a stencil having a plurality of openings therein. The
compression head cap and the stencil form a contained environment.
The pressure source then applies pressure against the viscous
material contained in the reservoir forcing it from the reservoir
into the housing and to the compression head cap. The contiguous
walls of the compression head cap act to contain and to direct flow
of the pressurized viscous material to the top surface of the
stencil and then through the openings in the stencil.
[0015] It is accordingly an object of the present invention to
provide a novel apparatus for compressing a viscous material
through openings in a stencil by means of a pressure source. It is
a further object of the present invention to increase the
efficiency of printing viscous material onto a desired area of a
printed wiring board and to minimize waste of the viscous material
during the printing process.
[0016] According to another object of the present invention, an
apparatus is provided for selectively dispensing viscous material.
The apparatus includes a selectively expandable diaphragm which
selectively and expandably causes said contained viscous material
to be dispensed.
[0017] According to yet another object of the present invention, a
method to selectively dispense viscous material is provided. The
method includes the steps of providing the viscous material;
placing the provided viscous material within a container having a
dispensing aperture; placing a member over the contained viscous
material; providing a selectively inflatable diaphragm in close
proximity to the member; and selectively inflating the diaphragm
effective to selectively move the member within the container,
thereby causing the member to force at least a portion of the
contained viscous material through the dispensing aperture.
[0018] Other objects, features or advantages of the present
invention will become apparent from the following description taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In the course of the detailed description of certain
preferred embodiments to follow, reference will be made to the
attached drawings, in which,
[0020] FIG. 1 is a perspective view of the apparatus of the present
invention, partially exploded.
[0021] FIG. 2 is a side cross-sectional view of a compression head,
a compression head cap, a stencil and a printed wiring board of the
present invention showing movement of the solder paste through the
compression head, the compression head cap and the openings of the
stencil onto the printed wiring board.
[0022] FIG. 3 is a bottom perspective view of the compression head
cap of the present invention, partially broken away.
[0023] FIG. 4 is an exploded perspective view of the compression
head of the present invention showing components of the compression
head cap and one embodiment of a diffuser of the present
invention.
[0024] FIG. 5 is an exploded perspective view of the compression
head of the present invention showing components of the compression
head cap and a second embodiment of a diffuser of the present
invention.
[0025] FIG. 6 is a cross-sectional view of a viscous material
dispenser made in accordance with the teachings of a second
embodiment of the invention and having a selectively expandable
diaphragm which is shown in a selectively contracted position;
[0026] FIG. 7 is a view similar to that of FIG. 6 but showing the
contained diaphragm in a selectively expanded and material
dispensing position;
[0027] FIG. 8 is a top view of the viscous material dispensing
apparatus shown in FIGS. 6 and 7;
[0028] FIG. 9 is a bottom unassembled perspective view of the cap
and retaining ring portion of the viscous material dispensing
apparatus shown in FIGS. 6 and 7;
[0029] FIG. 10 is a cross-sectional view of a viscous material
dispensing apparatus made in accordance with the teachings of an
alternate embodiment of the invention and having a selectively
expandable diaphragm which is shown in a selectively contracted
position;
[0030] FIG. 11 is a view similar to that of FIG. 10 but showing the
contained diaphragm in a selectively expanded and material
dispensing position;
[0031] FIG. 12 is a cross-sectional view of a viscous material
dispensing apparatus made in accordance with the teachings of
another alternate embodiment of the invention and having a
selectively expandable diaphragm which is shown in a selectively
contracted position;
[0032] FIG. 13 is a view similar to that of FIG. 12 but showing the
contained diaphragm in a selectively expanded and material
dispensing position;
[0033] FIG. 14 is a cross-sectional view of a viscous material
dispensing apparatus made in accordance with the teachings of yet
another alternative embodiment of the invention and having a
selectively expandable diaphragm which is shown in a selectively
contracted position; and
[0034] FIG. 15 is a view similar to that of FIG. 14 but showing the
contained diaphragm in a selectively expanded and material
dispensing position.
DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
[0035] The principles of the present invention may be applied with
particular advantage to obtain an apparatus for compressing a
viscous material through openings in a stencil, preferred
embodiments of which may be seen at FIGS. 1, 2, 3, 4, and 5 which
are described more fully below.
[0036] FIG. 1 is a partially exploded perspective view of one
embodiment of the apparatus of the present invention. As can be
generally seen at FIG. 1, the apparatus has a pressure source 2
which is operably connected to a reservoir 4 containing a supply of
a viscous material, a compression head 6 and a compression head cap
8.
[0037] More particularly, FIG. 1 shows a pressure source depicted
as an air cylinder 2 having a piston (not shown) connected to a rod
10 contained in a cylinder housing 12. Pressure inlet 14 allows for
the introduction of air pressure at the top of air cylinder 2
thereby displacing the piston causing piston rod 10 to move
downward. The air cylinder 2 is mounted via base 16 to cylinder
mount 18 which in turn is removably mounted to casing 20 via a
twist socket connector having posts 22 and socket grooves, one of
which is shown at 24. Base 16 has air inlet 26 for the introduction
of air pressure at the bottom of air cylinder 2 thereby displacing
the piston causing piston rod 10 to move upward.
[0038] Piston rod 10 extends through opening 28 of cylinder mount
18 and is fixedly connected to syringe pusher 30 at contact 32
which in turn engages displacement piece 34 which is movably
disposed within syringe 4 which contains a viscous material.
Displacement piece 34 acts as a plunger and is designed to mate
with the interior of syringe 4 to ensure effective displacement of
viscous material with minimal waste. Pressure source 2 is designed
to mechanically meter out viscous material through operation of the
syringe pusher 30 on the displacement piece 34. The syringe pusher
30, displacement piece 34 and syringe 4 are all vertically housed
in operative fashion within the cylinder mount 18, the casing 20
and the syringe housing 36.
[0039] The vertical arrangement of the pressure source 2 and the
syringe 4 containing the viscous material is a preferred
arrangement which advantageously provides for even and direct
pressure in metering out the viscous material onto the top surface
of a stencil. It is to be understood that pressure source 2 is not
limited to an air cylinder of the type depicted in FIG. 1, but that
other suitable pressure sources may be used by one of ordinary
skill in the art based upon the teachings of the present invention.
Such pressure sources include those which mechanically,
electrically, or hydraulically operate a mechanical force, such as
a piston rod and displacement piece, to meter out viscous material
from a syringe housing or other reservoir which contains viscous
material. In addition, pneumatic pressure may be used directly to
force viscous material from a reservoir housing. Also, pressure
source and reservoir configurations other than the vertical
configuration depicted in FIG. 1 are useful in the present
invention. Such configurations include side mounted reservoirs and
pressure sources or other configurations readily known to those
skilled in the art.
[0040] The syringe 4 is preferably a disposable unit which can be
replaced when desired by disconnecting cylinder mount 18 from
casing 20 via the twist socket connector, removing the syringe and
replacing it with an alternate syringe. Examples of disposable
syringes useful within the teachings of the present invention
include those which are readily commercially available from Methods
Engineering, Vauxhall, N.J. The cartridges may be purchased
prefilled with suitable viscous materials or they may be purchased
empty and then filled with suitable viscous materials, such as
solder pastes, which are useful within the practice of the present
invention. Useful solder pastes may be readily commercially
available from Alpha Metals, Jersey City, N.J.
[0041] Typical solder pastes useful with surface mount technology
generally contain an alloy of tin, lead and silver in various
proportions in combination with other useful solder paste metals,
viscosity agents, flux and/or solvents depending upon the desired
use of the solder paste. Solder pastes useful in the present
invention will become apparent to one of ordinary skill in the art
based upon the teachings herein.
[0042] The syringe housing 36 is mounted to a housing referred to
herein as a compression head generally depicted at 6 in FIG. 1 and
shown in a cross-sectional side view in FIG. 2. The syringe 4 has
flange opening 38 which is inserted into and mates with first
opening 40 of compression head 6 which is described hereafter with
reference to both FIGS. 1 and 2 and FIG. 3 which is a bottom
perspective view of the compression head cap 8, partially broken
away. The compression head 6 terminates in a substantially uniform
second opening 42 which is defined by compression head cap 8. The
compression head cap 8 is formed from contiguous walls which define
a volume 44 within compression head cap 8. The contiguous walls may
be either unitary or formed from separate elements and are designed
to contact stencil 46 to provide a uniform and substantially flush
union with stencil 46 at the point of contact. As can be seen in
FIG. 2, stencil 46 has openings 48 and is placed in an operable
relationship with a printed wiring board 50. The stencil 46 may be
placed in intimate contact with printed wiring board 50 or, as
shown in FIG. 2, it may be placed a distance above printed wiring
board 50 such that pressure from the compression head 6 forces the
stencil 46 into contact with printed wiring board 50. Although
stencil 46 is shown in cross-section, it is to be understood that
openings 48 may have any desired orientation on stencil 46. Further
openings 48 may differ in size depending upon the area of the
printed wiring board 50 to be printed with the viscous material.
The compression head cap 8 and stencil 46 together form a contained
environment 44 for the viscous material during operation of the
apparatus of the present invention.
[0043] As can be seen in FIG. 1, cross bar mount 52 is attached to
syringe housing 36 via flange 54. Cross bar mount 52 is also
attached to a mechanism (not shown) for horizontally displacing the
apparatus of the present invention along the stencil 46.
[0044] The compression head 6 is preferably formed from metal, such
as iron or stainless steel or other material suitable for use with
pressurized viscous material. The compression head 6 has top
surface 56 which serves as the base to which the syringe housing 36
is attached. Side surfaces 58 and 60 extending from top surface 56
slope away from each other as depicted in FIG. 1 to define an
increasing length of compression head 6. Front and back surfaces 62
and 64 are contiguous with side surfaces 58 and 60 and slope toward
each other as depicted in FIG. 2 to define a decreasing width of
compression head 6. The side surfaces join with the front and back
surfaces to define a tapered interior chamber 66 as shown in FIG. 2
which acts to restrict flow of viscous material through compression
head 6. Interior chamber 66 terminates in generally rectangular
exit 68. Compression head 6 preferably acts as a nozzle to direct
and constrict the flow of viscous material through generally
rectangular exit 68. The compression head cap 6 defines a volume 44
surrounding the rectangular exit 68 and into which viscous material
flows after exiting the interior chamber 66 of compression head 6.
As shown in FIG. 2, the volume 44 is preferably a separate chamber
into which the viscous material flows after exiting the interior
chamber 66 via rectangular exit 68. The compression head cap 8
defines a generally rectangular opening 42 which is to be contacted
with stencil 48. The compression head cap 8 acts to contain and
direct the flow of viscous material to the stencil 46. In an
alternate embodiment, it is to be understood that the interior
chamber 66 may terminate directly into compression head cap 8
without the need for rectangular exit 68 or volume 44.
[0045] As can be seen in FIG. 4, the compression head 6 has two
half sections 70 which are fixedly connected by screws (not shown)
via screw holes 72. The bottom side section 74 of each half section
70 is provided with ledge area 76 to engage the compression head
cap 8. As depicted in FIGS. 2, 3 and 4, compression head cap 8 has
rectangular blades 78 and end caps 80, which define generally
rectangular opening 42. Blades 78 are each fixedly mounted to a
corresponding ledge area 76 of front surface 62 and back surface
64, respectively, by means of corresponding rectangular blade
holders 82 and screws (not shown) via screw holes 84. Blades 78
each extend along substantially the entire length of corresponding
ledge area 76. End caps 80 are attached to a corresponding ledge
area 76 of bottom side section 74 via corresponding cap mounts 86
and screws (not shown) via screw holes 88. The end caps 80 are
contiguous with blades 78 and together form the compression head
cap 8. As can be seen more clearly in FIG. 2, blades 78 parallel
the slope of corresponding front and back surfaces 62 and 64, and
are, therefore, seen to be angled inward relative to the interior
chamber 66 of compression head 8.
[0046] Blades 78 are preferably thin and formed from rigid material
such as iron or stainless steel. End caps 80 are preferably formed
from a flexible substance such as polyurethane to avoid damage to
the stencil during operation of the apparatus of the present
invention. Cap mounts 86 and blade holders 82 are formed from any
solid material capable of securing the corresponding end cap or
blade.
[0047] While the compression head cap 8 is depicted in FIGS. 2, 3,
and 4 as being formed from integral parts, it is to be understood
that compression head caps having a unitary structure are within
the teachings of the present invention. Such unitary compression
head caps are formed from a single rectangular shaped unit and are
designed to encircle the ledge area 76 of the compression head 6 or
otherwise operatively engage compression head 6. Such compression
head caps may be either fixed or removably mounted to the
compression head and may have various sizes of opening 42.
[0048] The compression head 6 and compression head cap 8, in
combination with the pressure source 2 and syringe 4 advantageously
provide a vertical down force to move the viscous material evenly
and directly to the stencil. The compression head cap 8 of the
present invention advantageously provides a contained environment
to direct and to aid in the extruding of pressurized viscous
material through openings in the stencil. The extruded viscous
material is then deposited on the pattern of the printed wiring
board. The apparatus of the present invention provides for very
high speed printing capability while maintaining print definition
and reduced cycle time. Waste of viscous material is minimized due
to the contained environment provided by the compression head cap
8. The length of the compression head cap 8 allows for simultaneous
compression printing through a plurality of openings 48 in stencil
46. Furthermore, the trailing blade 78 relative to the direction of
operation advantageously operates to shear off the viscous material
contacting the stencil within the compression head cap 8 when the
apparatus of the present invention is horizontally disposed across
the stencil. The blades 78 are rigid and angled to advantageously
achieve a smooth shearing of the viscous material. The compression
head 6 and compression head cap 8 are advantageously rectangular in
shape so that they may operate over a significant area of the
stencil with each pass. Additionally, given the dual blade design
of the compression head cap 8, the apparatus of the present
invention may operate in both the forward and reverse directions
thereby improving the efficiency of the compression printing
process of the present invention.
[0049] As can be further seen in FIGS. 2 and 4, compression head 6
has diffuser 90 which is fixedly mounted within interior chamber
66. Diffuser 90 has a plurality of diffuser plates 92 which are
horizontally disposed within interior chamber 66 via grooves 94.
Each diffuser plate 92 has a series of openings 96 through which
viscous material is to flow. Each opening 96 may be either circular
or oblong and decreases in average size as the diffuser plates
progress from the first opening 40 to the compression head cap 8.
The openings 96 also increase in number as the diffuser plates
progress from the first opening 40 to the compression head cap 8.
The diffuser 90 advantageously serves to break up the flow of
viscous material and evenly and uniformly distribute it from side
to side of the rectangular exit 42. The diffuser 90 may also serve
to reduce the velocity of the viscous material flowing through the
compression head and increase the static pressure of the viscous
material which aids in the compression printing process.
[0050] FIG. 5 shows an alternate embodiment of a diffuser 90 useful
in the present invention. The diffuser 90 has a plurality of
diffuser islands 98 which are horizontally disposed in rows within
interior chamber 66. The diffuser islands 98 may be fixedly
installed within the interior chamber 66 or they may be molded
directly within the interior chamber 66. As with the diffuser 90 of
FIG. 4, each diffuser island 98 acts to break up the flow of the
viscous material and uniformly and evenly distribute it from side
to side of rectangular exit 42. The diffuser islands may be either
circular or oblong and decrease in average size as the rows
progress from the first opening 40 to the compression head cap 8.
The diffuser islands 98 also increase in number as the rows
progress from the first opening 40 to the compression head cap 8.
The diffuser islands 98 of the present invention are advantageous
in that they provide for ease of fabrication of the compression
head and ease of cleaning.
[0051] Operation of the apparatus of the present invention is now
described as follows with reference to FIGS. 1 and 2. When
compression printing according to the teachings of the present
invention, the compression head cap 8 of the apparatus of the
present invention is brought into contact with the top surface of
stencil 46 which forces the stencil downward until it is in
intimate contact with the printed wiring board below as shown in
FIG. 2. The apparatus is then moved in a horizontal direction, as
shown in FIG. 2, across the stencil 46.
[0052] During movement of the stencil, pressure source 2 acts on
syringe 4 to force viscous material 100 from the syringe 4 into the
interior chamber 66 of compression head 6 where it is diffused by
diffuser 90 and directed to rectangular exit 68. The viscous
material then enters volume 44 of compression head cap 8 which
provides a contained environment via blades 78 and end caps 80 to
direct the pressurized viscous material under pressure to the top
surface of stencil 46. The viscous material is then extruded
through openings 48 in the stencil 46 over which the compression
head cap 8 travels. The extruded viscous material 100 is thereby
printed on the printed wiring board 50. Movement of the compression
head cap 8 across the stencil surface causes the trailing blade 78
which is angled inwardly relative to the interior chamber 66 to
shear off the viscous material from the top surface of stencil 46.
Once the apparatus has traversed the length of the stencil, the
apparatus may simply reverse its direction and continue the
compression printing process since the compression head cap 8 has
dual blades 78 to accomplish the shearing process in either
direction of movement.
[0053] Operating variables of the apparatus of the present
invention, such as run speed and pressure, may be adjusted to
accommodate either viscous materials having a wide range of
viscosities or stencils with holes having a wide range of
diameters. The following data in Table 1 is representative of the
parameters at which the apparatus has successfully operated. Print
speed is measures in inches per second, air pressure is measured in
pounds per square inch, viscosity of the solder paste is measured
in centipoises per second, stencil apertures are measured in
inches, and the particle sizes of the solder pastes used are
between 10-37 microns.
1TABLE 1 Print Speed Viscosity Aperture (inches/sec.) (cps)
(inches) Low High Air Pressure (psi) Low High Low High 0.94 1.26 20
850K 1.0M 0.0055 >0.025 1.45 1.70 20 850K 1.0M 0.0055 >0.025
2.27 2.31 20 850K 1.0M 0.0055 >0.025 3.10 3.89 30 850K 1.0M
0.0055 >0.025 4.20 4.77 30 850K 1.0M 0.0055 >0.025 5.98 6.62
40-50 850K 1.0M 0.0075 >0.025 6.69 7.23 50-60 850K 1.0M 0.0075
>0.025 7.70 12 50-60 850K 1.0M 0.0075 >0.025
[0054] As indicated by the above data, the apparatus of the present
invention successfully operated over a wide range of print speeds,
air pressures and stencil openings. The compression printing method
disclosed herein advantageously provides for quicker print speeds,
better quality of printing, and less waste of solder paste material
than is encountered with conventional printing methods.
[0055] While the above-delineated invention provides significant
improvement over prior dispensers and dispensing methods, it has
several drawbacks. Particularly, the stroke of the pneumatically
driven piston must be substantially as long as the syringe in order
to selectively expel the entire contained quantity of the viscous
material from the syringe. The use of relatively small and
inexpensive conventional pistons therefore requires the concomitant
use of many short syringes which must be frequently replaced and/or
"re-filled", thereby undesirably increasing production time and
concomitantly decreasing production efficiency. The use of longer
more expensive pistons allows for the use of larger syringes which
contain more viscous material and require less frequent replacement
and/or "re-filling" of material. However, these large pistons are
relatively heavy, thereby requiring the compression head to be
undesirably and structurally modified and "strengthened" in order
to accommodate the increased piston weight. These large pistons are
also difficult to package and are difficult and awkward to replace
and service.
[0056] These drawbacks are addressed by the following additional
embodiments which substantially eliminate the need for a
pneumatically driven piston or air cylinder 2 and which allow for
the selective distribution of a relatively large amount of
contained material.
[0057] Referring now to FIGS. 6 through 9, there is shown an
apparatus 200 which selectively dispenses viscous material and
which is made in accordance with the teachings of a second
embodiment of the invention.
[0058] Apparatus 200 includes a substantially cylindrical and
generally hollow elongated housing 202 containing a substantially
uniform cavity 203 having a generally circular cross-sectional
area. Housing 202 is manufactured from a relatively strong and
durable conventional and commercially available material, such as
plastic or metal, and further includes an integrally formed base or
flange portion 206 having four substantially identical openings or
apertures 208 which are each adapted to selectively receive a
conventional fastener or screw 210. Cavity 203 terminates within
portion 206 by forming a relatively small and generally circular
material dispensing aperture 211. Housing 202 further includes two
opposing and laterally extending connector posts 212, which are
used to selectively allow cap 222 to be removably secured upon the
housing 202.
[0059] Apparatus 200 further includes a generally flat mounting
member 226 having four substantially identical apertures 228 which
are each adapted to be selectively and communicatively aligned with
a unique one of the apertures 208 and to selectively receive a
unique one of the fasteners 210. Apertures 208, 228 and fasteners
210 cooperatively and selectively allow housing 202 to be
selectively mounted upon a compression printing head. Mounting
member 226 further forms and/or includes an aperture or channel 230
and an integrally formed and generally circular raised projection
portion 231 which is adapted to be operatively inserted within the
aperture 211 and which cooperates with the interior surface of
housing 202 to form a generally circular retention groove 233.
Aperture 230 communicates with cavity 203, through aperture 211,
and selectively receives and directs the flow of viscous material
to the compression head in a manner which will be explained.
[0060] Syringe 204 is adapted to be selectively and removably
placed within cavity 203. Particularly, syringe 204 contains a ring
or projection portion 235 which is adapted to be frictionally and
removably deployed within groove 233. Syringe 204 further includes
a material containment cavity 205 which generally conforms to
cavity 203, and a plunger or selectively moveable viscous material
displacement piece 214, which, in one embodiment, is substantially
similar in function and structure to displacement piece 34.
Particularly, piece 214 is selectively, matably, and movably
disposed within syringe cavity 205 between a first position in
relative close proximity to the upper opening 215 of syringe 204,
as illustrated in FIG. 7, and a second position in relative
proximity to the material dispensing aperture 216 which is formed
within the syringe 204, which is illustrated in FIG. 8, and which
operatively communicates with aperture 230.
[0061] Apparatus 200 further includes a selectively expandable and
generally tubular shaped membrane or diaphragm 218 having a first
closed end portion 219 which operatively engages the generally
concave surface 217 of displacement piece 214, and which is
manufactured from a relatively thin, flexible and durable material
such as latex, butyl rubber or commercially available "Nitrile"
material. In one non-limiting embodiment, diaphragm 218 has a
thickness ranging from three thousandths of an inch (0.003") to ten
thousandths of an inch (0.010"), although other thicknesses may be
employed. Particularly, in one non-limiting embodiment, the
thickness of diaphragm 218 decreases along its length with the
thickness being minimized near the material dispensing aperture 230
of apparatus 200 and maximized near opening 215.
[0062] Diaphragm further includes a second open end 225 which is
foldably and compressibly secured around a substantially circular
retaining ring 220, thereby causing open end 225 to substantially
and operatively conform to the shape of ring 220. Ring 220 is
selectively, operatively, frictionally and removably contained
within an integrally formed and generally circular channel 223 of
cap 222, thereby securely positioning diaphragm 218 within syringe
cavity 205.
[0063] Cap 222 includes a relatively small and generally circular
air reception aperture 232 which communicates with the hollow and
selectively expandable interior 250 of diaphragm 218, thereby
allowing for the introduction of a gaseous material, such as air,
to be selectively and expandably communicated to the interior 250
of diaphragm 218. Cap 222 is removably mounted upon housing 202 in
a manner which has been previously explained. That is, socket
grooves 224, which are similar in function and structure to grooves
24, selectively, removably and cooperatively receive laterally
extending posts 212 which are similar in function and structure to
posts 22 (see FIG. 1), thereby allowing cap 222 to be selectively
and removably secured to housing 202.
[0064] When mounted upon housing 202, cap 222 fits snugly and
compressibly over retaining ring 220 and diaphragm 218 and
supportably positions the ring 220 upon the upper lip 227 of
syringe 204, thereby securing diaphragm 218 within housing 202 and
causing substantially all of the gas or air which is introduced
through opening 232 to travel and be expansively retained within
the interior 250 of diaphragm 218.
[0065] In operation, mounting piece 226 is selectively placed upon
and operatively secured to a print or compression head, such as
compression head 6, by use of conventional and commercially
available fasteners 210. Air or other gaseous material is
selectively introduced into the interior 250 of diaphragm 218
through communicating aperture 232. As the air pressure within
diaphragm 218 increases, diaphragm 218 expands forcing plunger 214
towards the bottom of syringe 204, thereby forcing viscous material
100 through communicating apertures 216 and 230, and into the
compression head, until plunger 214 reaches its bottom-most
position, which is illustrated in FIG. 7. The rate and force at
which plunger 214 expels viscous material 100 is selectively
controlled in a conventional manner by selectively modifying the
pressure introduced through opening 232, such as by way of a
conventional pressure regulator.
[0066] In such a manner, the selectively expandable diaphragm 218
obviates the need for a relatively large piston assembly to
selectively cause material 100 to be desirably dispensed, and
concomitantly reduces the overall cost and complexity of the
assembly 200.
[0067] Referring now to FIGS. 10 and 11, an apparatus 300 is
provided and is made in accordance with the teachings of an
alternate embodiment of the invention. Particularly, apparatus 300
is substantially similar to apparatus 200, except that the
generally elastic diaphragm 218 has been replaced with a "bellows"
type diaphragm 318. With the exception of diaphragm 318, apparatus
300 includes substantially identical components as apparatus 200.
Unless otherwise noted, components having a substantially identical
structure and function are defined by the same reference numerals
as used with respect to apparatus 200, delineated in FIGS. 6
through 9, with the exception that these components will have these
reference numerals incremented by 100. In this alternate
embodiment, diaphragm 318 is manufactured from a relatively stiff
and durable material such as rubber, plastic, metal or a composite
and has a plurality of integrally formed "bellows" or selectively
expandable pleats 321 which are adapted to selectively and
cooperatively expand or contract, thereby expanding and contracting
diaphragm 318.
[0068] In operation, air or gas is introduced through aperture 332
and into interior 350, thereby causing the pleats 321 to expand at
respective, integrally formed and substantially air-tight joints
329. Accordingly, the diaphragm 318 is selectively forced from a
compressed or constricted position, as shown in FIG. 10, to a
expanded or extended position, as shown in FIG. 11. As diaphragm
318 expands from its compressed to its expanded position, plunger
314 is forced towards the bottom of syringe 304, thereby forcing
viscous material 100 through communicating apertures and/or
openings 316 and 330 and into the compression head until plunger
314 reaches its bottom-most position, as illustrated in FIG. 11. It
should be appreciated that the use of integrally formed and
selectively expandable "air-tight" pleats 321 allows diaphragm 318
to be manufactured from a relatively thicker and more durable
material than diaphragm 218, thereby resulting in a longer
functional life.
[0069] In yet another alternate embodiment of the invention, an
apparatus 400 for dispensing viscous material is provided.
Apparatus 400 is substantially similar to apparatus 200 with the
exception that diaphragm 218 has been replaced with a telescopic
diaphragm 418, as illustrated in FIGS. 12 and 13. With the
exception of diaphragm 418, apparatus 400 includes substantially
identical components as apparatus 200. Unless otherwise noted,
components having a substantially identical structure and function
are defined by the same reference numerals used with respect to
apparatus 200, delineated in FIGS. 6 through 9, with the exception
that these components will have the reference numerals incremented
by 200.
[0070] Telescoping diaphragm 418, in one embodiment, is
manufactured from a relatively stiff and durable material such as
rubber, plastic, metal or a composite. Diaphragm 418 includes
integrally formed and overlapping concentric or tubular shaped
segments 450-462. Each segment 450-462, in one non-limiting
embodiment, is substantially similar and cylindrical in shape and
has a diameter which is slightly smaller than the diameter of the
preceding segment (e.g., the diameter of segment 462 is slightly
smaller than the diameter of segment 460 which is slightly smaller
than the diameter of segment 458). Diaphragm 418 includes a
plurality of conventional and generally circular rubber or metal
seals 464 which reside around the perimeter of each juncture 466
occurring and/or formed between adjacent segments 450-462. Seals
464 provide an air-tight seal at each juncture 466 and cooperate
with the "closed" end 468 of segment 462 to substantially prevent
the escape of air from diaphragm 418. It should be understood that
while a diaphragm having six tubular segments is illustrated in
this non-limiting example, any number of segments 450-462 may be
used without departing from the scope of the invention.
[0071] In operation, gas is introduced through aperture 432 causing
the air pressure within the interior 470 of diaphragm 418 to
increase, thereby forcing concentric tubular segments 452-462
"downward" toward the bottom (e.g., toward aperture 430) of the
assembly 400. As the concentric tubular segments 452-462 are forced
"downward", diaphragm 418 expands from a compressed or constricted
position, as shown in FIG. 12, to a expanded or extended position,
as shown in FIG. 13. As diaphragm 418 expands from its compressed
position to its expanded position, plunger 414 is forced towards
the bottom of syringe 404, thereby forcing viscous material 100
through opening 416 and central channel 430 and into the
compression head, until plunger 414 reaches its bottom-most
position, illustrated in FIG. 13. The use of telescoping tubular
segments 450-462 allows diaphragm 418 to be manufactured from a
relatively thicker and more durable material than diaphragm 218,
thereby resulting in a longer functional life.
[0072] In yet another alternate embodiment of the invention, an
apparatus 500 for dispensing viscous material is provided and is
illustrated in FIGS. 14 and 15. Apparatus 500 is substantially
similar to apparatus 200 with the exception that diaphragm 218 has
been replaced with diaphragm 518. With the exception of diaphragm
518, apparatus 500 includes substantially identical components as
apparatus 200. Unless otherwise noted, components having a
substantially identical structure and function are defined by the
same reference numerals with respect to apparatus 200, with the
exception that these components will have reference numerals
incremented by 300.
[0073] Particularly, apparatus 500 includes a selectively
expandable diaphragm 518 which has a substantially constant and/or
uniform cross sectional area and which has a shape, as shown best
in FIG. 15, which generally conforms to the syringe cavity 505 even
when not filled with air or other gaseous material. Particularly,
diaphragm 518 is simply folded to fit within the top of apparatus
500 when material 100 is not to be dispensed. Upon receipt of air
or other gases, diaphragm 518 expands and selectively and
operatively moves piece 514 within the cylinder cavity 505,
effective to cause the material 100 to be selectively emitted from
aperture 530.
[0074] It is to be understood that the embodiments of the invention
which have been described are merely illustrative of some
applications of the principles of the invention. Numerous
modifications may be made by those skilled in the art without
departing from the true spirit and scope of the invention.
* * * * *