Note: Descriptions are shown in the official language in which they were submitted.
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1 ~ackground of the Invention
In the United States Patent Application Serial No. 299,979 filed
September 8, 1981 (assigned to the assignee of the invention disclosed
herein) there is disclosed an invention for a machine for placing chip
stype electronic components on a printed circuit board at a very high
rate of speed. This machine requires an adhesive dispenser for
dispensing a non-conductive adhesive onto a printed circuit board
between the conductive lands on the board. The chip is subsequently
placed onto the adhesive to make the chip adhere to the board between
the conductive lands. The board can be later processed through wave
soldering apparatus to make the final electrical bond between the
component and the conductive lands on the board.
In investigating available apparatus for dispensing the adhesive
it became apparent that such an apparatus must accurately dispense very
small amounts of a thick paste-like material at a rate of at least four
times a second with sufficient reliability to be incorporated into an
automatic syste~ without causing any potential system down-time to
exceed the time necessary to repair any other operating parts of the
system. All of these requirements additionally must be accomplished by
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using the mechanical and electrical resources available on the
component placement machine.
There are generally two methods of applying or depositing drops of
fluid at specified locations; the transfer method and by the direct
application. An example of the transfer method is a rubber ink stamp
where the fluid is picked up by an applicator and deposited where
desired. Available apparatus using this method of applying adhesives
to a printed circuit board are undesirable since they are not general
purpose devices, must be especially designed and built for specific
10 applications and as a rule are not programmable.
Direct application of a fluid to a substrate is accomplished by
inducing the fluid to flow from a reservoir to an applicator having an
orifice that deposits the fluid. The fluid is caused to flow through a
conduit from the reservoir to an applicator by some type of
displacement means caused either by compressed air (pneumatic) or
15 mechanical reduction of the reservoir volume to move the fluid.
There are two ways of using the pneumatic displacement method to
induce fluid flow. The simple way is to apply pressure to a reservoir
when the flow of material is desired and relieve pressure when the
required amount is obtained from the applicator. When used with
relative thin fluids, these devices are sometimes rigged so that a mild
vacuum (termed "suckback") is applied to the reservoir when the
pressure is removed in order to prevent the fluid from escaping
spuriously (drooling) from the applicator under the effects of gravity
or capillary action. In these devices, blunt hollow needles are
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commonly used as the outlet orifice of the applicator.
The second method of using pneumatics for dispensing fluids
involves keeping the reservoir pressurized constantly whenever the
system is in use. A valve is interposed between the reservoir and the
applicator to control the release of the fluid. These valves can be
manually operated or actuated by electrical, pneumatic, hydraulic or
various mechanical linkages. In these devices the fluid must travel
through the inner workings of the valve and when the fluid is an
adhesive that can setup or harden, the valve becomes non-functional
until cleaned
With regard to using a mechanical means to reduce the reservoir
volume to move the fluid, this can be done by either using a plunger
acting on the fluid or by squeezing the reservoir.
None of the prior art devices of the nature described provide for
metering a small amount of paste-like adhesive with a degree of
15 repeatability and reliability within a specified limited time interval
for application to a chip type component placement machine. The
devices mentioned utilized a hollow needle as the outlet of the
applicator. The object is to have the adhesive protrude beyond the end
of the needle and bring the needle outlet adjacent the printed board
substrate to apply the small amount of adhesive to the desired
location. In theory, the protruding material will separate from the
main mass of adhesive at the plane of the outlet and remain on the
substrate when the needle is removed. In practice, however, the
contact of the needle to the substrate tends to pack the fluid back
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into the needle orifice and upon removal of needle, the fluid separates
up inside the orifice leaving a void at the end of the needle which may
not be completly filled in the next cycle, resulting in no deposit
occurring at that time. Conversely, upon contact between the needle
and substrate, a sufficient amount of material may be pushed back into
the needle orifice so that enough grip between the adhesive and the ID
of needle occurs to overcome the cohesion and surface tension of the
adhesive to the substrate so that a deposit of adhesive on the
substrate does not take place. These problems can be partially
10 overcome when the material droplet is fairly large compared to the bore
diameter of the needle. However, in the application of small metered
amounts of adhesives, the droplet size is approximately the same as the
size of the needle and thus a hollow needle applicator is insufficient
for this application.
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It is an object of this invention to provide
a mechanism that accurately meters very small amounts
of thick adhesive paste in droplet form on a substrate
such as a printed circuit board.
It is another object of this invention to provide
an adhesive dispenser having an outer cylinder carried
on a support that moves an adhesive metering device
toward and away from a substrate to place minute amounts
of adhesive on the substrate.
It is a further object of this invention to provide
an adhesive metering device that makes a direct line
deposit of the adhesive on substrate; the device being
unaffected by pressure or viscosity of the adhesive.
According to a broad aspect of the present inven-
lS tion, there is provided an adhesive dispensing device
for rapidly placing a minute droplet of adhesive on
a substrate. The device comprises a support housing
and an adhesive metering device adapted to be supplied
with adhesive under constant pressure from an adhesive
supply source. The metering device has means passing
through the metering device for collecting supplied
adhe~ive and making a direct line deposit of a measured
amount of adhesive to the substrate. A dispensing
mechanism is carried by the support housing and sup-
ports the metering device for movement of the meteringdevice vertically toward and away from the substrate
when applying adhesive to the substrate. The metering
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device includes a nozzle and the collecting means
is adapted to pass through the nozzle to deposit the
adhesive on the substrate.
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Brief Description of the Drawings
_ _
Attention is now directed to the Figures of the drawing which
illustrate:
Figure 1 is a side elevational view of the adhesive dispensing
device in a non-operative condition;
Figure 2 is a view similar to Figure 1 with the metering pin in a
retracted position to collect a metered amount of adhesive;
Figure 3 is a view similar to Figure 1 with the metering pin in a
downward position after collecting the adhesivei and
Figure 4 is a view showing the dispenser in a downward position to
apply a droplet of adhesive to a substrate.
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Description of the Preferred Embodiment
Attention is now directed to Figure 1 which illustrates the
adhesive dispenser in a static or non-operative position. This
dispenser was developed for metering small amounts of adhesive between
the conductive lands on a printed circuit board to secure chip type
electronic components to the board. However, as will become apparent
hereinafter, this dispenser could be utilized in other environments
where rapid application of small amounts of material to a substrate, is
required.
1~ The dispenser 10 is carried on a support housing 12 positioned on
a machine frame (not shown). When used in a chip placement machine,
the dispenser would be positioned as illustrated in copending U.S.
Patent application Serial No. 299,979 filed September 8, 1981 and would
place a droplet "D" of adhesive on the printed circuit board 14 between
conductive lands on the board. The support housing 12 has a stepped
15 cylindrical opening or bore 16 which houses a dispensing cylinder 18
and a metering cylinder 20 for reciprocable movement toward and away
from the board during the pickup and application of the adhesive
thereon.
The dispensing cylinder 18 comprises a sleeve 22 having a threaded
cap 24 on the lower end thereof and a piston 26 on the upper end
thereof. A lower sleeve bearing 28 is carried in the bore 16 by lock
pins 30. The sleeve bearing 28 has inner and outer seals 32 and 34
respectively. An upper sleeve bearing 36 is also carried in the bore
16 by a pair of lock pins 38 and is sealed in the bore by an 0-ring 40.
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The piston 26 is sealed in bore 16 by an 0-ring 42 and carries a
tubular housing 44 secured thereto by a lock nut 46. A seal 48 in
sleeve bearing 36 surrounds the tubular housing 44 to provide an air
tight chamber above the piston 26. The opposite end of bore 16 is
sealed by a cap 50 and an annular seal 52.
The metering cylinder 20 comprises a piston 54 mounted within the
bore 56 of sleeve 22. The piston 54 has a central land 58, and end
lands 60 and 62 to contain seals 64, 66. The end land 60 of piston 54
carries an adhesive metering pin 68.
Secured within the bore 56 is a non-wettable gland 70 by means of
a cap 72 sweat fit within bore 56. The gland 68 also has a shoulder 74
positioned against threaded cap 24. As illustrated, metering pin 68
passes down through the bore 76 in gland 70. The pin 68 is a solid
rigid member with a tight fit in the bore 76 of the gland 70. Threaded
on the lower end 78 of gland 70 is a nose or nozzle member 80.
The adhesive is supplied to the metering pin by means of a
flexible supply line 82 attached to a fitting 84 carried on the gland
70. The fitting has an opening or port 86 in communication with the
bore 76 in which the metering pin 68 slides.
The adhesive supply line 82 is connected to a reservoir of
adhesive 88 which is pressurized through an air supply 90. An air
pressure regulator 92 maintains the desired constant air pressure on
the reservoir to supply the adhesive to the metering cylinder at the
desired rate. A shut-off valve 94 is also disposed in the adhesive
supply line.
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The dispensing cylinder 18 is operated for up and down movement by
air supply lines 96, 98 which are in communication with bore 16 at
opposite ends of the piston 26. The metering cylinder piston 54 has an
air line 100 in communication with the lower end of the piston 54
through opening 101 in sleeve 22. The tubular housing 44 has an
opening 102 in communication with flexible air line 104 placing the
upper end of piston 54 under pressure at the desired sequence in the
operation of the device, as will become apparent hereinafter.
In operation, from the static condition illustrated in Figure 1,
lO the adhesive supply line 82 and air line 100 are pressurized which
raises piston 54 and metering rod or pin 68 to the position illustrated
in Figure 2 at this time the adhesive enters the bore 76 of the gland
70. The gland 70 is a non-wettable material such as tetrafluoroethlene
"TEFLON" to which the adhesive will not adhere.
After this start-up stage, the adhesive reservoir is constantly
- 15 pressurized. The amount of adhesive flowing into the bore 76 is a
function of the flow characteristics and viscosity of the material
versus flow resistance of the system, reservoir pressure and length of
time that the opening or port 86 into bore 76 is open by withdrawal of
metering pin 68. After raising piston 54 and metering pin 68 and the
lapse of the correct time to collect the required size of a globule of
adhesive in bore 76, air line 104 is activated to move pin 68
downwardly in bore 76 to collect and sever the required amount of
adhesive from the main mass along the intersection of opening or port
86 into bore 76. Thereafter, the opening 86 is sealed by pin 68 so
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further adhesive cannot enter bore 76. This position of the dispenser
and resulting placement of a dot "D" of adhesive on the end of pin 68
at the outlet of the dispenser is illustrated in Figure 3. None of the
droplets are lost from the collection point to the dispenser outlet
because the gland is a non-wettable material and because of the close
fit of the pin 68 in bore 76.
Attention is now directed to Figure 4 wherein the dispenser is
shown moved downwardly to place the adhesive on the substrate 14. As
the air line 98 is energized and the air line 104 activated, the
1O dispensing cylinder 18 and sleeve 22 move downwardly through the
support housing to a point where the nozzle or outlet 80 of the
dispenser is placed in contact with the substrate and the droplet of
adhesive is squeezed between the end of the pin and the work surface.
This causes the droplet to spread out and ensures a good grip between
the substrate and the deposit since the contact area of the droplet to
15 the substrate is greater than the contact area of the droplet to the
end of the pin 68. If in the process the adhesive contacts the gland,
no adhesion occurs because the gland is a non-wettable material.
In the continued operation of the dispenser, the sequences of
operation illustrated in Figures 2 to 4 are repeated. That is, after
placement o~ the droplet as illustrated in Figure 4, the air lines 96
and 100 are energized to return the dispensor and metering pin to the
adhesive pickup position shown in Figure 2. On the return stroke, the
bumpers 106 and 108 absorb impact of the bottoming out of the pistons
26 and ~4.
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The above described operation of the dispenser and specifically
the air lines and adhesive reservoir pressuring source can all be
controlled by any computer command programmed to the remaining
functions of the other elements of a machine; in this instance a chip
placement machine.
It should also be noted that an optical brightener such as "UVITEX
O.B." mixed with the adhesive would aid visual inspection. When viewed
under black light, adhesive droplets would stand out allowing visual
inspection of missing droplets or a missing chip which should have been
O placed upon a droplet in the subsequent chip placement phase of the
machine operation. Also, automatic inspection could be accomplished
from a digitized read out of the luminous pattern of the droplets on
the substrate.
It can thus be seen that the above described adhesive dispenser
makes a rapid direct line deposit of a minute droplet of adhesive from
15 the bore 76 onto a substrate. The amount of adhesive flowing into bore
76 is a function of the adhesive flow characteritics and viscosity of
the material versus the flow resistance of the system, as well as the
adhesive reservoir pressure and the length of time that the port 86 and
the bore 76 are in communication. Since the adhesive characteristics,
system resistance and reservoir pressure are all constant for a given
set-up, controlling the amount of time the port 86 is open (by rapidity
of movement of metering pin 68) controls the amount of adhesive
- admitted into bore 76 and thus the amount of the adhesive subsequently
deposited on the substrate.
