Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2000-07-24
2002-05-21
Bareford, Katherine A. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C118S712000, C118S323000, C073S866500
Reexamination Certificate
active
06391378
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method and apparatus for measuring the height of a substrate, and more particularly, to a method and apparatus for measuring the height of a substrate in a dispensing system that dispenses viscous materials onto the substrate. The height measurement is used to ensure that a dispensing nozzle of the dispensing system is at a predetermined distance above the substrate prior to dispensing the material.
DISCUSSION OF THE RELATED ART
There are several types of prior art dispensing machines used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards or integrated circuit chips, wherein dispensing machines are used for encapsulating integrated circuits and/or for underfilling flip integrated circuit chips. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards. The liquid epoxy or solder is used to connect components to the circuit boards. The dispensing systems described above include those manufactured and distributed by Camelot Systems Inc., the assignee of the present invention, under the name CAM/A LOT®).
In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z), typically using servo motors controlled by a computer system or controller. To dispense a dot of liquid on a circuit board at a desired location, the pump and dispenser assembly is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z-axis until the nozzle is at an appropriate height over the board. The pump and dispenser assembly dispenses a dot of liquid, is then raised along the z-axis, moved along the x and y axes to a next desired location, and lowered along the vertical z-axis to dispense a next liquid dot.
In these dispensing systems, it is critical that the distance between the dispensing nozzle and the circuit board be carefully maintained to ensure that the dot of material is properly dispensed onto the circuit board. Although the absolute location of the nozzle can be precisely controlled by the servo motors and the controller, the z-axis position at which the nozzle must be located to obtain the precise distance above the circuit board is variable because of variations in height among circuit boards that are to receive the dispensed material. Thus, the proper z-axis dispensing position of the nozzle for one circuit board may not be equal to the proper z-axis dispensing position of the nozzle for a second circuit board. Further, in addition to there being variations in height among circuit boards, the upper surface of each circuit board may have irregularities such that the height of a circuit board is different at one location on the circuit board than it is at another location on the circuit board.
In one prior art dispensing system, a touch probe, incorporated into the pump and dispenser assembly, is used to position the nozzle at the desired distance above a circuit board. The touch probe
20
will now be described with reference to
FIGS. 1A
,
1
B and
1
C, which show the touch probe
20
disposed over a circuit board
10
. Each of
FIGS. 1A
,
1
B and
1
C show the touch probe
20
during a different stage of the positioning process.
The touch probe
20
includes a lower housing
22
, a pneumatic actuator
24
, and a cylinder
26
that extends from the pneumatic actuator to the lower housing. The pneumatic actuator is coupled to an air tube
18
which is coupled to a pressurized air source (not shown). The lower housing
22
is shown in a partially broken away view to show the position of the cylinder
26
within the lower housing. The cylinder
26
has a probe end
28
that during operation of the touch probe extends from the lower housing to contact the circuit board
10
. Mounted on one side of the lower housing is a proximity sensor
36
that is implemented using an electromagnetic field to detect a metal target. The proximity sensor is electrically coupled to a controller (not shown) of the dispensing system. The cylinder
26
has a ring
30
made from stainless steel that can be readily detected by the proximity sensor
36
.
The touch probe
20
operates in the dispensing system as follows. A circuit board to receive dispensed material at a number of dispensing locations on the top surface of the circuit board is loaded into the dispensing system. For each of the dispensing locations, the touch probe is used to determine the z-axis position of the pump and dispenser assembly that will result in the desired distance between the nozzle and the circuit board. It should be noted, however, that depending on the tolerance of the circuit board, the touch probe may measure the z-axis position at some number of dispensing locations less than the total number of dispensing locations. The touch probe
20
, as shown in
FIG. 1A
, is positioned at a distance d
1
above a first dispensing location of the circuit board
10
. In
FIG. 1
, the cylinder
26
is shown in a retracted position such that the entire cylinder is contained within the lower housing
22
. The cylinder
26
is held in the retracted position by a spring located in the pneumatic actuator
24
. Once the touch probe
20
is in the position shown in
FIG. 1A
, the controller controls the pressurized air source to supply pressurized air to the pneumatic actuator
24
to actuate the touch probe. The pressurized air compresses the spring releasing the force exerted on the cylinder
26
by the spring, and allowing the cylinder to fall to an actuated position as shown in FIG.
1
B.
Once the touch probe is in the actuated position, the controller controls the servo motors of the moving assembly to slowly lower the pump and dispenser assembly, thereby lowering the touch probe
20
which is attached to the pump and dispenser assembly. The controller continues to lower the touch probe until receiving an indication from the proximity sensor
36
that the ring
30
on the cylinder
26
is aligned with the proximity sensor (see FIG.
1
C). Upon receipt of the indication from the proximity sensor, the controller stops the movement of the touch probe assembly, and stores the z-axis position of the pump and dispenser assembly. When the controller stops the movement of the pump and dispenser assembly, the lower housing
22
is at a distance d
2
from the circuit board. The position of the touch probe on the pump and dispenser assembly is precalibrated such that when the lower housing is at the distance d
2
from the circuit board, the nozzle of the pump and dispenser assembly is at the desired dispensing distance above the circuit board.
The calibration procedure described above is repeated for each of the dispensing locations on the circuit board to obtain the proper z-axis dispensing position for each dispensing location. The pump and dispenser assembly is then moved to each of the dispensing locations, positioned at the proper z-axis dispensing position previously determined using the touch probe, and material is dispensed onto the top surface of the circuit board.
There are drawbacks associated with the touch probe and calibration procedure described above. First, the procedure is relatively time consuming since at each dispensing location, the pump and dispenser assembly must be slowly lowered towards the circuit board. If the pump and dispenser assembly is moved too quickly, then any time delay associated with the detection of the ring
30
and the stopping of the servo motors will result in errors in determining the proper z-axis dispensing position. Even when the probe is moved relatively slowly, any delay in stopping the servo motors may still result in unacceptable error.
SUMMARY OF THE INVENTION
Embodiments of the present invention are directed to a method and apparatus for measuring the height of the surfa
Carr Gregory L.
Cavallaro William
Bareford Katherine A.
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
Speedline Technologies, Inc.
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