U.S. patent application number 12/389542 was filed with the patent office on 2009-06-18 for method of controlling contact load in electronic component mounting apparatus.
This patent application is currently assigned to Panasonic Corporation (formerly known as Matsushita Electric Industrial Co., Ltd.). Invention is credited to Shuichi HIRATA, Makoto MORIKAWA, Yasuharu UENO, Hiroyuki YOSHIDA, Noriaki YOSHIDA.
Application Number | 20090151149 12/389542 |
Document ID | / |
Family ID | 35501043 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090151149 |
Kind Code |
A1 |
HIRATA; Shuichi ; et
al. |
June 18, 2009 |
METHOD OF CONTROLLING CONTACT LOAD IN ELECTRONIC COMPONENT MOUNTING
APPARATUS
Abstract
A method of controlling contact load in an apparatus for
mounting electronic components on a substrate includes a head
holding an electronic component being lowered at a first speed to a
first position where the electronic component does not contact the
substrate. The head is lowered at a second speed slower than the
first speed from the first position until a predetermined target
contact load is detected. The head is moved down by a small step
for a predetermined distance at the second speed and a contact load
is measured after moving the head down. The method includes
determining whether a measured contact load has reached the
predetermined target contact load. The moving and the measuring is
sequentially repeated until the measured contact load reaches the
predetermined target contact load. The predetermined distance is
set to a first predetermined distance when moving the head down
until the electronic component contacts the substrate. The
predetermined distance is set to a second predetermined distance
when moving the head down after the electronic component contacts
the substrate and the second predetermined distance is smaller than
the first predetermined distance.
Inventors: |
HIRATA; Shuichi; (Osaka,
JP) ; UENO; Yasuharu; (Osaka, JP) ; MORIKAWA;
Makoto; (Nara, JP) ; YOSHIDA; Hiroyuki;
(Osaka, JP) ; YOSHIDA; Noriaki; (Osaka,
JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
Panasonic Corporation (formerly
known as Matsushita Electric Industrial Co., Ltd.)
Osaka
JP
|
Family ID: |
35501043 |
Appl. No.: |
12/389542 |
Filed: |
February 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10596218 |
Jun 5, 2006 |
7513036 |
|
|
PCT/JP05/16376 |
Aug 31, 2005 |
|
|
|
12389542 |
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|
Current U.S.
Class: |
29/593 ;
324/754.01 |
Current CPC
Class: |
B23K 3/087 20130101;
Y10T 29/49137 20150115; B23K 37/047 20130101; H01L 2224/75502
20130101; Y10T 29/49133 20150115; Y10T 29/53187 20150115; Y10T
29/4913 20150115; Y10T 29/49004 20150115 |
Class at
Publication: |
29/593 ;
324/754 |
International
Class: |
G01R 31/28 20060101
G01R031/28 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2004 |
JP |
2004-254532 |
Claims
1. A method of controlling contact load in an apparatus for
mounting electronic components on a substrate, in which a head
holding an electronic component is lowered at a first speed to a
first position where the electronic component does not contact the
substrate, the head being lowered at a second speed slower than the
first speed from the first position until a predetermined target
contact load is detected, the method comprising: moving the head
down by a small step for a predetermined distance at the second
speed; measuring a contact load after moving the head down; and
determining whether a measured contact load has reached the
predetermined target contact load, the moving and the measuring
being sequentially repeated until the measured contact load reaches
the predetermined target contact load, wherein the predetermined
distance is set to a first predetermined distance when moving the
head down until the electronic component contacts the substrate,
wherein the predetermined distance is set to a second predetermined
distance when moving the head down after the electronic component
contacts the substrate, and wherein the second predetermined
distance is smaller than the first predetermined distance.
2. The method according to claim 1, further comprising: halting the
head for a predetermined period of time after moving the head down
and before measuring the contact load.
3. The method according to claim 1, wherein the second
predetermined distance is adjustably set in accordance with the
predetermined target contact load.
4. The method according to claim 1, wherein the predetermined
distance is set to a first predetermined distance when the measured
contact load is zero, wherein the predetermined distance is set to
a second predetermined distance when the measured contact load
exceeds zero, and wherein the second predetermined distance is less
than the first predetermined distance.
5. The method according to claim 4, wherein the second
predetermined distance is adjustably set in accordance with a
difference between the measured contact load and the predetermined
target contact load.
6. The method according to claim 1, wherein the measuring of the
contact load is repeated until a different contact load is measured
when the measured contact load exceeds zero and the measured
contact load is the same as a previously measured contact load.
7. The method according to claim 1, wherein the second
predetermined distance is adjustably set such that the movement and
the measurement is sequentially repeated until the measured contact
load reaches the predetermined target contact load.
8. The method according to claim 1, wherein the predetermined
distance is adjustably set within a range of 0.2 um to several
um.
9. A method of controlling contact load in an apparatus for
mounting electronic components on a substrate, in which a head
holding an electronic component is lowered at a first speed, to a
first position where the electronic component does not contact the
substrate, the head being lowered at a second speed slower than the
first speed from the first position until a predetermined target
contact load is detected, the method comprising: moving the head
down by a small step for a predetermined distance at the second
speed from the first position until the electronic component
contacts the substrate; measuring contact load, while the head is
not moving down, after moving the head down by a predetermined
distance; and determining whether the measured contact load has
reached the target contact load, the moving and the measuring being
sequentially repeated, while the head is not moving down, until the
measured contact load reaches the predetermined target contact
load.
10. The method according to claim 9, wherein the predetermined
distance is set to a first predetermined distance when moving the
head down until the electronic component contacts the substrate,
wherein the predetermined distance is set to a second predetermined
distance when moving the head down after the electronic component
contacts the substrate, and wherein the second predetermined
distance is smaller than the first predetermined distance.
11. The method according to claim 9, wherein the predetermined
distance is set to a first predetermined distance when moving the
head down until the electronic component contacts the substrate,
wherein the predetermined distance is set to a second predetermined
distance when moving the head down after the electronic component
contacts the substrate, and wherein the second predetermined
distance is adjustably set in accordance with a difference between
the measured contact load and the predetermined target contact
load.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of pending U.S. patent
application Ser. No. 10/596,218, filed Jun. 5, 2006, which is a
National Stage Application of International Application No.
PCT/JP05/16376, filed Aug. 31, 2005, which claims priority under 35
U.S.C. .sctn.119 of Japan Application No. 2004/254532, filed Sep.
1, 2004 which are expressly incorporated herein by reference in
their entireties.
TECHNICAL FIELD
[0002] The present invention relates to a method of controlling
contact load between an electronic component and a substrate when
mounting the electronic component held on a head onto the substrate
set on a stage in an electronic component mounting apparatus.
BACKGROUND ART
[0003] In one of the methods of mounting electronic components such
as bare IC chips on a substrate, the electronic component is held
on a head while a substrate is set on a stage, and after the
electronic component is positioned relative to the substrate, the
head is lowered so that a bump on the electronic component makes
contact with a corresponding electrode pad on the substrate, to
bond the bump of the electronic component and the electrode pad of
the substrate. In one bonding method, a certain load is applied
between a gold bump provided on the electronic component and an
electrode pad on the substrate, and ultrasonic energy with or
without thermal energy is applied to bond the component on the
substrate. In another method, solder bumps are provided on the
electronic component, which are reflowed by applying thermal
energy, after the bumps are brought into contact with electrode
pads on the substrate, such that the bump is bonded to the pad by
solder.
[0004] As the circuit wiring pitch in circuits of the electronic
component is now in the order of nanometers, low dielectric
constant materials are used for the interlayer insulating film. One
problem with the low dielectric constant material is that it has
low strength and may crack when subjected to a large load in the
bonding process, which may lead to breakage of the electronic
component. The load applied to the electronic component when its
bump makes contact with the electrode pad on the substrate
(hereinafter, referred to as contact load) in the process of
lowering the head holding the electronic component onto the
substrate can readily be too large, and this load poses a risk of
damage to the electronic component using the above-noted low
dielectric constant material because of a crack in the interlayer
insulating film.
[0005] Now, an electronic component mounting method with a local
reflow process using solder will be described with reference to
FIG. 5A to FIG. 5D. In this method, discrete electronic components
with solder bumps are mounted on a substrate, after which the
electronic components are heated using a head to reflow and bond
the solder bumps with electrode pads on the substrate.
[0006] Referring to FIG. 5A to FIG. 5D, an electronic component 31
having solder bumps 32 is held by a tool 30 on a head. A substrate
33 having electrode pads 34 on which solder or flux has been
applied is carried in and set on a stage 35. The head is moved to
position the solder bumps 32 of the electronic component 31
relative to the electrode pads 34 on the substrate 33, as shown in
FIG. 5A. The head is lowered until the solder bumps 32 make contact
with the electrode pads 34 as shown in FIG. 5B. The electronic
component 31 is then heated with a heater disposed at the lower end
of the head to reflow the solder bumps 32 so that the electrodes on
the electronic component and the electrode pads 34 are bonded by
the solder bonds 36, as shown in FIG. 5C. Then, the heating is
stopped and the component is cooled to set the solder bonds 36,
after which the head releases the electronic component 31 and goes
up, as shown in FIG. 5D. After that, the substrate 33 on which the
electronic component 31 is mounted is carried out from the stage
35.
[0007] FIG. 6 and FIG. 7A to FIG. 7C illustrate how the head is
controlled in the process of lowering it until the component 31
(the solder bumps 32) make contact with the substrate 33 (the
electrode pads 34) in this electronic component mounting method.
The head is lowered at high speed from a predetermined waiting
position to a slow down starting position, which is set at a
position where there is no risk of accidental contact between the
component and the substrate. From there the head is lowered at a
low search speed of about 0.1 mm/s. The head has a build-in load
cell for measuring the load in real time, and it is determined
whether or not the load has reached a predetermined detection level
of contact load. The lowering movement of the head is continued at
the low speed until the load reaches the detection level, when it
is slowed down and stopped. This way, the component is brought into
contact with the substrate in a shortest possible time without the
risk of applying an impact load when the component touches the
substrate. After the electronic component makes contact with the
substrate, the mounting head is controlled to repeat the steps of
moving slightly and measuring the load, so that a predetermined
load is applied to them (see Japanese Patent Laid-Open Publication
No. 2003-8196).
[0008] In this process of bringing the component into contact with
the substrate, however, as shown in FIG. 7C, the head is slowed
down at a time point E, which is delayed by d from a time point D
when a detection level contact load is detected. There is a time
delay of e from the time point E to F when the head is stopped, as
a result of which the contact load at the stop time point F is much
larger than the contact load that was first detected. To be more
specific, if a detection level contact load of 0.5N is detected
while the head is moving at a search speed of 0.1 mm/s, the load
when the head is stopped will be as large as 2.0 to 3.0N. Moreover,
the load further increases and reaches a peak immediately after the
head is stopped by the inertia of the head in a period of about 5
to 10 msec as indicated by an imaginary line in FIG. 7C. This
large, instantly applied load may generate cracks in the interlayer
insulating film made of low dielectric constant material and cause
damage to the electronic component.
[0009] An object of the present invention is to solve the
above-described problems in the conventional technique and to
provide a method of controlling contact load in an electronic
component mounting apparatus, with which the contact load applied
on the components is precisely controlled to be as close as
possible to a predetermined target contact load of a low level, so
that electronic components using a low dielectric constant material
can be mounted without the risk of damage.
DISCLOSURE OF THE INVENTION
[0010] To achieve the above object, the present invention provides
a method of controlling contact load in an apparatus for mounting
electronic components on a substrate, in which a head is lowered at
high speed to a slow down starting position where there is no risk
that the electronic component makes contact with the substrate, and
from there the head is lowered at low speed until a predetermined
target contact load is detected. This process of lowering the head
at low speed includes the steps of moving down the head a
predetermined distance, measuring load after the step of moving
down the head, and determining whether the measured load has
reached the target contact load. The steps of moving down the head
and measuring the load are repeated until the measured load reaches
the target contact load.
[0011] With this method, the head is moved down by a very small
distance of, e.g., 0.2 to several .mu.m, and the load is measured
each time after the head is lowered. These steps of moving down the
head by a predetermined distance and measuring the load are
repeated until the measured contact load reaches a predetermined
target level, whereby the contact load is precisely controlled to
be close to a predetermined, very small level of, e.g., 0.4 to
0.6N. Accordingly, electronic components using low dielectric
constant material are mounted without the risk of damage.
[0012] The head is stopped for a set period of time after the step
of moving down the head and before the step of measuring load so as
to allow for the time required for measuring the load. This enables
accurate real-time measurement of the load before the head is moved
down in the next step, whereby precise control of the contact load
is possible.
[0013] The distance by which the head is moved down in the step of
moving down the head may be set variably in accordance with the
predetermined target contact load. If the target contact load is
large, the moving distance of the head in one lowering step is made
large without making the error ratio of the contact load relative
to the target contact load high, and the time required for the step
of lowering the head at low speed is reduced. On the other hand, if
the target contact load is small, the moving distance of the head
in one lowering step is made small, so as to keep the error ratio
of the contact load relative to the target contact load low, and to
achieve precise control of the contact load.
[0014] The moving distance in the step of moving down the head is
set at a first predetermined distance when the measured load is
zero, and is set at a second predetermined distance after the load
has exceeded zero, the second predetermined distance being smaller
than the first predetermined distance. Thus, the head is lowered by
a relatively large distance until the component makes contact with
the substrate and a load of more than zero is detected. This way,
the time required for the steps of lowering the head at low speed
is reduced. After the contact, the head is lowered by a relatively
small distance to achieve precise control of the contact load. A
good balance is thus achieved between productivity and
precision.
[0015] The second predetermined distance may be set variably in
accordance with a difference between the measured load and the
target contact load. This way, the head is lowered by a smaller
distance as the load comes close to the target contact load, and
the contact load is controlled more precisely.
[0016] If, after the load has exceeded zero, the measured load is
the same as the previously measured one in the step of measuring
load, the step of measuring load is repeated until a different load
is detected. This is for preventing a drop in the control precision
of the contact load, i.e., if the cycle time of the control routine
is as fast as or faster than the load measuring time, the load
measured before the previous lowering step may be detected as the
current load, and if the head is lowered further by the
predetermined distance based on this measurement, the contact load
may largely exceed the target contact load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic diagram illustrating the structure of
a head in one embodiment of a method of controlling contact load in
an electronic component mounting apparatus of the invention;
[0018] FIG. 2 is a diagram illustrating the structure of the
contact load control system in the same embodiment;
[0019] FIG. 3 is a flowchart of the contact load control operation
in the same embodiment;
[0020] FIG. 4 is a graph showing how the contact load changes with
the head position in the contact load control operation in the same
embodiment;
[0021] FIG. 5A to FIG. 5D are schematic diagrams illustrating the
processes of a contact-reflow type electronic component mounting
method;
[0022] FIG. 6 is a flowchart of a conventional contact load control
operation; and
[0023] FIG. 7A to FIG. 7C are graphs showing how the contact load
changes with the head position and head speed in the conventional
contact load control operation.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] One embodiment of a contact load controlling method in an
electronic component mounting apparatus of the present invention
will be hereinafter described with reference to FIG. 1 to FIG.
4.
[0025] Referring to FIG. 1, 1 denotes a head in an electronic
component mounting apparatus. A head body 2 that moves up and down
includes a shaft 3 in a lower part thereof such as to be movable up
and down. The shaft 3 extends down through a lower end support
frame 2a of the head body 2 and is supported on the lower end
support frame 2a via a spring 4 for counterbalancing the weight of
the movable part including the shaft 3. To the lower end of the
shaft 3 is provided a tool 5 for picking up an electronic component
by suction. Heating means 6 such as a ceramic heater and a
water-cooling jacket 7 for preventing heat transmission to the
shaft 3 are arranged between the shaft and the tool. To the top of
the shaft 3 is abutted a load cell 8 for measuring load. The upper
end of the load cell 8 is abutted on the lower end of a large
cylinder device 9 disposed above the head body 2.
[0026] The large cylinder device 9 includes a built-in piston 10
which is moved up and down by supplying and discharging compressed
air through a port 9a at the upper end. A piston rod 10a extending
from the lower end of the piston 10 makes contact with the load
cell 8 at the distal end. A stopper 11 is disposed such as to be
movable between an engaging position and a retracted position; it
stops the lowering movement of the piston 10 by engaging with a
recess 10b formed in the circumference of the piston 10. At the top
of the shaft 3 is formed a cylinder chamber of a small cylinder
device 12 with an open top, and a piston 13 that moves up and down
in this cylinder chamber makes contact with the load cell 8 at the
upper end. The cylinder chamber is provided with a port 12a through
which compressed air is supplied or discharged to or from the lower
part of the cylinder chamber. The large cylinder device 9 and small
cylinder device 12 are used for applying a predetermined load to an
electronic component when it is mounted. Since the contact load is
controlled by adjusting the position of the head 1 in this
embodiment, the shaft 3 is secured to the head body 2 and moves up
and down with the head body 2. As shown in FIG. 1, compressed air
is supplied through the port 9a of the large cylinder device 9 as
indicated by the white arrow with the stopper 11 being protruded to
the engaging position so as to secure the piston 10, and compressed
air is discharged from the port 12a of the small cylinder device
12, so that the piston 13 is secured at lower end position of the
cylinder chamber by the force of the spring 4.
[0027] A drive unit 14 for driving the head body 2 up and down is
disposed on one side in parallel to the shaft 3. The drive unit 14
is made up of a feed screw mechanism 15 using a ball screw and a
motor 16 for rotating the ball screw.
[0028] FIG. 2 illustrates the control unit for controlling the
contact load. A load cell input unit 17 reads an output voltage of
the load cell 8 at a cycle of, e.g., 100 msec, and outputs the load
cell signal, which is an analog voltage signal, to a motor control
unit 18. When a command signal to start lowering movement at low
speed is input from a machine control unit 20, the motor control
unit 18 refers to the load cell signal and outputs a control signal
to a motor driver 19 for driving the motor 16, based on a preset
operation program.
[0029] The load cell signal is also input to the machine control
unit 20 from the load cell input unit 17, so that the measured load
is displayed on a display 21. The motor 16 is for moving the head
body 2 up and down between a slow down starting position where
there is no risk that the electronic component accidentally makes
contact with the substrate and a position where the electronic
component makes contact with the substrate. The head 1 is moved
down at high speed from a waiting position to the slow down
starting position by another lifting mechanism (not shown)
controlled by the machine control unit 20. The machine control unit
20 outputs a command signal to start the slow lowering movement to
the motor control unit 18 when it receives a detection signal
indicating that the head has reached the slow down starting
position.
[0030] Next, how the contact load is controlled by controlling the
drive of the motor 16 through the motor control unit 18 is
described with reference to FIG. 3 and FIG. 4. First, the head is
lowered at high speed to the slow down starting position (step S1)
as noted above. The predetermined distance n by which the head is
lowered is set to be n1 of, e.g., one to several .mu.m (step S2).
The motor 16 is driven to lower the head body 2 or the electronic
component held by the tool 5 by the predetermined distance n (or
n1) (step S3). The head is stopped for a set period of time of,
e.g., several tens msec using a timer, for waiting a change in the
signal from the load cell 8 (step S4). The load cell signal is then
read (step S5), and it is determined whether the measured load is
zero or not (step S6). If the load is zero, the steps S3 to S6 are
repeated, i.e., the head is lowered by n1 and the load is read
repeatedly until a load more than zero is detected.
[0031] When the load exceeds zero at step S6, the predetermined
distance n by which the head is lowered is set to be n2 of, e.g.,
0.2 to 1.0 m (step S7). Then, it is determined whether or not the
load is the same as the load that was detected in the previous step
(step S8). As the load here is usually not the same as the
previously detected one, the process goes to the next step S9 where
it is determined whether the load has reached a predetermined
target contact load of, e.g., 0.5N (step S9). If the load has not
reached the target contact load, the process goes back to step S3,
and the steps S3 to S9 are repeated, i.e., the head is lowered by
n2 and the load is read repeatedly until the load reaches the
target level. When it is determined that the load has reached the
target level at step S9, the slow lowering movement is stopped.
Thus the contact load between the electronic component and the
substrate is precisely controlled to be close to the predetermined
target contact load.
[0032] If the load is the same as the previously detected one in
step S8, the head is not moved further down and the process goes
back to step S5 to repeat reading the measured load. This is for
preventing a drop in the control precision of the contact load: If
the cycle time of the control routine is as fast as or faster than
the load measuring time, the load measured before the previous
lowering step may be detected as the current load, and if the head
is lowered further by the predetermined distance based on this
measurement, the contact load may largely exceed the target
level.
[0033] According to the embodiment described above, the head is
moved down by a very small distance of, e.g., 0.2 to several .mu.m,
and the load is measured each time after the head is lowered. These
steps of moving down the head by a predetermined distance and
measuring the load are repeated until the contact load reaches a
predetermined target contact load, whereby the contact load is
precisely controlled to be close to a predetermined, very small
load of, e.g., 0.4 to 0.6N. Accordingly, electronic components
using low dielectric constant material are mounted without the risk
of damage.
[0034] The predetermined distance n by which the head is moved down
in the steps of lowering the head is set to be n1 (one to several
.mu.m) as long as the measured load is zero, and after the measured
load has exceeded zero, it is set to be n2 that is smaller than n1
(0.2 to 1.0 .mu.m), so that the head is lowered by a relatively
large distance until the component makes contact with the substrate
and a load of more than zero is detected. This way, the time
required for the step of lowering the head at low speed is reduced.
After the contact, the head is lowered by a relatively small
predetermined distance to achieve precise control of the contact
load. A good balance is thus achieved between productivity and
precision.
[0035] While the second predetermined distance n2 is set to be a
constant value in the above-described embodiment, it may be set
variably in accordance with a difference between the measured load
and the target contact load. This way, the head is lowered by a
smaller predetermined distance as the load comes close to the
target contact load, and the target contact load is controlled more
precisely.
[0036] While the moving distance n in the step of lowering the head
at low speed is set irrelevantly of the target contact load in the
above-described embodiment, it may be set variably in accordance
with the predetermined target contact load, using an appropriate
conversion equation or referring to a preset table. If the target
contact load is large, the moving distance of the head in one
lowering step is made large without making the error ratio of the
contact load relative to the target level high, and the time
required for the step of lowering the head at low speed is reduced.
On the other hand, if the target contact load is small, the moving
distance of the head in one lowering step is made small, so as to
keep the error ratio of the contact load relative to the target
level low, and to achieve precise control of the contact load.
INDUSTRIAL APPLICABILITY
[0037] As described above, according to the method of controlling
contact load in an electronic component mounting apparatus of the
present invention, the moving distance of the head in one lowering
step is set very small, and the load is measured each time after
the head is lowered the distance. These steps of moving down the
head by the predetermined distance and measuring the load are
repeated until the contact load reaches a target contact load,
whereby the contact load is precisely controlled to be close to the
target contact load, which may be set very low. Accordingly, the
invention is particularly applicable to the mounting of electronic
components using low dielectric constant material, as such
electronic components are mounted without the risk of damage.
* * * * *