U.S. patent application number 08/987202 was filed with the patent office on 2001-11-08 for apparatus and method for printing solder paste.
Invention is credited to HIGASHIDA, TAKAAKI, KABESHITA, AKIRA, NAITO, TAKAO, ONISHI, HIROAKI, SATO, SHOJI.
Application Number | 20010038882 08/987202 |
Document ID | / |
Family ID | 26468788 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038882 |
Kind Code |
A1 |
ONISHI, HIROAKI ; et
al. |
November 8, 2001 |
APPARATUS AND METHOD FOR PRINTING SOLDER PASTE
Abstract
A filling squeegee and a scraping squeegee are provided. The
filling squeegee is moved in a state without contact with a surface
of a mask thereby to fill a solder paste in openings of the mask,
then the unnecessary solder paste on the surface of the mask is
scraped by the scraping squeegee. The solder paste is prevented
from being filled in the openings improperly or scraped improperly
even if a speed of the squeegee is increased, so that the solder
paste is printed stably on circuit boards.
Inventors: |
ONISHI, HIROAKI;
(HIGASHIOSAKA-SHI, JP) ; SATO, SHOJI;
(NEYAGAWA-SHI, JP) ; NAITO, TAKAO; (YAMANASHI-KEN,
JP) ; HIGASHIDA, TAKAAKI; (KADOMA-SHI, JP) ;
KABESHITA, AKIRA; (HIRAKATA-SHI, JP) |
Correspondence
Address: |
WENDEROTH LIND AND PONACK
2033 K STREET N.W.
SUITE 800
WASHINGTON
DC
20006
|
Family ID: |
26468788 |
Appl. No.: |
08/987202 |
Filed: |
December 9, 1997 |
Current U.S.
Class: |
427/8 ; 118/692;
427/282; 427/357; 427/367; 427/98.4; 427/99.3 |
Current CPC
Class: |
B41F 15/42 20130101;
H05K 3/1233 20130101; H05K 2203/0139 20130101 |
Class at
Publication: |
427/96 ; 427/282;
427/357; 427/367; 118/692 |
International
Class: |
B05D 001/32; B05D
005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 1996 |
JP |
8-329758 |
May 26, 1997 |
JP |
9-134778 |
Claims
What is claimed is:
1. A solder paste printing apparatus wherein a squeegee device
moves in a printing direction to a surface of a mask having
openings formed therein, thereby to print and apply solder paste on
the surface via the openings to a face of a circuit board
positioned at a rear face of the mask, said squeegee device
comprising: a filling squeegee having a front end kept in a
noncontact state via a gap to the surface at the time of printing,
and filling the solder paste into the openings while moving in the
printing direction; and a scraping squeegee arranged behind the
filling squeegee in the printing direction, moving in the same
direction as the filling squeegee while keeping touch with the
surface at the time of printing thereby to remove unnecessary
solder paste on the surface.
2. A solder paste printing apparatus according to claim 1, wherein
the scraping squeegee is provided for each direction behind the
filling squeegee with respect to the printing direction in a case
where the squeegee reciprocates to the surface of the mask.
3. A solder paste printing apparatus according to claim 2, wherein
the filling squeegee is divided to two in the printing
direction.
4. A solder paste printing apparatus according to claim 1, further
comprising an angle setting device for setting the scraping
squeegee so that an angle of the scraping squeegee in an axial
direction thereof to the surface of the mask is an optional acute
or obtuse angle.
5. A solder paste printing apparatus according to claim 4, wherein
the scraping squeegee is inclined with the obtuse angle by the
angle setting device.
6. A solder paste printing apparatus according to claim 4, wherein
the scraping squeegee is inclined with the acute angle by the angle
setting device thereby to fill the solder paste into the openings
as well as remove the unnecessary solder paste.
7. A solder paste printing apparatus according to claim 1, wherein
the scraping squeegee is disposed so that an extending direction of
a line of contact between the scraping squeegee and the surface of
the mask intersects with an extending direction of a side edge part
defining one of the openings.
8. A solder paste printing apparatus according to claim 1, wherein
a face of the filling squeegee opposite to the surface of the mask
forms a filling pressuring face which is inclined upward from the
front end in the printing direction so as to press the solder paste
to the surface and fill the solder paste to the openings.
9. A solder paste printing apparatus according to claim 8, further
comprising a filling adjustment device for adjusting filling of the
solder paste to the openings by varying at least one of a size of
the gap and an intersection angle of the filling pressuring face
and the surface.
10. A solder paste printing apparatus according to claim 9, further
comprising a filling pressure detector for detecting a change of a
filling pressure of the solder paste filled into the openings at
the time of printing, and a control device for controlling the
filling adjustment device based on the filling pressure detected by
the filling pressure detector.
11. A solder paste printing apparatus according to claim 10,
wherein the filling pressure detector is a reaction force detector
for detecting a reaction force which is a sum of the filling
pressures of the solder paste acting to the whole filling
pressuring face at the time of printing.
12. A solder paste printing apparatus according to claim 10,
wherein the filling pressure detector is a pressure detector set at
the filling pressuring face for detecting the filling pressure of
the solder paste directly.
13. A solder paste printing method comprising: moving a filling
squeegee in a printing direction at time of printing while keeping
a front end of the filling squeegee in a noncontact state via a gap
to a surface of a mask having openings formed therein, thereby
filling a solder paste on the surface to the openings; and removing
unnecessary solder paste on the surface by a scraping squeegee
moving in touch with the surface in the printing direction.
14. A solder paste printing method according to claim 13, wherein
the scraping squeegee is set so that an angle of the scraping
squeegee in an axial direction thereof to the surface of the mask
is an optional acute or obtuse angle.
15. A solder paste printing method according to claim 14, wherein,
when the scraping squeegee is set with the obtuse angle, the
scraping squeegee removes the unnecessary solder paste without
adversely influencing the solder paste filled in the openings.
16. A solder paste printing method according to claim 14, wherein,
when the scraping squeegee is set with the acute angle, the
scraping squeegee fills the solder paste to the openings as well as
removes the unnecessary solder paste.
17. A solder paste printing method according to claim 13, wherein
the scraping squeegee is set so that an extending direction of a
line of contact between the scraping squeegee and the surface of
the mask intersects with an extending direction of a side edge part
defining one of the openings.
18. A solder paste printing method according to claim 13, wherein a
face of the filling squeegee opposite to the surface of the mask
forms a filling pressuring face which is inclined upward from the
front end in the printing direction so as to press the solder paste
to the surface and fill the solder paste to the openings.
19. A solder paste printing method according to claim 18, wherein a
change of a filling pressure of the solder paste when the solder
paste is filled by the filling squeegee to the openings at the time
of printing is detected by a filling pressure detector, and at
least one of an intersection angle of the filling pressuring face
and the surface and a size of the gap is adjusted based on the
detected filling pressure, thereby to change printing condition.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus and a method
for printing, applying solder paste onto surfaces of circuit boards
to be printed.
[0002] In the prior art of manufacturing electronic circuit boards,
solder paste has been primarily used to solder electronic
components such as chips or the like onto printed boards. A solder
paste printing apparatus has been employed to print, apply the
solder paste in a required pattern.
[0003] A squeegee head loaded to a conventional solder paste
printing apparatus 100 is constituted, for instance, as shown in
FIG. 20. Generally, a squeegee head 102 moves from left to right
and from right to left in FIG. 20 alternately for every printed
board 5 to print the solder paste. A right squeegee 101a is used
for printing in the right direction, namely, from left to right in
FIG. 20, and a left squeegee 101b is for printing in the opposite
left direction.
[0004] An operation for printing the solder paste to the printed
board 5 by the conventional solder paste printing apparatus 100
will be described with reference to FIGS. 20-22. In FIGS. 20-22,
references respectively indicate: 3 a mask having openings 4 formed
in a required pattern; 5 a printed board; 6 a land to which a
solder paste 7 is printed; and 8 a solder resist. The
above-mentioned required pattern of the mask 3 is a pattern in
which openings 4 are formed corresponding to lands 6 on the printed
board 5.
[0005] Firstly, in printing in the right direction, the printed
board 5 is positioned and overlapped with the mask 3 so that the
openings 4 agree with the lands 6. Thereafter, while the left
squeegee 101b is kept raised, the right squeegee 101a is lowered to
bring a squeegee front end part 103 in touch with a surface 3a of
the mask 3 with a suitable printing pressure. In this state, the
right squeegee 111a is linearly moved in the right direction,
thereby to fill the solder paste 7 provided at the surface 3a of
the mask 3 into the openings 4 of the mask 3. The printed board 5
is separated from the mask 3 after the right squeegee 101a is moved
to the right end of the mask 3, when the printing is finished.
Meanwhile, in the case of printing in the left direction, the
printed board 5 is positioned and overlapped with the mask 3,
similar to the above printing in the right direction. Then, the
left squeegee 101b is descended while the right squeegee 101a is
held up, to bring the squeegee front end part 103 in touch with the
mask 3. The operation afterwards is the same as in the case of
printing in the right direction. By repeating the operations in the
right direction and left direction alternately for every printed
board 5, the solder paste 7 is continuously printed, applied onto
the lands 6 of each printed board 5 via the mask 3.
[0006] In the conventional solder paste printing apparatus 100, the
squeegee 101a or 101b is moved while the front end part 103 of the
squeegee is kept in touch with the surface 3a of the mask 3 with a
suitable printing pressure. As is made clear from this fact, each
of the conventional squeegees 101a, 101b executes two kinds of
operations, i.e., a scraping operation of scraping the solder paste
7 at the surface 3a of the mask 3 and a filling operation of
filling the solder paste 7 to openings 4 of the mask 3, which will
be described with reference to FIGS. 21 and 22.
[0007] FIGS. 21 and 22 are enlarged views of the printing squeegee
101a, etc. when the printing is carried out in the right direction.
As shown in FIG. 21, when the right squeegee 101a is descended to
bring the front end part 103 in touch with the surface 3a of the
mask 3 and moved linearly in the right direction, the right
squeegee 101a reaching the solder paste 7 fed to the surface 3a of
the mask 3 moves while scraping the solder paste. The scraped
solder paste 7 flows accompanying a rotary movement called rolling
as indicated by an arrow I in FIG. 22. At this time, a fluid
pressure is generated inside the solder paste 7. When the right
squeegee 101a moves further right to reach the opening 4 of the
mask 3 in the above condition, the solder paste 7 is pressed into
the openings 4 because of the above-described fluid pressure, in
other words, the solder paste 7 is filled in the openings 4. A
pressure with which the solder paste 7 is pressed into the openings
4 will be denoted as a "filling pressure" hereinbelow.
[0008] Supposing a coordinate system as shown in FIG. 23 to the
printing squeegee 101a, when a viscosity of the solder paste 7 is
.eta., an angle of the surface 3a of the mask 3 to a face 104 of
the printing squeegee 111a facing the surface 3a (referred to as a
"squeegee angle" hereinafter) is .alpha., a speed of the moving
squeegee 101a (referred to as a "squeegee speed") is v, it is known
that a fluid pressure p produced inside the solder paste 7 is
expressed by an equation below.
p=(2.eta.v/r)*(A sin .theta.+B cos .theta.) (1
[0009] wherein r is an optional position in the polar coordinate
system of FIG. 23, .theta. is an angle of the surface 3a of the
mask 3 to the above r, A=sin.sup.2 .alpha./(.alpha..sup.2-sin.sup.2
.alpha.) and B=(.alpha.-sin .alpha.*cos
.alpha.)/(.alpha..sup.2-sin.sup.2 .alpha.).
[0010] From the above expression (1), a fluid pressure distribution
in the solder paste 7 and a pressure distribution at the face 104
of the printing squeegee 101a are as indicated in FIG. 24.
Specifically, a shaded part 105 in FIG. 24 is where the fluid
pressure p, namely, filling pressure is generated.
[0011] In the meantime, a print time for printing the solder paste
is required to be reduced in the printing process from the
viewpoint of improving productivity. However, if the squeegee speed
v is made faster in order to shorten the print time in the
conventional solder paste printing apparatus 100, the amount of the
solder paste 7 filled in the openings 4 of the mask 3 becomes
scarce as indicated in FIG. 25, resulting in printing failures with
non-filled parts 9 and hindering stable printing. The non-filled
part 9 is not generally brought about, for example, if ink is
printed in a method of screen printing, but is given rise to when a
paste-like substance of a mixture of a high viscosity flux with
powder solder, e.g., the solder paste 7 or the like is used. That
is, the non-filled part 9 is caused by the powder solder. In other
words, there is an issue that it is impossible to realize a
reduction of the print time through an increase of the squeegee
speed v in the conventional solder paste printing apparatus
100.
[0012] The non-filled part 9 resulting from an increase of the
squeegee speed v is a phenomenon as follows. When the squeegee
speed v is increased more than in the prior art, a time for the
front end part 103 of the printing squeegee 101a to pass over the
opening 4 is reduced. In consequence, a time for the solder paste 7
to be filled in the opening 4 (referred to as a "fill time") is
naturally shortened. The filling pressure becomes maximum when r=0,
i.e., at a contact point of the front end part 103 of the printing
squeegee 101a and the surface 3a of the mask 3, as is understood
from the expression (1) and FIGS. 23 and 24. Although
P.sub.r=P.sub.74=.infin. is theoretically held when r=0, the
contact point is practically a stagnation point and accordingly
shows a maximum value.
[0013] While the filling pressure itself is raised when the
squeegee speed v is increased, a high pressure range is narrow as
is seen from the pressure distribution of the shaded part of FIG.
24. In addition, since the front end part 103 passes over the
opening 4 instantaneously, the fill time cannot be secured enough.
As a result of this, the non-filled part 9 is formed.
[0014] In order to prevent an occurrence of the non-filled parts 9,
from the expression (1), it can be considered that the squeegee
angle .alpha. should be reduced and at the same time, the filling
pressure should be increased, whereby the filling is completed even
in a short fill time. However, since the conventional printing
squeegee 101a performs two operations, namely, the filling
operation to the solder paste 7 and the scraping operation from the
surface 3a of the mask 3 as described above, the front end part 103
is deformed large if the filling pressure is increased, making it
impossible to scrape the solder paste 7 from the surface 3a of the
mask 3. The solder paste 7 is left at the surface 3a of the mask 3,
as shown in FIG. 26. In the event that the front end part 103 of
the squeegee 101a is further tightly pressed in touch with the
surface 3a of the mask 3 so as to prevent the solder paste 7 from
remaining at the surface 3a of the mask 3, as shown in FIG. 27, the
solder paste 7 is actually scraped, whereas the amount of the
deformation of the front end part 103 of the squeegee is increased
due to the larger contact pressure. Therefore, when the front end
part 103 reaches the opening 4, a part of the front end part 103
enters the opening 4 subsequent to the restoration of the front end
part 103, undesirably scraping the solder paste 7 already filled in
the opening 4. Moreover, the powder solder included in the solder
paste 7 facilitates the scraping. The amount of the solder paste 7
filled in the opening 4 is hence decreased, obstructing stable
printing.
[0015] Under the circumstances, when a printing is performed,
conventionally, a worker sets, adjusts and changes printing
conditions based on experiments in order to fully achieve both the
scraping operation and the filling operation and print the solder
paste stably. In other words, the printing conditions are set,
adjusted and changed with a great personal difference and to
maintain stable printing is a hard task as an issue.
SUMMARY OF THE INVENTION
[0016] The present invention is devised to solve the
above-described inconveniences, and has for its object to provide a
solder paste printing apparatus and a solder paste printing method
whereby a solder paste can be printed stably even when a print time
is increased as compared with the prior art.
[0017] In accomplishing these and other aspects, according to a
first aspect of the present invention, there is provided a solder
paste printing apparatus wherein a squeegee device moves in a
printing direction to a surface of a mask having openings formed
therein, thereby to print and apply solder paste on the surface via
the openings to a face of a circuit board positioned at a rear face
of the mask, said squeegee device comprising: a filling squeegee
having a front end kept in a noncontact state via a gap to the
surface at the time of printing, and filling the solder paste into
the openings while moving in the printing direction; and a scraping
squeegee arranged behind the filling squeegee in the printing
direction, moving in the same direction as the filling squeegee
while keeping touch with the surface at the time of printing
thereby to remove unnecessary solder paste on the surface.
[0018] According to a second aspect of the present invention, there
is provided a solder paste printing apparatus according to the
first aspect, wherein the scraping squeegee is provided for each
direction behind the filling squeegee with respect to the printing
direction in a case where the squeegee reciprocates to the surface
of the mask.
[0019] According to a third aspect of the present invention, there
is provided a solder paste printing apparatus according to the
second aspect, wherein the filling squeegee is divided to two in
the printing direction.
[0020] According to a fourth aspect of the present invention, there
is provided a solder paste printing apparatus according to any one
of the first to third aspects, further comprising an angle setting
device for setting the scraping squeegee so that an angle of the
scraping squeegee in an axial direction thereof to the surface of
the mask is an optional acute or obtuse angle.
[0021] According to a fifth aspect of the present invention, there
is provided a solder paste printing apparatus according to the
fourth aspect, wherein the scraping squeegee is inclined with the
obtuse angle by the angle setting device.
[0022] According to a sixth aspect of the present invention, there
is provided a solder paste printing apparatus according to the
fourth aspect, wherein the scraping squeegee is inclined with the
acute angle by the angle setting device thereby to fill the solder
paste into the openings as well as remove the unnecessary solder
paste.
[0023] According to a seventh aspect of the present invention,
there is provided a solder paste printing apparatus according to
any one of the first to sixth aspects, wherein the scraping
squeegee is disposed so that an extending direction of a line of
contact between the scraping squeegee and the surface of the mask
intersects with an extending direction of a side edge part defining
one of the openings.
[0024] According to an eighth aspect of the present invention,
there is provided a solder paste printing apparatus according to
any one of the first to seventh aspects, wherein a face of the
filling squeegee opposite to the surface of the mask forms a
filling pressuring face which is inclined upward from the front end
in the printing direction so as to press the solder paste to the
surface and fill the solder paste to the openings.
[0025] According to a ninth aspect of the present invention, there
is provided a solder paste printing apparatus according to the
eighth aspect, further comprising a filling adjustment device for
adjusting filling of the solder paste to the openings by varying at
least one of a size of the gap and an intersection angle of the
filling pressuring face and the surface.
[0026] According to a tenth aspect of the present invention, there
is provided a solder paste printing apparatus according to the
ninth aspect, further comprising a filling pressure detector for
detecting a change of a filling pressure of the solder paste filled
into the openings at the time of printing, and a control device for
controlling the filling adjustment device based on the filling
pressure detected by the filling pressure detector.
[0027] According to an eleventh aspect of the present invention,
there is provided a solder paste printing apparatus according to
the tenth aspect, wherein the filling pressure detector is a
reaction force detector for detecting a reaction force which is a
sum of the filling pressures of the solder paste acting to the
whole filling pressuring face at the time of printing.
[0028] According to a twelfth aspect of the present invention,
there is provided a solder paste printing apparatus according to
the tenth aspect, wherein the filling pressure detector is a
pressure detector set at the filling pressuring face for detecting
the filling pressure of the solder paste directly.
[0029] According to a thirteenth aspect of the present invention,
there is provided a solder paste printing method comprising: moving
a filling squeegee in a printing direction at time of printing
while keeping a front end of the filling squeegee in a noncontact
state via a gap to a surface of a mask having openings formed
therein, thereby filling a solder paste on the surface to the
openings; and removing unnecessary solder paste on the surface by a
scraping squeegee moving in touch with the surface in the printing
direction.
[0030] According to a fourteenth aspect of the present invention,
there is provided a solder paste printing method according to the
thirteenth aspect, wherein the scraping squeegee is set so that an
angle of the scraping squeegee in an axial direction thereof to the
surface of the mask is an optional acute or obtuse angle.
[0031] According to a fifteenth aspect of the present invention,
there is provided a solder paste printing method according to the
fourteenth aspect, wherein, when the scraping squeegee is set with
the obtuse angle, the scraping squeegee removes the unnecessary
solder paste without adversely influencing the solder paste filled
in the openings.
[0032] According to a sixteenth aspect of the present invention,
there is provided a solder paste printing method according to the
fourteenth aspect, wherein, when the scraping squeegee is set with
the acute angle, the scraping squeegee fills the solder paste to
the openings as well as removes the unnecessary solder paste.
[0033] According to a seventeenth aspect of the present invention,
there is provided a solder paste printing method according to any
one of the thirteenth to sixteenth aspects, wherein the scraping
squeegee is set so that an extending direction of a line of contact
between the scraping squeegee and the surface of the mask
intersects with an extending direction of a side edge part defining
one of the openings.
[0034] According to an eighteenth aspect of the present invention,
there is provided a solder paste printing method according to any
one of the thirteenth to seventeenth aspects, wherein a face of the
filling squeegee opposite to the surface of the mask forms a
filling pressuring face which is inclined upward from the front end
in the printing direction so as to press the solder paste to the
surface and fill the solder paste to the openings.
[0035] According to a nineteenth aspect of the present invention,
there is provided a solder paste printing method according to the
tenth aspect, wherein a change of a filling pressure of the solder
paste when the solder paste is filled by the filling squeegee to
the openings at the time of printing is detected by a filling
pressure detector, and at least one of an intersection angle of the
filling pressuring face and the surface and a size of the gap is
adjusted based on the detected filling pressure, thereby to change
printing condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] These and other aspects and features of the present
invention will become clear from the following description taken in
conjunction with the preferred embodiments thereof with reference
to the accompanying drawings, in which:
[0037] FIG. 1 is a diagram showing the schematic structure of a
solder paste printing apparatus according to one embodiment of the
present invention;
[0038] FIG. 2 is a diagram of a front end part of a filling member
of a filling squeegee of FIG. 1;
[0039] FIG. 3 is a diagram of a model for obtaining a filling
pressure of solder paste by the filling member of the filling
squeegee of FIG. 1;
[0040] FIG. 4 is a diagram of a pressure distribution obtained from
the model of FIG. 3;
[0041] FIG. 5 is a diagram of the filling member of the filling
squeegee of FIG. 1 in a different embodiment;
[0042] FIG. 6 is a diagram of the filling squeegee of FIG. 1 in a
different embodiment;
[0043] FIG. 7 is a diagram of the filling member of the filling
squeegee of FIG. 1 in a yet different embodiment;
[0044] FIG. 8 is a flow chart of the operation of the solder paste
printing apparatus of FIG. 1;
[0045] FIG. 9 is a diagram of a modified example of the solder
paste printing apparatus in FIG. 1;
[0046] FIG. 10 is a diagram of an arrangement relation between a
line of contact of the scraping squeegee and mask, and the opening
in the solder paste printing apparatus of FIG. 9;
[0047] FIG. 11 is a diagram of a state when the solder paste is
scraped while a side face of the scraping squeegee is set at an
obtuse angle to a surface of the mask in the solder paste printing
apparatus of FIG. 9;
[0048] FIG. 12 is a diagram of a model explanatory of why the
solder paste is scraped by the scraping squeegee of FIG. 11;
[0049] FIG. 13 is a diagram of a state when the solder paste is
filled in the openings while the side face of the scraping squeegee
is set at an acute angle to the surface of the mask in the solder
paste printing apparatus of FIG. 9;
[0050] FIG. 14 is a diagram when the angle of the side face of the
scraping squeegee to the surface of the mask is changed variously
in the solder paste printing apparatus of FIG. 9;
[0051] FIG. 15 is a diagram when the angle of the side face of the
scraping squeegee to the surface of the mask is changed variously
in the solder paste printing apparatus of FIG. 9;
[0052] FIG. 16 is a diagram when the angle of the side face of the
scraping squeegee to the surface of the mask is changed variously
in the solder paste printing apparatus of FIG. 9;
[0053] FIG. 17 is a diagram of a further modification of the solder
paste printing apparatus of FIG. 1;
[0054] FIG. 18 is a perspective view of a filling member of a
filling squeegee in the solder paste printing apparatus of FIG.
17;
[0055] FIG. 19 is a sectional view of the filling member of FIG.
18;
[0056] FIG. 20 is a diagram showing the schematic structure of a
conventional solder paste printing apparatus;
[0057] FIG. 21 is a diagram showing a state when printing is
conducted with the use of a squeegee of FIG. 20;
[0058] FIG. 22 is a diagram of a state when the solder paste is
filled in the openings by the squeegee of FIG. 20;
[0059] FIG. 23 is a diagram of a model for obtaining a filling
pressure produced to the solder paste by the squeegee of FIG.
20;
[0060] FIG. 24 is a diagram of a distribution of a filling pressure
generated in the solder paste by the squeegee of FIG. 20;
[0061] FIG. 25 is a diagram of a state when non-filled parts are
brought about in the openings of the mask;
[0062] FIG. 26 is a diagram of a state where the solder paste is
left on the surface of the mask when a front end part of the
squeegee of FIG. 20 is deformed large;
[0063] FIG. 27 is a diagram of a state where the solder paste
filled in the openings is scraped when the front end part of the
squeegee of FIG. 20 is deformed large;
[0064] FIG. 28 is a diagram of a state when a reaction force
detector is set to the printing squeegee in the conventional solder
paste printing apparatus of FIG. 20; and
[0065] FIG. 29 is a diagram explanatory of how the reaction force
detector of FIG. 28 cannot detect a reaction force of the solder
paste.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0066] Before the description of the present invention proceeds, it
is to be noted that like parts are designated by like reference
numerals throughout the accompanying drawings.
[0067] An apparatus and a method for printing a solder paste
according to one embodiment of the present invention will be
described with reference to the drawings. The printing method is
carried out by the printing apparatus. Parts functioning the same
or similarly are designated by the same reference numerals
throughout the drawings, the description of which will be omitted
here. In the specification, a solder paste is a paste-like solder
obtained by mixing powder solder with a high viscosity flux. An
up-down driving device 11 and an angle variable device 12 for a
filling squeegee 10 which will be described later correspond to an
embodiment fulfilling the function of the filling adjustment
device. A reaction force detector 13 and pressure detectors 532a,
532b to be described later correspond to an embodiment achieving
the function of the filling pressure detector.
[0068] FIG. 1 is a schematic diagram in the neighborhood of a
squeegee in a solder paste printing apparatus 51 of the embodiment.
The squeegee moves both in the right and in the left directions in
the solder paste printing apparatus 51.
[0069] In addition to a scraping squeegee 14a for use in printing
in the right direction and a scraping squeegee 14b for use in
printing in the left direction, the solder paste printing apparatus
51 has a filling squeegee 10 arranged at a position between the
squeegees 14a and 14b in a printing direction for filling a solder
paste 7 to openings 4 of a mask 3.
[0070] Each of the scraping squeegees 14a, 14b scraping unnecessary
solder paste 7 on the mask 3 at the time of printing is moved up
and down between a standby position 18 and a scrape position 19 by
an up-down driving device 15, 16 mounted to a bed plate 17 of a
squeegee head constituting the printing apparatus 51. The bed plate
17 is moved in the left, right printing direction by a driving
device 49 controlled by a control device 48. In FIG. 1 showing a
state when the printing is conducted in the right direction, the
scraping squeegee 14a is lowered to the scrape position 19, while
the scraping squeegee 14b is raised at the standby position 18.
When the scraping squeegee 14a, 14b is at the scrape position 19, a
front end part 20 of each squeegee comes in touch with a surface 3a
of the mask 3 so that a suitable pressure is impressed to the
surface 3a. Although a side face 21 of the front end part 20 of
each of the scrape squeegees 14a, 14b is indicated to extend
orthogonally to the surface 3a in FIG. 1, the side face 21 of each
of the squeegees 14a, 14b is inclined at the actual time of
printing with an optional acute or obtuse angle to the surface 3a
of the mask 3, for example, as shown in FIGS. 11, 13, thereby
scraping unnecessary solder paste 7 on the surface 3a. The
unnecessary solder paste 7 on the surface 3a is a solder paste
present swelling over the surface 3a and openings 4 at the surface
3a and openings 4 of the mask 3.
[0071] The driving device 49 and up-down driving devices 15, 16 are
respectively connected to the control device 48 controlling
operations of the solder paste printing apparatus 51.
[0072] The filling squeegee 10 schematically has a filling member
22 and a holding member 23 holding the filling member 22 and is
coupled via the reaction force detector 13 to a driving shaft 11a
of an up-down driving device 11 therefor mounted to the bed plate
17. The up-down driving device 11 is connected to the control
device 48 and driven via the control device 48 based on output
information from the reaction force detector 13 thereby to move the
driving shaft 11a up and down as will be described in detail
later.
[0073] In the embodiment, one filling squeegee 10 is provided for
both, right and left printing directions. The filling member 22 is
formed schematically in the shape of the bottom of a ship as shown
in the figure. A face at a front end part of the filling member 22
opposing the surface 3a constitutes, as is illustrated in a
detailed manner in FIG. 2, a filling pressuring face 25 inclined
upward from a front end 24 of the filling member 22 to each
printing direction. The filling member 22 can be formed of rubber,
metal or the like material used in the conventional squeegees. On
the occasion of printing, the filling squeegee 10 is arranged so
that the front end 24 has a gap H2 of a size h2 to the surface 3a,
and moreover, an intersecting part 26 between a side face 22a at
the side of the printing direction of the filling member 22 and the
filling pressuring face 25 assumes a gap H1 of a size h1 to the
surface 3a.
[0074] Owing to the filling squeegee 10 with the above-described
filling member 22 and the scraping squeegees 14a, 14b provided in
the apparatus, a part 9 is never left without being filled with the
solder paste 7 in the openings 4 of the mask 3 unlike the
conventional apparatus even when a squeegee speed of the filling
squeegee 10 is increased, and stable printing is achieved. The
reason for this will be described below.
[0075] The filling pressure generated when the solder paste 7 is
filled in the openings 4 by the filling squeegee 10 will be
depicted with reference to FIG. 2. In the state shown in FIG. 2,
when the filling squeegee 10 is moved right as indicated by an
arrow, the solder paste 7 enters from the side of the gap H1 to the
filling pressuring face 25 of the filling member 22 and flows out
of the gap H2. This phenomenon can be explained by an example of a
flow of a substance entering a narrow wedge-like gap, and
concretely, a model shown in FIG. 3 is used here to depict the
phenomenon. The model is a generally known one used in the
description of fluid lubrication at a bearing or the like and is
approximate to the filling member 22 of the right half from the gap
H2 to the gap H1. In FIG. 3, supposing that a size of a gap at the
entrance side of a fluid between a wall body 301 and a reference
face. 302 is h.sub.1, a size of the gap at the exit side is
h.sub.2, a distance between the entrance and exit gaps is L, a size
of a gap between the wall body 301 and reference face 302 at a
distance x from the entrance gap is h, a speed of the moving wall
body 301 is v, and a viscosity of the fluid is .eta., a pressure p'
generated because of a flow of the fluid at the distance x is
expressed by the following equation. A distribution of the pressure
p' is as shown in FIG. 4, as is well known.
p'=(6.eta.vL/(h.sub.1.sup.2-h.sub.2.sup.2))*((h.sub.1-h)(h-h.sub.2)/h.sup.-
2) (2)
[0076] The filling pressure and a pressure distribution generated
to the solder paste 7 by the filling member 22 of the filling
squeegee 10 can be considered in the same way. In comparing a
shaded part 303 in FIG. 4 with the shaded part 105 in FIG. 24, it
is clear that the filling pressure is generated high in a wide
range with the employment of the filling squeegee 10. Accordingly,
the solder paste is perfectly filled into the openings 4 even if
the fill time is short. A filling defect or failure such as the
non-filled part, etc. is never brought about even at an increased
squeegee speed, thus accomplishing stable printing.
[0077] The above-described filling member 22 is held by the holding
member 23 in a manner to be able to swing both in the right and in
the left printing directions at a pin 27 coaxial with the driving
shaft 11a. As will be described later, the holding member 23 is
provided with the angle variable device 12 such as a motor or a
cylinder so as to make variable an intersection angle of the
filling pressuring face 25 of the filling member 22 and the surface
3a of the mask 3 and maintain the filling member 22 which can swing
centering the pin 27, properly at the intersection angle. One end
of a main body of the angle variable device 12 is supported
rotatably by the holding member 23 and a front end part of a
driving shaft 12a which can move forward and backward to the main
body is rotatably coupled to a shoulder part 22a of the filling
member 22. Therefore, the filling member 22 swings at a fulcrum of
the pin 27 when the driving shaft 12a is moved forward and
backward. The angle variable device 12 is also connected to the
control device 48, changing the intersection angle by advancing or
retreating the driving shaft 12a under the control of the control
device 48.
[0078] According to the present embodiment, the holding member 23
is connected to the driving shaft 11a of the up-down driving device
11 via the reaction force detector 13 such as a load cell so as to
detect a reaction force acting to the filling pressuring face 25 of
the filling member 22 via the solder paste 7 at the time of
printing. The reaction force cannot be detected simply by providing
the conventional solder paste printing apparatus with the reaction
force detector 13. The reason will be discussed with reference to
FIG. 28. The front end part of the conventional printing squeegee
101a moves while keeping touch with the surface 3a of the mask 3,
and consequently is deformed large due to a friction, as shown in
FIG. 29. What's worse, a contact point between the front end part
of the squeegee 101a and the surface 3a of the mask 3 is not
present on a vertical direction of the reaction force detector.
When the contact point of the squeegee 101a is pressed up by the
reaction force of the solder paste 7, an end part of the squeegee
101a at the side opposite to the contact point is pulled towards
the mask 3. The reaction force detector virtually detects this
tensile force to the mask 3 in spite of the reaction force by the
solder paste 7 acting to the squeegee 101a. The reaction force
detector hence cannot detect the reaction force of the solder paste
7. In contrast, the filling squeegee 10 of the printing apparatus
51 of the embodiment moves without touch with the surface 3a of the
mask 3, whereby the reaction force of the solder paste 7 can be
detected.
[0079] As is clear from FIG. 3 and expression (2), the reaction
force acting to the filling pressuring face 25 can be obtained by
integrating the pressure p' in a range of x=0-L. A state of the
filling pressure can be known from the reaction force of the solder
paste 7 detected by the reaction force detector 13. Moreover, the
pressure p' can be changed by adjusting the sizes h1 and h2 of the
gaps H1 and H2, as is understood from the expression (2), and the
sizes h1 and h2 can be adjusted by driving at least either of the
up-down driving device 11 and angle variable device 12 of the
squeegee 10.
[0080] For the above purpose, the reaction force detector 13 is
connected to the control device 48. The control device 48 controls
the drive of the up-down driving device 11 based on information of
the reaction force detected by the reaction force detector 13
thereby to move the filling member 22 up/down via the driving shaft
11a so as to adjust the size h2 of the gap H2 or the size h1 of the
gap H1 to prevent the non-filled part 9 from being formed in the
openings 4 of the mask 3, or the drive of the angle variable device
12 to adjust the intersection angle. For example, even if physical
properties of the solder paste 7, particularly the viscosity .eta.
is changed due to an environmental change or the like influence and
the filling pressure is changed or, the kind of the solder paste 7
is changed when the type of products is to be switched, etc., the
control device 48 operates at least one of the up-down driving
device 11 and angle variable device 12 so that the information of
the reaction force of the solder paste 7 detected by the detector
13 is approximated to a preset reaction force value or a reaction
force value before the type is switched. In this manner, at least
one of a height of the filling squeegee 10 and the intersection
angle is changed and the sizes h1 and h2 are adjusted, in other
words, printing conditions are automatically adjusted and changed,
achieving stable printing. The controlling to the up-down driving
device 11 and angle variable device 12 by the control device 48 may
be carried out in real time along with the movement of the filling
squeegee 10 or for every circuit board or at every time of
printing.
[0081] The printing conditions are thus automatically adjusted and
changed, maintaining stable printing and shortening a work
time.
[0082] Although the filling pressuring face 25 of the filling
member 22 of the filling squeegee 10 is flat in the embodiment, the
face 25 is not limited to this, but may be a curved face projecting
to the surface 3a as exemplified in FIG. 5. In other words, a shape
of the filling pressuring face 25 is not specified so long as the
size h1 of the gap between the filling pressuring face 25 and the
surface 3a of the mask 3 is larger than the size h2 with respect to
the printing direction, i.e., h1>h2 is satisfied. At the same
time, the front end 24 of the filling member 22 may be sharp as in
FIG. 2 or flat parallel to the surface 3a over a suitable length in
the printing direction as shown in FIG. 7.
[0083] The reaction force detector 13 and angle variable device 12
can be set at any positions so long as respective functions are
fulfilled, not restricted to the above-described positions.
[0084] Since the printing apparatus 51 is a type moving both in the
right and left directions, the printing apparatus is equipped with
two scraping squeegees 14a, 14b. The printing apparatus may be a
type moving in either direction only, and in that case, the
scraping squeegee 14a or 14b corresponding to the moving direction
is provided.
[0085] In the present printing apparatus 51, the filling member 22
of the filling squeegee 10 is formed to be symmetric right and left
and the same filling squeegee 10 is used for both printing
directions. However, as shown in FIG. 6, the filling squeegee may
be divided to a right filling squeegee 305a and a left filling
squeegee 305b to operate and print individually. To install two
filling squeegees 305a, 305b has the following merit. In the case
of the single filling squeegee 10, when the height or the
intersection angle of the squeegee 10 is not controlled in real
time, but is set before the printing is started, and if the height
or intersection angle of the squeegee 10 is changed during printing
in the right direction, the up-down driving device 11 or angle
variable device 12 should be operated before the start of the left
printing in order to obtain the same printing conditions in the
left printing as well. To contrary, when two filling squeegees
305a, 305b are provided, the up-down driving devices 11 and angle
variable devices 12 can be driven separately beforehand in
accordance with the printing directions.
[0086] The operation when the solder paste is printed with the use
of the above-constituted printing apparatus 51 will be described
with reference to FIG. 8. The up-down driving device(s) 11 and
angle variable device(s) 12 are controlled in real time in the
description hereinbelow.
[0087] The following operations are carried out in step 1
(indicated by "S1" in FIG. 8). A predetermined amount of the solder
paste 7 is supplied to the surface 3a of the mask 3. When the
printing is performed in the right direction, the printed board 5
is positioned and overlapped with the mask 3 and the filling
squeegee 10 and right scraping squeegee 14a are descended
respectively by the up-down driving devices 11 and 15. At this
time, the front end part 20 of the scraping squeegee 14a is brought
in touch with the surface 3a of the mask 3 with a suitable pressing
force. The filling squeegee 10 is, as shown in FIG. 2, not in touch
with the surface 3a of the mask 3, securing the gap H2 of the
predetermined size h2. The squeegee 10 is moved down so that the
gap H2 is located behind the supplied solder paste 7 in the
printing direction.
[0088] In step 2, while the state is maintained, the bed plate 17
is moved right by the driving device 49 and the filling squeegee 10
and scraping squeegee 14a are moved linearly in the right printing
direction. The filling of the solder paste 7 to the openings 4 of
the mask 3 by the filling squeegee 10 is thus started.
[0089] The reaction force acting to the filling squeegee 10 is
detected by the reaction force detector 13 in step 3. Whether or
not the detected reaction force is, for example, within the preset
reaction force value as described before is judged in step 4. When
the detected reaction force is outside a proper range, the control
device 48 drives at least one of the up-down driving device 11 and
angle variable device 12 to bring the detected reaction force
within the proper range in step 5. At least one of the height and
the intersection angle of the filling squeegee 10 is changed
accordingly.
[0090] In step 6, a layer of the solder paste 7 formed on the
surface 3a of the mask 3 because of the gap H2 of the filling
squeegee 10 is scraped by the scraping squeegee 14a. Through the
scraping by the scraping squeegee 14a, the unnecessary solder paste
7 on the surface 3a of the mask 3 is removed, so that the solder
paste 7 filled in the openings 4 to swell over the surface 3a is
turned to be even with the surface 3a.
[0091] Thereafter, the printed board 5 is separated from the mask 3
to print the solder paste 7. In the left printing similar to the
right printing, after the printed board 5 is positioned and
overlapped with the mask 3, the filling squeegee 10 and the left
scraping squeegee 14b are lowered by the up-down driving devices 11
and 16. In this case also, the front end part 20 of the scraping
squeegee 14b are brought in touch with the surface 3a of the mask 3
with a suitable pressing force, while the filling squeegee 10 is
not in direct touch with the surface 3a of the mask 3 with
maintaining the gap H2 of the predetermined size h2. The filling
squeegee 10 is lowered so that the gap H2 is positioned behind the
solder paste 7 in the printing direction leftward. The subsequent
operations are carried out in the same manner as in the right
printing.
[0092] The above-described printing operations are repeated
alternately, whereby the solder paste 7 is continuously printed and
applied on lands 6 of the printed board 5 via the mask 3.
[0093] According to the present embodiment, the side face 21 of the
scraping squeegee 14a, 14b is inclined with an optional acute or
obtuse angle to the surface 3a of the mask 3 at the time of actual
printing thereby to scrape unnecessary solder paste 7. However, the
scraping squeegee 14a, 14b may be inclined beforehand axially to
the surface 3a of the mask 3, concretely, so that the side face 21
of the squeegee 14a, 14b may be inclined beforehand with an
optional acute or obtuse angle, as will be described
hereinbelow.
[0094] More specifically, in a solder paste printing apparatus 501
shown in FIG. 9, the scraping squeegees 14a, 14b are held by
holders 507, 510 which are set to holding members 506, 509 fitted
to driving shafts 15a, 16a of the up-down driving devices 15, 16
via pins 505, 508. The pins 505, 508 are arranged coaxially with
the driving shafts 15a, 16a, supporting the holders 507, 510 so
that the holders 507, 510 can swing in the left and right printing
directions to the holding members 506, 509. In consequence, the
side face 21 of each scraping squeegee 14a, 14b can be set to the
surface 3a of the mask 3 with an optional angle in a range from an
acute angle to right angles to an obtuse angle. The pins 505, 508
are, for instance, constituted of clamping members such as bolts
and nuts. The holders 507, 510 are stopped to swing and the
squeegees 14a, 14b are fixed at the optional angle by clamping of
the pins 505, 508.
[0095] The holders 507, 510 may be adapted to swing centering the
pins 505, 508 by a known mechanism using, e.g., a motor or the like
thereby to be fixed at the optional angle.
[0096] As described hereinabove, the pins 505, 508, holding members
506, 509 and holders 507, 510 constitute angle setting devices 502,
503 for the scraping squeegees 14a, 14b.
[0097] The solder paste printing apparatus 501 of FIG. 9 is in the
same constitution except the above points as the printing apparatus
51 described with reference to FIG. 1.
[0098] In the case where the side face 21 of the scraping squeegee
14a, 14b is set, for example, at an obtuse angle to the surface 3a
of the mask 3, as indicated in FIG. 11, the unnecessary solder
paste 7 on the surface 3a can be removed without influencing to the
utmost the solder paste 7 filled in the openings 4 of the mask 3 by
the filling squeegee 10. The reason will be made clear with
reference to FIG. 12 showing a general shearing model of cutting a
structure 521 by a tool 520. When the structure 521 is cut by the
tool 520 as shown as the above model, a shear force by the tool 520
acts mainly to an upper part than a finish face 522, namely, a
shaded shear area 524 in FIG. 12. That is, the shear force acts
only to a portion which becomes a chip part 523. Therefore, in FIG.
12, if the tool 520 is replaced with the scraping squeegee 14a,
14b, the work 521 lower than the finish face 522 with the solder
paste 7 filled in the openings 4, and the chip part 523 with the
unnecessary solder paste 7 on the surface 3a, the shear force acts
solely to the unnecessary solder paste 7 on the surface 3a when the
side face 21 of the scraping squeegee is set at an obtuse angle,
and accordingly the unnecessary solder paste 7 on the surface 3a
can be removed without affecting the solder paste 7 filled in the
openings 4.
[0099] On the other hand, when the side face 21 of the scraping
squeegee 14a, 14b is set to be an acute angle to the surface 3a of
the mask 3, the following effect is obtained. For instance, even
when the solder paste 7 is filled insufficiently by the filling
squeegee 10 to the openings 4 thereby forming the non-filled parts
9, the solder paste 7 can be surely filled in the openings 4 by the
scraping squeegee 14a, 14b with the acute angle. That is, when the
scraping squeegee 14a, 14b is set with the acute angle as in FIG.
13, not only the filling squeegee 10, but the scraping squeegee
14a, 14b supplementarily produces the filling pressure. Therefore,
the scraping squeegee 14a, 14b can be effective to re-fill the
solder paste 7 to the openings 4 where the non-filled parts 9 are
present and at the same time, remove the unnecessary solder paste 7
on the surface 3a.
[0100] As shown in FIGS. 14-16, the same effect as described above
can be attained also when the side face 21 is set with an obtuse
angle or right angles to the surface 3a. That is, when, depending
on the configuration of the front end part 20 of each of the
squeegee 14a, 14b, an angle of the face 21a which is arranged
beforehand in the printing direction and is separated from the side
face 21 is acute to the surface 3a as compared with the front end
part 20 of the scraping squeegee 14b being brought in touch with
the surface 3a, even though an angle of the side face 21 is set to
be obtuse or right angle, the effect similar to that in a case
where the angle is acute can be obtained. The solder paste 7 is
filled to the openings 4 mainly by the filling squeegee 10, while
the scraping squeegee 14a, 14b assists the filling. Therefore, it
is enough that the filling pressure generated by the scraping
squeegee 14a, 14b is smaller than that of the filling squeegee 10,
thereby allowing the side face 21 of the squeegee 14a, 14b to be
set with a large angle, without inviting the issue as when the
squeegee angle a is reduced in the conventional squeegee. The
non-filled part 9 can be prevented even when the squeegee speed is
enhanced, and stable printing can be achieved.
[0101] Further, as indicated in a schematic view of an upper face
of the mask in FIG. 10, the scraping squeegee 14a, 14b is
preferably arranged so that a line of contact 515 between the front
end part 20 of the squeegee and the surface 3a of the mask 3 is not
parallel to an extending direction of a side edge part defining the
opening 4 in the mask 3. The openings 4 of the mask 3 are sometimes
formed in a pattern so that the extending direction of the side
edge part defining the opening 4 is linear and a straight part 4a
is formed having its extending direction orthogonal to a printing
direction shown by an arrow. In this state, if the scraping
squeegee 14a, 14b is moved in the printing direction while an
extending direction of the line of contact 515 is orthogonal to the
printing direction, namely, the extending direction of the line of
contact 515 is in parallel to the extending direction of the
straight part 4a, the front end part 20 of the scraping squeegee
14a, 14b is caught by the straight part 4a of the opening 4 of the
mask 3, whereby the front end part 20 or opening 4 is possibly
broken. Therefore, the scraping squeegee 14a, 14b is preferably
fitted to the driving shaft 15a, 16b of the up-down driving device
15, 16 so that an angle 516 of the extending direction of the line
of contact 515 to the extending direction of the straight part 4a
is acute or an angle 517 is obtuse to let the extending direction
of the line of contact 515 intersect with the extending direction
of the side edge part defining the opening 4. The above angle 516
is preferably approximately 1 to 45.degree., most preferably
45.degree..
[0102] The scraping squeegee 14a, 14b may be fitted to the driving
shaft 15a, 16b in a manner to make the angle 516, 517
changeable.
[0103] In the foregoing embodiment, the scraping squeegee 14a, 14b
is orientated to the mask 3 so that the openings 4 of the mask 3
are not parallel to the extending direction of the line of contact
515. Opposite to the above, the mask 3 may be shifted to the
scraping squeegee 14a, 14b so as to make the straight part 4a not
parallel to the line of contact 515 with the extending direction of
the line of contact 515 kept orthogonal to the printing
direction.
[0104] In the event that the openings 4 of the mask 3 are formed in
pattern not to have the straight parts 4a parallel to the extending
direction of the line of contact 515, it is unnecessary to orient
the scraping squeegee 14a, 14b, for example, to assume the acute
angle 516.
[0105] In the embodiment as above, the reaction force detector 13
is set to the driving shaft 11a of the up-down driving device 11
for the filling squeegee 10 to detect the reaction force of the
solder paste 7 acting to the whole face of the filling squeegee 10.
However, the filling pressure by the solder paste 7 to the opening
4 can be detected directly in a constitution as will be described
below.
[0106] In a solder paste printing apparatus 535 shown in FIG. 17, a
filling squeegee 530 corresponding to the above filling squeegee 10
generally includes, similar to the filling squeegee 10, a filling
member 531 corresponding to the filling member 22 and a holding
member 23 holding the filling member 531, and is coupled to the
driving shaft 11a of the up-down driving device 11, for the filling
squeegee 530, mounted to the bed plate 17. The up-down driving
device 11 is connected to a control device 536 and is driven via
the control device 536, as will be detailed later, based on
information of outputs of a pressure detector 532a or 532b such as
a pressure detecting sensor thereby to raise or lower the driving
shaft 11a.
[0107] As shown in FIGS. 18 and 19, the pressure detector 532a,
532b is built in the filling member 531 in the vicinity of
approximately the center in an axial direction of the filling
member 531 and at a front end part 534 of the filling member 531
inside a filling pressuring face 533. The pressure detector 532a,
532b is set at a position where the solder paste 7 is present at
the time of printing so as to detect the filling pressure generated
when the solder paste 7 is filled in the openings 4 by the filling
squeegee 530. At least one detector is provided for each filling
pressuring face 533. As described earlier, the filling pressure
shows a maximum value in the distribution in the vicinity of the
front end 534 of the filling member 531, and therefore the pressure
detector 532a, 532b is preferably set in the vicinity of the front
end 534 of the filling member 531. Moreover, in order to more
correctly detect the filling pressure, the pressure detector 532a,
532b is built in the filling member 531 so as to have its pressure
detection face exposed to the filling pressuring face 533 as
illustrated in the drawings.
[0108] The other structure of the solder paste printing apparatus
535 in FIG. 17 is equal to those of the solder paste printing
apparatuses 51, 501 shown in FIGS. 1 and 9, except the above
points.
[0109] A difference of the reaction force detector 13 of the
printing apparatus 51 and the pressure detectors 532a, 532b of the
printing apparatus 535 in the above embodiments will now be
described. Although both detectors are installed to detect a state
change of the filling pressure of the solder paste 7 at the time of
printing, the pressure detector 532a, 532b directly detects the
filling pressure, whereas the reaction force detector 13 detects
the reaction force which is a sum of the filling pressures acting
to the whole face of the filling pressuring face 25, in other
words, detects the filling pressure indirectly.
[0110] Even when the filling pressure is the same, the reaction
force detector 13 detects the reaction force different in
accordance with an area of the filling pressuring face 25. For
example, if a size of the filling member 22 is changed to fit the
printed board 5, it takes a lot of labor to refer to the previously
accumulated information of reaction forces, thus causing to
reproduce printing conditions. Needless to say, it is easy to refer
to the previously accumulated information unless the area of the
filling pressuring face 25 is changed when the same filling member
22 is used. On the other hand, since the filling pressure is
detected directly with the use of the pressure detector 532a, 532b,
the previously detected information of pressures can be readily
referred to even if the filling member 531 is changed in size,
whereby printing conditions can be reproduced easily, which is
preferable.
[0111] The thus-constituted printing apparatus 535 operates in the
same manner to print the solder paste as the printing apparatus 51
of the above embodiment. Fundamentally, the "reaction force" in
steps 3, 4 in FIG. 8 is replaced with the "pressure". More
specifically, the filling pressure generated when the solder paste
7 is filled in the openings 4 by the filling squeegee 530 is
detected by the pressure detector 532a in step 3, and whether or
not the detected pressure is, for instance, within a preliminarily
set value range is judged in step 4. If the detected pressure is
outside the proper range, in step 5, the control device 536 drives
at least one of the up-down driving device 11 and angle variable
device 12 so as to set the detected pressure in the proper range.
In consequence, at least one of the height and intersection angle
of the filling squeegee 530 is changed.
[0112] The other operations than the above are the same as in the
printing apparatus 51. The solder paste 7 is continuously printed
and applied onto lands 6 of the printed board 5 via the mask 3
through the alternate repetition of the above operations.
[0113] In the foregoing description, only one of the reaction force
detector 13 and the pressure detectors 532a, 532b is arranged in
the apparatus. However, both of the detectors may be set in the
printing apparatus to detect both the reaction force and the
filling pressure.
[0114] According to the solder paste printing apparatus according
to the first aspect of the present invention and the solder paste
printing method according to the second aspect of the present
invention, as is fully described above, the filling squeegee and
scraping squeegees are provided. The filling squeegee is moved in a
state without contact with the surface of the mask thereby to fill
the solder paste in openings of the mask, then the unnecessary
solder paste on the mask is removed by the scraping squeegee.
Accordingly, the solder paste is prevented from being filled in the
openings defectively or scraped improperly even when the squeegee
speed is increased, so that the solder paste can be printed stably
on the circuit board. The print time can be reduced, thereby
improving productivity.
[0115] The entire disclosure of Japanese Patent Applications No.
8-329758 filed on Dec. 10, 1996 and No. 9-134778 filed on May 26,
1997, including specification, claims, drawings, and summary are
incorporated herein by reference in its entirety.
[0116] Although the present invention has been fully described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications are apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims unless they depart therefrom.
* * * * *