Printing – Stenciling – Processes
Reexamination Certificate
2000-11-09
2002-04-16
Funk, Stephen R. (Department: 2854)
Printing
Stenciling
Processes
C101S484000
Reexamination Certificate
active
06371017
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a printing method for transferring a printing paste retained on a stencil (plate) onto an object on which a print is to be formed and printing apparatus for implementing the printing method.
BACKGROUND ART
Conventionally, according to a planographic stencil (screen) type printing for printing, for example, solder paste on lands of a printed circuit board, as shown in FIG.
18
A and
FIG. 18B
, a screen mask (metal mask)
1
having through holes
1
a
arranged in a specified pattern in correspondence with lands
5
of the printed circuit board
4
is placed in a specified position on the board
4
while being brought in contact with the board. Next, as shown in
FIG. 18C
, FIG.
19
A and
FIG. 19B
, solder paste
2
is supplied to one end of the screen mask
1
, and this solder paste
2
is moved by a squeegee
3
from the one end of the screen mask
1
in a specified direction, thereby filling the solder paste
2
into each through hole
1
a
of the screen mask
1
. Next, as shown in
FIG. 18D
, the screen mask
1
is separated from the board
4
so as to move the solder paste
2
inside the through holes
1
a
of the screen mask
1
onto the lands
5
of the board
4
, thereby forming solder paste layers
2
a
on the lands
5
of the board
4
as shown in FIG.
18
E.
However, according to the above structure, as shown in
FIG. 19C
, part of the solder paste
2
is left inside the through hole
1
a
of the screen mask
1
while adhering to the inner wall of the through hole due to the viscosity of the solder paste itself when the screen mask
1
is separated from the board
4
, and this disadvantageously causes a phenomenon that the solder paste continuously extends across the left solder paste
2
and the solder paste
2
placed on the land
5
of the board
4
. Consequently, as the screen mask
1
moves away from the board
4
, the relative deformation (shear rate gradient) of the continuously extending solder paste increases to be pulled and broken at an arbitrary portion between the screen mask
1
and the board
4
. Part of the solder paste that has been pulled and broken adheres to a portion other than the land
5
on the board
4
as shown in FIG.
19
D and adheres to the peripheral portion of the through hole
1
a
on the rear surface of the screen mask
1
on the board side. This has disadvantageously caused a printing blur in the next printing stage, the occurrence of a bridge defined by the inadvertent adhesion of the solder paste to the adjacent solder paste layer
2
a
on the board
4
, and the insufficient formation of a solder paste layer on the board due to the adhesion of the solder paste to the screen mask.
Accordingly, the object of the present invention is to solve the aforementioned issues and provide a printing method and printing apparatus capable of accurately pulling and breaking the printing paste between the stencil on which the printing paste is retained and the board while causing no bridging, causing no printing blur attributed to the printing paste left on the stencil side and causing no shortage of supply of the printing paste onto the board.
DISCLOSURE OF INVENTION
In order to achieve the above object, the present invention is constructed so that the temperature of the portion which belongs to the stencil and on which the printing paste of the stencil is retained is increased so as to reduce the viscosity of the printing paste that adheres to the printing paste retaining portion and allow the printing paste to be easily separated from the retaining portion, thereby making the printing paste easy to be printed on the object on which a print is to be formed.
According to a first aspect of the present invention, there is provided a printing method comprising:
retaining on a stencil a printing paste having a characteristic that a viscosity reduces as temperature increases;
increasing a temperature of a portion which belongs to the stencil and on which the printing paste is retained so as to reduce the viscosity of the printing paste to be brought in contact with the portion, thereby making the printing paste easy to separate from the stencil; and
separating the printing paste retained on the stencil from the stencil so as to print the printing paste on an object on which a print is to be formed.
According to a second aspect of the present invention, there is provided a printing method based on the first aspect, wherein the portion which belongs to the stencil and on which the printing paste is retained is heated by electromagnetic induction heating to increase the temperature of the portion.
According to a third aspect of the present invention, there is provided a printing method based on the second aspect, wherein the stencil has an opening portion to be arranged in a specified pattern for retaining the printing paste, and the stencil and the object are relatively separated apart after the stencil comes in contact with the object, thereby printing the printing paste inside the opening portion onto the object.
According to a fourth aspect of the present invention, there is provided a printing method based on the third aspect, wherein an electromagnetic induction heating unit for performing the electromagnetic induction heating performs the electromagnetic induction heating of the stencil in a noncontact manner.
According to a fifth aspect of the present invention, there is provided a printing method based on the fourth aspect, wherein an interval between the electromagnetic induction heating unit and the stencil is constructed so as to have a dimension such that a specified induction current flows through the stencil by the electromagnetic induction heating unit.
According to a sixth aspect of the present invention, there is provided a printing method based on the third aspect, wherein an electromagnetic induction heating unit for performing the electromagnetic induction heating performs the electromagnetic induction heating of the stencil in a contact manner.
According to a seventh aspect of the present invention, there is provided a printing method based on any one of the third through sixth aspects, wherein the electromagnetic induction heating is performed after retention of the printing paste on the opening portion of the stencil is finished.
According to an eighth aspect of the present invention, there is provided a printing method based on any one of the third through seventh aspects, wherein the opening portion is a through hole, the stencil is a screen mask, and the printing paste is filled into the through hole by moving a squeegee.
According to a ninth aspect of the present invention, there is provided a printing method based on any one of the third through eighth aspects, wherein a print state is detected after the printing paste is printed on the object, and an electromagnetic induction heating condition of the stencil or a condition of separation of the stencil from the object is controlled on the basis of a result of detection.
According to a tenth aspect of the present invention, there is provided a printing method based on any one of the third through ninth aspects, wherein the print material has a temperature gradient such that the portion put in contact with the portion retained by the stencil has a high temperature and the temperature gradually reduces departing from the portion in the electromagnetic induction heating.
According to an eleventh aspect of the present invention, there is provided a printing method based on any one of the third through tenth aspects, wherein an induction current for generating the electromagnetic induction heat flows in the lengthwise direction of the opening portion of the stencil.
According to a twelfth aspect of the present invention, there is provided a printing apparatus comprising:
a heating unit for increasing a temperature of a portion which belongs to a stencil for retaining a printing paste having a characteristic that a viscosity reduces as temperature increases and on which the printing paste is retained so as to reduce the viscosity of
Ishimoto Kazumi
Kuwabara Kimihito
Mimura Toshinori
Yamauchi Toshiaki
Yamazaki Osamu
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