Printing – Stenciling – Processes
Reexamination Certificate
1996-12-20
2001-09-11
Eickholt, Eugene (Department: 2854)
Printing
Stenciling
Processes
C101S128100, C101S127000
Reexamination Certificate
active
06286424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a mask unit for paste printing for forming patterns by use of an ink, an adhesive, solder paste, or a paste-like resin on a printing material, and more particularly to a plastic mask unit which has a long life and is capable of performing paste printing of a superior quality.
This invention also relates to a method of fabricating the above-mentioned plastic mask unit.
2. Discussion of the Background
In the field of paste printing, several different types of conventional masks have been put in practice for forming printed patterns on a printing material by use of various pastes, such as, solder paste, an ink, an adhesive agent, and a paste resin (hereinafter referred to as the paste). An example of conventional printing masks for the paste printing is a mask known as a punch press mask which can be prepared by forming round through-holes in a metal sheet with a punch. Another example is a YAG laser mask which can be prepared by forming through-holes in a metal sheet with a YAG laser. Another example is an etching mask which can be prepared by forming through-holes in a metal sheet using a metal etching process. Still another example is an additive mask which can be prepared by forming through-holes in a metal plate formed by being plated around a pattern of through-holes.
In addition to the above-mentioned metal masks, a mask made of a plastic sheet has been recently introduced which is disclosed in the official gazette for Japanese Laid Open Patent Application TOKUKAI HEI 7-81027. This plastic mask can be prepared by forming slit-shaped through-holes in a plastic sheet by excimer laser abrasion. As a result, the plastic mask becomes free from various known shortcomings, such as, for example, burr in the edges of the through-holes, deposition of dross in the through-holes, and so forth, that occur in the conventional metal masks. Also, such a plastic mask meets increasing demands for highly precise paste printing of a micro pattern with high quality, which arise from the recent trend whereby electronic appliances and parts are made smaller and smaller in size.
In these conventional masks, a metal sheet or a plastic sheet is secured to a mask frame with a mesh screen inserted in between. A fabrication procedure for these conventional masks is now explained with reference to FIGS.
10
(
a
)-
10
(
h
).
In FIG.
10
(
a
), reference numeral
301
denotes a mask frame to which a rectangular cross section aluminum pipe is commonly adopted. Such an aluminum mask frame is coated with a coating agent suitable for gluing aluminum so that a first thin film
302
suitable for gluing aluminum is formed in a square frame on the edge of the mask frame
301
as shown in FIG.
10
(
a
). A rubber adhesive diluted with a diluent is commonly applied to this coating material. A rough finish may be provided to the edge of the mask frame
301
before the first thin film
302
is formed thereon.
In a similar manner, a mesh screen
303
is coated with a coating material suitable for gluing polyester, for example, so that a second thin film suitable for gluing polyester is formed in a square frame on the mesh screen
303
. For the mesh screen
303
, either a polyester mesh screen of about 180 to 225 mesh or a nylon mesh screen of about 180 to 225 mesh can be applied.
Next, a step of gluing the polyester mesh screen
303
to the mask frame
301
is illustrated in FIG.
10
(
b
). An example of an adhesive is an epoxy type adhesive which is suitable for gluing both the first thin film formed on the mask frame
301
and the second thin film formed on the polyester mesh screen
303
. Such an epoxy adhesive is coated on either one or both of the first thin film formed on the mask frame
301
and the second thin film formed on the polyester mesh screen
303
. After that, the polyester mesh screen
303
is affixed to the mask frame
301
with the application of a predetermined tension thereto in the directions as indicated by arrows in FIG.
10
(
b
).
As a result, the mesh screen
303
is secured to the mask frame
301
as shown in FIG.
10
(
c
). Since, in addition to extension caused by the predetermined tension, the mesh screen
303
is prepared in a predetermined size larger than the mask frame
301
, there are overhanging edges
303
a
of the mesh screen relative to the periphery of the mask frame
301
as shown in FIG.
10
(
c
). Accordingly, these overhanging edges
303
a
of the mesh screen
303
are cut off so that the mesh screen
303
becomes equal in size to the mask frame
301
in the horizontal plain in the drawing.
Next, a step of drawing register marks for accurately registering the mesh screen relative to the mask plate is shown in FIG.
10
(
d
). A register mark
303
b
is drawn at the centers of all four sides of the mesh screen
303
secured to the mask frame
301
. The register marks
303
b
are drawn softly and visibly using a sharp-pointed pencil on the mesh screen
303
so that the mask plate
304
can be accurately registered relative to the mesh screen
303
in the following step.
The mask plate
304
is then coated with a coating agent as shown in FIG.
10
(
e
). This mask plate
304
includes a number of slit-shaped through-holes for serving as a print pattern for paste printing. The edge of the mask plate
104
is coated with a coating agent suitable for gluing the mask plate
304
. As a result, a thin film
304
b
suitable for gluing the mask plate
304
is formed. Then, the mask plate
304
is secured to the mesh screen
303
. In this event, a rubber type adhesive diluted with a diluent is usually applied to the coating agent. In addition, the edge frame of the mesh screen
303
may be coated with another coating agent suitable for gluing polyester, for example, so that a polyester thin film suitable for gluing polyester can be formed on the edge frame of the mesh screen
303
. Moreover, a rough finish or a number of fine holes may be provided at the edge of the mask plate
304
before the thin film
304
b
is formed. thereon.
Next, the step of securing the mask plate
304
to the mesh screen
303
on the mask frame
301
is shown in FIG.
10
(
f
). In this step, the position of the mask plate
304
on the mesh screen
303
is manually adjusted so that center holes
304
c
on each side of the mask plate
304
and the register marks
303
b
of the mesh screen
303
can be finely registered. Then, the mask plate
304
is temporarily taped to the mask frame
301
and the mesh screen
303
to form an integrated unit. After that, this one unit of the mask frame
301
, the mesh screen
303
, and the mask plate
304
is turned upside down and masking tape is placed over a relatively large area of the mesh screen
303
, leaving an area in the form of a square frame to be coated with adhesive, while the taped area is not coated with the adhesive. This masking tape must be in place before an epoxy type adhesive, for example, is coated onto the square frame of the mesh screen
303
. The masking tape is removed after the adhesive is cured on the mesh screen
303
.
The step of making an opening
303
c
is explained in FIG.
10
(
g
). The opening
303
c
is formed by cutting out the mesh screen
303
. The area cut must not be secured by the mask plate
304
so that a portion
305
in which the adhesive is cured on the mesh screen
303
can be left. After that, each glued portion is provided with guard tapes to prevent peeling-off so that the mask frame
301
and the mesh screen
303
, the mask plate
304
and the mesh screen
303
are mutually secured.
In this way, the conventional mask unit for paste printing is fabricated. Consequently, the thus fabricated printing mask unit has a three-layer structure wherein the mask frame
301
and the mask plate
304
are secured with the mesh screen
303
inserted in between, as shown in FIGS.
10
(
g
) and
10
(
h
).
However, there has been a problem in which registration of through-holes relative to the printing material becomes inaccurate in the case where a plastic sheet
Eickholt Eugene
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh Microelectronics Co.,
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