JP2005138318A - Screen process printing method and screening mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly fill the pits of a screening mask with a paste-like material which is equivalent to an ink, in a screen process printing method which prints a material to be printed using the screening mask as well as the screening mask. <P>SOLUTION: In this screen process printing method, the screening mask is structured of a first surface which is apart from the material to be printed retained on a printing table and yet to come into contact with the material and has a plurality of nearly circular perforated openings; a plurality of grooves which communicate with the openings in the first surface material and engraved in one direction; and a second surface which has a plurality of grooves, engraved in one direction communicating with the openings in the first surface and receiving a pressure from a squeegee. The screen mask is set opposite to the material to be printed, then the squeegee is pressed to the second surface of the screening mask through a paste and the first surface of the screening mask is brought into contact linearly with the material, Further, the squeegee is moved in a direction where it crosses the direction where the material comes into contact with the screening mask so that this contact position moves, and thus the paste is transferred to the material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a screen printing method for printing on an object to be printed with a screen mask (screen plate), and the screen mask, and more particularly to a screen suitable for filling paste-like objects corresponding to ink in pits of the screen mask without variations. The present invention relates to a printing method and a screen mask.

  In order to form a fine structure on an object surface, a technique using screen printing is used in various situations. One of them is to form conductive bumps as fine structures on a wiring board or metal foil. Since the conductive bumps printed and formed by such a method have a sharp point, the conductive bumps can easily pass through the semi-cured insulating plate (prepreg) and can be used as an interlayer connection between the insulating plates by the penetration.

  The formation of the conductive bumps requires a certain height to penetrate the insulating plate. Further, the formation height is required to be uniform. This is because if the uniformity is poor, the probability of occurrence of conductive bumps that are incompletely penetrated into the insulating plate increases, and the production yield as a wiring board deteriorates.

In the conventional screen printing technique, there is a screen printing different from the formation of conductive bumps, for example, one described in Japanese Utility Model Laid-Open No. 4-137874. In the technique of this document, another mask portion serving as a spacer in the thickness direction is provided so as to be laminated on the original mask portion and to overlap an opening having a diameter larger than that of the opening in the mask. A sufficient amount of paste is transferred (transferred) by the pits (through holes) where the openings overlap. However, there is no mention of reducing variations in paste transfer amount.
Japanese Utility Model Publication No. 4-137874

  In the formation of the conductive bumps, the amount of paste-like objects at the time of printing filled in the pits of the screen mask by the squeegee varies as a cause of variation in the formation height. The variation in filling amount can be caused by the following reasons. Since the conductive bump formation is required to have a cone shape when the paste-like object after printing is transferred onto the surface of the printing material, its viscosity is generally high (for example, 1000 Pa · s to 3000 Pa at room temperature).・ S). When the viscosity is high, the reaction force from the paste-like object to the squeegee when the squeegee is pressed against the screen mask is considerably large due to the amount of microscopic paste-like objects in the vicinity of each part that contacts the screen mask. Different.

  Therefore, the microscopic deformation amount of the screen mask varies depending on the amount of the microscopic pasty object in the vicinity. As a result, the amount of deformation (the amount to be pushed) of the edge of the screen mask into the pit varies, and the amount of paste-like objects that are cut off by the edge and filled into the pit varies.

  The present invention has been made in consideration of the above circumstances, and a screen printing method for printing on a printing material using a screen mask and the screen mask, in which paste-like objects corresponding to ink are filled in the pits of the screen mask without variations. It is an object of the present invention to provide a screen printing method and a screen mask that can be used.

  In order to solve the above-described problems, a screen printing method according to the present invention includes a step of holding a printing material on a printing table and a plurality of substantially circular openings that are spaced apart from the held printing material. A screen having a first surface to be in contact with the substrate and a second surface to be pressed from a squeegee, wherein a plurality of grooves communicating with the opening of the first surface are carved in one direction. A step of facing a mask to the substrate, and a squeegee is pressed against the second surface of the screen mask via a paste so that the first surface of the screen mask is in linear contact with the substrate. And a step of transferring the paste to the printing material by moving the squeegee in a direction intersecting the abutting direction so that a contact position between the printing material and the screen mask is moved. And wherein the door.

  That is, in this screen printing method, a screen mask to be used is different from a normal one, and a plurality of substantially circular openings are perforated, and the first surface to be in contact with the substrate to be printed is communicated with the openings on the first surface. A groove having a plurality of grooves formed in one direction and having a second surface to be pressed from the squeegee is used. In such a screen mask, even if microscopic deformation (indentation amount) of each part of the squeegee contacting the screen mask differs, the deformation remains at the groove portion and does not reach the circular opening portion. Therefore, the filling amount of the paste-like object in the circular opening is made uniform.

  Accordingly, the screen mask according to the present invention has a plurality of substantially circular openings perforated in a single direction, and a first surface to be in contact with the substrate and a plurality of grooves communicating with the openings on the first surface. And a second surface to be pressed from the squeegee. The operation and effect of this screen mask are as described above.

  According to the present invention, in the screen printing method and the screen mask, it becomes possible to fill the pits of the screen mask with the paste-like object corresponding to the ink without variation.

  As an embodiment of the present invention, the ratio of the dimension in the plate thickness direction between the opening on the first surface and the groove on the second surface of the screen mask can be 7 to 3 to 3 to 7. This level is easy to manufacture when the depth of the groove is actually designed.

  As an embodiment, the thickness of the screen mask may be 0.5 to 2 times the diameter of the opening on the first surface. This is because if the thickness of the screen mask is too thin or too thick with respect to the diameter of the opening, it does not contribute much to the increase in the transfer amount of the paste-like object. If it is too thin, the filling amount will be insufficient, and if it is too thick, the amount remaining by being pulled by the inner wall of the opening will increase.

  As an embodiment, the width of the groove of the second surface of the screen mask may be 2 to 20 times the diameter of the opening of the first surface. This is a practical design value.

  As an embodiment, the length of the groove on the second surface of the screen mask can be 10 times or more the diameter of the opening on the first surface. It is the same.

  As an embodiment, a plurality of openings on the first surface communicating with the grooves on the second surface of the screen mask may exist per groove. This is the case when the distance between the openings is small. Even if it does in this way, there is no difference in the effect | action for producing an effect.

  Here, a plurality of openings on the first surface per groove in the screen mask may have a vertical and horizontal spread with respect to the direction in which the groove is carved. As an embodiment, in the case of being in a straight line corresponding to the direction of the groove engraving, in the case of being in a straight line corresponding to the direction perpendicular to the direction of the groove engraving, and in the direction of the groove engraving and its vertical Any of the cases where there is a vertical and horizontal spread irrespective of the direction can be considered.

  Based on the above, embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view schematically showing a configuration of an apparatus suitable for carrying out a screen printing method according to an embodiment of the present invention. FIG. 2 is a schematic top view showing only the squeegee and the screen mask. Corresponding parts in FIGS. 1 and 2 are denoted by the same reference numerals.

  To explain the configuration, as shown in FIG. 1, for example, a wiring board substrate 10 as a printing material can be held on a printing table 2 by, for example, vacuum suction. The screen mask 5 is stretched by the screen mask setting portions 3 and 4 so as to face and separate from the held wiring board substrate 10. The distance between the wiring board substrate 10 and the screen mask 5 is, for example, about 1 mm to 3 mm.

  As the material of the screen mask 5, aluminum, nickel, stainless steel, copper, brass, or the like can be used. A thickness (total thickness) of about 50 μm to 500 μm can be used. As the substrate, a rigid or flexible resin substrate, a metal foil (copper foil), a glass plate, a ceramic plate, or the like can be applied.

  In the screen mask 5, pits 6a, 6b,... For moving, transferring and adhering the conductive paste 6 to the printed material are formed on the surface facing the printed material. The pits 6a and the like have a substantially circular cross-sectional shape, and the diameter can be, for example, about 50 μm to 500 μm. The pits 6a, 6b,... Communicate with grooves 7a, 7b,... Carved on the surface of the screen mask 5 facing the squeegee 1 (described later). That is, referring to FIG. 2, each pit 6a communicates with one of the grooves 7a engraved in a certain direction of the screen mask 5, and a plurality of pits exist in one groove. Sometimes. When there are a plurality of pits in the groove, the arrangement of the pits in the groove may have a vertical and horizontal spread with respect to the certain direction of the groove.

  A squeegee 1 is provided above the screen mask 5, and the squeegee 1 pushes down the screen mask 5 linearly (in a line perpendicular to the paper surface), and the screen mask 5 is applied to the wiring board substrate 10 in the same linear form. It can be made to contact. The squeegee 1 can be made of a resin such as a urethane resin, a metal, or a metal coated with a resin. Further, since the squeegee 1 is used for printing and wears over time, the squeegee 1 may be configured to be replaceable as an apparatus.

  The squeegee 1 is inclined with respect to the main surface of the wiring board base material 10, and the screen mask 5 is pressed down from the right side to the left side of the sheet (that is, in the direction in which the lower part of the squeegee 1 follows the inclined squeegee 1). It moves while being guided by a squeegee movement guide rail 11 as a squeegee moving mechanism. This moving direction coincides with the installation direction of the grooves 7a, 7b,... Provided in the screen mask 5. In this movement, the conductive paste 8 is positioned in front of the squeegee 1 and on the screen mask 5. As the conductive paste 8, for example, a paste in which metal particles (silver, gold, copper, solder, etc.) are dispersed in a paste-like resin and a volatile solvent is mixed is used. The viscosity is, for example, 1000 Pa · s to 3000 Pa · s at normal temperature (20 ° C.).

  Next, to describe the operation, due to the movement of the squeegee 1 as described above, a part of the conductive paste 8 is filled in the pits 6b via the grooves 7b near the squeegee 1. Here, the filling amount of the conductive paste 8 into the pits 6b becomes more uniform due to the presence of the grooves 7b. This is because when there is no groove 7b, the microscopic deformation of the squeegee 1 near the pit 6b caused by the squeegee 1 being pushed downward becomes a deformation that is pushed into the pit 6b. If the amount of such deformation varies, the amount of the conductive paste 8 to be filled also varies. On the other hand, when there is the groove 7b, even if the microscopic deformation of the squeegee 1 pushed into the groove 7b varies, the filling amount of the conductive paste 8 into the pit 6b is affected. Disappear. This point will be further described later (FIG. 3).

  When the squeegee 1 moves and the screen mask 5 starts to be separated from the wiring board substrate 10, a part of the conductive paste 8 filled in the pits 6 b adheres to the wiring board substrate 10 and is pulled, The part is pulled so as to remain in the pit 6b. When the squeegee 1 further moves leftward in FIG. 1, the distance between the screen mask 5 and the wiring board substrate 10 is further separated behind the squeegee 1, and a part remains in the pits 6b (6c, 6d, 6e). A portion pulled by the wiring board substrate 10 is divided and attached to the wiring board substrate 10 in a sharp shape (becomes conductive bumps 9).

  After the conductive bumps 9 are formed, the wiring board substrate 10 is taken out from the screen printing apparatus, and the wiring board substrate 10 having the conductive bumps 9 is dried at, for example, hundreds of degrees C. It can be cured. The wiring board substrate 10 having the cured conductive bump 9 is laminated and pressed with a semi-cured insulating plate (prepreg), and the conductive bump 9 penetrates the prepreg to form an interlayer connection. Such an interlayer connection body has improved connection reliability because variation in height is suppressed. Moreover, since the choice of a material can also be expanded as a prepreg to be used, cost and productivity can be improved.

  In order to form the conductive bumps 10 higher in order to improve penetrability, the conductive bumps 9 are dried and cured, and the conductive paste 8 is printed a plurality of times using the same pattern screen mask. obtain. Even in such a case, for example, a wiring board can be manufactured with high productivity by reducing the variation in the formation height compared to the conventional case.

  FIG. 3 is an enlarged view of the vicinity of the squeegee and the pit for explaining the mechanism of equalizing the amount of the conductive paste filled in the pit by the screen printing method described above in comparison with the conventional case. It is typical sectional drawing. In FIG. 3, the same components as those already described are denoted by the same reference numerals.

  FIG. 3A shows the case of the above embodiment of the present invention. As the squeegee 1 progresses, the squeegee 1 fills the grooves 7b and pits 6b with the immediately preceding conductive paste 8, and at the same time immediately after the squeegee 1, the conductive paste 8 is worn to form an upper surface. By such an action, the conductive paste 8 has a shape like a hatched portion with a rough pitch in FIG. The squeegee 1 is microscopically deformed by application of a downward force and is slightly pushed into the groove 7 b of the screen mask 5. Here, the deformation of the squeegee 1 remains in a range smaller than the depth of the groove 7b. Therefore, there is no variation in the amount of the conductive paste 8 (portion indicated by the dot pattern in the figure) filled in the pits 6b.

  On the other hand, FIG. 3B shows a case where the screen mask 5A has no grooves 7b and only pits 6Ab. In this case, when the squeegee 1 is pressed downward and deformed microscopically, the squeegee 1 is pushed into the pit 6Ab as shown in the figure. In this state, immediately after the squeegee 1, the conductive paste 8 is worn to form the upper surface. Therefore, in this case, the conductive paste 8 has a shape like a hatched portion with a rough pitch in FIG. The squeegee 1 receives a reaction force F1 from the conductive paste 8 existing immediately before.

  The state of FIG. 3C is almost the same as that of FIG. 3B, but is a case where the amount of the conductive paste 8 existing immediately before the squeegee 1 is different (less). In this case, the reaction force F2 from the conductive paste 8 existing immediately before the squeegee 1 is smaller than the above F1. Therefore, the amount of deformation by which the squeegee 1 is pushed into the pit 6Ab is larger than that shown in FIG.

  The portions indicated by the dot patterns in FIGS. 3B and 3C indicate the conductive paste 8 filled in the pits 6Ab, respectively. That is, the degree of deformation of the squeegee 1 varies depending on the amount of the conductive paste 8 existing immediately before the squeegee 1, and this indicates that the amount of the conductive paste 8 filled in the pits 6Ab varies. Such variations in the filling amount cause variations in the height of the conductive bumps to be formed.

  Actually, the amount of the conductive paste 8 present immediately before the squeegee 1 varies depending on the position of the squeegee 1 in the longitudinal direction or decreases by printing a plurality of times. In addition, depending on the position of printing and the time of printing, it always varies with time. In this embodiment, the amount of the conductive paste 8 filled in the pits 6a,. Therefore, variation in the height of the conductive bump 9 to be formed can be reduced.

  In the experiment, the variation in the formation height of the conductive bumps 9 could be reduced as follows. As a condition, a silver paste containing phenol melamine resin is used as the conductive paste 8, the screen mask 5 has a thickness of 0.2 mm, a pit diameter of 0.15 mm, a groove depth of 0.1 mm, and the groove width is the pit diameter. 5 to 10 times, and the groove length is about 30 times the pit diameter. For the screen printing of the comparative example, the same silver paste was used, and the screen mask 5A having a thickness of 0.15 mm and a pit diameter of 0.15 mm was used. In both cases, printing was performed three times. Note that the thicknesses of the screen masks 5 and 5A are different because the average heights of the conductive bumps to be formed are substantially uniform.

  In the case of the screen mask 5, the average height was 138 μm, and the height variation 3σ (3σ is three times the standard deviation as is well known) was 21 μm. In the screen mask 5A, the average formation height was 132 μm, and the height variation 3σ was 27 μm. Therefore, the ratio of variation to the average is about 15% for the screen mask 5 and about 20% for the screen mask 5A. That is, the variation in formation height could be reduced to about 3/4.

  FIG. 4 is a front view and a side view for explaining the dimensions of the pits and grooves in the screen mask 5. The difference between FIG. 4 (a) and FIG. 4 (b) is that pits and grooves are formed on the same plate member (FIG. 4 (a)) and on a different plate member (FIG. 4 ( b)). In both cases, the ratio between the pit penetration depth D2 and the groove depth D1 is preferably about 7 to 3 to 3 to 7 in consideration of ease of manufacture and effects. The thickness T is related to the pit diameter D, and is preferably 0.5 to 2 times D. If it is too thin, the amount of paste filling will be insufficient, and if it is too thick, the amount of paste remaining will be increased by being pulled by the inner wall of the opening, and both will not contribute to an increase in the amount of paste transferred.

  Further, it is a rough guide that the length L1 of the groove is 10 times or more the diameter D of the pit. If it is too short, depending on the viscosity of the paste at the end of the groove length L1, there will be an effect on the filling of the paste into the pits when a gap is generated. As a guideline, the width L2 of the groove is set to be 2 to 20 times the diameter D of the pit. If it is too narrow, the flexibility of the arrangement of the pits in the groove is reduced, and if it is too wide, the squeegee 1 may be deformed on the bottom surface of the groove depth D1.

  4A, for example, a photoresist mask is pasted or applied to a plate that has been formed with pits or is used as a previous screen mask, and is patterned so that the groove pattern portion is removed. And the method of etching the said board can be used. Alternatively, a method using an NC (numerical control) processing machine is also conceivable. Further, in the case of the laminated structure shown in FIG. 4B, there are a method of pasting through both of the laminated layers in advance and a method of pasting and a method of forming grooves or pits on both sides after the pasting. . In the latter method, chemical etching can be applied depending on the material.

The side view which shows typically the structure of the apparatus suitable for enforcing the screen printing method which concerns on one Embodiment of this invention. FIG. 2 is a schematic top view showing only the squeegee and screen mask portions of the apparatus shown in FIG. 1. The squeegee and the vicinity of the pits are enlarged for explaining the mechanism of equalizing the amount of the conductive paste filled in the pits by the screen printing method according to the embodiment of the present invention as compared with the conventional case. FIG. The front view and side view for demonstrating each dimension of the dimension of the pit in the screen mask 5 in one Embodiment of this invention, and a groove | channel.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Squeegee, 2 ... Printing stand, 3, 4 ... Screen mask installation part, 5 ... Screen mask, 6a, 6b, 6c, 6d, 6e ... Pit, 7a, 7b, 7c, 7d ... Groove, 8 ... Conductive paste , 9 ... conductive bumps, 10 ... wiring board substrate, 11 ... squeegee movement guide rail.

Claims (14)

Holding the substrate on the printing table;
A plurality of substantially circular openings that are spaced apart from the held substrate to be printed, and a groove that communicates with the openings on the first surface in one direction. A step of facing a screen mask having a second surface to be pressed from the squeegee, which is engraved on the substrate,
Pressing the squeegee against the second surface of the screen mask via a paste to bring the first surface of the screen mask into linear contact with the substrate;
Moving the squeegee in a direction intersecting the abutting direction so that the abutting position between the printed material and the screen mask is moved, and transferring the paste to the printed material. Screen printing method.   2. The screen according to claim 1, wherein the ratio of the dimension in the plate thickness direction between the opening on the first surface and the groove on the second surface of the screen mask is 7 to 3 to 3 to 7. 3. Printing method.   2. The screen printing method according to claim 1, wherein the thickness of the screen mask is 0.5 to 2 times the diameter of the opening of the first surface.   2. The screen printing method according to claim 1, wherein the width of the groove on the second surface of the screen mask is 2 to 20 times the diameter of the opening on the first surface.   2. The screen printing method according to claim 1, wherein the length of the groove on the second surface of the screen mask is 10 times or more the diameter of the opening on the first surface.   The screen printing method according to claim 1, wherein a plurality of openings on the first surface communicating with the grooves on the second surface of the screen mask exist per groove.   The screen printing method according to claim 6, wherein a plurality of openings on the first surface per groove in the screen mask have a vertical and horizontal extension with respect to a direction in which the groove is carved. . A first surface having a plurality of substantially circular apertures to be in contact with the substrate;
A screen mask comprising: a second surface to be pressed from a squeegee, wherein a plurality of grooves communicating with the opening of the first surface are carved in one direction.   8. The screen mask according to claim 7, wherein the ratio of the dimension in the plate thickness direction between the opening of the first surface and the groove of the second surface is 7 to 3 to 3 to 8.   9. The screen mask according to claim 8, wherein the thickness is 0.5 to 2 times the diameter of the opening of the first surface.   8. The screen mask according to claim 7, wherein the width of the groove on the second surface is 2 to 20 times the diameter of the opening on the first surface.   9. The screen mask according to claim 8, wherein the length of the groove on the second surface is at least 10 times the diameter of the opening on the first surface.   9. The screen mask according to claim 8, wherein there are a plurality of openings on the first surface communicating with the grooves on the second surface per groove.   14. The screen mask according to claim 13, wherein a plurality of openings in the first surface per groove are present in a vertical and horizontal extent with respect to a direction in which the groove is carved.

Images