Patent Description:
Printed electronics technology for forming minute circuits such as RFID tags by printing (application) systems have been rapidly developed. In printed electronics technology, a system including an application needle is one of the choices in that it enables fine application using materials in a wide range of viscosities.

One of methods of performing fine application using an application needle is a method using an application unit as described in <CIT> (PTL <NUM>). In this application unit, a through hole is provided at the bottom face of a liquid material container. An application needle that can be moved up and down in the through hole is arranged for applying a liquid material. A liquid material in the liquid material container adheres to the tip end of the application needle and is transferred to a surface of a substrate serving as an application target. In the liquid material in the liquid material container, the surface tension at the edge of a hole through which the application needle of the liquid material container protrudes and the pressure by the weight of the liquid material in the liquid material container are in balance. The liquid material in the liquid material container therefore does not leak to the outside through the hole in the liquid material container.

<CIT> discloses an application unit according to the preamble of claim <NUM>.

<CIT> discloses another application unit.

The application unit disclosed in <CIT> enables application to a minute region using liquid materials in a wide range of viscosities. However, when a liquid material containing metal powder with a high viscosity and a large mean specific gravity is applied, the liquid material wets and spreads on the periphery of the hole through which the application needle of the liquid material container protrudes, as a result of repeating application multiple times, thereby forming liquid accumulation. This liquid accumulation changes the amount of liquid material adhering to the tip end of the application needle. Accordingly, the amount of application of the liquid material to the application target may vary. According to <CIT>, therefore, it seems to be difficult to apply a liquid material having a high viscosity stably for a long time. However, in order to draw a minute circuit such as an RFID tag, it is necessary to apply a liquid material having a high viscosity stably for a long time.

The present invention is made in view of the problem above. An object of the present invention is to provide a liquid material unit and a liquid application apparatus capable of applying a liquid material having a high viscosity stably for a long time.

A liquid application unit according to the present invention is defined in claim <NUM>.

According to the present invention, the wetting and spreading suppressing structure for a liquid material enables a liquid material having a high viscosity to be applied stably for a long time.

Like or corresponding parts in the following drawings are denoted by like reference numerals and a description thereof will not be repeated.

<FIG> is a front view of a liquid application unit according to a first embodiment as viewed from the negative Y direction. <FIG> is a side view of the liquid application unit according to the first embodiment as viewed from the positive X direction. In other words, <FIG> and <FIG> show the same liquid application unit. In the following description, the X direction, the Y direction, and the Z direction are introduced for convenience of explanation. Referring to <FIG> and <FIG>, the liquid application unit in the present embodiment applies a liquid material <NUM> to a surface of a substrate or the like serving as a target, using an application needle <NUM>. The liquid application unit mainly includes application needle <NUM>, a liquid material container <NUM>, and a servo motor <NUM>. It is noted that the liquid application unit includes many members other than those described above. A wetting and spreading suppressing structure, which is a characteristic part of the present embodiment, will be detailed later.

Liquid material container <NUM> is a member that accommodates and retains, that is, stores liquid material <NUM> in its inside. Application needle <NUM> is a member for supplying liquid material <NUM> in liquid material container <NUM> onto a target. Application needle <NUM> is an elongated member extending along the Z direction. The lowermost portion in the Z direction of application needle <NUM> has any shape, such as a corner portion, a curved portion, or a flat portion. The tip end of application needle <NUM> has a tapered portion that narrows toward the tip end (that is, the area of a cross section vertical to the axial line decreases as it goes toward the lower side in the Z direction and approaches the tip end).

In the liquid application unit in the present embodiment, application needle <NUM> directly applies liquid material <NUM>, for example, onto a surface of a target from liquid material container <NUM>. This will be described below.

The liquid application unit includes, in addition to liquid material container <NUM> described above, an application needle holder <NUM>, an application needle holder housing <NUM>, and an application needle holder fixing part <NUM>. Application needle holder housing <NUM> is fixed to the lower end of application needle holder fixing part <NUM>. A depression (not shown) is formed at the lower end of application needle holder housing <NUM>. The upper end of application needle <NUM> is fixed vertically to the center of the lower end of application needle holder <NUM>. A projection (not shown) is formed at the top of application needle holder <NUM>. The projection of application needle holder <NUM> is fitted in the depression of the application needle holder housing <NUM> so that application needle holder <NUM> is aligned with application needle holder housing <NUM>. Application needle holder <NUM> is fixed to application needle holder housing <NUM> by screws.

Application needle holder fixing part <NUM> is attached to the lower end of a movable part <NUM>. Movable part <NUM> is coupled to a bearing <NUM> through a cam coupling plate <NUM>. Bearing <NUM> is arranged so as to be installed on the uppermost surface in the Z direction of a cam <NUM>. Servo motor <NUM> is arranged above cam <NUM>. Servo motor <NUM> has a rotation axis AX extending along the Z direction. Servo motor <NUM> is rotatable around rotation axis AX.

Cam <NUM> is attached to rotation axis AX of servo motor <NUM>. Cam <NUM> is thus rotatable around rotation axis AX of servo motor <NUM>. Cam <NUM> has a center portion and a flange portion arranged on the outer periphery of the center portion. The lowermost surface with respect to the Z direction of cam <NUM> extends in the horizontal direction along the XY plane. On the other hand, the uppermost surface with respect to the Z direction of the flange portion of cam <NUM> varies in position (for example, is lower) with respect to the Z direction, for example, according to the position with respect to the X direction or the Y direction. In this way, the uppermost surface with respect to the Z direction of the flange portion of cam <NUM> has an inclined shape relative to the XY plane. In <FIG>, as an example, the uppermost surface of the flange portion of the cam is shaped such that the position in the Z direction is lower on the X-direction negative side than on the X-direction positive side.

When cam <NUM> with the uppermost surface having such an inclined shape rotates around rotation axis AX, bearing <NUM> installed on the uppermost surface of the flange portion of cam <NUM> moves in the up-down direction with respect to the Z direction. This is because the rotation of cam <NUM> with the flange portion of the uppermost surface having an inclined shape changes the Z-direction position of the uppermost surface of cam <NUM> equipped with bearing <NUM>.

When the rotation of cam <NUM> changes the position in the Z direction of bearing <NUM>, the position in the Z direction of cam coupling plate <NUM> and movable part <NUM> coupled thereto also changes. Application needle holder fixing part <NUM> is attached to the lower end of movable part <NUM>. The position in the Z direction of application needle holder fixing part <NUM> therefore also changes with the change in position in the Z direction of bearing <NUM> and the like by the rotation of cam <NUM>. Furthermore, the positions in the Z direction of application needle holder housing <NUM>, application needle holder <NUM>, and application needle <NUM> fixed to application needle holder fixing part <NUM> also change.

Movable part <NUM> is fixed to one end of a spring <NUM> (an upper end in the Z direction) through a fixing pin 30A. As shown in a region on the Y-direction positive side in <FIG>, a base plate <NUM> is arranged so as to be hidden behind the members shown in <FIG>. This base plate <NUM> is fixed to the other end (a lower end in the Z direction) on the opposite side to the one end of spring <NUM>, through a fixing pin 30B. Because of such a configuration, vibration due to rattling of bearing <NUM> does not occur at movable part <NUM> at a time of actuation. Preload may be applied to bearing <NUM> to eliminate rattling, and in this case, spring <NUM> is not necessarily provided. The tension of spring <NUM> can be adjusted by a tension adjuster <NUM>.

Base plate <NUM> holds liquid material container <NUM> and a not-shown linear guide. The linear guide held by base plate <NUM> guides the movement of the movable part along the Z direction. On the linear guide, a linear guide movable part <NUM> is attached for restricting movement of the movable part along a direction other than the extending direction described above. Application needle holder housing <NUM> and application needle holder fixing part <NUM> are fixed to linear guide movable part <NUM> and are movable in synchronization with the movement along the Z direction of linear guide movable part <NUM>. A linear guide <NUM> is attached to movable part <NUM>. Linear guide <NUM> supports movable part <NUM> having application needle holder <NUM> fixed thereto such that movable part <NUM> can move up and down.

Base plate <NUM> has a flat plate shape extending lengthwise in the Z direction and includes a container holding portion <NUM> at its lower portion in the Z direction. Container holding portion <NUM> removably holds liquid material container <NUM>. Container holding portion <NUM> includes, for example, a not-shown magnet and holds liquid material container <NUM> by magnetic force produced by the magnet. In a different point of view, liquid material container <NUM> includes, for example, a not-shown magnet and is removably held on container holding portion <NUM> by magnetic force produced between the magnet and the magnet of container holding portion <NUM>.

Application needle <NUM> moves in the up-down direction with respect to the Z direction. Application needle <NUM>, application needle holder <NUM>, application needle holder housing <NUM>, application needle holder fixing part <NUM>, and movable part <NUM> are connected to linear guide movable part <NUM>. Application needle <NUM> and the like therefore can be collectively referred to as a first vertical drive mechanism. The members that constitute the first vertical drive mechanism are connected to each other, whereby these members can be driven along the vertical direction, that is, the Z direction. On the other hand, liquid material container <NUM> and container holding portion <NUM> holding this, and base plate <NUM> including container holding portion <NUM> can be collectively referred to as a second vertical drive mechanism different from the first vertical drive mechanism. The members that constitute the second vertical drive mechanism are connected to each other, whereby these members can be driven along the vertical direction. As described above, application needle <NUM> connected to the first vertical drive mechanism can be moved relative to liquid material container <NUM> connected to the second vertical drive mechanism with respect to the Z direction.

In the following description, the whole of the liquid application unit shown in <FIG> and <FIG>, including servo motor <NUM>, application needle holder housing <NUM>, application needle holder fixing part <NUM>, and the like is denoted as liquid application unit <NUM>.

<FIG> is a perspective view showing an overall configuration of a liquid material application apparatus according to an embodiment of the present invention, equipped with the liquid application unit shown in <FIG>. Referring to <FIG>, liquid material application apparatus <NUM> in the present embodiment mainly includes an observation optical system <NUM>, a CCD camera <NUM>, and liquid application unit <NUM>. Observation optical system <NUM> includes a light source for illumination, an objective lens, and the like and is used for observing a surface state of a substrate <NUM> that is a target and a state of liquid material <NUM> (see <FIG>) applied by liquid application unit <NUM>. An image observed by observation optical system <NUM> is converted into an electrical signal by CCD camera <NUM>. Liquid application unit <NUM> applies conductive liquid material <NUM> (see <FIG>), for example, to a disconnected portion in a wiring pattern formed on substrate <NUM> to correct the disconnected portion. In this case, observation optical system <NUM>, CCD camera <NUM>, and liquid application unit <NUM> constitute a correction head. Furthermore, liquid material application apparatus <NUM> may apply liquid material <NUM> (see <FIG>), for example, to a surface of substrate <NUM> to form a predetermined pattern.

Liquid material application apparatus <NUM> further includes a Z-axis table <NUM> that moves the correction head in the vertical direction (Z-axis direction) relative to the application target substrate <NUM>, an X-axis table <NUM> having Z-axis table <NUM> mounted thereon to move the Z-axis table <NUM> in the lateral direction (X-axis direction), a Y-axis table <NUM> having substrate <NUM> mounted thereon to move the substrate <NUM> in the front-back direction (Y-axis direction) and serving as a stage to hold substrate <NUM> that is a target, a control computer <NUM> that controls the operation of the entire apparatus, a monitor <NUM> to display an image captured by CCD camera <NUM>, and an operation panel <NUM> for inputting an instruction from the operator to control computer <NUM>. Z-axis table <NUM>, X-axis table <NUM>, and Y-axis table <NUM> constitute a positioning device.

This apparatus configuration is illustrated by way of example, and, for example, a gantry system may be employed in which Z-axis table <NUM> having observation optical system <NUM> and the like mounted thereon is mounted on the X-axis table, the X-axis table is further mounted on the Y-axis table, and Z-axis table <NUM> is moved in the XY direction. The apparatus configuration may be any configuration that can move Z-axis table <NUM> having observation optical system <NUM> and the like mounted thereon, relative to the application target substrate <NUM> in the XY direction.

<FIG> is a cross-sectional view schematically showing a configuration of a part of the liquid material container included in the liquid application apparatus according to the first embodiment, and a liquid material application method. In <FIG>, liquid material container <NUM> and a part of application needle <NUM> arranged in its inside are specifically shown, and the other part is not shown. The shape of the part in <FIG> is collectively illustrated as a characteristic shape of the embodiments described below and may be sometimes different from the actual characteristic shape of the invention of the subject application.

The left diagram in <FIG> shows a state in which application needle <NUM> is elevated by change in position in the Z direction of application needle <NUM> described above. The right diagram in <FIG> shows a state in which application needle <NUM> is lowered by change in position in the Z direction of application needle <NUM> described above. Referring to <FIG>, a space <NUM> for storing liquid material <NUM> is formed in the interior of liquid material container <NUM> according to the present embodiment. Furthermore, a hole <NUM> connecting the lower end of the space <NUM> to the outside is formed at the bottom, that is, the lowermost portion in the Z direction of liquid material container <NUM>. Hole <NUM> allows application needle <NUM> to pass through space <NUM>. It is therefore preferable that another hole is formed in liquid material container <NUM> at a position two-dimensionally overlapping with hole <NUM>, and application needle <NUM> is arranged so as to penetrate through hole <NUM> and another hole.

Application needle <NUM> includes a holding portion <NUM> and a tip end <NUM>. Application needle <NUM> extends along the Z direction. Holding portion <NUM> is a member that holds tip end <NUM> on its lower side in the Z direction. In other words, tip end <NUM> is a portion that applies liquid material <NUM> to a target such as a substrate. Holding portion <NUM> is a portion arranged closer to the base side than tip end <NUM>, that is, on the upper side in the Z direction. It is preferable that holding portion <NUM> has a larger dimension (thickness) in the width direction than tip end <NUM>. For example, as shown in <FIG>, in one aspect, application needle <NUM> may have tip end <NUM> partially immersed in liquid material <NUM> in space <NUM> in liquid material container <NUM>.

<FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to a first example of the first embodiment, which is not in accordance with the invention. Referring to <FIG>, a wetting and spreading suppressing structure for liquid material <NUM> is arranged on the periphery of hole <NUM> in liquid material container <NUM>. As used herein, hole <NUM> refers to a region extending along the vertical direction (the Z direction), in which, as shown in <FIG>, the lower portion in the Z direction of an inner wall surface that accommodates liquid material <NUM> in the interior of liquid material container <NUM> has a smaller width in the X direction (the Y direction) than the width of the upper portion. As used herein, the periphery of hole <NUM> refers to a region of the body of liquid material container <NUM> that is arranged at the same Z-direction coordinate position as the Z-direction lowermost portion of hole <NUM> and the coordinate position therebelow in the Z direction.

Specifically, in <FIG>, the wetting and spreading suppressing structure is formed as a protruding portion <NUM> at the periphery of hole <NUM> based on the definition above. In protruding portion <NUM>, liquid material container <NUM> has a shape protruding toward the tip end <NUM> side of application needle <NUM>. As used herein, the tip end <NUM> side means the lower side in the Z direction, irrespective of the position of tip end <NUM>. Therefore, for example, even when application needle <NUM> elevates to the upper side in the Z direction as described later and tip end <NUM> is arranged on the upper side in the Z direction relative to protruding portion <NUM>, protruding portion <NUM> is curved so as to project toward the tip end <NUM> side of application needle <NUM>, that is, the lower side in the Z direction. Similarly, as used herein, the holding portion <NUM> side means the upper side in the Z direction, irrespective of its position.

In the first example of the first embodiment in <FIG>, which is not in accordance with the invention, in a cross section along hole <NUM>, protruding portion <NUM> includes a first shape portion <NUM> and a second shape portion <NUM>. First shape portion <NUM> has a shape in which a protruding portion surface that is a surface of protruding portion <NUM> in the cross section is inclined such that the width of hole <NUM> is larger on the lower side in the Z direction of application needle <NUM> than on the upper side in the Z direction. That is, a region inside of first shape portion <NUM> is hole <NUM>. Second shape portion <NUM> has a shape in which the protruding portion surface is inclined on the outside of hole <NUM> such that the width of protruding portion <NUM> increases from the lower side toward the upper side in the Z direction. As used herein, the width means a dimension in the X direction in <FIG>.

First shape portion <NUM> forms the lowermost portion of hole <NUM>. First shape portion <NUM> is therefore arranged on the hole <NUM> side in the X direction, that is, on the inside of liquid material container <NUM>. Second shape portion <NUM> is arranged on the opposite side to the hole <NUM> in the X direction, that is, on the outside of liquid material container <NUM>.

In other words, in <FIG>, first shape portion <NUM> forms a flared shape such that hole <NUM> becomes wider downward on the inside in the X direction of liquid material container <NUM>. Second shape portion <NUM> has an inclined shape such that the width of a portion of liquid material container <NUM> becomes larger upward on the outside in the X direction of liquid material container <NUM>. First shape portion <NUM> and second shape portion <NUM> are arranged to as to be generally aligned in the X direction.

In the cross section shown in <FIG>, at least one of first shape portion <NUM> and second shape portion <NUM> is arc-shaped. That is, the protruding portion surface of at least one of first shape portion <NUM> and second shape portion <NUM> has an arc-like shape. In <FIG>, both of first shape portion <NUM> and second shape portion <NUM> are arc-shaped surfaces RS as arc-shaped protruding portion surfaces. That is, first shape portion <NUM> and second shape portion <NUM> are arc-shaped curves.

<FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to a second example of the first embodiment, which is not in accordance with the invention. Referring to <FIG>, protruding portion <NUM> in the second example of first embodiment further includes a connection portion <NUM> connecting first shape portion <NUM> and second shape portion <NUM>. Connection portion <NUM> is arranged between first shape portion <NUM> and second shape portion <NUM> specifically in the X direction.

Connection portion <NUM> is preferably a flat surface along the XY plane. That is, in the cross section in <FIG>, connection portion <NUM> is preferably a linear surface along the X direction. Even when connection portion <NUM> is a flat surface, the whole including this portion as well as first shape portion <NUM> and second shape portion <NUM> is defined as protruding portion <NUM>. In the cross section shown in <FIG>, therefore, in the protruding portion surface that forms protruding portion <NUM>, first shape portion <NUM> and second shape portion <NUM> are arc-shaped surfaces RS, whereas connection portion <NUM> is a linear surface LS.

The X direction in <FIG> is a radial direction from the center in a two-dimensional view of application needle <NUM>. This radial direction is a direction extending radially from the center in a two-dimensional view of application needle <NUM>, including the X direction and the Y direction. In the present embodiment, which is not in accordance with the invention, in which the wetting and spreading suppressing structure is formed as protruding portion <NUM>, it is preferable that connection portion <NUM> has a dimension equal to or less than <NUM> in the radial direction in a two-dimensional view from the center of application needle <NUM>. This connection portion <NUM> is more preferably equal to or less than <NUM>, further more preferably equal to or less than <NUM>.

<FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to a third example of the first embodiment. Referring to <FIG>, in protruding portion <NUM> in the third example of the first embodiment in the cross section shown in <FIG>, at least one of first shape portion <NUM> and second shape portion <NUM> is linear. That is, the protruding portion surface of at least one of first shape portion <NUM> and second shape portion <NUM> has a linear shape. In <FIG>, both of first shape portion <NUM> and second shape portion <NUM> are linear surfaces LS as linear protruding portion surfaces. That is, first shape portion <NUM> and second shape portion <NUM> are straight lines extending in an inclined direction relative to all of the X direction, the Y direction, and the Z direction in the cross section shown in <FIG>. For example, first shape portion <NUM> and second shape portion <NUM> may be linear surfaces LS extending in a direction inclined by approximately <NUM>° relative to the X direction and the Z direction. That is, first shape portion <NUM> and second shape portion <NUM> may have a chamfered (C) surface shape.

In the third example in <FIG>, similarly to the second example in <FIG>, connection portion <NUM> is formed as linear surface LS between first shape portion <NUM> and second shape portion <NUM>.

In the present embodiment, second shape portion <NUM> has a steeper slope than first shape portion <NUM> with respect to the extending direction of hole <NUM>, that is, the Z direction. That is, in <FIG> and <FIG>, the angle formed by a tangent at a point at a certain Z coordinate in arc-shaped surface RS of second shape portion <NUM> with the Z direction is smaller than the angle formed by a tangent at a point at the same Z coordinate as the certain Z coordinate of first shape portion <NUM> with the Z direction. In <FIG>, it is preferable that the angle formed by linear surface LS of second shape portion <NUM> with the Z direction is smaller than the angle formed by linear surface LS of first shape portion <NUM> with the Z direction.

In the present embodiment, at least one of first shape portion <NUM> and second shape portion <NUM> may be arc-shaped. Furthermore, at least one of first shape portion <NUM> and second shape portion may be linear. Therefore, although not shown in the drawings, for example, at least one of first shape portion <NUM> and second shape portion <NUM> of liquid material container <NUM> may be arc-shaped and the other may be linear.

It is preferable that liquid material <NUM> for use in the present embodiment is a conductive material containing metal fine particles. Specifically, it is preferable that liquid material <NUM> is, for example, any one selected from the group consisting of solder paste, silver paste, and copper paste. It is preferable that the viscosity of liquid material <NUM> is typically equal to or higher than <NUM> Pa·s and equal to or lower than <NUM> Pa·s. It is preferable that the mean specific gravity of liquid material <NUM> is typically equal to or more than <NUM> and equal to or less than <NUM>. However, the viscosity and the mean specific gravity of liquid material <NUM> widely vary depending on the usage and the printing method.

Referring to <FIG> again, as shown in the left drawing, liquid material <NUM> is held in space <NUM> of liquid material container <NUM>. Tip end <NUM> of application needle <NUM> is immersed in liquid material <NUM> in space <NUM> of liquid material container <NUM>. In this state, tip end <NUM> is arranged to face substrate <NUM> that is a target to which liquid material <NUM> is applied. The left drawing in <FIG> shows a step of applying liquid material <NUM> to tip end <NUM>, as a stage before liquid material <NUM> is supplied to a surface of substrate <NUM>. The left drawing in <FIG> corresponds to a first state in which the tip end of application needle <NUM> is positioned in space <NUM> of liquid material container <NUM>.

Referring to the right drawing in <FIG>, application needle <NUM> is lowered from the state in the left diagram in <FIG> and comes into contact with an application target surface (a main surface on the upper side) of substrate <NUM>. Consequently, application needle <NUM> having tip end <NUM> accommodated in liquid material container <NUM> until then moves downward, compared with the state in the left drawing in <FIG>. With the lowering of application needle <NUM>, tip end <NUM> protrudes to the outside of liquid material container <NUM> through hole <NUM> and comes into contact with the application target surface of substrate <NUM>. Liquid material <NUM> adhering to tip end <NUM> is then supplied onto the application target surface of substrate <NUM>. As described above, application needle <NUM> is lowered to bring tip end <NUM> into contact with the application target surface. The right diagram in <FIG> corresponds to a second state in which the tip end of application needle <NUM> is positioned outside of liquid material container <NUM>. Once the application step shown by the right diagram in <FIG> is finished, application needle <NUM> elevates again into the state in the left drawing in <FIG>. In this way, the state on the left side (first state) and the state on the right side (second state) of <FIG> can be alternately repeated.

The operation and effect of the present embodiment will be described below with reference to a comparative example in <FIG> and <FIG>. <FIG> is a cross-sectional view schematically showing the position of the application needle and change in state of the liquid material container by repeating a liquid material application method in a comparative example. <FIG> is a cross-sectional view schematically showing change in state of the liquid material container by repeating the liquid material application method in the comparative example. Referring to <FIG>, the drawings are denoted as first to five drawings in order of time as shown by the arrows. The first drawing, the third drawing, and the fifth drawing correspond to the first state described above in <FIG>, and the second drawing and the fourth drawing correspond to the second state described above in <FIG>. By repeating the first state and the second state in <FIG>, as shown in the fifth drawing in <FIG>, liquid material <NUM> adhering to tip end <NUM> of application needle <NUM> adheres to immediately below hole <NUM> and to the surface of liquid material container <NUM> on the periphery of hole <NUM>. Referring to <FIG>, the first state and the second state in <FIG> are further repeated with liquid material <NUM> thus adhering to immediately below hole <NUM> and to the surface of liquid material container <NUM>. Consequently, liquid material <NUM> wets and spreads at the lower portion of liquid material container <NUM> as time passes as shown by the arrows in <FIG>. This wetting and spreading of liquid material <NUM> is due to the action of surface tension. More specifically, because of the action of surface tension, liquid material <NUM> spreading out of the lowermost portion of hole <NUM> accumulates on the periphery of hole <NUM> and wets and spreads when application needle <NUM> elevates and returns into liquid material container <NUM>.

In this way, the wetting and spreading of the liquid material on the periphery of hole <NUM> of liquid material container <NUM> causes liquid accumulation. This liquid accumulation changes the amount of liquid material <NUM> adhering to the tip end of application needle <NUM>. As a result, the amount of application of liquid material <NUM> to the application target may vary.

One of the reasons why liquid material <NUM> wets and spreads on the periphery of hole <NUM> is that liquid material container <NUM> in the comparative example has an edge EG at the lowermost portion. Edge EG is a region in which liquid material container <NUM> has a curved shape at its lowermost portion so as to extend toward the center side of application needle <NUM>, that is, the inside in a two-dimensional view relative to the other region. Edge EG forms narrow hole <NUM> within the curved shape portion. Liquid material <NUM> tends to intensively accumulate at the portion where edge EG is formed. This is because hole <NUM> adjacent to edge EG has a width narrower than a region other than hole <NUM> in space <NUM>. Presumably, if liquid material <NUM> intensively accumulates at hole <NUM>, liquid material <NUM> leaking out therefrom is likely to wet and spread on a surface portion of liquid material container <NUM> on the periphery.

Another possible reason why liquid material <NUM> wets and spreads on the periphery of hole <NUM> is that the viscosity and the specific gravity of liquid material <NUM> are large. If the viscosity and the specific gravity of liquid material <NUM> are large, liquid material <NUM> leaking out from hole <NUM> with protrusion of tip end <NUM> fails to return to space <NUM> of liquid material container <NUM> as a result of repeating application fast multiple times. Consequently, liquid material <NUM> gradually wets and spreads on the periphery of hole <NUM>. Furthermore, with variations in surface properties of the periphery of hole <NUM>, the degree of wetting and spreading of liquid material <NUM> to hole <NUM> becomes uneven. This is also the cause of variation in the amount of application of liquid material <NUM>.

Then, in liquid application unit <NUM> in the present embodiment, the wetting and spreading suppressing structure for liquid material <NUM> is arranged on the periphery of hole <NUM> in liquid material container <NUM>. With this structure, the wetting and spreading of liquid material <NUM> to the outside of liquid material container <NUM> is suppressed, and then, variation in the amount of application of liquid material <NUM> to the application target is suppressed. As a result, the amount of application is stabilized so that a liquid material having a high viscosity can be applied stably for a long time.

In liquid application unit <NUM> in the present embodiment, in a cross section along hole <NUM>, protruding portion <NUM> includes first shape portion <NUM> having a shape in which the protruding portion surface that is a surface of protruding portion <NUM> is inclined such that the width of hole <NUM> is larger on the tip end <NUM> side than on the holding portion <NUM> side. Protruding portion <NUM> includes second shape portion <NUM> having a shape in which the protruding portion surface is inclined on the outside of hole <NUM> such that its width increases from the tip end <NUM> side toward the holding portion <NUM> side. With first shape portion <NUM>, hole <NUM> has a portion having a width increasing downward at its lowermost portion. This width-increasing portion is a structure that makes it easier for liquid material <NUM> protruding from hole <NUM> at the time of lowering of application needle <NUM> to return to the interior of hole <NUM> at the time of subsequent elevation of application needle <NUM>. This is because first shape portion <NUM> has a shape that increases the width of hole <NUM>, contrary to the surface portion on the hole <NUM> side of edge EG, and therefore suppresses concentration and accumulation of liquid material <NUM> in hole <NUM>. With this configuration, liquid material <NUM> temporarily discharged to the outside of hole <NUM> is returned to the inside of liquid material container <NUM>, thereby suppressing wetting and spreading on the outside of liquid material container <NUM>. Even if liquid material <NUM> protruding to the outside of liquid material container <NUM> wets and spreads to reach second shape portion <NUM>, liquid material <NUM> need to climb on second shape portion <NUM> to wet and spread on second shape portion <NUM>. Liquid material <NUM> reaching second shape portion <NUM> is inevitably subjected to the action of gravity, and therefore, it is difficult to climb on second shape portion <NUM>. Thus, because of the provision of second shape portion <NUM>, wetting and spreading of liquid material <NUM> to the outside of liquid material container <NUM> is suppressed.

In other words, the present embodiment provides a wetting and spreading suppressing structure that does not have edge EG but has a shape having first shape portion <NUM> and the like. With this structure, liquid material <NUM> leaking out from hole <NUM> of liquid material container <NUM> together with tip end <NUM> of application needle <NUM> can smoothly return into liquid material container <NUM> together with tip end <NUM> of application needle <NUM>. Therefore, unlike the comparative example, the phenomenon in which liquid material <NUM> accumulates at the lowermost portion of liquid material container <NUM> is suppressed. Accordingly, variation in the amount of application by application needle <NUM> can be reduced. The reduction of variation in the amount of application by application needle <NUM> according to the present embodiment is advantageous over reduction of variation in the amount of application by surface treatment such as liquid-repellent coating, in view of manufacturing and quality. This is because the present embodiment does not include a chemical treatment process in surface treatment such as a liquid-repellent coating and can eliminate the possibility that liquid material <NUM> drops off from hole <NUM>.

In liquid application unit <NUM> in the present embodiment, protruding portion <NUM> may further include connection portion <NUM> connecting first shape portion <NUM> and second shape portion <NUM>. Connection portion <NUM> is a portion that remains as a flat portion during processing of first shape portion <NUM> and second shape portion <NUM>, in a cross section along hole <NUM>. Even when connection portion <NUM> is formed to some degree depending on the processing condition and the like, there is no harm to the operation effect of the present embodiment achieved by protruding portion <NUM> having first shape portion <NUM> and second shape portion <NUM>. However, in light of maintaining the operation effect, it is preferable that connection portion <NUM> has a dimension equal to or less than <NUM> in the radial direction from the center of application needle <NUM>.

In liquid application unit <NUM> in the present embodiment, at least one of first shape portion <NUM> and second shape portion <NUM> is arc-shaped. For example, first shape portion <NUM> is formed into an arc-like shape, that is, a rounded (R) shape so that liquid material <NUM> leaking out from hole <NUM> of liquid material container <NUM> together with tip end <NUM> of application needle <NUM> can smoothly return into liquid material container <NUM> together with tip end <NUM> of application needle <NUM>. As a result, liquid material <NUM> is held at a certain position where the surface tension and the gravity are in balance on first shape portion <NUM> as arc-shaped surface RS. Therefore, unlike the comparative example, the phenomenon in which liquid material <NUM> accumulates at the lowermost portion of liquid material container <NUM> is suppressed. When second shape portion <NUM> is arc-shaped, the action of pulling back liquid material <NUM> reaching second shape portion <NUM> quickly to the hole <NUM> side can be enhanced. However, even when at least one of first shape portion <NUM> and second shape portion <NUM> is linear, the action of pulling back liquid material <NUM> to the interior of liquid material container <NUM> can be achieved as described above.

In liquid application unit <NUM> in the present embodiment, second shape portion <NUM> has a steeper slope than first shape portion <NUM> with respect to the extending direction of hole <NUM>. With this configuration, the climbing of the leaking liquid material <NUM> on second shape portion <NUM> can be suppressed more reliably. This enhances the effect of pulling back liquid material <NUM> reaching second shape portion <NUM> to the interior of liquid material container <NUM>.

<FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to a first example of a second embodiment. <FIG> is an enlarged plan view schematically showing a manner in which the region shown in <FIG> is two-dimensionally viewed from the lower side in the Z direction. Referring to <FIG> and <FIG>, a wetting and spreading suppressing structure for liquid material <NUM> is arranged on the periphery of hole <NUM> in liquid material container <NUM> according to the first example of the present embodiment. Specifically, in <FIG> and <FIG>, the wetting and spreading suppressing structure is annular grooves <NUM>. A plurality of annular grooves <NUM> are spaced apart from each other in the radial direction in a two-dimensional view from the center of application needle <NUM>. In the annular grooves <NUM>, a plurality of depressions depressed in the Z direction and a plurality of projections protruding in the Z direction are alternately arranged in the radial direction to form a configuration including the depressions and the projections spaced apart from each other in the radial direction. In this way, in the present embodiment, a surface of regions that sandwich hole <NUM> of liquid material container <NUM> therebetween forms a grooved surface GS in which a plurality of depressions and a plurality of projections are arranged. Grooved surface GS extends concentrically in a two-dimensional view to form annular grooves <NUM>.

In <FIG> and <FIG>, grooved surface GS is formed on a surface along the X direction in a cross section along hole <NUM> shown in <FIG>. The surface is formed at the central portion in the X direction, and linear surfaces LS are formed on the left side and the right side in the X direction such that this surface is sandwiched therebetween. Linear surface LS is formed on the hole <NUM> side of annular grooves <NUM>, that is, on the inside in the X direction in a two-dimensional view, in a cross section along hole <NUM> shown in <FIG>. Linear surface LS is a third shape portion <NUM> in which the surface of liquid material container <NUM> has an inclined shape such that the width of hole <NUM> is larger on the lower side in the Z direction than on the upper side.

In <FIG>, linear surface LS is also formed as a fourth shape portion <NUM>, in addition to the above-noted third shape portion <NUM>. Linear surface LS serving as fourth shape portion <NUM> is formed on the opposite side to hole <NUM> of annular grooves <NUM>, that is, on the outside in the X direction, in a cross section along hole <NUM> shown in <FIG>. Linear surface LS serving as fourth shape portion <NUM> has an inclined shape on the outside of hole <NUM> such that the width of the body of liquid material container <NUM> increases from the lower side in the Z direction toward the upper side.

In <FIG>, therefore, third shape portion <NUM> has a manner similar to first shape portion <NUM> in the first embodiment, and fourth shape portion <NUM> has a manner similar to second shape portion <NUM> in the first embodiment. In other words, the body of liquid material container <NUM> has a shape like protruding portion <NUM> in the first embodiment. In this way, the present embodiment may also have a shape similar to protruding portion <NUM> in the first embodiment. However, in <FIG>, the dimension in the radial direction from the center of application needle <NUM> of the region of annular grooves <NUM> having grooved surface GS corresponding to connection portion <NUM> in the first embodiment may exceed <NUM>. Furthermore, the difference in height with respect to the Z direction between the depression and the projection of grooved surface GS is preferably equal to or more than <NUM>, more preferably equal to or more than <NUM>. The difference in height is further preferably equal to or more than <NUM>. The dimensions and shape of grooved surface GS, including the difference in height between the depression and the projection, will be theoretically described later.

The region having linear surfaces LS in <FIG> described above has linear surfaces LS inclined to the X direction and the Z direction, for example, such that a chamfered surface shape is formed on the hole <NUM> side and the opposite side to hole <NUM> of annular grooves <NUM>. However, in the present embodiment, which is not in accordance with the invention only the linear surface LS serving as third shape portion <NUM> at least on the hole <NUM> side may be formed as in the following second example. Alternatively, in the present embodiment, which is not in accordance with the invention, either of linear surfaces LS serving as third shape portion <NUM> and fourth shape portion <NUM> is not provided, and only the annular grooves <NUM> having grooved surface GS may be formed at the flat lowermost surface, as in the following third example. <FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to the second example of the second embodiment, which is not in accordance with the invention. <FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to the third example of the second embodiment, which is not in accordance with the invention. Referring to <FIG>, the second example of the present embodiment, which is not in accordance with the invention, differs from the first example in that, for example, the chambered surface-shaped portion that is linear surface LS serving as fourth shape portion <NUM> is not formed. Referring to <FIG>, the third example of the present embodiment, which is not in accordance with the invention, differs from the second example in that, for example, the chambered surface-shaped portion that is linear surface LS serving as third shape portion <NUM> is not formed.

In liquid application unit <NUM> in the present embodiment, the wetting and spreading suppressing structure is a plurality of annular grooves <NUM> spaced apart from each other in the radial direction from the center of application needle <NUM>. Because of such a configuration, the angle of contact between liquid material <NUM> and the surface of the lowermost portion of liquid material container <NUM> on the periphery of hole <NUM>, that is, grooved surface GS having annular grooves <NUM> is large. The liquid repellency of grooved surface GS is thus enhanced. Therefore, for example, unlike the comparative example in <FIG> and <FIG>, the inconvenience of wetting and spreading of liquid material <NUM> leaking out from hole <NUM> of liquid material container <NUM> to the surface of liquid material container <NUM> can be suppressed. The present embodiment therefore also can suppress variation in the amount of application of liquid material <NUM> to an application target, similarly to the first embodiment. As a result, the amount of application is stabilized so that a liquid material having a high viscosity can be applied stably for a long time.

Liquid application unit <NUM> in the present embodiment includes third shape portion <NUM> having a shape in which the surface of liquid material container <NUM> is inclined such that the width of hole <NUM> is larger on the tip end <NUM> side than on the holding portion <NUM> side, on the hole <NUM> side of annular grooves <NUM>, in a cross section along hole <NUM>. In a cross section along hole <NUM>, for example, shown in <FIG>, this third shape portion <NUM> is linear. The wettability of liquid material <NUM> is higher on such linear surface LS serving as third shape portion <NUM> than in the other region on the periphery. In other words, third shape portion <NUM> has a smaller angle of contact for liquid material <NUM> to wet than the other region on the periphery. Therefore, liquid material <NUM> that attempts to leak out from hole <NUM> is guided to be held on third shape portion <NUM> formed at the lowermost portion of hole <NUM>. This suppresses a phenomenon in which liquid material <NUM> is held disproportionately at a part of the surface of the lowermost portion of liquid material container <NUM> due to variation in liquid repellency at the portion of annular grooves <NUM> and axial misalignment between application needle <NUM> and hole <NUM>. Accordingly, variation in the amount of application of liquid material <NUM> to an application target can be suppressed.

The present embodiment is also advantageous over reduction of variation in the amount of application by surface treatment such as a liquid-repellent coating, in view of manufacturing and quality, similarly to the first embodiment.

Patterns of liquid repellency achieved by the depressions and projections of grooved surface GS of annular grooves <NUM> in the present embodiment include two kinds, namely, a pattern on the Cassie-Baxter theory and a pattern on the Wenzel theory. First, in the pattern on the Cassie-Baxter theory, liquid material <NUM> is unable to reach the bottom of the depression of grooved surface GS. A liquid droplet of liquid material <NUM> is therefore in a composite contact state in which it is in contact with both of the projection and the air in the depression. In this state, the area in which liquid material <NUM> is in contact with the air having the highest liquid phobicity increases, resulting in high liquid repellency. On the other hand, in the pattern on the Wenzel theory, liquid material <NUM> intrudes into the bottom of the depression of grooved surface GS. A liquid droplet of liquid material <NUM> is thus in contact with the liquid droplet and the surface of substrate <NUM> (see <FIG>) rather than in the composite contact state as described above. In this state, the area in which liquid material <NUM> is in contact with the liquid droplet and the surface of substrate <NUM> increases. Accordingly, interface free energy at the interface of the liquid droplet with the surface of substrate <NUM> increases, and the wettability of substrate <NUM> is enhanced. Therefore, when liquid material container <NUM> is formed of a material with high liquid repellency, the liquid repellency of liquid material container <NUM> can be further increased. Specifically, it is preferable that liquid material container <NUM> in the present embodiment is formed of a material with high liquid repellency, such as resin or stainless steel. It is noted that the preferred materials of liquid material container <NUM> described above are applicable to the first embodiment.

In the pattern on the Cassie-Baxter theory, the angle of contact is large and liquid repellency is improved. However, since the contact area between the liquid droplet and the surface of substrate <NUM> is small, the adsorption force at the interface between the liquid droplet and substrate <NUM> is small. In the pattern on the Cassie-Baxter theory, therefore, the adsorption force of liquid material <NUM> at a surface of tip end <NUM> of application needle <NUM> is weak. Therefore, due to the inertial force when application needle <NUM> protrudes from hole <NUM>, the amount of application of liquid material <NUM> to substrate <NUM> may increase drastically or a large liquid accumulation may be formed.

On the other hand, in the pattern on the Wenzel theory, the contact area between the liquid droplet and the surface of substrate <NUM> increases, and the adsorption force at the interface between the liquid droplet and substrate <NUM> is large. This is effective in stabilizing the amount of application to substrate <NUM> when application needle <NUM> protrudes from hole <NUM> and in suppressing formation of liquid accumulation. It is therefore preferable to design parameters such as groove shape, groove width, and groove depth so that the pattern on the Wenzel theory is developed, considering the properties of liquid material <NUM>.

As shown in <FIG>, in the present embodiment, grooved surface GS has a concentric shape. More specifically, the depressions and the projections of grooved surface GS are formed so as to extend, for example, in a direction (circumferential direction) intersecting (orthogonal to) the direction in which liquid material <NUM> wets and spreads on the surface of liquid material container <NUM>. This configuration provides the pinning effect that increases the contact angle of liquid material <NUM> on the surface of liquid material container <NUM> at an edge portion (an edge at the entrance of the depression, an edge of the uppermost portion of the projection, etc.) in a cross section of the depressions and the projections, in addition to the effect of improving liquid repellency as described above. Accordingly, the liquid repellency is further improved at the edge portion.

In <FIG>, grooved surface GS (annular grooves <NUM>) is formed on the entire circumferential portion in the circumferential direction on the periphery of hole <NUM>. However, the present invention is not limited to such a manner. For example, although not shown in the drawings, grooved surface GS (annular grooves <NUM>) may be formed only partially in the circumferential direction on the periphery of hole <NUM>.

<FIG> is an enlarged cross-sectional view schematically showing region A surrounded by the dotted line in <FIG> according to a third embodiment. Referring to <FIG>, a wetting and spreading suppressing structure for liquid material <NUM> is arranged on the periphery of hole <NUM> in liquid material container <NUM> according to the present embodiment. Specifically, in <FIG>, the wetting and spreading suppressing structure is formed as a liquid-repellent coating <NUM> having liquid repellency. Specifically, liquid-repellent coating <NUM> is a thin film having high liquid repellency to liquid material <NUM>. For example, when liquid material <NUM> is a conductive material, liquid material <NUM> contains an organic substance commonly called rosin as a flux. It is therefore preferable that a thin film having high oil repellency is formed as liquid-repellent coating <NUM>.

For example, when liquid material container <NUM> has protruding portion <NUM> similar to the first embodiment, it is preferable that liquid-repellent coating <NUM> is formed at least on a surface on the periphery of hole <NUM> at the lowermost portion of protruding portion <NUM>. However, when the process of forming liquid-repellent coating <NUM> locally in this way is complicated or when there is concern about unevenness of the thickness and the like of the locally formed liquid-repellent coating <NUM>, liquid-repellent coating <NUM> may be formed on the entire surface of liquid material container <NUM> including the region described above.

The present embodiment achieves the effect of suppressing wetting and spreading of liquid material <NUM> by liquid-repellent coating <NUM>, similarly to the first and second embodiments.

The features described in the foregoing embodiments (and the examples included therein) may be combined as appropriate and applied in a technically consistent manner.

Embodiments disclosed here should be understood as being illustrative rather than being limitative in all respects. The scope of the present invention is shown not in the foregoing description but in the claims.

Claim 1:
A liquid application unit (<NUM>) for applying a liquid material to a surface of a target (<NUM>) using an application needle (<NUM>), the liquid application unit (<NUM>) comprising:
the application needle (<NUM>); and
a liquid material container (<NUM>) that stores the liquid material, wherein
the liquid material container (<NUM>) has a space (<NUM>) that stores the liquid material and a hole (<NUM>) that allows the application needle (<NUM>) to pass through the space (<NUM>), and
a wetting and spreading suppressing structure for the liquid material is disposed at a periphery of the hole (<NUM>) in the liquid material container (<NUM>), wherein
the application needle (<NUM>) includes a tip end (<NUM>) that applies the liquid material to the target (<NUM>) and a holding portion (<NUM>) disposed closer to a base side than the tip end (<NUM>),
the wetting and spreading suppressing structure is a protruding portion (<NUM>) in which the liquid material container (<NUM>) has a protruding shape toward a tip end side of the application needle (<NUM>), and
in a cross section along the hole (<NUM>), the protruding portion (<NUM>) includes a first shape portion (<NUM>) and a second shape portion (<NUM>), the first shape portion (<NUM>) having a shape in which a protruding portion surface that is a surface of the protruding portion (<NUM>) is inclined such that a width of the hole (<NUM>) is larger on the tip end side than on the holding portion side, the second shape portion (<NUM>) having a shape in which the protruding portion surface is inclined outside of the hole (<NUM>) such that a width of the protruding portion (<NUM>) increases from the tip end side toward the holding portion side,
characterized in that the second shape portion (<NUM>) has a steeper slope than the first shape portion (<NUM>) with respect to an extending direction of the hole (<NUM>).