Droplet discharge device

Abstract

To provide a droplet discharge device capable of applying a pressure for discharging a liquid in a liquid chamber properly even with a slight downward movement of a plunger.SOLUTION: A droplet discharge device includes: a housing having a liquid chamber, a discharge port for discharging a liquid material in the liquid chamber, and a supply port for supplying the liquid material to the liquid chamber; and a plunger having a small diameter part formed at a tip portion, and a large diameter part having a diameter larger than that of the small diameter part and formed at the base end side of the small diameter part, the plunger provided in a manner that the plunger can enter the liquid chamber and reciprocate. In a retreat end position where the plunger is retreated, at least part of the supply port faces a side surface of the small diameter part. In an advanced end position where the plunger is advanced, the at least part of the supply port faces a side surface of the large diameter part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a droplet ejection device. [Background technology]

[0002] A droplet ejection device is known that applies a liquid material such as solder paste to a substrate or the like in order to mount small electronic components (Patent Document 1). As electronic components become smaller, there is a demand for a droplet ejection device that can eject minute amounts of droplets with high precision.

[0003] 7 is a diagram showing a conventional droplet ejection device 1. The droplet ejection device 1 has a housing 2 provided with a liquid chamber 29 to which a liquid material 50 is supplied, and a plunger 3 whose tip is located within the liquid chamber 29 and is provided so as to be able to reciprocate up and down (in the ±Z direction).

[0004] The housing 2 has a main body 21 in which a liquid chamber 29 is formed, a nozzle plate 24 in which a discharge port 25 is formed and which covers the liquid chamber 29 from below, and a cover 26 in which a plunger port 27 is formed and which covers the liquid chamber 29 from above. A supply path 23 is further formed in the main body 21, and the supply path 23 communicates with the liquid chamber 29 via a supply port 22 formed in a side wall 30 of the liquid chamber 29.

[0005] The plunger 3 is inserted into the plunger opening 27. The plunger 3 is driven up and down by an actuator (not shown).

[0006] A ring-shaped seal 28 is provided on the inner peripheral surface of the plunger port 27 to provide a liquid-tight seal between the cover 26 and the plunger 3 .

[0007] 8A to 8C are diagrams showing the operation when the plunger 3 is driven up and down to eject droplets 51. Fig. 8A shows the state in which the plunger 3 has risen to its retracted end. The liquid chamber 29 is filled with liquid material 50 supplied from the supply path 23.

[0008] 8B shows the state in which the plunger 3 has descended to the forward end and droplets 51 have been ejected from the ejection port 25. When the plunger 3 descends, the liquid material 50 in the liquid chamber 29 is pressurized, and the pressure causes droplets 51 to be ejected from the ejection port 25.

[0009] 8C shows the state in which the plunger 3 has risen and is again at the retracted end. When the plunger 3 rises, liquid material 50 is supplied from a tank (not shown) through the supply path 23 into the liquid chamber 29, and the state returns to that shown in FIG. 8A.

[0010] 8A to 8C are repeated to repeatedly eject droplets 51 toward an ejection target such as a substrate. The ejection speed and size of the ejected droplets 51 are adjusted by controlling the speed and amount of descent of the plunger 3. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-221442 Summary of the Invention [Problem to be solved by the invention]

[0012] Assuming that the liquid material 50 is incompressible and that the change in volume of the liquid material 50 due to the pressure applied by the plunger 3 can be ignored, ideally the volume of the droplet 51 is proportional to the amount of downward movement of the plunger 3. Therefore, while it should be possible to eject a minute droplet 51 by reducing the amount of downward movement of the plunger 3, in reality, if the amount of downward movement of the plunger 3 is small, the volume of the droplet 51 becomes smaller than intended, and in some cases the droplet 51 may not be ejected. The inventors of the present disclosure investigated the cause and found that, as described below, the pressure applied to the liquid material 50 in the liquid chamber 29 by the plunger 3 escapes from the supply port 22 toward the supply path 23, and the pressure required to eject the droplet 51 from the ejection port 25 is not being properly applied to the liquid material 50.

[0013] 9A shows an outline of the flow of liquid material 50 in liquid chamber 29 when plunger 3 descends, and FIG. 9B shows the change in pressure in liquid chamber 29 at that time. In FIG. 9A, when plunger 3 descends, pressure is applied to liquid material 50, and this pressure causes some of liquid material 50 to flow back toward the tank through supply path 23. Therefore, the droplets discharged from discharge port 25 are small compared to the amount of descent of plunger 3.

[0014] In Figure 9B, the horizontal axis represents the time of pressure application by plunger 3, and the vertical axis represents the pressure within liquid chamber 29. The solid line represents the case where the plunger 3 is lowered for a longer period of time, thereby increasing the amount of plunger 3 descent, and then the plunger is raised after maintaining the lowered state for a certain period of time. The dashed line represents the case where the plunger 3 is lowered for a shorter period of time, thereby decreasing the amount of plunger 3 descent, and then the plunger is raised immediately after the plunger descent. As shown in Figure 9A, when plunger 3 descends, part of the liquid material 50 flows toward supply channel 23, so the pressure within liquid chamber 29 increases slowly, and it takes longer for the pressure to exceed the discharge pressure (the pressure required to discharge the liquid material as droplets against the flow resistance at the discharge port). As a result, the amount of plunger 3 descent and the volume of droplet 51 are not proportional. As shown by the dashed line, if the plunger 3 descends too quickly, the plunger's descent may end before the pressure within liquid chamber 29 increases sufficiently, resulting in no droplet 51 being discharged.

[0015] 10 is a diagram showing the relationship between the time the plunger 3 is lowered and the amount of droplets ejected. If the time the plunger 3 is lowered is short, the pressure in the liquid chamber will not exceed the ejection pressure, and no liquid will be ejected. However, if the plunger 3 is lowered for a predetermined time Tmin, droplets of a predetermined minimum ejection volume Vmin will be ejected. Therefore, to eject minute droplets, Tmin and Vmin must be small, but there are limits to this with the conventional droplet ejection device 1.

[0016] As described above, in the conventional droplet ejection device 1, the amount of descent of the plunger 3 is not proportional to the amount of droplets ejected, and it is difficult to reduce the minimum descent time Tmin and the minimum ejection amount Vmin at that time, making it difficult to eject tiny droplets at high speed.

[0017] The present disclosure aims to provide a droplet ejection device that can quickly and accurately apply the pressure required for ejection to a liquid material in a liquid chamber, even when the plunger's downward movement is small in order to eject tiny droplets. [Means for solving the problem]

[0018] The droplet ejection device disclosed herein comprises a housing having a liquid chamber, an ejection port for ejecting liquid material from the liquid chamber, and a supply port for supplying the liquid material into the liquid chamber; and a plunger having a small diameter portion formed at the tip and a large diameter portion larger in diameter than the small diameter portion and formed on the base end side of the small diameter portion, the plunger being arranged to be able to enter the liquid chamber and move back and forth, wherein when the plunger is in a retracted end position, at least a portion of the supply port faces the side surface of the small diameter portion, and when the plunger is in an advanced end position, at least a portion of the supply port faces the side surface of the large diameter portion. [Effects of the Invention]

[0019] According to the droplet ejection device of the present disclosure, when the plunger descends, the large diameter portion blocks the supply port, making it difficult for the liquid material to flow from the liquid chamber toward the supply channel. Furthermore, the presence of the small diameter portion creates flow resistance in the liquid material flowing between the small diameter portion and the sidewall of the liquid chamber, making it difficult for the liquid material to flow from the liquid chamber toward the supply channel. Therefore, the pressure of the liquid material in the liquid chamber rises quickly as the plunger descends, allowing for the rapid and accurate ejection of minute droplets. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating a droplet ejection device. [Figure 2] FIG. 2 is a diagram showing details of the droplet ejection device. [Figure 3A]FIG. 10 is a diagram showing a state in which the plunger is at its retracted end. [Figure 3B] FIG. 10 is a diagram showing a state in which the plunger is at the forward end. [Figure 3C] FIG. 10 is a diagram showing a state in which the plunger rises. [Figure 4A] FIG. 10 illustrates the flow of liquid material as the plunger descends. [Figure 4B] 10A and 10B are diagrams illustrating changes in pressure in a liquid chamber when a plunger descends. [Figure 5A] 10A and 10B are diagrams illustrating the relationship between the pressure applied by the plunger and the droplet ejection speed. [Figure 5B] 10A and 10B are diagrams illustrating the relationship between the pressure applied by the plunger and the droplet ejection speed. [Figure 6A] 10A and 10B are diagrams showing how fine particles are crushed by the tip surface of a plunger. [Figure 6B] 10A and 10B are diagrams showing a state in which crushing of fine particles by the tip surface of the plunger is prevented. [Figure 7] FIG. 1 is a diagram showing a conventional droplet ejection device. [Figure 8A] FIG. 10 is a diagram showing a state in which a conventional plunger is positioned at its retracted end. [Figure 8B] FIG. 10 is a diagram showing a conventional plunger at its forward end position. [Figure 8C] FIG. 10 is a diagram showing a conventional plunger rising state. [Figure 9A] FIG. 10 is a diagram showing the flow of liquid material when a conventional plunger moves down. [Figure 9B] FIG. 10 is a diagram showing a change in pressure in a liquid chamber when a conventional plunger descends. [Figure 10] 10A and 10B are diagrams illustrating the relationship between pressure application time and discharge amount of the droplet discharge device. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the components, the arrangement positions and connection forms of the components, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0022] Furthermore, each drawing is a schematic diagram and is not necessarily an exact illustration. In each drawing, substantially the same components are denoted by the same reference numerals, and redundant explanations will be omitted or simplified.

[0023] 1 is a diagram showing the overall structure of a droplet ejection device 1 of the present disclosure. The droplet ejection device 1 has a housing 2 provided with a liquid chamber 29 to which a liquid material 50 is supplied, and a plunger 4 whose tip is located within the liquid chamber 29 and is provided so as to be able to reciprocate up and down (in the ±Z direction).

[0024] The housing 2 has a main body 21 in which a liquid chamber 29 is formed, a nozzle plate 24 in which a discharge port 25 is formed and which covers the liquid chamber 29 from below, and a cover 26 in which a plunger port 27 is formed and which covers the liquid chamber 29 from above. A supply path 23 is further formed in the main body 21, and the supply path 23 communicates with the liquid chamber 29 via a supply port 22 formed in a side wall 30 of the liquid chamber 29.

[0025] The discharge port 25 is an opening through which the liquid material 50 pressurized by the plunger 4 passes and is discharged toward the target object, and its diameter is designed according to the type of liquid material 50, the size of the droplets to be discharged, etc.

[0026] The plunger 4 is inserted into the plunger opening 27. The plunger 4 is driven up and down by an actuator (not shown).

[0027] A ring-shaped seal 28 is provided on the inner peripheral surface of the plunger port 27 to provide a liquid-tight seal between the cover 26 and the plunger 4 .

[0028] 2 is a diagram showing the details of the plunger 4. The plunger 4 is formed with a small diameter portion 41 on the tip side (lower end side) and a large diameter portion 42 above the small diameter portion 41. A tapered portion 43 that gradually increases in diameter from the tip side to the base end side of the plunger 4 is formed at the end of the small diameter portion 41 on the large diameter portion 42 side. This tapered portion 43 is included as part of the small diameter portion 41.

[0029] A gap 31 is formed between the small diameter portion 41 and the side wall 30 of the liquid chamber 29. A gap 32 is also formed between the large diameter portion 42 and the side wall 30. The gap 31 has a size g1 that provides an appropriate flow resistance to the liquid material 50 in order to suppress the flow of the liquid material 50 from the liquid chamber 29 through the gap 31 toward the supply path 23 when the plunger 4 descends to pressurize the liquid material 50 in the liquid chamber 29. The gap g1 is also set so that the liquid material 50 can quickly flow through the gap 31 into the liquid chamber 29 when the liquid material 50 is supplied from the supply path 23 to the liquid chamber 29 by pressurization using a pump or the like (not shown). In other words, the gap g1 is set so that the liquid material 50 does not flow easily when pressurized by the plunger 4 descending, but flows easily when pressurized by a pump or the like. When the liquid material 50 contains fine particles such as solder paste, the diameter is set to about 12 to 20 times the diameter of the fine particles so that the fine particles are not crushed between the small diameter portion 41 and the side wall 30 when the plunger 4 moves up and down.

[0030] Here, the shape of the microparticles in this embodiment is defined as follows: The liquid material used contains at least 90% spherical particles with a ratio of the long diameter to the short diameter of 1.2 or less, and the long diameter is taken as the diameter of the microparticles. The particle size is measured, for example, by the following methods: (1) observing the particles under a microscope; (2) measuring by a sieve-type particle size distribution measurement test using a sieve with a specified particle range; or (3) measuring the particle size distribution of the microparticles contained in the liquid material using a laser diffraction particle size distribution measurement device, and taking the average value as the particle size. There are various methods for measuring the diameter of microparticles, but method (3) was adopted in this embodiment.

[0031] 2, the width g2 of the gap 32 is set so as to minimize the amount of liquid material that flows into the gap 32. However, if the liquid material contains fine particles, such as solder paste, the width g2 is set to about 1.5 to 2 times the diameter of the fine particles so that the fine particles are not crushed between the large diameter portion 42 and the side wall 30 when the plunger moves up and down.

[0032] When plunger 4 is raised to its retracted end position, lower end 421 of large diameter portion 42 is located above lower edge 222 of supply port 22, and the side surface of small diameter portion 41 is set to a position facing at least a part of supply port 22. In this case, lower end 421 may be located above upper edge 221 of supply port 22, and the entire supply port 22 may be set to a position facing the side surface of small diameter portion 41.

[0033] Furthermore, when plunger 4 is in the lowered forward end position, lower end 421 of large diameter portion 42 is located below upper edge 221 of supply port 22, and is set at a position where the side surface of large diameter portion 42 faces at least a part of supply port 22. In this case, lower end 421 may be located below lower edge 222, and may be set at a position where the entire supply port 22 faces the side surface of large diameter portion 42.

[0034] 3A to 3C are diagrams showing an example of the operation of the plunger 4 of the present disclosure when it moves up and down. Fig. 3A shows the state in which the plunger 4 is at the raised, retracted end. The lower end 421 of the large diameter portion 42 is positioned at approximately the same height as the upper edge 221 of the supply port 22.

[0035] The liquid material 50 is pressurized by a pump (not shown) or the like and supplied from the supply port 22 through the gap 31 to the liquid chamber 29. At this time, the liquid material 50 flows smoothly through the gap 31 and is supplied to the liquid chamber 29 quickly.

[0036] 3B shows the state in which the plunger 4 is driven downward by an actuator (not shown) and positioned at the forward end. The liquid material 50 in the liquid chamber 29 is pressurized by the plunger 4, and the pressure causes droplets 51 to be ejected from the ejection port 25. At this time, the lower end 421 of the large diameter portion 42 descends below the lower edge 222 of the supply port 22.

[0037] When plunger 4 descends, the side surface of large diameter portion 42 reaches a position opposite supply port 22, blocking supply port 22 and making it difficult for pressurized liquid material 50 to flow into supply path 23. Furthermore, because gap 31 between small diameter portion 41 and side wall 30 is narrow, flow resistance makes it difficult for liquid material 50 to flow through gap 31, making it difficult for liquid material 50 in liquid chamber 29 to flow into supply path 23. Therefore, the pressure applied to liquid material 50 by plunger 4 does not cause liquid material 50 to flow back into supply path 23, and almost all of the pressure applied by plunger 4 acts as pressure for discharging droplets 51, making it possible to quickly and efficiently discharge minute droplets 51.

[0038] 3C shows a state in which plunger 4 has risen to its uppermost position. When plunger 4 rises, lower end 421 of large diameter portion 42 moves above lower edge 222 of supply port 22, and liquid material 50 is supplied from supply port 22. At this time, gap 31 between the side surface of small diameter portion 41 and side wall 30 is set to an extent that does not interfere with the supply of liquid material 50, so liquid material 50 is quickly supplied to liquid chamber 29, and the state returns to that of FIG. 3A.

[0039] FIG. 4A shows an outline of the flow of liquid material 50 in liquid chamber 29 when plunger 4 descends, and FIG. 4B shows the change in pressure in liquid chamber 29 at that time. In FIG. 4A, pressure is applied to liquid material 50 when plunger 4 descends. Because the gap between small diameter portion 41 and side wall 30 of liquid chamber 29 is narrow, liquid material 50 does not easily flow between small diameter portion 41 and side wall 30. Furthermore, when plunger 4 descends, supply port 22 is blocked by large diameter portion 42, making it difficult for liquid material 50 to flow toward supply path 23. Therefore, a quantity of droplets proportional to the amount of descent of plunger 4 can be ejected.

[0040] In Figure 4B, the horizontal axis represents the time of pressurization by plunger 4, and the vertical axis represents the pressure within liquid chamber 29. The solid line represents the case where the plunger 3 is lowered for a longer period of time, thereby increasing the amount of descent of the plunger 3, and the plunger is then raised after maintaining the lowered state for a certain period of time. The dashed line represents the case where the plunger 3 is lowered for a shorter period of time, thereby decreasing the amount of descent of the plunger 3, and the plunger is then raised immediately after the descent. As shown in Figure 4A, when plunger 4 descends, almost no liquid material 50 flows into supply channel 23, so the pressure within liquid chamber 29 rises rapidly. When the pressure exceeds the discharge pressure required for discharge, liquid material 50 is discharged from discharge port 25.

[0041] When ejecting minute droplets, the time for pressurizing the droplets is shortened, as shown by the dashed line. In this embodiment, the pressure in the liquid chamber rises quickly once pressurization begins, so it takes a short time for the pressure in the liquid chamber to exceed the ejection pressure. Therefore, minute droplets can be ejected with a short pressurization period.

[0042] In this embodiment, when the plunger 4 starts pressurizing the liquid material 50, the pressure inside the liquid chamber 29 rises rapidly, so the amount of droplets ejected (droplet size) is roughly proportional to the pressurization time, so if a small amount needs to be ejected, pressurization can be applied for a short period of time, and if a large amount needs to be ejected, pressurization can be applied for a long period of time. Therefore, the required amount of droplets can be ejected quickly and appropriately.

[0043] Figures 5A and 5B are diagrams showing the relationship between the plunger descending time and the velocity of the ejected droplets. Using solder paste containing solder particles with a particle diameter of 10 μm as the liquid material, Figure 5A shows the case where the droplet ejection device of this embodiment was used, while Figure 5B shows the case where a conventional droplet ejection device was used. The plunger descending time T is the time when the ejection velocity reaches its maximum in the conventional droplet ejection device, and the ejection velocity at this time is defined as 1.

[0044] In Figure 5A, shortening the drop time does not decrease the ejection speed, whereas in Figure 5B, shortening the drop time decreases the ejection speed. In Figure 5B, if the drop time is short, the pressure in the liquid chamber does not increase sufficiently, so even if droplets are ejected, their speed will decrease.

[0045] Therefore, in the droplet discharge device of this embodiment, even if the time for which the plunger 4 pressurizes the liquid material 50 is short, minute droplets can be discharged quickly.

[0046] 6A and 6B are diagrams illustrating the amount of downward movement of the plunger 4 when the liquid material 50, such as solder paste, contains fine particles 52. As shown in Fig. 6A, if the plunger 4 gets too close to the nozzle plate 24, the fine particles 52 may be crushed by the tip surface of the plunger 4 and the nozzle plate 24. Therefore, as shown in Fig. 6B, at the forward end of the plunger 4, it is desirable to leave a gap between the tip surface of the plunger 4 and the nozzle plate 24 that is large enough not to crush the fine particles 52; for example, it is desirable to ensure a gap of at least 12 times the diameter of the fine particles 52.

[0047] In this embodiment, the pressure of the liquid material 50 increases rapidly as the plunger 4 descends, so there is no need to make the amount of descent of the plunger 4 greater than necessary, and therefore the distance between the tip surface of the plunger 4 and the nozzle plate 24 can be appropriately maintained.

[0048] As described above, according to the droplet ejection device 1 of the present disclosure, the pressure inside the liquid chamber 29 rises rapidly as the plunger 4 descends, making it possible to eject minute droplets 51 quickly and accurately. Furthermore, since the fine particles 52 contained in the liquid material 50 are not crushed, the droplets 51 can be ejected while maintaining the quality of the liquid material 50, and problems such as clogging of the ejection port 25 can be prevented. [Industrial Applicability]

[0049] The device can be suitably used as a droplet ejection device for ejecting minute droplets. [Explanation of symbols]

[0050] 1 Droplet discharge device 2. Case 4 plungers 21 Main body 22 Supply port 221 Upper edge 222 Lower edge 23 Supply route 24 nozzle plate 25 Outlet 26 Cover 27 Plunger port 28 stickers 29 Liquid chamber 30 side wall 41 Small diameter section 42 Large diameter section 43 Tapered section 50 liquid materials

Claims

1. a housing having a liquid chamber, a discharge port for discharging a liquid material in the liquid chamber, and a supply port for supplying the liquid material into the liquid chamber; a plunger having a small diameter portion formed at a tip end thereof and a large diameter portion having a diameter larger than that of the small diameter portion and formed on a base end side of the small diameter portion, the plunger being provided so as to be able to advance into the liquid chamber and move back and forth; and When the plunger is at its retracted end position, at least a portion of the supply port faces a side surface of the small diameter portion, When the plunger is at its forward end position, at least a portion of the supply port faces a side surface of the large diameter portion. Droplet ejection device.

2. A tapered portion is formed between the small diameter portion and the large diameter portion, the diameter of which increases from the small diameter portion toward the large diameter portion. The droplet ejection device according to claim 1 .

3. a distance between a side surface of the small diameter portion and an inner surface of the liquid chamber facing the side surface is 12 to 20 times the diameter of the fine particles contained in the liquid material; The droplet ejection device according to claim 1 .

4. a distance between a side surface of the large diameter portion and an inner surface of the liquid chamber facing the side surface is 1.5 to 2 times the diameter of the fine particles contained in the liquid material; The droplet ejection device according to claim 1 .

5. At the forward end position, a distance between a tip end surface of the plunger and an inner surface of the liquid chamber facing the tip end surface is equal to or greater than 12 times the diameter of fine particles contained in the liquid material. The droplet ejection device according to claim 1 .

6. At the forward end position, the entire supply port faces a side surface of the large diameter portion. The droplet ejection device according to claim 1 .

7. At the retracted end position, the entire supply port faces a side surface of the small diameter portion. The droplet ejection device according to claim 1 .

8. At the retracted end position, the entire supply port faces a side surface of the small diameter portion. The droplet ejection device according to claim 6 .

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