WO2005009626A1

WO2005009626A1 - Fluid discharging device

Info

Publication number: WO2005009626A1
Application number: PCT/DE2004/001527
Authority: WO
Inventors: Wolfgang Wehl; Jörg WILD
Original assignee: Fachhochschule Heilbronn Hochschule für Wirtschaft und Technik
Priority date: 2003-07-17
Filing date: 2004-07-14
Publication date: 2005-02-03
Also published as: DE10332760B3; DE112004000045D2

Abstract

The invention relates to a fluid droplet discharging device comprising a fluid reservoir that is open for discharging fluid droplets and comprising an actuator for pressurizing the fluid serving the discharge thereof. The invention provides that the actuator for acting upon the fluid reservoir operates with actuator sound wave-induced alternating pressure pulses.

Description

Title: Fluid Dispenser

description

The present invention relates to the preamble and thus deals with the generation of droplets of fluids, in particular in a hot fluid pressure device and the like.

There are a large number of applications in which fine droplets are generated in a controlled manner. These include, for example, ink printers in which ink is sprayed from a supply onto a paper or the like in order to print texts, graphics, etc. A number of techniques are known to achieve a more precise printed image.

It has also already been proposed to dispense hot fluids, in particular metal solder or the like, drop by drop from a hot fluid supply in order to build up the structures required from the hot fluid. One application is found, for example, in the production of solder bumps, which can form a connection between the corresponding contact area on the silicon piece forming the processor and a further chip or a holder or the like for contacting semiconductor chips such as processors and the like which the chip is cast in or fixed in some other way.

The problem now is that, especially for the applications mentioned, a very high level of precision and accuracy of the position and

Size of droplets to be dispensed is required. This is countered by problems in that the hot fluid is only in heated state can be output, which means that the entire arrangement required for the output must be brought to a correspondingly high operating temperature. Since different materials are required for individual parts of the device from which the hot fluid is dispensed, thermal stresses and strains very often occur. These reduce the desired precision when, as is typical, hot fluid droplets are dispensed from a hot fluid supply in a hot fluid supply chamber, which is a

Has 10 membrane-like thin walls and which in turn acts on an actuator. While the actuator presses on the membrane, hot fluid is pressed out of an outlet. It is now understood that different dimensions, etc., of the different parts of the hot fluid dispenser result in

15 can, or must, that an actuator path or force curve that is required per se cannot be generated, at least not in the often required exact reproducibility.

20 In order to supply hot fluid droplet dispensers to a broader application, it is also desirable to enable inexpensive design, problem-free control and / or rapid repetitive dispensing of hot fluid droplets. It would be desirable to at least

25 some of these problem areas at least partially to provide an at least partial solution. In addition, it is clear that, in addition to options for dispensing hot fluid droplets, new dispensing options for non-hot fluids are also desirable.

, 30 The object of the present invention is to provide something new for commercial use. The solution to this problem is claimed in an independent form. Preferred embodiments can be found in the subclaims.

The present invention thus proposes a first

The basic idea is to provide a fluid droplet dispenser with a fluid supply opened for dispensing hot fluid droplets and with an actuator for applying fluid pressure to effect fluid dispensing, in which the actuator is designed to apply alternating pressure pulses induced by actuator sound waves.

A first essential basic idea of the invention thus consists in the knowledge that hot fluid droplets can be dispensed much more precisely if the supply, from which they are pressed out of dispensing openings by pressure impulses, is acted upon by alternating pressure impulses, that is to say both overpressure and underpressure in pulse-like form is exercised on the fluid supply. This is preferred to a monopolar pressurization, in which only an overpressure pulse is applied and, if necessary, a slight, slow undershoot can occur when the actuator is reset. It is noteworthy that not only the feasibility of applying alternating pressure impulses, as was known in principle from ink printers, also had to be recognized for other fluid output devices, which is the case for general fluids because of the often typically completely different droplet parameters, for example with regard to droplet density, mass, viscosity etc. was not to be expected, but that, moreover, a special type of alternating pressure pulse generation is also taught, namely by sound waves that actuator-induced in a solid, that is, by \ generated. This type of sound wave generation in a solid and the coupling of the solid into the fluid are to be strictly differentiated from the known generation of sound waves in the fluid itself. The present invention, because of the sound wave generation in the solid which is remote from the fluid, also allows fluids with high or if necessary, spray out very low temperatures without affecting the actuator. The solid body can typically be identical to the actuator; then the sound waves pass through the actuator, which is excited to generate them, and finally hit the fluid.

In a preferred variant, the fluid will be a hot fluid and preferably will have a temperature of at least 150 ° C .; the temperatures are preferably still above.

They can be around 350 ° C. or be raised further, the resulting temperature of the actuator being critical, for example if it is formed as preferably as possible as a piezoelectric actuator whose Curie temperature limits the maximum permissible operating temperature. This is possible because the fluid can be located away from the location at which the actuator generates sound waves; the distance between the fluid and the active actuator area is then thermally insulated.

A molten metal is typically used as the hot fluid. This metal can in particular be a solder or a solder alloy, so that the hot fluid droplet dispenser can in particular be part of a solder printhead, such as can be used for the contacting of semiconductor chips. In a preferred variant, the (hot) fluid supply is formed as a chamber, which can be heated in particular from one side in order to heat or maintain the fluid to the desired temperature, and which from the other side in particular alternating pressure pulses can be applied to a membrane wall by the actuator.

A preferred variant is obtained if the chamber is provided with discharge openings which are provided as capillary openings with a diameter between in particular 20 to 150 μm. In a practical embodiment, a capillary opening of around 70 μm was used. However, it is clear that, especially when semiconductor structures become smaller, an adaptation of the contact areas is also desired, and thus the droplet sizes of solder droplets provided for this purpose are to be reduced, which is possible by adapting the output opening sizes. Furthermore, it is clear that when we speak of a discharge opening diameter, this size refers to an equivalent area, without the need for a circular discharge opening. In particular, it should be pointed out that instead of round openings, output openings with a square cross section can also be obtained, for example, by etching the openings in silicon structures and / or using high-energy laser beams.

The actuator will typically be designed as a piezoelectric actuator. It can have lamellar structures such as are known per se, for example, from DE 199 31 110 AI. In these piezoelectric actuators, sound waves can be generated as required. It should also be pointed out here that they are generally concerned with hot fluid droplet production. the earlier patent applications of the present inventor are incorporated in its entirety for purposes of disclosure, the present Anmeldung- ^'.

In a preferred variant, the actuator is formed in such a way that it has at least one active and at least one inactive region, which is different from the end of action at which the actuator acts on the particular membrane-like delimitation of the fluid supply.

As an alternative to providing an active and an inactive area, it would be possible to provide a continuously active actuator which is excited in different ways, which could happen in the case of a piezoelectric actuator with a lamellar structure, for example by the fact that electrical electrodes are offset in time and / or in different directions Pulses are applied to it, although the use of unipolar electrical pulses is highly preferred.

It is possible for the actuator to have a plurality of active areas, which can be advantageous if very strong pulses and / or pulses running in quick succession or alternating pulses are to be generated. The actuator itself can be monolithic, as is known per se for actuators.

In a particularly preferred embodiment, the active area or at least one active area is spaced from one or the end of the actuator, which faces away from the fluid supply. The actuator end side can therefore be designed to reflect a shock wave or sound wave extending in the actuator. In other words, the actuator is preferred Variant generates a longitudinal wave in an active area, this is reflected at the end of the actuator and then, in particular by superimposing further pulses from the active area, a shock wave shape running through the actuator is achieved, which results in the desired alternating pressure application. While it is possible in principle to design an actuator in such a way that it generates both an overpressure and a vacuum pulse in a (hot) fluid supply, even without resorting to a piezoelectric actuator, the arrangement described as preferred is shown in which are generated in the actuator by piezoelectric shock or sound waves, from which the required alternating pressure pulses are obtained by superimposing several actuator excitations, particularly preferred because they allow the hot fluid droplet dispensing device to be designed in a structurally and very simple manner.

In a preferred variant, the shock and / or sound wave reflection is achieved by additional masses, in particular at the end facing away from the fluid supply, such as hammer-shaped thickenings or the like, and / or by the actuator stretching at least almost unhindered and / or can shorten, so not firmly attached, in one piece with a rear support or z. B. is determined in its position only by a sliding guide. This arrangement leads on the one hand to the desired reflection at the end of the actuator with or without phase reversal of shock and / or sound waves running in the interior of the actuator and also reduces the occurrence of thermal stresses in the actuators, the thermal stresses and the like in turn improving the precision and / or droplet output accuracy is achieved. It is clear that if the acoustic impedance to the fluid supply or the fluid supply wall is mismatched, an impedance jump for the acoustic impedance could also occur there. Typically, however, constructive measures are taken, for example to adjust the impedance of the actuator and the transition point to the hot fluid system, in order to bring about an extensive coupling of the sound energy into the hot fluid supply. At the end of the actuator facing away from the fluid side, on the other hand, a strong impedance transition is typically provided in particular in order to allow shock and / or sound waves running there to be reflected. On the one hand, a jump point to large impedances is possible in principle, at which sound waves are reflected without a phase change; Such an impedance jump can be brought about by an additional mass attached at the end. A jump point to very small impedances can shock and / or sound waves, however, likewise reflect, with the difference, the phase of the wave by 180 ° that ^this' change. Such an impedance jump is structurally particularly easy to achieve in that the actuator end is attached to air and is not fastened. The jump in sound impedance does not have to be exactly as large as it results in an actuator that is freely movable in air, because cooling fluids could be provided that cool the actuator and, as will be immediately clear, it is possible, even at the front end, that Sound impedances cannot be matched exactly to those of the hot fluid supply wall membrane. However, the larger change at the end facing away from the hot fluid supply ensures that at least a predominant part of the pressure impulses act on the hot fluid supply while being largely reflected on the other side. The actuator will typically be in pressure and / or tensile connection with the (hot) fluid chamber wall, ie be in engagement with it in such a way that both overpressure and underpressure pulses can be transmitted. In the case of the typically always open, valve-free drop-on-demand systems, only pulse-like pressure pulses are generated, but not static or quasi-static pressures. However, it should be mentioned that overpressure or underpressure pulses are also mentioned if the actuator per se already exerts a slight overpressure on average, which is only reduced in the case of underpressure pulses. Such a design could be advantageous if it is only to be achieved that the hot fluid withdraws somewhat from a capillary opening before the actual ejection, but a very high pressure is required for squeezing out of the hot fluid chamber wall.

The chamber wall, in preferred variants, in particular for solder printheads, will consist of silicon material which can be structured particularly well and, moreover, is sufficiently temperature-resistant. The use of other materials should also be mentioned as possible.

In a preferred variant, the actuator is at least largely thermally decoupled from the hot fluid supply. This can be done, for example, by a tip-like tapering of the actuator end acting on the hot fluid supply wall and / or by thermally insulating coatings on the hot fluid supply wall and / or the actuator tip. It is clear that regardless of the thermal decoupling that is desired, adequate adjustment of the sound impedance must be ensured. The voltage supply with which piezoelectric actuators are excited can, in particular, exclusively generate unipolar or, at least slightly undershoot, at least largely unipolar pulses. This allows a particularly cost-effective configuration of the voltage supply, which only has to be able to output sufficiently short and / or strong voltage pulses that are output in the required chronological order to the actuator or the active actuator area or areas.

Protection is also claimed for a method for (hot ') ^' fluid droplet delivery, in which the (hot) fluid supply is subjected to alternating pulses.

The invention is described below only by way of example with reference to the drawings. This is shown by:

1: a hot fluid droplet dispenser according to the present invention; 2: an illustration of the pressure wave course in the actuator; 3: the alternating pressure pulse curve occurring at the hot fluid supply; Fig. 4: Variants of the actuator design.

According to FIG. 1, a hot fluid droplet dispenser, generally designated by 1, with an hot fluid supply 3 opened at an opening 2 for dispensing hot fluid droplets, comprises an actuator 4, which is designed to act on the hot fluid reservoir with sound wave-induced alternating pressure pulses generated by this actuator. In the present case, the hot fluid droplet dispenser 1 serves to dispense solder alloy droplets with a high repetition frequency and high accuracy. It is movably arranged in a suitable holder, which serves as a sliding guide (not shown).

The opening 2 is formed as a capillary opening in a structured silicon element, as is known per se in the prior art, and is dimensioned here for dispensing hot fluid droplets with a diameter of 70 μm. The opening is arranged transversely to the longitudinal direction of the actuator for hot fluid ejection.

The hot fluid supply 3 is arranged in a silicon chamber 3a, which has a silicon membrane 3b toward the actuator 4 and which communicates with a larger hot fluid supply (not shown) through an elongated throttle opening. The hot fluid chamber 3a is arranged on a carrier which is formed here from Pyrex glass 3c and which is heated from the side facing away from the actuator 3d to the desired operating temperature of z. B. 350 ° C is brought.

The actuator 4 is constructed as a piezoelectric lamella actuator in a monolithic manner, as is known per se, and thus also has a tip 4a which adjusts the sound impedance here and in which the tensile and pressure-resistant transition to the membrane wall 3b takes place. In a departure from known actuators, however, only a partial area 4b of the actuator, which is shown bright in FIG. 1, is acted upon by a unipolar voltage, as shown by arrow 5. This individual active area according to FIG. 1 is spaced from the end 4c of the actuator, which faces away from the hot fluid supply, and from the active tip 4a. Examples of practical realizations of the breadth of a single An active area 4b, the actuator tip 4a, the area in between 4e and the distance between the active area 4b and the end 4c are shown by the arrows a, b, c, d in FIG. 2. It should be pointed out that the dimensioning of these elements can be used to change the pulse running times and the force curves that arise.

The actuator 4 is held in the rear area β by a sliding guide that guides the actuator without significant impairment of its mobility, that the joint between the actuator _... 4 and the diaphragm wall 3b cannot act as a stressful moment, since the sliding guide 6 prevents vertical movements, but allows shock and / or sound waves that run through the actuator 4 forwards or backwards to pass unhindered and undamped.

The arrangement is used as follows:

The fluid is first heated up to the required temperature in the usual way. A voltage U is then applied to the active region 4b for a time t = to to t ₂ (cf. FIG. 2). This contracts when the voltage pulse is applied and there is a contraction wave running through the actuator, which on the one hand runs in the direction of the front tip 4a and on the other hand in the direction of the rear end. At the rear end, a reflection with phase reversal occurs due to the sudden reduction in impedance. The contraction wave is converted into a pressure wave, ie the material is expanded instead of the previous contraction. While the reflected pulse runs through the active area as an expansion wave at time t ₂ , the voltage at the actuator is reduced again. connected. As a result, the actuator area 4b expands again and the expansion wave, which runs in the direction of the actuator tip, is raised. It is obvious that the required pulse duration of the voltage pulse U can be determined from the propagation times of the sound wave through the actuator, the extension of the active area and the distance d 'of the active area to the free end 4c of the actuator, and it is also clear that a permanent pulse does not have to be applied exclusively. Rather, possibly a pulse would be applied to the other flank form and / or a ^'train of pulses to excite, if this would be desired, with a certain pulse development could be given.

At time t ₃ , the contraction wave from switching on the voltage pulse at time t ₀ almost ran to the actuator tip, the wave reflected at the rear end of the actuator is overlaid with the relaxation-generated pressure wave and has left the active area in the direction of the actuator tip while the relaxation-generated wave that runs through the actuator in the direction of the free actuator end 4c is reflected at this free actuator end 4c, which in turn leads to a vacuum wave in the actuator due to the phase jump. If these sound wave packets now run in the direction of the actuator tip, as indicated in the partial images t, ts, t ₆ , t ₇ , ts in FIG. 2, an underpressure initially results on the actuator tip or the hot fluid membrane 3b, then, briefly Time later, a much greater overpressure, and then, some time later, another underpressure.

This acoustic pressure curve leads to that in the

When the nozzle capillary fluid material is withdrawn somewhat, the fluid is then drawn out of the quasi-predefined position high pressure is ejected and then, almost immediately afterwards, any hot fluid still present in the capillary opening is withdrawn again. This contributes to a very exact repeatability, regardless of capillary effects, expansions etc. and allows high output frequencies.

In the time until the next shock, material flows from the supply into the hot fluid chamber.

It is obvious that other pulse shapes can be obtained by suitable pulse shapes and / or actuator area arrangements, if this is desired. The manner in which this can be done with simple means will also be evident from the foregoing. A first variant of the actuator arrangement is shown in FIG. 4a, according to which the active area 4b 'is chosen to be larger and, in addition, an inertia-increasing thickening 4c' is provided at the free actuator end 4c '. 4b shows that a plurality of active areas 4b 'can be provided separately from inactive areas 4e' '.

Claims

claims

1. Fluid droplet dispensing device with a fluid supply which is open for dispensing fluid droplets and with an actuator for pressurizing the fluid causing fluid dispensing, characterized in that the actuator is designed to apply alternating pressure pulses induced by actuator sound waves.

2. Fluid droplet dispenser according to the preceding claim, characterized in that the fluid has a temperature of at least 150 ° C, preferably around 350 ° C or above.

3. Fluid droplet dispenser according to one of the preceding claims, characterized in that the hot fluid is a molten metal.

4. Fluid droplet dispenser according to the preceding claim, characterized in that the hot fluid is a solder or a solder alloy.

5. Fluid droplet dispenser, characterized in that it is part of a solder printhead.

Fluid droplet dispenser according to one of the preceding claims, characterized in that the hot fluid supply opened for dispensing hot fluid droplets is formed as a chamber with capillary openings.

7. Fluid droplet dispenser according to the preceding claim, characterized in that the chamber is connected to a larger hot fluid storage area.

8. Fluid droplet dispenser according to one of the two preceding claims, characterized in that the chamber has at least one dispensing opening which is dimensioned for dispensing fluid droplets with a diameter of approximately 20-150 μm, in particular 70 μm.

9. Fluid droplet dispenser according to one of the preceding claims, characterized in that the actuator is formed as a piezoelectric actuator.

10. Fluid droplet dispenser according to one of the preceding claims, characterized in that the actuator is formed with a lamella structure.

11. Fluid droplet dispenser according to one of the preceding claims, characterized in that the actuator has at least one active and at least one inactive area which is different from the end of the action.

12. Fluid droplet dispenser according to one of the preceding claims, characterized in that the actuator has a plurality of active areas.

13. Fluid droplet dispenser, characterized in that the actuator is formed monolithically.

14. Fluid droplet dispenser according to one of the preceding claims, characterized in that an active ver area is separated from an actuator end side facing away from the fluid supply and the actuator end side is designed for shock and / or sound wave reflection.

15. Fluid droplet dispenser according to one of the preceding claims, characterized in that in the vicinity of the actuator end facing away from the fluid supply, a region of low acoustic impedance is provided, which is formed in particular by air, gas or vacuum.

16..fluid droplet dispenser according to one of claims 1-14, characterized in that an additional mass for increasing the sound impedance is arranged at the actuator end.

17. Fluid droplet output device, characterized in that the actuator is designed to generate alternating pressure pulses running through it as tensile and / or pressure wave pulses.

18. Fluid droplet dispenser according to one of the preceding claims, characterized in that the sound impedance at the end facing away from the fluid supply makes a jump larger by at least a factor of 2, preferably by at least a factor 5, than at the fluid supply.

19. Fluid droplet dispenser according to one of the preceding claims, characterized in that the actuator is in a tensile and / or .compression-resistant connection with an in particular membrane-like fluid chamber wall.

20. Fluid droplet dispenser according to one of the preceding claims, characterized in that the chamber wall consists of silicon.

21. Fluidtröpfenausgabevorrichtung according to one of vorherge- ^• Henden claims, characterized in that the actuator is assigned a sliding guide.

22. Fluid droplet dispenser according to one of the preceding claims, characterized in that the actuator is at least largely decoupled thermally from the fluid supply.

23. Fluid droplet output device, characterized in that a voltage supply is provided for the actuator excitation, which is designed to generate unipolar and / or at least substantially unipolar pulses.

24. Fluid droplet output device, characterized in that the voltage supply is designed to generate pulses in such a sequence that a first pressure surge generated by reflection at the rear end of the actuator occurs in and / or in the active area with an actuator contracted by expansion of a previously contracted one - Overlaid area received pressure pulse.

25. A method for dispensing hot fluid droplets from a hot fluid supply by applying alternating pressure pulses to a hot fluid supply, the alternating pressure pulses first applying a negative pressure to the hot fluid supply, then an increased pressure and then again a negative pressure on the hot fluid supply.