Dispensing device for molten metal and method for dispensing molten metal

Abstract

A syringe (3) has a storage part (3a) that holds molten metal (1), a dispensing nozzle (3b) that dispenses the molten metal (1) stored in the storage part (3a), an opening (3c) extending from the dispensing nozzle (3b), and a bypass path (3d) that connects the opening (3c) and the storage part (3a) and through which the molten metal (1) flows. A heating device (5) is provided around the syringe (3) and heats the molten metal (1) to keep it in a molten state. A shaft (4) slides within the syringe (3) to apply pressure to the molten metal (1) stored within the storage part (3a). A cover (9) is provided on the opening (3) and opens and closes. The opening (3c) is positioned above an upper surface of the molten metal (1) within the syringe (3).

Description

Area

[0001] The present disclosure relates to a molten metal dispensing apparatus and a molten metal dispensing method for dispensing a molten metal. background

[0002] Molten metal dispensers are used, for example, to apply molten metal to electrodes of semiconductor devices such as Si chips and SiC chips for connecting them to base plates, lead frames, and the like (see, for example, PTL 1). Typical molten metal dispensers include, for example, a syringe and a stem formed of glass. The stem is pulled upward while the tip end of the syringe is immersed in molten metal, creating negative pressure inside the syringe to draw in the molten metal. Subsequently, the tip end of the syringe is moved to a predetermined position, and then the stem is pushed down to pressurize the interior of the syringe to dispense the molten metal. Citation listPatent literature

[0003] [PTL 1] JP 2014-004567 A SummaryTechnical problem

[0004] Recent shifts from Si chips to SiC chips and higher packaging densities are leading to smaller semiconductor devices. Smaller semiconductor devices result in smaller interconnect area. In contrast, in power semiconductor devices and the like, molten metal is used instead of metal wire bonding to connect the main current paths to achieve higher currents, longer lifetimes, and higher reliability. In other words, molten metal dispensed onto the interconnect on the semiconductor device directly connects the external electrode and the semiconductor device. The smaller interconnect area also reduces the amount of molten metal required for each interconnect.In other words, it is necessary to stabilize the amount of molten metal to be dispensed per dispensing operation, that is, the amount of supply per dispensing operation, with greater accuracy. The molten metal dispensing device dispenses molten metal in accordance with the volume change in the syringe as the shaft moves up and down. Unfortunately, controlling the dispensing amount was difficult, and the dispensing amount per dispensing operation was unstable.

[0005] The present disclosure has been made to solve the above-mentioned problem, and it is an object of the disclosure to obtain a molten metal discharge apparatus and a method for discharging a molten metal which can control a discharge amount of the molten metal with high accuracy. Solution to the problem

[0006] A molten metal dispensing device according to the present disclosure includes: a syringe having a storage portion that stores molten metal, a dispensing nozzle that dispenses the molten metal stored in the storage portion, an orifice diverging from the dispensing nozzle, a bypass path that connects the orifice and the storage portion and through which the molten metal flows; a heater that is provided around the syringe and heats the molten metal to keep the molten metal in a molten state; a shaft that slides inside the syringe to apply pressure to the molten metal stored in the storage portion; and a cover that is provided on the orifice and opens and closes, the orifice being positioned above an upper surface of the molten metal inside the syringe. Advantageous effects of the invention

[0007] In the present disclosure, a bypass path is provided connecting the opening other than the discharge nozzle and the storage portion. Opening the cover provided at the opening during the discharge operation allows a certain amount of molten metal to flow into the bypass path while the molten metal is discharged from the discharge nozzle. This allows the molten metal to be discharged at a volume smaller than the volume change in the syringe due to the downward movement of the stem, thus controlling the discharge amount of molten metal with high precision. Short description of the characters Fig. 1 is a cross-sectional view showing a suction operation of a molten metal of a molten metal discharge device according to Embodiment 1. Fig. 2 is a cross-sectional view showing the molten metal discharging operation of the molten metal discharge device according to Embodiment 1. Fig. 3 is a cross-sectional view showing the suction operation of the molten metal of the molten metal discharge device according to Embodiment 2. Fig. 4 is a cross-sectional view showing the molten metal discharging operation of the molten metal discharge device according to Embodiment 2. Description of the embodiments

[0008] A molten metal discharge apparatus and a molten metal discharge method according to embodiments of the present disclosure will be described with reference to the figures. The same components are denoted by identical reference numerals, and repeated descriptions thereof may be omitted. Embodiment 1.

[0009] Fig. 1 is a cross-sectional view showing a suction operation of a molten metal of a molten metal discharge device according to Embodiment 1. Fig. 2 is a cross-sectional view showing the molten metal discharge process of the molten metal discharge device according to Embodiment 1. A molten metal discharge device 100 discharges molten metal 1 to a connecting part of a component 2. The discharged molten metal 1 connects the component 2 and other members such as a lead frame. The molten metal 1 is, for example, a solder material having Sn, Pb, or the like as a main component and containing an additive element such as Ag or Cu.

[0010] The component 2 may be, for example, an IGBT, a diode, or a reverse conducting IGBT formed of silicon (Si); it may be a MOSFET or a Schottky diode formed of a material with a wider band gap than Si, such as silicon carbide (SiC) or gallium nitride (GaN); or it may be merely a metal lead frame formed of copper or the like, or a circuit pattern on an insulating substrate for forming a circuit. The semiconductor device and the metal lead frame may be connected by positioning a metal lead frame with a hole on top of the semiconductor device and discharging the molten metal 1 through the hole.

[0011] The molten metal dispenser 100 includes a syringe 3, a shaft 4, and a heater 5. Note that the molten metal dispenser 100 includes a moving mechanism (not shown) having three axes of X, Y, and Z orthogonal to each other for reciprocating between a molten metal storage tank 6 and the component 2.

[0012] The syringe 3 includes a storage portion 3a that stores the molten metal 1, a discharge device 3b that discharges the molten metal 1 stored in the storage portion 3a, an orifice 3c that diverges from the discharge nozzle 3b, and a bypass path 3d that connects the orifice 3c and the storage portion 3a and through which the molten metal 1 flows. The orifice 3c is positioned above the surface of the molten metal 1 within the syringe 3. The material of the syringe 3 is preferably a material with which the molten metal 1 does not form a diffusion bond, such as glass or ceramic, but is not limited thereto.

[0013] The heater 5 is provided around the syringe 3 and heats the molten metal 1 inside the syringe 3 to maintain it in a molten state. A temperature control unit 7 controls the heater 5 to maintain the molten metal 1 at a temperature equal to or greater than its melting point. The heater 5 can heat the molten metal 1 by radiation, induction heating, convection heat transfer, or the like.

[0014] The shaft 4 slides within the syringe 3 to exert pressure on the molten metal 1 stored within the storage portion 3a. The shaft 4 has a sealing portion 8 for isolating the molten metal 1 within the syringe 3 from outside air. A cover 9 is provided over the opening 3c.

[0015] The control unit 10 controls a drive unit 11 to slide the shaft 4 up and down, and another drive unit to open and close the cover 9. The control unit 10 can individually control the sliding of the shaft 4 and the opening and closing of the cover 9. The drive unit 11 includes a mechanism such as an actuator, an air cylinder, and a single-axis robot.

[0016] When the cover 9 is closed, the bypass path 3d is isolated from outside air. Only when the cover 9 is opened can outside air enter and exit from the bypass path 3d. The cover 9 may be an object that can be controlled to open and close, such as an air cylinder or an actuator, or a switching valve such as a general shutoff valve or a throttle valve. Note that a case where only one bypass path 3d is provided is shown, but a plurality of bypass paths 3d may be provided for one syringe 3.

[0017] The molten metal 1 within the syringe 3 is sucked into the molten metal storage tank 6. The heater 12 is provided around the molten metal storage tank 6, and it heats the molten metal 1 within the molten metal storage tank 6 to maintain it in a molten state. A temperature control unit 13 controls the heater 12 to maintain the molten metal 1 at a temperature equal to or higher than its melting point. To prevent the surface of the molten metal 1 from oxidizing, the entire molten metal storage tank 6 is preferably disposed in an atmosphere such as an inert gas.

[0018] The following describes the molten metal suction operation and the discharge operation of the molten metal discharge device 100 according to the present embodiment.

[0019] First, as in Fig. 1, the discharge nozzle 3b of the syringe 3 is brought into close contact with the liquid surface of the molten metal 1 within the molten metal storage tank 6. Subsequently, while the cover 9 of the bypass path 3d of the syringe 3 is closed, the shaft 4 is pulled upward. As a result, the pressure in the syringe 3 decreases, and the syringe 3 draws the molten metal 1 inward (step 1).

[0020] Next, the molten metal discharge device 100, which includes the syringe 3, the shaft 4, and the temperature control unit 7, moves using the three-axis movement mechanism (not shown), and positions the discharge nozzle 3b above the component 2 such as a semiconductor device (step 2).

[0021] Next, as in Fig. 2, while the cover 9 of the bypass path 3d of the syringe 3 is opened, the stem 4 is pushed down to discharge the molten metal 1 from the discharge nozzle 3b onto the component 2 (step 3). Note that the cover 9 of the bypass path may be open for the entire period when the stem 4 is pushed down, or the cover 9 may be open only for part of the period when the stem 4 is pushed down. Finally, the discharged molten metal 1 is cooled and solidified (step 4). This allows the component 2 and other members to be bonded by the molten metal 1.

[0022] As described above, in the present embodiment, a bypass path 3d is provided connecting the opening 3c, which deviates from the discharge nozzle 3b, and the storage part 3a. Opening the cover 9 provided at the opening 3c during the discharge operation of the molten metal allows a certain amount of the molten metal 1 to flow into the bypass path 3d while the molten metal 1 is discharged from the discharge nozzle 3b. This makes it possible to discharge the molten metal 1 with a volume smaller than the amount of volume change in the syringe 3 due to a downward movement of the shaft 4, thereby controlling the discharge amount of the molten metal 1 with high precision.

[0023] Note that it is also possible to control the discharge amount of the molten metal 1 from the discharge nozzle 3b by discharging the molten metal 1 that has passed through the bypass path 3d to the outside and adjusting the flow rate with a flow control valve. However, the control accuracy of the discharge amount decreases due to the thermal resistance of the flow control valve and thermal expansion at high temperatures. In the present embodiment, however, the orifice 3c is positioned above the surface of the molten metal 1 inside the syringe 3. As a result, the molten metal 1 that has passed through the bypass path 3d is not discharged to the outside from the orifice 3c, so this problem does not occur.

[0024] Furthermore, the control unit 10 individually controls the sliding of the shaft 4 and the opening and closing of the cover 9. This allows the cover 9 to be opened depending on the amount of molten metal 1 to be discharged, and allows the molten metal 1 to flow into the bypass path 3s for any desired period of time. For example, instead of opening the cover 9 for the entire period of the molten metal discharge, the cover 9 can be opened only during a portion of the molten metal discharge. This allows the discharge amount of the molten metal 1 to be controlled with high precision. Embodiment 2.

[0025] Fig. 3 is a cross-sectional view showing the suction operation of the molten metal of the molten metal discharge device according to Embodiment 2. Fig.4 is a cross-sectional view showing the molten metal discharging operation of the molten metal discharge device according to Embodiment 2.

[0026] In the present embodiment, a flow control valve 14 is provided at the opening 3c of the bypass path 3d instead of the cover 9. The flow control valve 14 continuously adjusts the flow of air discharged from the inside of the bypass path 3d to the outside. The flow control valve 14 is, for example, a diaphragm valve or a throttle valve. The other components are identical to those in Embodiment 1.

[0027] By closing the flow control valve 14 while discharging the molten metal 1, the air pressure within the bypass path 3d increases with a rise in the liquid level in the bypass path 3d, acting as a resistance to the rise in the liquid level in the bypass path 3d. In contrast, opening the flow control valve 14 allows a certain amount of the molten metal 1 to flow into the bypass path 3d while discharging the molten metal 1 from the discharge nozzle 3b. Subsequently, opening the flow control valve 14 while adjusting the flow rate releases the compressed air and controls the rate of rise of the liquid level in the bypass path 3d. This makes it possible to precisely adjust the flow rate of the molten metal 1 flowing into the bypass path 3d, enabling control of the discharge amount of the molten metal 1 with even higher accuracy. List of reference symbols 1 molten metal; 3 syringe; 3a storage part; 3b discharge nozzle; 3c orifice; 3d bypass path; 4 shaft; 5 heater; 9 cover; 14 flow control valve; 100 molten metal discharge device QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2014-004567 A

[0003]

Claims

[1] A molten metal dispensing device comprising: • a syringe comprising a storage part which stores molten metal, a discharge nozzle which discharges the molten metal stored in the storage part, an opening which deviates from the discharge nozzle, and a bypass path which connects the opening and the storage part and through which the molten metal flows; • a heater provided around the syringe which heats the molten metal to keep the molten metal in a molten state; • a shaft which slides within the syringe to exert pressure on the molten metal stored within the storage part; and • a cover provided on the opening and opening and closing, wherein • the opening is positioned above a surface of the molten metal within the syringe. [2] A molten metal discharge device according to claim 1, wherein opening and closing of the cover and sliding of the shaft are individually controlled. [3] The molten metal discharge device according to claim 1 or 2, wherein the cover is a flow control valve that adjusts a flow of air discharged from an inside of the bypass path to an outside. [4] A molten metal discharge device according to any one of claims 1 to 3, wherein the molten metal which has passed through the bypass path is not discharged from the opening to the outside. [5] A method of discharging a molten metal using the molten metal discharge device according to any one of claims 1 to 4, comprising: • Bringing the discharge nozzle of the syringe into close contact with a liquid surface of the molten metal within a molten metal storage tank and withdrawing the stem upward while the cover is closed to draw the molten metal into the syringe; and • Position the dispensing nozzle above a component and press down on the stem while the cover is open to dispense the molten metal from the dispensing nozzle onto the component. [6] A method of discharging a molten metal 5, wherein the cover is opened only during a period when the shaft is pressed downward.

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