Equipment and methods for solder pulse welding of workpieces

Abstract

This invention provides a device for pulse welding of workpieces with solder. According to the order of the welding wire's movement and position, it comprises, in sequence, a welding wire spool and traction wheel at the top, a welding wire passage pipe in the middle, a welding wire conveying mechanism at the bottom, and a horizontally placed workpiece conveying platform at the bottom. A DC high-voltage power supply is connected between the workpiece conveying platform and the wire feed wheel. The workpiece conveying platform and the workpiece are in electrical contact, and the driven wheel and the welding wire are in electrical contact. When the welding wire is pulled downwards by the wire feed wheel and contacts the workpiece on the workpiece conveying platform, the high temperature generated by the discharge instantly melts a section of the welding wire, forming a weld point on the workpiece. The workpiece of this invention is virtually free from melting and oxidation corrosion; the device consumes little energy, and the welding wire melts to form a weld point extremely quickly.

Description

Technical Field

[0001] This invention relates to a soldering technique for soldering solder to workpieces. Background Technology

[0002] In the microelectronics industry, lead frames and other solder components are mainly made of copper. Sometimes, a spot tinning or tin painting process is used to melt some solder on the surface of the copper to facilitate direct bonding with chips or chip leads in subsequent processes. However, melting requires high temperatures to dissolve the solder. If the high temperature of the solder component is maintained for a long time, the surface of the solder component is easily oxidized and corroded by oxygen in the air, affecting the electrical performance and appearance quality of the solder component.

[0003] Application number 202211127818.0 relates to the field of surface mount technology for semiconductor device lead frames, specifically a method for chip soldering. The method includes the following steps: heating and melting solder to obtain molten solder; placing the chip above the molten solder, and dipping the bottom surface of the chip in the molten solder to obtain a chip with the bottom surface coated with molten solder; placing the chip with the bottom surface coated with molten solder directly above a substrate island, parallel to the surface of the substrate island, for soldering. This invention requires preheating for soldering, the entire soldering process is heated, consumes a lot of heat energy, and the soldering temperature is generally high, making it prone to oxidation and corrosion.

[0004] Utility model application No. 202222399034.5 relates to a die-loading device, including a worktable and a guide rail disposed on the worktable. A laser heating assembly, a spot solder assembly, and a core-loading assembly are sequentially arranged on the worktable along the moving direction of the lead frame. This die-loading device uses a laser to instantly heat the die-loading area of ​​the lead frame for die loading. Although this avoids oxidation of the lead frame due to prolonged exposure to high temperatures in the guide rail, the laser generator is expensive, and it directly heats the workpiece while indirectly transferring heat to the spot solder, resulting in reduced thermal efficiency. Summary of the Invention

[0005] Purpose of the invention:

[0006] A device and method for solder pulse welding of workpieces that relies on instantaneous discharge to melt solder, consumes less energy, and prevents workpiece oxidation are provided.

[0007] Technical solution:

[0008] The equipment for pulse welding of workpieces according to the present invention comprises, in order of wire travel and position, a wire spool (which may be equipped with a support bracket) and a traction wheel (for pulling and guiding the wire) located at the top, a wire passage pipe located in the middle (the wire passage pipe is a vertically arranged section of pipe through which the wire travels), a wire conveying mechanism located at the bottom, and a horizontally placed workpiece conveying platform located at the bottom (for intermittently conveying workpieces, such as lead frames).

[0009] The welding wire conveying mechanism comprises a wire feeding wheel (consisting of a driving wheel and a driven wheel), a drive motor, etc. The driving and driven wheels have parallel axes of rotation and are essentially located in the same horizontal plane, with their surfaces tangential (leaving a gap for the welding wire to pass through). The driving motor drives the driving wheel, generating power, and the driving wheel rubs against the driven wheel, both rotating downwards from the inner side of their mating surfaces. The drive motor drives the driving wheel to rotate, causing the driven wheel to rotate, and the welding wire is drawn downwards between the two wheels.

[0010] A DC high-voltage power supply (which may be equipped with a power switch) is connected between the workpiece conveying platform and the wire feed wheel (such as the driven wheel, both made of metal). The workpiece conveying platform and the workpiece are in electrical contact, and the driven wheel and the welding wire are in electrical contact. The welding method for the above equipment is as follows:

[0011] After the welding wire comes out of the welding wire passage, it is pulled down by the wire feeder. The downward welding wire can contact the workpiece on the bottom workpiece conveying platform and touch the point where solder is needed.

[0012] At the moment of contact, the power supply, driven wheel, welding wire, workpiece and workpiece conveying platform form a connected circuit, which will discharge at the touching tip instantly. The high temperature generated by the discharge instantly melts a section of welding wire (the melting point of solder wire is much lower than that of copper, the welding wire melts before the workpiece, the workpiece is not easily eroded by high voltage; moreover, the workpiece is only heated at a very small solder joint, and other parts are not heated, so it is not easy to oxidize and corrode), leaving molten solder on the workpiece to become the solder joint.

[0013] Shortly after a section of the welding wire has melted, the circuit is broken, preventing further melting of the wire. The wire continues to move downwards under the drive of the motor. Simultaneously, the workpiece is intermittently moved to the next position on the welding platform, where the welding wire touches the workpiece again, melting a section and forming the next solder joint. This process is repeated, with intermittent soldering forming different solder joints at different points.

[0014] In addition, a high-voltage pulse capacitor is preferably connected in parallel with the high-voltage power supply. When the above circuit is not connected, the high-voltage capacitor is charged by the high-voltage DC power supply and stores a certain amount of electricity. When the contact circuit is turned on, the high-voltage capacitor will also release the stored electricity instantly, assisting in melting the solder wire of the contact section, generating more heat, melting more solder wire, and forming the required number of solder joints.

[0015] Further preferred, a cooling pipe is pre-embedded in the driving wheel or driven wheel, in which coolant is stored or flows, so as to cool the welding wire coming down from above or a small section below, to prevent excessive heat transfer from the molten welding wire below, to prevent wire breakage above, and to ensure that the welding wire can be released in contact with the downward flow.

[0016] Both the drive motor and the welding workpiece conveying platform are connected to the controller, which controls the start and stop of both the motor and the platform. The downward speed of the welding wire (drive motor speed) and the translational speed of the workpiece need to be calculated and tested to determine the controller's program.

[0017] By taking into account parameters such as the speed V1 of the workpiece travel, the speed V2 of the welding wire descending, the melting point of the welding wire, the resistance of the circuit, the resistance (R) of a section of the welding wire (length L, cross-sectional area S) melted, the specific heat c of the welding wire, the mass m of a section of the welding wire melted, and the contact time t, the required voltage U of the high-voltage power supply can be calculated as (220-800V), and the capacitance C of the high-voltage capacitor can be calculated as (200μF-20000μF).

[0018] The heat required to melt the welding wire: Q1 = cm, the heat generated by contact: Q2 = U 2 t / R, where R=ρL / S, t=L / V2.

[0019] By calculating Q1=Q2, the voltage of the power supply can be determined.

[0020] When a high-voltage capacitor is present, the stored charge Q3 = 1 / 2CU 2

[0021] Q1 = Q2 + Q3. At this point, touching the wire once can melt a longer section of the welding wire, forming a larger weld joint.

[0022] Beneficial effects:

[0023] The weldment of this invention is basically not subject to melting or oxidation corrosion.

[0024] The majority of the workpiece is at room temperature, resulting in minimal energy waste and low energy consumption by the equipment. Because the welding wire is thin, the power required to drive the wire by the motor is also relatively low.

[0025] The heat from the discharge is concentrated on the welding wire, which makes the welding wire melt and form a weld point very quickly.

[0026] The weldment, which does not require heating, has no heating and cooling process, so the internal metallographic structure remains almost unchanged and the electrical properties are not degraded; there is almost no oxidation or discoloration, and the appearance quality is excellent.

[0027] By selecting different values ​​of the DC power supply voltage U and the capacitance C of the high-voltage capacitor, solder joints of different sizes can be obtained. The size of the obtained solder joints is relatively stable and uniform, making this invention suitable for mass production. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of component connections according to the present invention.

[0029] Figure 2 yes Figure 1 Circuit diagram of the medium- and high-voltage discharge section.

[0030] In the diagram, 1-welding wire feeding mechanism; 2-guide wheel; 5-welding wire spool; 6-support bracket; 7-welding wire passage pipe; 8-welding workpiece platform; 9-welding workpiece; 10-welding point; 11-DC power supply; 12-high voltage capacitor; 19-switch (whether the welding workpiece is in contact with the welding wire constitutes the switch); 20-drive motor; 21-drive wheel; 22-driven wheel; 30-welding wire. Detailed Implementation

[0031] like Figure 1 The equipment shown for pulse welding of workpieces has, in order of wire travel and position, a wire hopper 5 at the top, a wire travel pipe 7 in the middle, a wire conveying mechanism at the bottom, and a horizontally placed workpiece conveying platform at the bottom.

[0032] The wire feeding mechanism consists of a wire feeding wheel and a drive motor 20. The wire feeding wheel is composed of a driving wheel 21 and a driven wheel 22. The axes of rotation of the driving wheel 21 and the driven wheel 22 are parallel and are basically located in the same horizontal plane. The wheel surfaces of the driving wheel 21 and the driven wheel 22 are tangent. The driving wheel 21 is driven by the drive motor 20 to generate power. The driving wheel 21 rubs against the driven wheel 22, and the welding wire is pulled down from between the two wheels.

[0033] A 650VDC high-voltage power supply 11 is connected between the welding workpiece conveying platform and the wire feeding wheel, and a 1200VDC / 2500μF high-voltage pulse capacitor 12 is connected in parallel with the high-voltage power supply 11.

[0034] During operation, the following operational steps are performed:

[0035] (1) When the welding wire comes out of the welding wire passage pipe 7, it is pulled down by the wire feeding wheel, contacts the welding part 9 on the bottom welding part conveying platform, and touches the point where the solder is to be applied.

[0036] (2) At the moment of contact, an instant discharge occurs at the tip of the contact. The high temperature generated by the discharge instantly melts a 1-2cm long and 1.5mm diameter welding wire, leaving molten solder on the workpiece 9 to become the solder point 10.

[0037] (3) The circuit is broken within a short time after a section of welding wire is melted, and the welding wire cannot be melted by continued discharge;

[0038] Driven by the drive motor 20, the welding wire continues to move downwards. At the same time, the workpiece 9 is intermittently translated on the workpiece platform 8 to the next point. The welding wire touches the welding again, melts a length, and forms the next weld point 10 on the workpiece 9.

[0039] (5) By analogy, different solder joints 10 are formed at different points by intermittent soldering, which makes it easier to solder the chip on the solder joints 10 in the subsequent process.

Claims

1. A device for pulse welding of workpieces with solder, comprising, in order of the movement and position of the welding wire, a welding wire hopper (5) located at the top, a welding wire passage pipe (7) located in the middle, a welding wire conveying mechanism located at the bottom, and a horizontally placed workpiece conveying platform located at the bottom. The welding wire conveying mechanism consists of a wire feeding wheel and a drive motor (20). The drive motor (20) can drive the wire feeding wheel to rotate, causing the welding wire to be pulled down and contact the welding workpiece (9) on the welding workpiece conveying platform. Its features are: A DC high voltage power supply (11) is connected between the welding workpiece conveying platform and the wire feeding wheel. The welding workpiece conveying platform and the welding workpiece (9) are in electrical contact, and the driven wheel (22) and the welding wire are in electrical contact. A high-voltage pulse capacitor (12) with a capacitance value of C is connected in parallel with the DC high-voltage power supply (11). Cooling pipes are pre-embedded in the drive wheel (21) or driven wheel (22) for storing or flowing coolant to cool the nearby welding wire; Welding methods with the following sequence: (1) When the welding wire comes out of the welding wire passage pipe, it is pulled down by the wire feeding wheel and comes into contact with the workpiece on the bottom workpiece conveying platform, and touches the workpiece at the point to be welded. (2) At the moment of contact, the DC high voltage power supply (11), driven wheel, welding wire, welding workpiece and welding workpiece conveying platform form a connected circuit, which will discharge at the tip of contact in an instant. The high voltage pulse capacitor (12) will also release the stored electricity in an instant. The high temperature generated by the discharge will melt a section of welding wire in an instant, leaving molten welding wire on the welding workpiece to become a welding point. (3) If the circuit is broken shortly after a section of welding wire is melted, the welding wire cannot be discharged and melted again. The cooling pipes pre-embedded in the drive wheel or driven wheel are used to cool the area near the small section of welding wire coming down from above or below, to prevent the wire from breaking at the top and to ensure that the welding wire continues to be released downward under the drive of the drive motor. (4) The workpiece is intermittently moved to the next point on the workpiece platform, the welding wire touches the welding again, melts a length, and forms the next weld point on the workpiece; (5) By analogy, different weld points are formed by intermittent welding at different locations.

2. The apparatus for solder pulse welding of workpieces as described in claim 1, characterized in that: The voltage U of the DC high voltage power supply (11) is 220-800V, and the capacitance C of the high voltage pulse capacitor (12) is 200μF-20000μF.

3. The apparatus for solder pulse welding of workpieces as described in claim 1 or 2, characterized in that: The heat required for a section of welding wire to melt is Q1, the heat generated by the touch is Q2, and the charge stored in the high voltage pulse capacitor (12) is Q3. The voltage U of the DC high voltage power supply (11) and the capacitance C of the high voltage pulse capacitor (12) are selected to satisfy the relationship: Q1=Q2+Q3.

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