A soldering method for a large surge current transient voltage suppression diode

Abstract

The application discloses a welding method suitable for large-through-flow transient voltage suppression diodes, and a vertical vacuum welding furnace used in the welding method comprises a welding furnace body and a temperature controller, the welding furnace body comprises a furnace body base, a furnace body upper cover, a lower heating body, an upper heating body, a welding graphite plate, a welding graphite plate cover plate, a gas filling rod and a vacuum pumping pipe, the welding graphite plate is provided with an actual temperature thermocouple, and the welding graphite plate cover plate is provided with an upper heating body temperature control thermocouple; the welding method comprises the following steps: step a, placing a TVS diode between the welding graphite plate and the welding graphite plate cover plate; step b, vacuum pumping; step d, nitrogen filling; step e, heating and welding; and step f, cooling after vacuum pumping. The application can make the TVS diode generate uniform IMC intermetallic compounds between layers, that is, can improve the adhesion and mechanical strength between layers of the TVS diode, and can improve the current wave impact capacity and product reliability of the TVS diode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diodes, in particular to a welding method suitable for large-current transient voltage suppression diodes. BACKGROUND

[0002] Transient voltage suppression diodes, also known as TVS diodes, are electronic components used for protection, which can protect electrical equipment from voltage spikes introduced by wires. When used, when subjected to a high-energy transient overvoltage pulse, its working impedance can immediately drop to a very low on-state value, allowing a large current to pass through and clamping the voltage to a predetermined level, thereby effectively protecting precision components in electronic circuits from damage. As a commonly used circuit protection component, TVS diodes have the outstanding characteristics of fast action speed, high breakdown voltage precision and low impedance, with an action speed of 1.0 pS, a capacitance voltage precision controllable within ±10%, and can effectively and precisely protect the circuit; among them, large-current TVS can pass through 8 / 20us surge current of thousands of amperes to tens of thousands of amperes.

[0003] It should be noted that for transient voltage suppression diodes that require large current (i.e. large-current transient voltage suppression diodes), high-temperature lead-tin solder is required to completely solder the TVS die whole electrode to the conductive metal to reduce resistance. And in the packaging process of large-current TVS, TVS dies greater than 200 mils are required and multiple TVS dies are stacked to increase the operating voltage. Due to the large size and multiple layers of TVS dies, the existing welding method will cause uneven IMC intermetallic compound generation between the solder and the die due to uneven welding temperature in different areas during welding processing. Due to the characteristics of silicon semiconductor with high compressive strength and low bending strength, i.e. the brittleness of silicon semiconductor, the die will be broken down when a large current passes through. This situation is not significant in 10 / 1000us waveform, but it is more significant in 8 / 20us current wave impact or 7637 throw load thermal impact. Uneven IMC intermetallic compounds can cause brittle fracture failure of TVS dies during environmental testing, especially during temperature cycle testing.

[0004] In view of the above situation, it is necessary to improve the welding method of large-current transient voltage suppression diodes. SUMMARY

[0005] The present application aims at the deficiencies of the prior art and provides a welding method suitable for large-current transient voltage suppression diodes, which can generate uniform IMC intermetallic compounds between the solder and the TVS die and between the solder and the metal conductive layer, effectively improving the adhesion and mechanical strength between the layers of the large-current transient voltage suppression diode, and effectively improving the current surge capacity and product reliability of the large-current transient voltage suppression diode.

[0006] To achieve the above-mentioned purpose, the present application is realized by the following technical solutions.

[0007] A welding method suitable for large-current transient voltage suppression diodes, which adopts a vertical vacuum welding furnace.

[0008] The vertical vacuum welding furnace comprises a welding furnace body and a temperature controller, the welding furnace body comprises a furnace body base and a furnace body upper cover arranged on the upper end of the furnace body base, and the inside of the welding furnace body is shaped into a welding chamber surrounded by the furnace body base and the furnace body upper cover.

[0009] A lower heating body is arranged at the bottom of the welding chamber, and an upper heating body is arranged at the top of the welding chamber, and the lower heating body and the upper heating body are electrically connected to the temperature controller.

[0010] The welding chamber is embedded with a welding graphite plate arranged horizontally and transversely and a welding graphite plate cover plate located at the upper end side of the welding graphite plate, the welding graphite plate is provided with a real temperature thermocouple, and the welding graphite plate cover plate is provided with an upper heating body temperature control thermocouple, and the real temperature thermocouple and the upper heating body temperature control thermocouple are electrically connected to the temperature controller.

[0011] The welding furnace body is provided with a gas filling rod extending into the welding chamber and a vacuum pipe for vacuumizing the welding chamber.

[0012] The welding method suitable for large-current transient voltage suppression diodes comprises the following steps, specifically:

[0013] Step a, placing the TVS diode between the welding graphite plate and the welding graphite plate cover plate, the TVS diode having a plurality of TVS dies and a plurality of conductive metal layers, all the TVS dies and all the conductive metal layers being arranged in turn and staggered from top to bottom, and the adjacent TVS dies and conductive metal layers having lead-tin solder therebetween.

[0014] Step b, starting the vacuumizing equipment and vacuumizing the welding chamber through the vacuum pipe, the welding chamber being vacuumized to below 1000 Pa.

[0015] Step d, after the vacuumizing action is completed, nitrogen is filled into the welding chamber through the inflation rod, and the nitrogen is filled to above the standard atmospheric pressure;

[0016] Step e, the lower heating body and the upper heating body are started by the temperature controller, the heat generated by the lower heating body is radiated and conducted to the graphite welding plate, and the heat generated by the upper heating body is radiated and conducted to the welding graphite plate cover plate. In this process, the real-time temperature of the welding graphite plate is collected by the real-time temperature thermocouple, the temperature of the welding graphite plate cover plate is collected by the upper heating body temperature control thermocouple in real time, and the temperature signal of the welding graphite plate cover plate is fed back to the temperature controller in real time. The working state of the upper heating body and the lower heating body is controlled by the controller, so that the welding graphite plate is heated to the peak temperature according to the set temperature curve, the peak temperature is greater than the melting temperature of the lead-tin solder, and the time that the welding graphite plate maintains the peak temperature is the temperature maintaining time, which is greater than 14 minutes;

[0017] Step f, after the temperature maintaining time of the welding graphite plate ends, the vacuumizing equipment is started and the welding chamber is vacuumized through the vacuumizing pipe, and the welding chamber is vacuumized to below 1000 Pa; then the temperature controller controls the upper heating body and the lower heating body to stop action, and the TVS diode after welding is cooled with the furnace.

[0018] Among them, for the TVS diode containing 3-4 layers of TVS crystal grains, the temperature maintaining time during welding is greater than 14 minutes;

[0019] For the TVS diode containing 5-8 layers of TVS crystal grains, the temperature maintaining time during welding is greater than 16 minutes;

[0020] For the TVS diode containing 9-11 layers of TVS crystal grains, the temperature maintaining time during welding is greater than 18 minutes;

[0021] For the TVS diode containing 12-15 layers of TVS crystal grains, the temperature maintaining time during welding is greater than 20 minutes;

[0022] For the TVS diode containing 15-18 layers of TVS crystal grains, the temperature maintaining time during welding is greater than 22 minutes;

[0023] For the TVS diode containing 19-20 layers of TVS crystal grains, the temperature maintaining time during welding is greater than 24 minutes.

[0024] Among them, the welding chamber is also provided with a heat-conducting graphite plate below the welding graphite plate, the welding graphite plate is arranged on the upper surface of the heat-conducting graphite plate, and the heat-conducting graphite plate is installed on the furnace body base through the fixing seat;

[0025] The heat-conducting graphite plate is provided with a lower heating body temperature control thermocouple, and the lower heating body temperature control thermocouple is electrically connected with the temperature controller.

[0026] The welding chamber is further provided with a supporting net below the welding graphite plate, the welding graphite plate is arranged on the upper surface of the supporting net, and the supporting net is installed on the furnace body base through the fixing seat.

[0027] Compared with the prior art, the welding method suitable for large-current transient voltage suppression diodes has the following beneficial effects: the welding method can generate uniform IMC intermetallic compounds between the solder and the TVS die and between the solder and the metal conductive layer, which can effectively improve the adhesion and mechanical strength between the layers of the large-current transient voltage suppression diode and effectively improve the current wave impact capacity and product reliability of the large-current transient voltage suppression diode. BRIEF DESCRIPTION OF DRAWINGS

[0028] The application will be further described below with reference to the drawings, but the embodiments in the drawings do not constitute any limitation on the application.

[0029] Figure 1 It is a structural schematic diagram of the large-current transient voltage suppression diode.

[0030] Figure 2 It is a structural schematic diagram of the vertical vacuum welding furnace.

[0031] Figure 3 It is a structural schematic diagram of another embodiment of the vertical vacuum welding furnace.

[0032] Figure 4 It is a furnace temperature curve of the application.

[0033] In Figures 1 to 4 comprise:

[0034] 1-welding furnace body; 11-furnace body base; 12-furnace upper cover; 13-welding chamber; 141-upper heating body; 142-lower heating body; 151-welding graphite plate; 152-welding graphite plate cover plate; 153-heat-conducting graphite plate; 154-supporting net; 161-actual temperature thermocouple; 162-upper heating body temperature control thermocouple; 163-lower heating body temperature control thermocouple; 17-gas filling rod; 18-vacuum exhaust pipe; 19-fixing seat; 2-TVS diode; 21-TVS die; 22-conductive metal layer; 23-lead-tin solder. DETAILED DESCRIPTION

[0035] The application will be described below in combination with specific embodiments.

[0036] Example one, as Figure 2 and Figure 3As shown, a welding method suitable for high-current transient voltage suppression diodes is provided, which employs a vertical vacuum welding furnace.

[0037] Among them, such as Figure 2 and Figure 3 As shown, the vertical vacuum welding furnace includes a welding furnace body 1 and a temperature controller. The welding furnace body 1 includes a furnace body base 11 and a furnace body cover 12 installed at the upper end of the furnace body base 11. The welding furnace body 1 has a welding chamber 13 formed by the furnace body base 11 and the furnace body cover 12.

[0038] Among them, such as Figure 2 and Figure 3 As shown, the furnace base 11 is equipped with a lower heating element 142 at the bottom of the welding chamber 13, and the furnace cover 12 is equipped with an upper heating element 141 at the top of the welding chamber 13. The lower heating element 142 and the upper heating element 141 are electrically connected to the temperature controller.

[0039] Furthermore, such as Figure 2 and Figure 3 As shown, the welding chamber 13 is fitted with welding graphite plates 151 arranged horizontally and a welding graphite plate cover 152 located on the upper side of the welding graphite plates 151. The welding graphite plates 151 are equipped with a real-temperature thermocouple 161, and the welding graphite plate cover 152 is equipped with an upper heating element temperature control thermocouple 162. The real-temperature thermocouple 161 and the upper heating element temperature control thermocouple 162 are electrically connected to the temperature controller.

[0040] Furthermore, such as Figure 2 and Figure 3 As shown, the welding furnace body 1 is equipped with an air-filling rod 17 that extends into the welding chamber 13 and a vacuum tube 18 for evacuating the welding chamber 13.

[0041] It should be noted that the welding method applicable to high-current transient voltage suppression diodes includes the following steps:

[0042] Step a: Place the TVS diode 2 between the welding graphite plate 151 and the welding graphite plate cover plate 152, as follows: Figure 1 As shown, the TVS diode 2 has a plurality of TVS chips 21 and a plurality of conductive metal layers 22. All TVS chips 21 and all conductive metal layers 22 are arranged alternately from top to bottom. There is lead-tin solder 23 between adjacent TVS chips 21 and conductive metal layers 22.

[0043] Step b: Start the vacuum equipment and evacuate the welding chamber 13 through the vacuum tube 18 to a vacuum level below 1000 Pa. The purpose of this vacuuming is to remove the air from the welding chamber 13 to reduce product oxidation during subsequent welding.

[0044] Step d, after the vacuumizing operation is completed, nitrogen is filled into the welding chamber 13 through the inflation rod 17, and the nitrogen is filled to above the standard atmospheric pressure;

[0045] Step e, the lower heating element 142 and the upper heating element 141 are started by the temperature controller, the heat generated by the lower heating element 142 is radiated and conducted to the graphite welding plate, and the heat generated by the upper heating element 141 is radiated and conducted to the welding graphite plate cover plate 152. In this process, the real-time temperature of the welding graphite plate 151 is collected by the real-time temperature thermocouple 161, the temperature of the welding graphite plate cover plate 152 is collected by the upper heating element temperature control thermocouple 162 in real time, and the temperature signal of the welding graphite plate cover plate 152 is fed back to the temperature controller in real time. The controller controls the working state of the upper heating element 141 and the lower heating element 142, so that the welding graphite plate 151 is heated to the peak temperature according to the set temperature curve, as shown in the figure. The peak temperature is greater than the melting temperature of the lead-tin solder 23, and the time for the welding graphite plate 151 to maintain the peak temperature is the temperature holding time, which is greater than 14 minutes; Figure 4

[0046] Step f, after the temperature holding time of the welding graphite plate 151 ends, the vacuumizing equipment is started and the welding chamber 13 is vacuumized through the vacuumizing pipe 18, and the welding chamber 13 is vacuumized to below 1000 Pa; then the temperature controller controls the upper heating element 141 and the lower heating element 142 to stop working, and the TVS diode 2 after welding is cooled with the furnace. The purpose of this vacuumizing is to reduce the air hole rate of the product welding.

[0047] It should be emphasized that for the TVS diode 2 containing 3-4 layers of TVS grains 21, the temperature holding time during welding is greater than 14 minutes;

[0048] For the TVS diode 2 containing 5-8 layers of TVS grains 21, the temperature holding time during welding is greater than 16 minutes;

[0049] For the TVS diode 2 containing 9-11 layers of TVS grains 21, the temperature holding time during welding is greater than 18 minutes;

[0050] For the TVS diode 2 containing 12-15 layers of TVS grains 21, the temperature holding time during welding is greater than 20 minutes;

[0051] For the TVS diode 2 containing 15-18 layers of TVS grains 21, the temperature holding time during welding is greater than 22 minutes;

[0052] For the TVS diode 2 containing 19-20 layers of TVS grains 21, the temperature holding time during welding is greater than 24 minutes.

[0053] ​For the welding furnace body 1 in this embodiment, during the heating process by the upper heating element 141 and the lower heating element 142, the temperature of the welding graphite plate 151 collected by the real-temperature thermocouple 161 is the actual welding temperature of the TVS diode 2. The upper heating element temperature control thermocouple 162 collects the temperature of the welding graphite plate cover 152. During operation, the heat generated by the upper heating element 141 is radiated and conducted to the welding graphite plate cover 152, and the heat generated by the lower heating element 142 is radiated and conducted to the welding graphite plate 151. The controller controls the working state of the upper heating element 141 and the lower heating element 142 according to the temperature feedback of the thermocouples, so that the actual welding temperature changes according to the set temperature curve, thereby achieving accurate control of the welding temperature.

[0054] It should be further pointed out that by accurately controlling the peak temperature and temperature holding time of the welding graphite plate 151, the welding method of this embodiment for high current transient voltage suppression diodes can make the peak temperature of each layer and region of the TVS diode 2 uniform and consistent, thereby enabling the formation of uniform and appropriately thick IMC between the solder and the TVS die 21, and between the solder and the conductive metal layer 22.

[0055] In summary, the welding method for high-current transient voltage suppression diodes in this embodiment can generate uniform IMC intermetallic compounds between the solder and the TVS die 21, and between the solder and the metal conductive layer. On the one hand, this can effectively improve the adhesion and mechanical strength between the layers of the high-current transient voltage suppression diode, and on the other hand, it can effectively improve the current surge impact capability and product reliability of the high-current transient voltage suppression diode.

[0056] Example 2, as Figure 1 As shown, the difference between this embodiment 2 and embodiment 1 is that: a heat-conducting graphite plate 153 located below the welding graphite plate 151 is also installed in the welding chamber 13. The welding graphite plate 151 is installed on the upper surface of the heat-conducting graphite plate 153, and the heat-conducting graphite plate 153 is installed on the furnace base 11 through the fixing seat 19.

[0057] Among them, the heat-conducting graphite plate 153 is equipped with a lower heating element temperature control thermocouple 163, which is electrically connected to the temperature controller.

[0058] For the welding method of the high-current transient voltage suppression diode in this embodiment 2, the heat generated by the lower heating element 142 is directly radiated and conducted to the thermally conductive graphite plate 153, and the thermally conductive graphite plate 153 then conducts the heat to the welding graphite plate 151.

[0059] In the process of welding the TVS diode by using the welding method for the large-current transient voltage suppression diode of the second embodiment, the real-time thermocouple 161 collects the temperature of the welding graphite plate 151 in real time and records it, the lower heating element temperature control thermocouple 163 collects the temperature of the heat-conducting graphite plate 153 in real time and feeds back the temperature information of the heat-conducting graphite plate 153 to the temperature controller in real time, the upper heating element temperature control thermocouple 162 collects the temperature of the welding graphite plate cover plate 152 in real time and feeds back the temperature signal of the welding graphite plate cover plate 152 to the temperature controller in real time, and the controller controls the working state of the upper heating element 141 and the lower heating element 142 according to the temperature signals fed back by the lower heating element temperature control thermocouple 163 and the upper heating element temperature control thermocouple 162, so that the welding graphite plate 151 is heated to the peak temperature according to the set temperature curve.

[0060] As shown in the third embodiment, Figure 3 The difference between the third embodiment and the first embodiment is that the welding chamber 13 is additionally provided with a supporting net 154 located below the welding graphite plate 151, the welding graphite plate 151 is arranged on the upper surface of the supporting net 154, and the supporting net 154 is installed on the furnace body base 11 through the fixing seat 19.

[0061] For the supporting net 154 of the third embodiment, it has a hollow mesh structure; when working, the heat generated by the lower heating element 142 is directly radiated and conducted to the welding graphite plate 151 through the supporting net 154.

[0062] In the process of welding the TVS diode by using the welding method for the large-current transient voltage suppression diode of the third embodiment, the real-time thermocouple 161 collects the temperature of the welding graphite plate 151 in real time and feeds back the temperature information of the welding graphite plate 151 to the temperature controller in real time, the upper heating element temperature control thermocouple 162 collects the temperature of the welding graphite plate cover plate 152 in real time and feeds back the temperature signal of the welding graphite plate cover plate 152 to the temperature controller in real time, and the controller controls the working state of the upper heating element 141 and the lower heating element 142 according to the temperature signals fed back by the real-time thermocouple 161 and the upper heating element temperature control thermocouple 162, so that the welding graphite plate 151 is heated to the peak temperature according to the set temperature curve.

[0063] The above is only the preferred embodiment of the present application, and for those skilled in the art, according to the idea of the present application, the specific implementation and application range can be changed, and the content of the description should not be understood as a limitation of the present application.

Claims

1. A welding method suitable for large-current transient voltage suppression diodes, which adopts a vertical vacuum welding furnace; characterized in that The vertical vacuum welding furnace comprises a welding furnace body (1) and a temperature controller, the welding furnace body (1) comprises a furnace body base (11) and a furnace body upper cover (12) arranged on the upper end of the furnace body base (11), and the inside of the welding furnace body (1) is shaped into a welding chamber (13) surrounded by the furnace body base (11) and the furnace body upper cover (12); A lower heating element (142) is arranged on the bottom of the welding chamber (13) of the furnace body base (11), and an upper heating element (141) is arranged on the top of the welding chamber (13) of the furnace body upper cover (12), and the lower heating element (142) and the upper heating element (141) are electrically connected with the temperature controller respectively; A welding graphite plate (151) arranged horizontally and transversely and a welding graphite plate cover plate (152) located on the upper end side of the welding graphite plate (151) are embedded in the welding chamber (13), the welding graphite plate (151) is provided with a real temperature thermocouple (161), and the welding graphite plate cover plate (152) is provided with an upper heating element temperature control thermocouple (162), and the real temperature thermocouple (161) and the upper heating element temperature control thermocouple (162) are electrically connected with the temperature controller respectively; The welding furnace body (1) is provided with a gas filling rod (17) extending into the welding chamber (13) and a vacuum pump (18) for vacuumizing the welding chamber (13); The welding method suitable for large-current transient voltage suppression diodes comprises the following steps: Step a, placing a TVS diode (2) between the welding graphite plate (151) and the welding graphite plate cover plate (152), the TVS diode (2) having a plurality of TVS grains (21) and a plurality of conductive metal layers (22), all the TVS grains (21) and all the conductive metal layers (22) being arranged in an alternating manner from top to bottom, and the adjacent TVS grains (21) and conductive metal layers (22) having lead-tin solder (23) therebetween; Step b, starting a vacuumizing device and vacuumizing the welding chamber (13) through the vacuumizing pipe (18), and vacuumizing the welding chamber (13) to below 1000 Pa; Step d, after the vacuumizing operation is completed, filling nitrogen into the welding chamber (13) through the gas filling rod (17), and filling the nitrogen to above the standard atmospheric pressure; Step e, start the lower heating body (142) and the upper heating body (141) through the temperature controller, the heat generated by the lower heating body (142) is radiated and conducted to the graphite welding plate, and the heat generated by the upper heating body (141) is radiated and conducted to the graphite welding plate cover plate (152), in the process, the real-time temperature of the welding graphite plate (151) is collected by the real-time temperature thermocouple (161), the temperature of the welding graphite plate cover plate (152) is collected by the upper heating body temperature control thermocouple (162) in real time, and the temperature signal of the welding graphite plate cover plate (152) is fed back to the temperature controller in real time, and the working state of the upper heating body (141) and the lower heating body (142) is controlled by the controller, so that the welding graphite plate (151) is heated to the peak temperature according to the set temperature curve, the peak temperature is greater than the melting temperature of the lead-tin solder (23), and the time that the welding graphite plate (151) maintains the peak temperature is the temperature maintaining time, which is greater than 14 minutes; Step f, after the temperature maintaining time of the welding graphite plate (151) ends, the vacuumizing equipment is started and the welding chamber (13) is vacuumized through the vacuumizing pipe (18), the welding chamber (13) is vacuumized to below 1000 Pa, then the temperature controller controls the upper heating body (141) and the lower heating body (142) to stop working, and the TVS diode (2) after welding is cooled with the furnace.

2. A soldering method for a surge current transient voltage suppression diode according to claim 1, wherein: For the TVS diode (2) containing 3-4 layers of TVS grains (21), the temperature maintaining time during welding is greater than 14 minutes; For the TVS diode (2) containing 5-8 layers of TVS grains (21), the temperature maintaining time during welding is greater than 16 minutes; For the TVS diode (2) containing 9-11 layers of TVS grains (21), the temperature maintaining time during welding is greater than 18 minutes; For the TVS diode (2) containing 12-15 layers of TVS grains (21), the temperature maintaining time during welding is greater than 20 minutes; For the TVS diode (2) containing 15-18 layers of TVS grains (21), the temperature maintaining time during welding is greater than 22 minutes; For the TVS diode (2) containing 19-20 layers of TVS grains (21), the temperature maintaining time during welding is greater than 24 minutes.

3. The soldering method for a large surge current transient voltage suppression diode according to claim 1, wherein: The welding chamber (13) is further provided with a heat-conducting graphite plate (153) below the welding graphite plate (151), the welding graphite plate (151) is arranged on the upper surface of the heat-conducting graphite plate (153), and the heat-conducting graphite plate (153) is installed on the furnace body base (11) through the fixing seat (19); The heat-conducting graphite plate (153) is provided with a lower heating body temperature control thermocouple (163), and the lower heating body temperature control thermocouple (163) is electrically connected with the temperature controller.

4. The soldering method for a large surge current transient voltage suppression diode according to claim 1, wherein: The welding chamber (13) is further provided with a supporting net (154) below the welding graphite plate (151), the welding graphite plate (151) is arranged on the upper surface of the supporting net (154), and the supporting net (154) is installed on the furnace body base (11) through the fixing seat (19).

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