Welding method suitable for large-through-current transient voltage suppression diode

Abstract

A vertical vacuum welding furnace adopted in the welding method comprises a welding furnace body and a temperature controller, and 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, an inflation rod and a vacuumizing pipe. 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; the welding method comprises the following steps: step a, placing a TVS diode between a welding graphite plate and a welding graphite plate cover plate; step b, vacuumizing; step d, filling nitrogen; e, heating and welding; and f, vacuumizing and then cooling. According to the invention, uniform IMC intermetallic compounds can be generated between the layers of the TVS diode, that is, the adhesive force and mechanical strength between the layers of the TVS diode can be improved, and the current wave impact capability and product reliability of the TVS diode can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of diodes, and particularly to a soldering method applicable to a large-current transient voltage suppression diode. Background Art

[0002] A transient voltage suppression diode, also known as a TVS diode, is a protective electronic component that can protect electrical equipment from voltage spikes introduced by wires. When in use, when it withstands a high-energy instantaneous overvoltage pulse, its operating impedance can immediately drop to a very low conduction value, allowing a large current to pass through, and clamping the voltage to a predetermined level, thereby effectively protecting the precision components in the electronic circuit from damage. As a commonly used circuit protection component, the TVS diode has remarkable characteristics of fast action speed, high breakdown voltage accuracy, and low impedance. The action speed can reach 1.0 pS, and the capacitance voltage accuracy can be controlled within ±10%. It can effectively and precisely protect the circuit; among them, the large-current TVS can pass through a surge current of thousands of amperes to tens of thousands of amperes in 8 / 20 us.

[0003] It should be noted that for a transient voltage suppression diode that needs to pass a large current (i.e., a large-current transient voltage suppression diode), it is necessary to use a high-temperature lead-tin solder to completely solder the entire surface electrode of the TVS chip to the conductive metal to reduce the resistance. And during the packaging process of the large-current TVS, it is necessary to use a TVS chip larger than 200 mil, and in order to increase the working voltage, multiple layers of TVS chips need to be stacked. Due to the large size and multiple layers of the TVS chips, the existing soldering method will cause uneven generation of IMC (intermetallic compound) between the solder and the chips due to uneven soldering temperatures in different regions. Since the TVS chip is a silicon semiconductor and has the characteristics of high compressive strength and low bending strength, that is, the brittle characteristics of the silicon semiconductor, it will cause the chip to break down when a large current passes through. This situation is not significant in the 10 / 1000 us waveform, but it will be particularly significant during an 8 / 20 us current wave impact or a 7637 load-dump thermal shock. The uneven IMC will cause the TVS chip to fail due to brittle fracture in the environmental test, especially during the temperature cycle test.

[0004] In view of the above situation, it is necessary to improve the soldering method of the large-current transient voltage suppression diode. Summary of the Invention

[0005] The object of the present invention is to provide a soldering method applicable to large-current transient voltage suppression diodes in view of the deficiencies of the prior art. The soldering method applicable to large-current transient voltage suppression diodes can generate uniform intermetallic compounds (IMCs) between the solder and the TVS grains and between the solder and the metal conductive layer. On the one hand, it can effectively improve the adhesion and mechanical strength between the layers of the large-current transient voltage suppression diode. On the other hand, it can effectively enhance the current wave impact resistance and product reliability of the large-current transient voltage suppression diode.

[0006] To achieve the above object, the present invention is realized through the following technical solutions.

[0007] A soldering method applicable to large-current transient voltage suppression diodes, which uses a vertical vacuum soldering furnace;

[0008] The vertical vacuum soldering furnace includes a soldering furnace body and a temperature controller. The soldering furnace body includes a furnace body base and a furnace body upper cover installed at the upper end of the furnace body base. A soldering chamber formed by the common enclosure of the furnace body base and the furnace body upper cover is formed inside the soldering furnace body;

[0009] The furnace body base is provided with a lower heating element at the bottom of the soldering chamber, and the furnace body upper cover is provided with an upper heating element at the top of the soldering chamber. The lower heating element and the upper heating element are respectively electrically connected to the temperature controller;

[0010] The soldering chamber is embedded with a soldering graphite plate arranged horizontally and transversely and a soldering graphite plate cover located on the upper side of the soldering graphite plate. The soldering graphite plate is provided with a real-time thermocouple, and the soldering graphite plate cover is provided with an upper heating element temperature control thermocouple. The real-time thermocouple and the upper heating element temperature control thermocouple are respectively electrically connected to the temperature controller;

[0011] The soldering furnace body is provided with an inflation rod extending into the soldering chamber and a vacuum pumping tube for evacuating the soldering chamber;

[0012] The soldering method applicable to large-current transient voltage suppression diodes includes the following steps, specifically:

[0013] Step a: Place the TVS diode between the soldering graphite plate and the soldering graphite plate cover. The TVS diode has a plurality of TVS grains and a plurality of conductive metal layers. All the TVS grains and all the conductive metal layers are arranged alternately from top to bottom. There is a lead-tin solder between adjacent TVS grains and conductive metal layers;

[0014] Step b: Start the vacuum pumping equipment and evacuate the soldering chamber through the vacuum pumping tube. The soldering chamber is evacuated to less than 1000 Pa;

[0015] Step d: After the vacuum pumping operation is completed, nitrogen gas is filled into the welding chamber through the inflation rod, and the nitrogen gas is filled to above the standard atmospheric pressure;

[0016] Step e: Start the lower heating element and the upper heating element through the temperature controller. The heat generated by the lower heating element is radiated and conducted to the graphite welding plate, and the heat generated by the upper heating element is radiated and conducted to the welding graphite plate cover. During this process, the actual temperature thermocouple collects the temperature of the welding graphite plate in real time, and the upper heating element temperature control thermocouple collects the temperature of the welding graphite plate cover in real time and feeds back the temperature signal of the welding graphite plate cover to the temperature controller in real time. The controller controls the working states of the upper heating element and the lower heating element 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. The time for the welding graphite plate to maintain the peak temperature is the temperature holding time, and this temperature holding time is greater than 14 minutes;

[0017] Step f: After the temperature holding time of the welding graphite plate ends, start the vacuum pumping equipment and evacuate the welding chamber through the vacuum pumping pipe. The welding chamber is evacuated to below 1000 Pa; then the temperature controller controls the upper heating element and the lower heating element to stop operating, and the TVS diode after welding cools down with the furnace.

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

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

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

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

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

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

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

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

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

[0027] Compared with the prior art, the present invention has the following beneficial effects. Specifically, the welding method for the large-current transient voltage suppression diode of the present invention can generate uniform IMC intermetallic compounds between the solder and the TVS grains and between the solder and the metal conductive layer. On the one hand, it can effectively improve the adhesion and mechanical strength between the layers of the large-current transient voltage suppression diode. On the other hand, it can effectively enhance the current wave impact resistance and product reliability of the large-current transient voltage suppression diode. Description of the Drawings

[0028] The present invention will be further described below with the aid of the drawings, but the embodiments in the drawings do not constitute any limitation to the present invention.

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

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

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

[0032] Figure 4 It is the furnace temperature curve of the present invention.

[0033] In Figures 1 to 4 it includes:

[0034] 1 - Welding furnace body; 11 - Furnace body base; 12 - Furnace body upper cover; 13 - Welding chamber; 141 - Upper heating element; 142 - Lower heating element; 151 - Welding graphite plate; 152 - Welding graphite plate cover plate; 153 - Heat-conducting graphite plate; 154 - Support net; 161 - Actual temperature thermocouple; 162 - Upper heating element temperature control thermocouple; 163 - Lower heating element temperature control thermocouple; 17 - Inflation rod; 18 - Vacuum pumping pipe; 19 - Fixing seat; 2 - TVS diode; 21 - TVS grains; 22 - Conductive metal layer; 23 - Lead-tin solder. Specific Embodiments

[0035] The present invention will be described below in conjunction with specific embodiments.

[0036] Embodiment 1, as shown in Figure 2 and Figure 3As shown, a welding method applicable to a large-current transient voltage suppression diode, and this welding method uses a vertical vacuum welding furnace.

[0037] Among them, as Figure 2 and Figure 3 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 upper cover 12 installed at the upper end of the furnace body base 11. A welding chamber 13 formed by jointly enclosing the furnace body base 11 and the furnace body upper cover 12 is formed inside the welding furnace body 1.

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

[0039] Furthermore, as Figure 2 and Figure 3 shown, welding graphite plates 151 arranged horizontally and transversely and a welding graphite plate cover 152 located on the upper side of the welding graphite plates 151 are embedded in the welding chamber 13. A real-time temperature thermocouple 161 is installed on the welding graphite plates 151, and an upper heating element temperature control thermocouple 162 is installed on the welding graphite plate cover 152. The real-time temperature thermocouple 161 and the upper heating element temperature control thermocouple 162 are respectively electrically connected to the temperature controller.

[0040] Even further, as Figure 2 and Figure 3 shown, an inflation rod 17 extending into the welding chamber 13 and a vacuum pumping tube 18 for evacuating the welding chamber 13 are installed on the welding furnace body 1.

[0041] It should be noted that the welding method applicable to the large-current transient voltage suppression diode includes the following steps, specifically:

[0042] Step a: Place the TVS diode 2 between the welding graphite plates 151 and the welding graphite plate cover 152. As Figure 1 shown, the TVS diode 2 has 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 are arranged alternately from top to bottom, and there is a lead-tin solder 23 between adjacent TVS grains 21 and conductive metal layers 22;

[0043] Step b: Start the vacuum pumping equipment and evacuate the welding chamber 13 through the vacuum pumping tube 18 until the pressure in the welding chamber 13 is below 1000 Pa. The purpose of this evacuation is to evacuate the air in the welding chamber 13 to reduce the oxidation of the product during subsequent welding;

[0044] Step d: After the vacuum pumping operation is completed, nitrogen gas is filled into the welding chamber 13 through the inflation rod 17 until the nitrogen pressure is above the standard atmospheric pressure.

[0045] Step e: Start the lower heating element 142 and the upper heating element 141 through 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 152. During this process, the actual temperature thermocouple 161 collects the temperature of the welding graphite plate 151 in real time, and the upper heating element temperature control thermocouple 162 collects the temperature of the welding graphite plate cover 152 in real time and feeds back the temperature signal of the welding graphite plate cover 152 to the temperature controller in real time. The controller controls the working states 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 Figure 4 shown, the peak temperature is higher than the melting temperature of the lead-tin solder 23. The time during which the welding graphite plate 151 maintains the peak temperature is the temperature holding time, and this temperature holding time is greater than 14 minutes.

[0046] Step f: After the temperature holding time of the welding graphite plate 151 ends, start the vacuum pumping device and evacuate the welding chamber 13 through the vacuum pumping pipe 18 until the pressure in the welding chamber 13 is below 1000 Pa. Then the temperature controller controls the upper heating element 141 and the lower heating element 142 to stop operating, and the TVS diode 2 after welding cools down with the furnace. Among them, the purpose of this vacuum pumping is to reduce the void ratio of 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 of the first 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 actual temperature thermocouple 161 is the actual temperature for welding 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 radiatively conducted to the welding graphite plate cover 152, and the heat generated by the lower heating element 142 is radiatively conducted to the welding graphite plate 151. The controller controls the working states of the upper heating element 141 and the lower heating element 142 according to the temperature feedback of the above 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 the temperature holding time of the welding graphite plate 151, the welding method of the first embodiment applicable to the large-current transient voltage suppression diode can make the peak temperatures of each layer and each region of the TVS diode 2 uniform, so that a uniform and appropriately thick IMC can be formed between the solder and the TVS crystal grains 21 and between the solder and the conductive metal layer 22.

[0055] Based on the above situation, it can be seen that the welding method of the first embodiment applicable to the large-current transient voltage suppression diode can form a uniform IMC intermetallic compound between the solder and the TVS crystal grains 21 and between the solder and the metal conductive layer. On the one hand, it can effectively improve the adhesion and mechanical strength between the layers of the large-current transient voltage suppression diode, and on the other hand, it can effectively enhance the current wave impact resistance and product reliability of the large-current transient voltage suppression diode.

[0056] Embodiment 2, as Figure 1 shown, the difference between the second embodiment and the first embodiment is that a heat-conducting graphite plate 153 is further installed in the welding chamber 13 below the welding graphite plate 151. 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 body base 11 through a fixing seat 19.

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

[0058] For the welding method of the second embodiment applicable to the large-current transient voltage suppression diode, the heat generated by the lower heating element 142 is directly radiatively conducted to the heat-conducting graphite plate 153, and the heat-conducting graphite plate 153 then conducts the heat to the welding graphite plate 151.

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

[0060] Embodiment 3, as Figure 3 shown, the difference between this Embodiment 3 and Embodiment 1 is that: a support net 154 is further installed in the welding chamber 13 below the welding graphite plate 151. The welding graphite plate 151 is installed on the upper surface of the support net 154, and the support net 154 is installed on the furnace body base 11 through a fixing seat 19.

[0061] For the support net 154 in this Embodiment 3, it has a hollow mesh structure; during operation, the heat generated by the lower heating body 142 is directly radiated and conducted to the welding graphite plate 151 after passing through the support net 154.

[0062] During the process of welding the TVS diode using the welding method for the large-current transient voltage suppression diode in this Embodiment 3, the actual temperature 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 body temperature control thermocouple 162 collects the temperature of the welding graphite plate cover 152 in real time and feeds back the temperature signal of the welding graphite plate cover 152 to the temperature controller in real time. The controller controls the working states of the upper heating body 141 and the lower heating body 142 according to the temperature signals fed back by the actual temperature thermocouple 161 and the upper heating body 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 content is only the preferred embodiment of the present invention. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. The content of this specification should not be construed as a limitation to the present invention.

Claims

1. A welding method applicable to a large-current transient voltage suppression diode, which uses a vertical vacuum welding furnace; It is characterized in that: 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 upper cover (12) installed at the upper end of the furnace body base (11). A welding chamber (13) formed by jointly enclosing the furnace body base (11) and the furnace body upper cover (12) is formed inside the welding furnace body (1); The furnace body base (11) is provided with a lower heating element (142) at the bottom of the welding chamber (13), and the furnace body upper cover (12) is provided 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 respectively electrically connected to the temperature controller; The welding chamber (13) is internally embedded with a welding graphite plate (151) arranged horizontally and transversely and a welding graphite plate cover (152) located on the upper side of the welding graphite plate (151). The welding graphite plate (151) is provided with a real-time thermocouple (161), and the welding graphite plate cover (152) is provided with an upper heating element temperature control thermocouple (162). The real-time thermocouple (161) and the upper heating element temperature control thermocouple (162) are respectively electrically connected to the temperature controller; The welding furnace body (1) is provided with an inflation rod (17) extending into the welding chamber (13) and a vacuum pumping pipe (18) for evacuating the welding chamber (13); The welding method applicable to the large-current transient voltage suppression diode includes the following steps, specifically: Step a: Place the TVS diode (2) between the welding graphite plate (151) and the welding graphite plate cover (152). The TVS diode (2) has a number of TVS grains (21) and a number of conductive metal layers (22). All the TVS grains (21) and all the conductive metal layers (22) are arranged alternately from top to bottom. There is a lead-tin solder (23) between adjacent TVS grains (21) and conductive metal layers (22); Step b: Start the vacuum pumping equipment and evacuate the welding chamber (13) through the vacuum pumping pipe (18). The welding chamber (13) is evacuated to below 1000 Pa; Step d: After the vacuum pumping operation is completed, fill the welding chamber (13) with nitrogen through the inflation rod (17). Fill the nitrogen to above the standard atmospheric pressure; Step e: Start the lower heating element (142) and the upper heating element (141) through 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 (152). During this process, the actual temperature thermocouple (161) collects the temperature of the welding graphite plate (151) in real time, and the upper heating element temperature control thermocouple (162) collects the temperature of the welding graphite plate cover (152) in real time and feeds back the temperature signal of the welding graphite plate cover (152) to the temperature controller in real time. The controller controls the working states 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. The peak temperature is higher than the melting temperature of the lead-tin solder (23). The time for the welding graphite plate (151) to maintain the peak temperature is the temperature holding time, and this temperature holding time is greater than 14 minutes; Step f: After the temperature holding time of the welding graphite plate (151) ends, start the vacuum pumping device and pump the welding chamber (13) through the vacuum pumping pipe (18). The welding chamber (13) is pumped to below 1000 Pa; then the temperature controller controls the upper heating element (141) and the lower heating element (142) to stop operating, and the TVS diode (2) after welding cools down with the furnace.

2. The soldering method for a large-current transient voltage suppression diode according to claim 1, characterized in 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; For the TVS diode (2) containing 5 - 8 layers of TVS grains (21), the temperature holding time during welding is greater than 16 minutes; For the TVS diode (2) containing 9 - 11 layers of TVS grains (21), the temperature holding time during welding is greater than 18 minutes; For the TVS diode (2) containing 12 - 15 layers of TVS grains (21), the temperature holding time during welding is greater than 20 minutes; For the TVS diode (2) containing 15 - 18 layers of TVS grains (21), the temperature holding time during welding is greater than 22 minutes; For the TVS diode (2) containing 19 - 20 layers of TVS grains (21), the temperature holding time during welding is greater than 24 minutes.

3. A soldering method for a large-current transient voltage suppression diode according to claim 1, characterized in that: A heat-conducting graphite plate (153) is also installed in the welding chamber (13) below the welding graphite plate (151). 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 body base (11) through a fixing seat (19); The heat-conducting graphite plate (153) is equipped with a lower heating element temperature control thermocouple (163), and the lower heating element temperature control thermocouple (163) is electrically connected to the temperature controller.

4. A soldering method for a large-current transient voltage suppression diode according to claim 1, characterized in that: A support net (154) is also installed in the welding chamber (13) below the welding graphite plate (151). The welding graphite plate (151) is installed on the upper surface of the support net (154), and the support net (154) is installed on the furnace body base (11) through a fixing seat (19).

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