Testing method for welding quality of bipolar transistor

Abstract

The present application relates to a method for detecting the welding quality of bipolar transistors, belonging to the field of transistor detection technology, comprising: determining the corresponding reflow soldering peak temperature T in the application scenario of the transistor, setting the test temperature to T+ΔT, where ‑10°C ≤ ΔT ≤ 10°C; heating the ambient temperature of the transistor to the test temperature and then gradually cooling it to the detection temperature; obtaining the electrical performance parameters of the transistor, and determining that the transistor is a good product when the measured electrical performance parameters all meet the specification requirements. According to the method for detecting the welding quality of bipolar transistors of the present invention, defective products are quickly screened out through experimental schemes in the manufacturer's production environment and the incoming material inspection link to eliminate early failure products (manufacturing defects) to prevent them from being discharged to the subsequent process.

Description

Technical Field

[0001] The present application relates to the technical field of transistor detection, and in particular to a method for detecting the welding quality of a bipolar transistor. Background Art

[0002] Bipolar transistors are current-controlled devices with a wide range of applications. Their reliability plays a crucial role in product quality, and during use, they frequently report open circuit defects. Electrical performance parameters were tested, indicating compliance with the specifications. However, after subjecting the defective product to thermal shock tests and subsequent testing on a machine, both BVCEO and BVEB were found to be open circuits, indicating abnormal test results. Unsealing the samples confirmed two primary anomalies: 1) Laser decapsulation inspection revealed detachment of the E-pole inner lead from the chip bond, and oxidation was observed under the solder balls. 2) CT scans revealed poor pin-finishing and breakpoints. Combined with analysis of a large number of failed products, the causes and mechanisms of transistor failure were analyzed. The results indicate that manufacturing anomalies during the production process can lead to poor gold wire bonding. Immediately improving transistor reliability screening requires stricter quality control during production and incoming material testing to prevent unreliable transistors from being installed on motherboard circuits, potentially resulting in scrapped motherboards. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for detecting the welding quality of bipolar transistors, thereby quickly screening out defective products (manufacturing defects) in the factory production environment and during the incoming material inspection process through an experimental scheme to eliminate early failure products, thereby preventing them from being released to subsequent processes.

[0004] A method for detecting the welding quality of a bipolar transistor according to an embodiment of the present invention is characterized by comprising: determining a reflow soldering peak temperature T corresponding to an application scenario of the transistor, setting a test temperature to T+ΔT, where -10°C ≤ ΔT ≤ 10°C; heating the transistor to the test temperature and then gradually cooling it to the detection temperature; obtaining electrical performance parameters of the transistor, and determining that the transistor is a good product when the measured electrical performance parameters all meet specification requirements.

[0005] Optionally, heating the transistor to a test temperature and then gradually cooling it to a detection temperature specifically includes: heating the transistor according to a reflow soldering temperature curve corresponding to the application scenario, and then gradually cooling it to a detection temperature according to the reflow soldering temperature curve.

[0006] According to the method for detecting the welding quality of a bipolar transistor according to an embodiment of the present invention, obtaining the electrical performance parameters of the transistor specifically includes: measuring the base-collector terminal voltage VFBC and the base-emitter terminal voltage VFBE of the transistor, and determining that the transistor is a good product when both VFBC and VFBE are not less than the corresponding preset minimum voltage values.

[0007] Optionally, before obtaining the electrical performance parameters of the transistor, it also includes: applying the base current IB as the base saturation current to make the collector current IC enter the saturation region, measuring the base-collector terminal voltage VFBC and the base-emitter terminal voltage VFBE of the transistor, and when both VFBC and VFBE are not less than the corresponding preset minimum voltage values, determining that the transistor is a good product.

[0008] According to the method for detecting the welding quality of bipolar transistors in an embodiment of the present invention, obtaining the electrical performance parameters of the transistor specifically includes: measuring the resistance of the base-collector terminal and the resistance of the base-emitter terminal of the transistor, and when the resistance of the base-collector terminal and the resistance of the base-emitter terminal are both infinite, the transistor is judged as a defective product and is rejected.

[0009] The method for detecting the welding quality of a bipolar transistor according to an embodiment of the present invention further includes: applying a base current IB as a first current I1, and measuring a base-collector voltage VFBC1 and a base-emitter voltage VFBE1 of the transistor under the first current I1; applying a base current IB as a second current I2, and measuring a base-collector voltage VFBC2 and a base-emitter voltage VFBE2 of the transistor under the second current I2; and calculating the value of the bipolar transistor according to the formula and Calculate RE and RC. When |VFBE1-VFBE2|<0.5, RE<0.6, |VFBC1-VFBC2|<0.5, and RC<0.6 are all satisfied, the transistor is considered to be good.

[0010] Optionally, I2=nI1, I2 is less than or equal to the base saturation current, where n is greater than or equal to 2.

[0011] The method for detecting the welding quality of a bipolar transistor according to an embodiment of the present invention further includes: maintaining the transistor in a temperature environment of 125±2°C for at least 30 minutes, taking it out after N cycles and placing it at room temperature for a first time, wherein N≧30, and measuring the reverse breakdown voltage BV of the collector-emitter terminal of the transistor. CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO , BV CEO and BV EBO Transistors that do not show open circuit are judged to be good products.

[0012] Optionally, the method further includes: maintaining the transistor at a temperature of -40°C ± 2°C for at least 30 minutes, taking it out after N cycles and placing it at room temperature for a second time, wherein N≧30, and measuring the reverse breakdown voltage BV of the collector-emitter end of the transistor. CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO , BV CEO and BV EBO Transistors that do not show open circuit are judged to be good products.

[0013] Optionally, the first time and the second time are both greater than or equal to 1 hour.

[0014] The method for detecting the welding quality of bipolar transistors according to the embodiment of the present invention can quickly screen out abnormal and poor performance problems of early-stage switch failures (manufacturing defects), improve the screening detection rate of major hidden and reliability-deficient quality defects of transistors, avoid outflow to subsequent processes, and reduce the after-sales failure rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0017] Figure 1 2. A schematic flow chart of a method for detecting welding quality of a bipolar transistor according to an embodiment of the present invention;

[0018] Figure 2 Schematic diagram of reflow soldering temperature curve. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0020] like Figure 1As shown, a method for inspecting the welding quality of a bipolar transistor according to an embodiment of the present invention is characterized by comprising: determining the reflow soldering peak temperature T corresponding to the transistor's application scenario, setting the test temperature to T+ΔT, where -10°C ≤ ΔT ≤ 10°C. Raising the ambient temperature of the transistor to the test temperature and then gradually cooling it to the inspection temperature. Obtaining the electrical performance parameters of the transistor, and determining that the transistor is a good product when all the measured electrical performance parameters meet specification requirements.

[0021] Among them, the electrical performance parameters can be obtained by direct measurement or calculated based on the measurement data. In the process of the ambient temperature of the transistor being heated to the test temperature, the temperature can be heated linearly at a fixed rate or according to a set curve, and this application does not impose any restrictions. The speed at which the ambient temperature gradually cools down from the test temperature to the detection temperature is determined by the specific parameters of the heating equipment used, and this application does not impose any restrictions. In the actual inspection process, the transistor can be placed in a heating furnace, the heating furnace temperature can be heated to the test temperature and then gradually cooled to the detection temperature, the transistor can be taken out and the electrical performance parameters of the transistor can be tested. Among them, all the electrical performance parameters required by the transistor for the corresponding factory specifications can be tested to determine whether the transistor meets the factory requirements, or several electrical performance parameters that can directly show abnormalities after the poor welding line of the transistor is exposed can be tested, and this application does not impose any restrictions.

[0022] The detection temperature can be set according to test needs. The detection temperature is greater than or equal to room temperature. In some embodiments, the detection temperature is 75°C. When the detection temperature is higher than room temperature, after the heating furnace temperature drops to the detection temperature and the transistor is taken out, the electrical performance parameters of the transistor can be tested immediately or after the transistor is further cooled. The transistor needs to be soldered to different motherboards for use, and different reflow soldering temperature curves need to be used. The ambient temperature of the transistor is raised to the test temperature and then gradually cooled to the detection temperature. This is mainly to simulate in advance the temperature shock that the transistor will experience when soldered to the motherboard.

[0023] The method for detecting the welding quality of a bipolar transistor according to an embodiment of the present invention measures the electrical performance parameters of the transistor, and determines that the transistor is a good product when all the measured electrical performance parameters meet the specification requirements. Specifically, it includes: measuring the voltage VFBC at the base-collector terminal and the voltage VFBE at the base-emitter terminal of the transistor. When both VFBC and VFBE are not less than the corresponding preset minimum voltage values, it is determined that the transistor is a good product; or measuring the resistance R1 at the base-collector terminal and the resistance R2 at the base-emitter terminal of the transistor. When both R1 and R2 are infinite, the transistor is determined to be a defective product and excluded. For example, the preset minimum voltage value corresponding to VFBC is V1, and the preset minimum voltage value corresponding to VFBE is V2. When VFBC≥V1 and VFBE≥V2, it is determined that the transistor is a good product. On the contrary, when at least one of the equations VFBC<V1 and VFBE<V2 holds, it is determined that the transistor is a defective product.

[0024] The principle of this detection method is as follows: When the transistor enters the subsequent working steps, it needs to be installed on the corresponding main board, and during installation, it needs to be welded by reflow soldering. By simulating the subsequent reflow soldering in advance, the transistors with poor connection of the welding wires are screened out in advance. During reflow soldering, the temperature of reflow soldering is much higher than the storage temperature Tstg (–55 to 150 °C), the junction temperature Tj (150 °C), and the operating temperature range (–40 to 105 °C) of general transistors. In the actual production process, there are phenomena involving high temperatures exceeding the specified standard temperature. By subjecting the transistors to a temperature shock in advance, after the transistors are subjected to the shock of the test temperature, the base-collector terminal (i.e., the BC terminal) and the base-emitter terminal (i.e., the BE terminal) of the transistors with poor welding will become open-circuit states. In an open-circuit state, no current flows. When testing and screening the transistors, when at least one of VFBC and VFBE is 0, it indicates that the connection wires at least at one of the base terminal, emitter terminal, and collector terminal of the transistor are poorly welded. Therefore, the transistors with poor welding wires are screened out and excluded, and the transistors with both VFBC and VFBE not less than the corresponding preset minimum voltage values are determined to be good products and enter the subsequent production process. Additionally, it can also be to test the resistance at the base-emitter terminal and the base-collector terminal of the transistor after step 2. When measuring the resistance R1 at the base-emitter terminal and the resistance R2 at the base-emitter terminal, since in a normal transistor, one of R1 and R2 is infinite and the other is a relatively small value, when measuring R1 and R2 and both R1 and R2 are infinite, the transistor is determined to be a defective product and excluded.

[0025] During screening, the test temperature can be appropriately increased as needed to ensure the reliability of thermal stress screening. For example, the reflow soldering peak temperature of the lead-free tin furnace is measured to be 265±5℃, the reflow soldering peak temperature corresponding to the transistor is set to 265℃, and the test temperature is 265±50℃; for example, the reflow soldering peak temperature of lead-free flip-flop products and tin-carrier products is measured to be 270±5℃, the reflow soldering peak temperature corresponding to the transistor is set to 270℃, and the test temperature is 270±50℃; the temperature of the SMD red plastic board wave tin furnace is measured to be 260±5℃, the reflow soldering peak temperature corresponding to the transistor is set to 260℃, and the test temperature is 260±50℃; when soldering the bottom of the lead-free PCB board, the reflow soldering peak temperature is measured to be 245±5℃, the reflow soldering peak temperature corresponding to the transistor is set to 245℃, and the test temperature is 245±50℃. This application does not list them all. Preferably, ΔT=0 is selected so that the test can be as close as possible to the peak temperature that can be achieved by actual reflow soldering without wasting too much energy and causing damage to the transistor.

[0026] Other test conditions are based on the normal transistor specifications for ICBO, IEBO, V(BR)CBO, V(BR)CEO, V(BR)EBO, hFE (amplification factor), and VCE(sat). This test method can be used for both NPN and PNP transistors.

[0027] According to an embodiment of the present invention, a method for inspecting the welding quality of a bipolar transistor further includes applying a base current IB as a base saturation current to cause the collector current IC to enter a saturation region, measuring the base-collector voltage VFBC and the base-emitter voltage VFBE of the transistor, and determining the transistor as a good product when both VFBC and VFBE are not less than corresponding preset minimum voltage values. The base saturation current is the minimum base current required to maintain the collector current IC in the saturation region. This can accelerate the detection of products at risk of oxidation of the solder balls of the transistor connecting wires.

[0028] Since the emitter resistance and collector resistance inside the transistor are parasitic resistances connected in series on the emitter junction and collector junction, reflecting the silicon material characteristics of the emitter junction and collector junction, as well as resistances such as connecting wires and bonding, when there is degradation of ohmic contact or bonding under high current and high temperature, applying base current IB as the base saturation current and then testing the electrical performance parameters of the transistor can effectively determine the reliability differences of the transistor;

[0029] The method for detecting the welding quality of bipolar transistors according to an embodiment of the present invention is characterized in that the transistor is heated to a test temperature and then gradually cooled to the test temperature, specifically comprising: heating the transistor to the test temperature and then maintaining it at the test temperature t and then gradually cooling it, wherein t is greater than or equal to 30s. Figure 2 As shown in the figure, it is a general transistor reflow soldering temperature curve. In actual application scenarios, transistors require a certain operation time during reflow soldering. Maintaining a certain time t can be closer to the actual application soldering scenario. To a certain extent, the longer the test temperature is maintained, the easier it is to expose the transistor with poor soldering. In this way, the phenomenon of poor soldering of the transistor can be exposed as much as possible under the impact of the test temperature, thereby improving the accuracy of detection.

[0030] like Figure 2 As shown in the figure, it is a schematic diagram of the existing transistor reflow soldering temperature curve. According to the processing technology of different motherboard application scenarios of transistor applications, the specific graph of the reflow soldering temperature curve is different. The more consistent the soldering temperature curve selected for testing is with the reflow soldering temperature curve in subsequent processes, the more accurate the test result will be.

[0031] The method for detecting the welding quality of a bipolar transistor according to an embodiment of the present invention further includes: applying a base current IB as a first current I1, and measuring a base-collector voltage VFBC1 and a base-emitter voltage VFBE1 of the transistor under the first current I1; applying a base current IB as a second current I2, and measuring a base-collector voltage VFBC2 and a base-emitter voltage VFBE2 of the transistor under the second current I2; and calculating the value of the bipolar transistor according to the formula and Calculate RE and RC. If |VFBE1-VFBE2|<0.5, RE<0.6, |VFBC1-VFBC2|<0.5, and RC<0.6 simultaneously meet, the transistor is considered to be good. It is understandable that I1 is not equal to I2. Whether the first current I1 is greater than the second current I2 or the first current I1 is less than the second current I2, it does not affect the accuracy of this detection method. The following example uses the case where the first current I1 is less than the second current I2. The first current I1 is less than the base saturation current, and the second current I2 is less than or equal to the base saturation current. That is to say, when any of the following four conditions is not met: condition 1: |VFBE1-VFBE2|<0.5; condition 2: RE<0.6; condition 3: |VFBC1-VFBC2|<0.5; condition 4: RC<0.6, it means that the connecting wires of at least one of the base terminal, emitter terminal and collector terminal of the transistor are poorly welded. Therefore, the transistors with poor welding wires are screened out.

[0032] Optionally, I2=nI1, I2 is less than or equal to the base saturation current, where n is greater than or equal to 2. Within a certain range, the greater the difference between I2 and I1, the more likely the measured |VFBE1-VFBE2|, |VFBE1-VFBE2|, RE, and RC are to reveal whether the transistor has a poor soldering condition.

[0033] According to an embodiment of the present invention, the method for detecting the welding quality of bipolar transistors further includes: maintaining the transistor in a temperature environment of 125±2°C for at least 30 minutes, taking it out after N cycles and placing it at room temperature for a first time, wherein N≧30, measuring the voltage VFBC of the base-collector terminal and the voltage VFBE of the base-emitter terminal of the transistor, and judging the transistors whose VFBC and VFBE are not less than the corresponding preset minimum voltage values as good products. Among them, 125±2°C is selected in the national standards GB / T4587-94 and IEC747-7-1988, and can accelerate the oxidation of the solder balls of the exposed transistor connection wires under thermal shock. After the experiment, the appearance of the transistor is normal, and the reverse breakdown voltage BV of the collector-emitter terminal of the transistor is measured. CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO , BV CEO and BV EBO Transistors that do not show open circuit are judged to be good products.

[0034] Optionally, it also includes: keeping the transistor in a temperature environment of -40℃±2℃ for at least 30 minutes, taking it out after N cycles and placing it at room temperature for a second time, wherein N≧30, measuring the voltage VFBC of the base-collector terminal and the voltage VFBE of the base-emitter terminal of the transistor, and judging the transistor whose VFBC and VFBE are not less than the corresponding preset minimum voltage values as a good product. Among them, -40℃±2℃ is selected in the national standard GB / T4587-94 and IEC747-7-1988. Under low temperature shock, the appearance of the transistor is normal after the end of the experiment, and the reverse breakdown voltage BV of the collector-emitter terminal of the transistor is measured. CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO , BV CEO and BV EBO Transistors that do not show open circuit are judged to be good products.

[0035] The larger N is, the more cycles of high-temperature shock or low-temperature shock are applied to the transistor, and the more likely it is that oxidation of the solder balls of the transistor connecting wires will be exposed. N can be adjusted according to actual needs to select different cycles.

[0036] Optionally, the first time and the second time are both greater than or equal to 1 hour. Because temperature can affect the performance of transistors, after the transistors are subjected to high temperature shock and low temperature shock, leaving them at room temperature for a period of time until the transistor temperature approaches room temperature before testing can make the test more accurate.

[0037] The method for detecting the welding quality of bipolar transistors according to the embodiment of the present invention can quickly screen out abnormal and poor performance problems of early-stage switch failures (manufacturing defects), improve the screening detection rate of major hidden and reliability-deficient quality defects of transistors, avoid outflow to subsequent processes, and reduce the after-sales failure rate.

[0038] Verification testing: The transistors are NPN-type chip transistors packaged in a SOT-23 package. Full parameter testing is performed on defective products in advance, and the electrical parameters show that they meet the requirements of the specification. Therefore, defective products will not be exposed, as shown in Table 1.

[0039] Table 1

[0040]

[0041]

[0042] Determine the reflow soldering peak temperature T corresponding to the application scenario of the transistor, and set the test temperature to T+ΔT, where ΔT=0.

[0043] Heat the transistor to the peak temperature according to the reflow soldering temperature curve of the application scenario, and then gradually cool it down according to the reflow soldering temperature curve.

[0044] Table 2

[0045]

[0046] Keep the defective transistors at 125±2℃ for 168h, take them out after the corresponding number of cycles and place them at room temperature for 1h. Keep the defective transistors at -40℃±2℃ for 168h, take them out after the corresponding number of cycles and place them at room temperature for 1h. Then, test the transistors on the machine according to the conditions shown in Table 2. CBO is the collector junction saturation current when the emitter is open, I EBO is the emitter junction saturation current when the collector is open, h FE(1) For the amplification factor segment, Vce(sat) refers to the minimum voltage between CE required to reach the saturation region.

[0047] Table 3

[0048]

[0049]

[0050] The results are shown in Table 3. The reverse breakdown voltage BV of the collector-emitter terminal is CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO All show open circuit, collector-base reverse breakdown voltage BVCBO The display is normal.

[0051] In the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right", "inner", "outer", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. In addition, features with "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0052] In the description of the present invention, it should be noted that, unless otherwise expressly specified or applied, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0053] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Claims

1. A method for detecting the welding quality of a bipolar transistor, characterized in that: include: Determine the reflow soldering peak temperature T corresponding to the application scenario of the transistor, and set the test temperature to T+ΔT, where -10°C ≤ ΔT ≤ 10°C; Raising the ambient temperature of the transistor to the test temperature and then gradually cooling it to the detection temperature; Acquiring electrical performance parameters of the transistor, and determining that the transistor is a good product when the measured electrical performance parameters all meet specification requirements; The method for detecting the welding quality of the bipolar transistor further comprises: Applying a base current IB as a first current I1, and measuring a base-collector voltage VFBC1 and a base-emitter voltage VFBE1 of the transistor under the first current I1; Applying the base current IB as a second current I2, and measuring a base-collector voltage VFBC2 and a base-emitter voltage VFBE2 of the transistor under the second current I2; According to the formula RE= and RC= , calculate RE and RC, and when |VFBE1-VFBE2|<0.5, and RE<0.6, and |VFBC1-VFBC2|<0.5, and RC<0.6 are simultaneously satisfied, the transistor is judged to be a good product.

2. The method for detecting the welding quality of a bipolar transistor according to claim 1, wherein: The heating of the transistor to the test temperature and then gradually cooling it down to the detection temperature specifically includes: heating the transistor according to a reflow soldering temperature curve corresponding to the application scenario and then gradually cooling it down to the detection temperature according to the reflow soldering temperature curve.

3. The method for detecting the welding quality of a bipolar transistor according to claim 1, wherein: The obtaining of the electrical performance parameters of the transistor specifically includes: measuring the base-collector voltage VFBC and the base-emitter voltage VFBE of the transistor, and determining that the transistor is a good product when both the VFBC and the VFBE are not less than corresponding preset minimum voltage values.

4. The method for detecting the welding quality of a bipolar transistor according to claim 3, wherein: Before obtaining the electrical performance parameters of the transistor, the method further includes: Applying base current IB is the base saturation current, which makes the collector current enter the saturation region.

5. The method for detecting the welding quality of a bipolar transistor according to claim 1, wherein: The obtaining of the electrical performance parameters of the transistor specifically includes: measuring the resistance of the base-collector terminal and the resistance of the base-emitter terminal of the transistor, and when the resistance of the base-collector terminal and the resistance of the base-emitter terminal of the transistor are both infinite, the transistor is determined to be defective and is discarded.

6. The method for detecting welding quality of bipolar transistors according to claim 1, wherein: I2=nI1, I2 is less than or equal to the base saturation current, where n is greater than or equal to 2.

7. The method for detecting welding quality of bipolar transistors according to claim 1, wherein: Also includes: Keep the transistor at a temperature of 125±2°C for at least 30 minutes. After N cycles, take it out and place it at room temperature for the first time, where N≧30. Measure the reverse breakdown voltage BV of the collector-emitter end of the transistor. CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO , the BV CEO and the BV EBO The transistors that do not show an open circuit are determined to be good products.

8. The method for detecting welding quality of bipolar transistors according to claim 7, characterized in that: Also includes: The transistor is kept at a temperature of -40°C ± 2°C for at least 30 minutes. After N cycles, it is taken out and placed at room temperature for a second time, where N≧30. The reverse breakdown voltage BV of the collector-emitter end of the transistor is measured. CEO and the reverse breakdown voltage BV of the emitter-base terminal EBO , the BV CEO and the BV EBO The transistors that do not show an open circuit are determined to be good products.

9. The method for detecting welding quality of bipolar transistors according to claim 8, characterized in that: The first time and the second time are both greater than or equal to 1 hour.

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