Abstract: Thermal resistance has a significant impact on the reliability of transistors. By utilizing a mathematical relationship between the transistor's ΔVbe parameter and thermal resistance under certain conditions, the thermal resistance parameter can be indirectly tested by measuring the ΔVbe parameter, thus achieving transistor quality testing. This method offers advantages such as high measurement efficiency, low cost, and no damage to the device. Keywords: Transistor; Thermal resistance; Testing 1. Introduction Thermal resistance can reflect quality problems such as sintering or bonding of the chip, solder layer, and casing. Thermal resistance characteristics have a crucial impact on transistor reliability. Utilizing a mathematical relationship between the transistor's ΔVbe parameter and thermal resistance under certain conditions, the thermal resistance parameter can be indirectly tested by measuring the ΔVbe parameter. This method offers advantages such as high measurement efficiency, low cost, and no damage to the device. However, transistor thermal characteristics are complex, sensitive, and unstable. Achieving the required measurement accuracy is challenging. Currently, foreign countries have developed principle-based thermal resistance testing systems. The domestic market urgently needs cost-effective transistor testing and screening equipment. This system can measure the transient and steady-state thermal resistance of power bipolar transistors (NPN and PNP types), and can also test the thermal resistance of diodes and LEDs. By applying test conditions to the test system, the system displays the measurement data on the computer screen based on the temperature change reflected by the transistor's thermal resistance characteristics, and performs rapid filtering based on the test results. The system has contact detection and oscillation detection functions to prevent temperature measurement errors caused by poor contact and oscillation. The system also has an avalanche protection circuit and can be used to measure the safe operating area (SOA), thus improving the stability of the test system. 2. Thermal Resistance Testing Technology The thermal resistance of a transistor generally consists of the chip thermal resistance, the chip socket contact thermal resistance, and the case thermal resistance. The chip socket contact thermal resistance, which is related to chip sintering during production, is the most difficult to control. Poor sintering will greatly increase the chip-socket thermal resistance, leading to device failure due to excessively high junction temperatures during use. The thermal resistance of a transistor in pulsed operation mode is the ratio of the junction temperature rise to the amplitude of the dissipated pulse power. For power transistors, the case temperature is typically used as the temperature reference point, expressed as: θjc = (Tj - Tc) / P, where Tj is the chip junction temperature, Tc is the case temperature, and P is the pulse power. Thermal resistance measurement boils down to measuring the pulse power consumption P, Tc, case temperature, and junction temperature Tj. Obviously, the transistor's junction temperature Tj cannot be directly measured. Therefore, the forward voltage drop Vbe of the emitter junction has a good linear relationship with the junction temperature Tj within a certain range: ΔVbe = M·ΔTj, where M is a temperature-sensitive parameter. This relationship is used as the physical basis for measuring the thermal resistance of transistor devices. Measuring ΔVbe requires setting the following main parameters: Vcb (voltage between collector and base); Ie (loaded current); Im (induced current); Pt (power time); Dt (delay time); upper limit; and lower limit. Due to differences in manufacturing processes among various manufacturers, even transistors of the same model, belonging to different manufacturers, may have different applied pulse power, test time, and selected temperature-sensitive parameters. 3. Test System Architecture The basic architecture of the thermal resistance test system is a computer-controlled precision analog and digital circuit system that performs a series of program controls—condition application, result sampling, screening, calculation, comparison, and judgment—to automatically test the electrical parameters of the device under test. Each test process takes less than 0.2 seconds. The system mainly consists of an analog multiplexer board, a digital multiplexer board, an ADC board, an Im board, an Ie board, and a Vcb board, as shown in Figure 1. [align=center] Figure 1 System Architecture[/align] 4. ΔVbe Test Flowchart ΔVbe is an important parameter of a transistor, and it has a quantitative linear relationship with the transistor's thermal resistance. It reflects the transistor's power dissipation capability and has important guiding significance for transistor packaging processes and failure analysis. The ΔVbe test flowchart is shown in Figure 2 below. [align=center]Figure 2 Flowchart of the ΔVBE Test System[/align] 5. Software Function Implementation Modules The system software design is completed using a combination of Visual C++ and assembly language. The software function implementation modules include: 1. User Management Module: The program needs to determine the user's identity during runtime. User types include operator, maintenance personnel, engineer, and system administrator. Operators have the right to run test programs; maintenance personnel have the right to perform self-tests and calibrations on the test instruments; engineers have the right to edit test programs; and system administrators have all permissions. 2. Editing Module: Used for device selection, classification settings, debugging, and test program creation. The initial test program interface is shown in Figure 3: [align=center]Figure 3 Initial Test Program Interface[/align] 3. Running Module: Tests the devices according to the user's parameter settings and displays the test results and data on the computer screen. 4. Other Modules: Includes system tools, a filtering module, and a printing module. The system tools include a self-calibrating instrument for self-testing, calibration, and magnetic field testing of the thermal resistance testing system; a screening module that performs different tests on devices according to user-defined screening conditions and sends the test results to the screening machine; and a printing module that prints test results and data in a pre-set format for analysis and archiving. 6. Conclusion This paper analyzes thermal resistance testing technology, designs the architecture and flowchart of a thermal resistance testing system, and introduces the functional modules implemented in the software. Due to the complex and unstable characteristics of transistors, extensive practice and exploration are required in actual development to obtain various parameter values ​​and achieve low testing cost and high measurement efficiency while maintaining high measurement accuracy. References: [1] Zhang Xiaozhuang, Liao Xiaohua. 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