A basic electrical connector product consists of a plastic body, a contact spring element called a terminal, and a contact plating. The plastic body in this product isolates the contact springs from each other and cannot conduct with each other, and fixes the contact springs in the plastic body to provide mechanical protection and shielding protection for each contact spring. The contact spring provides a path for communication between the contact members when the products are mated with each other. The contact coating is a layer of coating on the surface of the contact assembly (usually a copper alloy) to prevent the base metal of the contact assembly from being corroded and optimize the structure of the contact interface. In the improvement of the temperature rise of the electrical connector, it is mainly aimed at the improvement of the three parts of the product.

1. The design of the terminal structure.

(I) selection aspects.

For electrical connectors with high rated current, the choice of terminal material should not only ensure the high conductivity of the material, but also ensure that the product meets certain mechanical performance requirements. The selection of materials generally follows the following principles: traditional power connectors have low rated current and high mechanical properties, and materials with low conductivity and good mechanical properties can be selected, such as brass, phosphor bronze, etc. The power connector LLCR has high requirements and large rated current, and must meet certain mechanical properties. Products with high conductivity must be selected, and the materials must also meet certain mechanical properties, such as chromium-zirconium-copper alloys. For electrical connector products that require particularly high current ratings and are used as quiescent terminals, the terminal material may be selected from a material having a conductivity of almost 100 percent, such as copper. In the selection of terminal materials, in addition to meeting the function, cost and procurement cycle are also important considerations. In terms of comprehensive performance and cost comparison, select the appropriate material.

(2) Setting of terminal length.

The terminal length of electrical connector products has a great influence on the temperature rise. The longer the terminal time, the more unfavorable the temperature rise. Therefore, when meeting the mechanical properties of the product and the contact friction distance requirements of the terminal, the length of the terminal should be shortened as much as possible.

(3) terminal cross-sectional area design.

The temperature rise of the electrical connector product is also related to the cross-sectional area of the terminal. The larger the cross-sectional area of the terminal, the lower the temperature rise of the product. Therefore, as long as the external dimensions of the product are met, as long as the electrical characteristics of the product are met without affecting the assembly, increasing the cross-sectional area of the terminal can greatly reduce the temperature rise.

2. Design of contact impedance.

The contact resistance includes compression resistance and film resistance. The smaller the contact resistance, the more favorable the temperature rise. Without considering the material properties, the factors that affect the contact resistance are as follows: the positive force when the terminal is in contact increases the positive force within a certain range and reduces the contact resistance. The design of the contact surface increases the number and area of contact points, and the reduction of resistance is beneficial to the temperature rise. Electroplating layer design, the contact area of the terminal is generally gold-plated, the thickness of the gold-plated film is conducive to temperature rise, but the cost must be considered, and the thickness of the gold-plated film must be determined according to actual needs. The terminal oxide layer, gold, and nickel in the plating layer are inactive metals. Copper is easy to react with oxygen, water vapor, sulfur dioxide, etc. An oxide layer is formed in the air, which reduces the effective contact point and causes the temperature to rise.

3. Plastic cooling structure design.

In the design of plastic parts, when the plastic structure meets the conditions for the terminal to maintain and cooperate with each other, ventilation holes should be opened on the plastic surface at the position where the high temperature point is generated in the contact area of the terminal, and a large amount of heat energy should be quickly and effectively dissipated through convection. The temperature rise here can be reduced. Similarly, in other parts of the product plastic, the use of escape holes can also be beneficial to the heat dissipation of the product.

4. Experimental specification design.

From product design to product physical assembly, product development is not over, it is only half of product development, and product testing to meet specifications is the final completion. Among them, the temperature rise test is the most critical test in the power connector test. Many products are misjudged due to non-standard testing and do not meet product requirements. Therefore, the design of product test specifications is also very important, mainly in the following aspects:

(1) Selection of initial temperature.

In the temperature rise test, the test result is to judge whether the product meets the requirements according to whether the difference between the temperature before and after the product is less than 30 ℃. Therefore, the selection of the initial temperature before the product test is equally important, because there is generally no specific requirement for the initial temperature of the environment in the test specification. Many laboratories in factories do not have the condition of constant temperature and use the same product, the same person and the same machine for test verification, the measured temperature rise is also very different, so when the general test, the laboratory is required to select the initial temperature measurement at 25 ℃.

(2) the selection of thermocouple.

In the current test specification, only the wire diameter of the test line is defined, but there is no specific definition of the wire diameter of the thermocouple. Thermocouples with different wire diameters are used to test the same sample, and the temperature rise varies greatly. Therefore, during the temperature rise test, large-diameter thermocouples can be used to ensure the stability of the measurement results.

(3) Test PCB structure design.

In the case of failure of the temperature rise test, it is found through thermal imaging that the high point of temperature heating is on the test PCB, which has a great impact on the product temperature rise test. In order to reduce the influence of the test PCB board on the temperature rise test of the product, the PCB design at this time can be improved from two aspects:(1) the thickness of the copper foil and the number of layers of the copper foil should be increased, which not only reduces the resistance of the copper foil but also increases the heat dissipation of the copper foil. (2) Increase the area of the copper foil and bring the heat to the PCB board through the trace to reduce the temperature rise.

(4) the influence of test conditions.

At present, many products have added air-cooled fans in the whole machine test. In the temperature rise test of the high-current power connector, whether to add air cooling will have a great impact on the test results of the product. For the same product, under the same other test conditions, with or without air cooling, the test results vary greatly. At present, many end customers have explicitly added air-cooled tests to the test. In the finite element analysis of our product design, it is necessary to add sub-cold conditions for analysis, so as to truly reflect the true situation of product testing.

At present, the market has higher and higher requirements for the rated current of power connectors, and the performance and quality requirements of products are gradually improving. While improving product quality, the cost of the finished product must also be considered. When developing products, it is necessary to develop suitable large connectors. Current connectors. In the design of high-current connectors, the following two aspects are mainly considered: reducing the conductor resistance and contact resistance of the terminal components as much as possible, and making the highest temperature point located in a favorable ventilation position, and using convection heat dissipation. Whether air cooling is added in the temperature rise test has a great influence on the results. At present, many customers have specifications in this regard. In the plastic design, the escape of the material of the product is cleverly used to ensure that there is enough air flow inside the product and it is absolutely necessary to avoid dead ends that generate heat. The accumulation of heat has a great influence on the temperature rise.