When choosing the correct terminal, you need to consider the circuit design and its application.

The plastic insulating material and conductive parts of the terminal are directly related to the quality of the terminal

Select the correct terminal

When choosing the correct terminal, you need to consider the circuit design and its application. The plastic insulating material and conductive parts of the terminal are directly related to the quality of the terminal, and they determine the insulation performance and conductive performance of the terminal respectively.

Any terminal failure may lead to the failure of the whole system engineering. As a precision operation of the accessories products, the quality of the terminal is always the attention of customers, how to effectively check and prevent become a topic of concern.

PART03

Common faults of terminals

From the perspective of use, the function that the terminal should achieve is that the place where the contact part should be conducted must be conducted and the contact must be reliable; the place where the insulation part should not be conducted must be insulated and reliable. Terminal common fatal failure in the form of the following three:

1. Poor contact

The metal conductor inside the terminal is the core part of the terminal, which transmits the voltage, current or signal from the external wire or cable to the contact corresponding to the connector. Therefore, the contact must have excellent structure, stable and reliable contact retention and good electrical conductivity. Due to unreasonable contact structure design, material selection error, mold instability, processing size tolerance, rough surface, heat treatment plating and other surface treatment process is unreasonable, improper assembly, storage environment and improper operation and use, will be in the contact parts and matching parts of the contact cause poor contact.

2. Poor insulation

The function of the insulator is to keep the contacts in the correct position and arrangement, and to insulate the contacts from the contact to the housing. Therefore, the insulation must have excellent electrical properties, mechanical properties and process molding performance. In particular, with the widespread use of high-density, miniaturized terminals, the effective wall thickness of insulators is becoming thinner. This puts forward more stringent requirements for insulation materials, injection mold accuracy and molding process. Due to the existence of excess metal on the surface or inside the insulator, surface dust, flux and other pollution and moisture, organic material precipitates and harmful gas adsorption film and surface water film fusion to form ionic conductive channels, moisture absorption, mold growth, aging of insulating materials and other reasons, will cause short circuit, leakage, breakdown, low insulation resistance and other insulation defects.

3. Poor fixation

The insulator not only plays an insulating role, but also provides precise centering and protection for the extended contact. At the same time, it also has the functions of installation and positioning, locking and fixing on the equipment. Poor fixation, light impact on contact and reliability, resulting in instant power failure, serious is the disintegration of products. Disintegration refers to the abnormal separation between the plug and the socket, and between the pin and the socket due to the unreliable structure of the terminal in the plugged state due to the material, design, process and other reasons, which will cause the power transmission and signal of the control system. Serious consequences of control interruption. Due to unreliable design, wrong material selection, improper selection of molding process, poor quality of heat treatment, mold, assembly, welding and other processes, poor assembly will cause poor fixation.

In addition, poor appearance caused by coating peeling, corrosion, bruising, plastic shell flash, cracking, rough contact processing, deformation and other reasons, poor exchange caused by positioning and locking fit size, poor consistency of processing quality, excessive total separation force and other reasons are also common diseases and frequently-occurring diseases. These kinds of faults can generally be found and eliminated in time during inspection and use.

PART04

How to check for preventive screening

In order to ensure the quality and reliability of the terminal and prevent the occurrence of the above-mentioned failure problems, it is recommended to study and formulate corresponding screening technical requirements according to the technical conditions of the product, and carry out the following targeted reliability inspection to prevent failure.

1. Prevention of poor contact

a. Conduction detection

Generally, there is no such item in the product acceptance test of the terminal manufacturer, and the user generally needs to conduct a conduction test after installation. Therefore, it is recommended that manufacturers should increase the point-by-point conduction detection by 100 for some key models.

B. Transient break detection

Some terminals are used in dynamic vibration environments. Experiments show that only testing the static contact resistance is qualified, and can not guarantee the use of dynamic environment contact reliable. Because often the contact resistance of qualified connectors in vibration, shock and other simulated environmental tests still appear instantaneous power failure phenomenon, so for some high reliability requirements of the terminal, it is best to 100 of its dynamic vibration test to assess its contact reliability.

c. Single hole separation force detection

Single-hole separation force refers to the separation force that the contact in the inserted state changes from static to moving, which is used to indicate that the pin and the socket are in contact. Experiments show that the separation force of single hole is too small, which may cause signal transient break when subjected to vibration and impact load. It is more effective to check the contact reliability by measuring the separation force of a single hole than to measure the contact resistance. Check and find that the single-hole separation force is out of tolerance of the jack, and the measured contact resistance is often still qualified. For this reason, in addition to developing a new generation of stable and reliable flexible plug-in contacts, the manufacturer should not use automatic plug-in force testing machine for key models for multi-point simultaneous testing, and should carry out 100 point-by-point single-hole separation force inspection for finished products to prevent instantaneous signal interruption caused by relaxation of individual jacks.

2. Prevention of poor insulation

a. Insulation material inspection

The quality of raw materials has a great influence on the insulation performance of insulators. Therefore, the choice of raw material manufacturers is particularly important, not blindly reduce costs and lose the quality of materials. Materials from large factories with good reputation should be selected, and important information such as batch number and material certificate should be carefully checked for each batch of incoming materials, and traceability data for the use of materials should be prepared.

B. Insulator insulation resistance inspection

By 2012, some production plants had stipulated that the electrical performance should be tested after assembling the finished products. As a result, the whole batch of finished products had to be scrapped due to the unqualified insulation resistance of the insulator itself. Reasonable process should be 100% process screening in the state of insulator parts to ensure qualified electrical performance.

3. Prevention of poor fixation

a. Interchangeability check

The interchangeability check is a dynamic check. It requires that the same series of matching plugs and sockets can be plugged and connected to each other, and it is found whether there is any reason why the plugs cannot be plugged, positioned and locked due to excessive size of insulators, contacts and other parts, missing parts or improper assembly, or even disassembled under the action of rotating force.

Another function of the interchangeability check is to find out whether there are metal superfluous objects that affect the insulation performance through the plug connection such as thread and bayonet. Therefore, 100% of the terminals for some important purposes should be inspected to avoid such major fatal failures.

B. Torque resistance inspection

Torque resistance inspection is a very effective inspection method to check the reliability of terminal structure. Such as the U.S. military standard MIL-L-39012 standards. According to the standard, each batch of samples should be sampled for torque resistance inspection to find problems in time.

C. general measurement of crimping wire

In electrical equipment, it is often found that individual core crimping wires are not sent to the position, or cannot be locked after being sent to the position, and the contact is unreliable. The reason for the analysis is that there are burrs or dirt on the screw teeth of individual mounting holes. In particular, the last few mounting holes that the factory has installed into a plug socket have to be removed one by one after the defect is found, and the plug socket has to be replaced.

In addition, due to improper selection of wire diameter and crimping aperture, or due to misoperation of crimping process, the crimping end will not be firm. For this reason, the manufacturer shall conduct a general test on all mounting holes of the delivered plug (seat) sample before the finished product leaves the factory, I .e. use the loading and unloading tool to touch and send the crimped wire with pin or socket to the position to check whether it can be locked. Check the pull-out force of each crimped wire according to the product specifications.

Terminal is the foundation, there is no reliable terminal, there is no reliable system engineering. Prevention and analysis is a necessary process for each enterprise. Through terminal reliability screening, various failure modes and failure mechanisms can be found, a large number of experiences and lessons can be analyzed and various hidden dangers can be eliminated, which can provide scientific basis for improving design, process, inspection and use. It is an important basis for revising and formulating terminal technical conditions and provides technical support for preventing unnecessary losses.