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The Past and Present Life of Connector Quality Inspection

Time:2018-08-24Click: Order

1. What is a connector?

Connector, also known as CONNECTOR. Also known as connectors, plugs, and sockets in China. Generally refers to electrical connectors. A device that connects two active devices to transmit current or signals.

The connector is a component that our electronic engineering technicians often come into contact with. Its function is very simple: to build a communication bridge between blocked or isolated circuits within the circuit, thereby allowing current to flow and enabling the circuit to achieve its intended function. Connectors are essential components in electronic devices, and when observed along the path of current flow, you will always find one or more connectors. The form and structure of connectors are ever-changing, and there are various forms of connectors depending on the application object, frequency, power, application environment, etc. For example, the connectors used for lighting on the court, the connectors for hard drives, and the connectors for igniting rockets are very different. However, regardless of the type of connector, it is necessary to ensure smooth, continuous, and reliable flow of current. In general, connectors are not limited to the current they connect to. In today's rapidly developing optoelectronic technology, the carrier for transmitting signals in fiber optic systems is light. Glass and plastic have replaced wires in ordinary circuits, but connectors are also used in the optical signal path, and their functions are the same as circuit connectors. Since we only care about circuit connectors, this course will closely integrate with Molex's products and focus on introducing circuit connectors and their applications.

2. Why use connectors?

Imagine what would happen if there were no connectors? At this point, continuous conductors should be permanently connected between the circuits. For example, if an electronic device is to be connected to a power source, both ends of the connecting wire must be securely connected to the electronic device and power source through some method (such as welding). In this way, both production and use have brought many inconveniences. Take car batteries as an example. Assuming that the battery cable is fixed and welded firmly to the battery, automobile manufacturers increase the workload, production time, and cost of installing the battery. When the battery is damaged and needs to be replaced, the car needs to be sent to a repair station, where the old one needs to be soldered off, and the new one needs to be soldered on again, which requires a higher labor cost. Having a connector can save you a lot of trouble. Just buy a new battery from the store, disconnect the connector, remove the old battery, install a new battery, and reconnect the connector. This simple example illustrates the benefits of connectors. It makes the design and production process more convenient and flexible, reducing production and maintenance costs.

Benefits of connectors:

1. Improving the production process

Connectors simplify the assembly process of electronic products. It also simplifies the batch production process;

2. Easy to repair

If a certain electronic component fails, it can be quickly replaced when a connector is installed;

3. Easy to upgrade

With the advancement of technology, when connectors are installed, the components can be updated and replaced with new and more complete components;

4. Improve design flexibility

The use of connectors allows engineers greater flexibility in designing and integrating new products, as well as in composing systems with components.

3. Basic performance of connectors

The basic performance of connectors can be divided into three categories: mechanical performance, electrical performance, and environmental performance. Another important mechanical property is the mechanical life of the connector. Mechanical lifespan is actually a durability indicator, referred to as mechanical operation in GB5095. It is evaluated based on whether the connector can complete its connection function (such as contact resistance value) normally after a specified insertion and extraction cycle, with one insertion and one extraction as a cycle.

1. In terms of connection function, the insertion and extraction force is an important mechanical performance. The insertion and extraction forces are divided into insertion force and extraction force (also known as separation force), and their requirements are different. In relevant standards, there are provisions for maximum insertion force and minimum separation force, which indicates that from a usage perspective, the insertion force should be small (resulting in structures with low insertion force LIF and no insertion force ZIF), and if the separation force is too small, it will affect the reliability of contact. The insertion and extraction force and mechanical life of connectors are related to the contact structure (positive pressure), the coating quality of the contact area (sliding friction coefficient), and the accuracy of the contact arrangement size (alignment).

2. The main electrical properties of connectors include contact resistance, insulation resistance, and electrical strength.

① High quality electrical connectors with contact resistance should have low and stable contact resistance. The contact resistance of connectors varies from a few milliohms to tens of milliohms.

② The insulation resistance is an indicator that measures the insulation performance between the contacts of an electrical connector and between the contacts and the shell, with an order of magnitude ranging from hundreds of megaohms to thousands of megaohms.

③ Electrical strength, also known as voltage resistance or dielectric withstand voltage, is the ability to withstand the rated test voltage between connector contacts or between contacts and the shell.

④ Other electrical performance.

Electromagnetic interference leakage attenuation is the evaluation of the electromagnetic interference shielding effect of a connector. Electromagnetic interference leakage attenuation is the evaluation of the electromagnetic interference shielding effect of a connector, generally tested in the frequency range of 100MHz to 10GHz.

For RF coaxial connectors, there are also electrical indicators such as characteristic impedance, insertion loss, reflection coefficient, and voltage standing wave ratio (VSWR). Due to the development of digital technology, a new type of connector, high-speed signal connector, has emerged to connect and transmit high-speed digital pulse signals. Correspondingly, in terms of electrical performance, in addition to characteristic impedance, some new electrical indicators have also emerged, such as crosstalk, transmission delay, and delay.

3. Common environmental performance includes resistance to temperature, humidity, salt spray, vibration, and impact.

① The maximum working temperature of the current connector is 200 ℃ (except for a few high-temperature special connectors), and the minimum temperature is -65 ℃. Due to the heat generated by the current at the contact point during the operation of the connector, resulting in a temperature rise, it is generally believed that the working temperature should be equal to the sum of the ambient temperature and the contact temperature rise. In certain specifications, the maximum allowable temperature rise of connectors under rated operating current is clearly specified.

② The invasion of moisture resistance can affect the insulation performance of the connection and corrode metal parts. The constant damp heat test conditions are a relative humidity of 90% to 95% (up to 98% according to product specifications), a temperature of+40 ± 20 ℃, and a test time of at least 96 hours according to product regulations. The alternating damp heat test is more rigorous.

③ When salt spray resistant connectors work in environments containing moisture and salt, the surface treatment layer of their metal structural components and contact parts may produce electrochemical corrosion, which affects the physical and electrical performance of the connectors. In order to evaluate the ability of electrical connectors to withstand this environment, a salt spray test is specified. It suspends the connector in a temperature controlled test chamber and sprays out a specified concentration of sodium chloride solution with compressed air to form a salt mist atmosphere. The exposure time is specified by the product specifications and is at least 48 hours.

④ Vibration and shock resistance are important properties of electrical connectors, especially in special application environments such as aviation and aerospace, railway and road transportation. They are important indicators for testing the robustness of the mechanical structure and electrical contact reliability of electrical connectors. There are clear provisions in the relevant test methods. The peak acceleration, duration, and pulse waveform of the impact test should be specified, as well as the time for electrical continuity interruption.

⑤ According to usage requirements, other environmental properties of electrical connectors include sealing (air leakage, liquid pressure), liquid immersion (resistance to specific liquids), low air pressure, etc.

4. Categories and definitions of connectors

Due to the increasing diversity of connector structures and the emergence of new structures and application fields, attempting to solve classification and naming problems with a fixed pattern has become difficult to adapt to. Nevertheless, some basic classifications are still valid.

1. Hierarchy of interconnections

According to the functions of the internal and external connections of electronic devices, interconnections can be divided into five levels.

① Internal connection of chip packaging

② The connection between the IC packaging pins and the PCB. Typical connector IC socket.

③ The connection between printed circuits and wires or printed boards. A typical connector is a printed circuit connector.

④ The connection between the base plate and the base plate. A typical connector is a cabinet type connector.

⑤ The connection between devices. A typical product is a circular connector.

There is some overlap between levels ③ and ④. Among the five levels of connectors, the products with the highest market value are those at levels ③ and ⑤, while currently the products with the fastest growth are those at level ③.

2. Hierarchy of connector specifications

According to the classification of the International Electrotechnical Commission (IEC), connectors belong to electromechanical components used in electronic equipment, and their specification levels are:

Family example: connectors

Sub family Example: Circular connectors

Example: YB type circular connector

Type (style) Example: YB3470

Specification (variant)

3. Definition of connectors in China

In the industry management of our country, connectors, switches, keyboards, etc. are collectively referred to as electrical plug-in components, while electrical plug-in components and relays are collectively referred to as electromechanical components.

4. Product categories of connectors

Although the classification of connector product types is somewhat confusing, technically speaking, there are only two basic methods for classifying connector product categories: ① according to the external structure: circular and rectangular (cross-sectional), ② according to the working frequency: low frequency and high frequency (bounded by 3MHz).

According to the above division, coaxial connectors belong to circular shapes, while printed circuit connectors belong to rectangular shapes (historically, printed circuit connectors have indeed been separated from rectangular connectors to form their own class). Currently, popular rectangular connectors have a trapezoidal cross-section, similar to a rectangular shape. The frequency division of low-frequency, high-frequency, and radio waves based on 3MHz is also basically consistent.

As for other types that can be classified according to their purpose, installation method, special structure, special performance, etc., they often appear in publications and manufacturers' promotional materials. However, they are generally only used to highlight a certain feature and purpose, and the basic classification still does not exceed the above classification principles.

Considering the technological development and actual situation of connectors, based on their universality and relevant technical standards, connectors can be divided into the following categories (sub categories): ① low-frequency circular connectors; ② Rectangular connector; ③ Printed circuit connectors; ④ RF connector; ⑤ Fiber optic connectors.

5. Model naming of connectors

The model naming of connectors is the basis for customer procurement and manufacturer organization of production. In the connector industry at home and abroad, there are two ways to name product models: one is to use letter codes and numbers to reflect the main structural characteristics of the product in the model naming. The advantage of this method is that it is easy to identify, but the arrangement is too long and complex, which brings many difficulties to printing as the connectors become smaller. At present, this method is still popular in China and has been stipulated in certain industry standards and even national standards, such as SJ2298-83 (printed circuit connectors), SJ2297-83 (rectangular connectors), SJ2459-84 (ribbon cable connectors), GB9538-88 (ribbon cable connectors), etc. Due to the increasing diversity of connector structures, it is becoming increasingly difficult to cover a certain type of connector with a naming convention in practice. Another approach is to combine Arabic numerals. The advantage of this method is its simplicity, ease of computer management, and printing of small product logos. The major international connector manufacturers currently adopt this approach. It can be expected that the naming method developed by each manufacturer to reflect their own characteristics will gradually replace the method of unified industry wide naming rules under the planned economy system.

5. Overview of connector market development

With the rapid growth of consumer electronics, automotive electronics, and communication terminal markets, as well as the continuous transfer of global connector production capacity to Asia and China, Asia has become the place with the most development potential in the connector market, while China will become the market with the fastest growth and largest capacity in the global connector market. It is estimated that the growth rate of the Chinese connector market will continue to exceed the global average in the future. In the past few years, the average annual growth rate of the Chinese connector market has reached 15%.

The main supporting fields of electrical connectors include transportation, communication, network, IT, healthcare, home appliances, etc. The rapid development of product technology and market growth in the supporting fields strongly drive the development of connector technology. So far, connectors have developed into a series and specialized product with a complete range of products, rich varieties and specifications, diverse structural types, segmented professional directions, obvious industry characteristics, and standardized standard systems.

Overall, the development of connector technology presents the following characteristics: high-speed and digitalization of signal transmission, integration of various signal transmissions, miniaturization and miniaturization of product volume, low-cost products, surface mounting of contact termination methods, modular combination, convenient insertion and removal, and so on. The above technologies represent the development direction of connector technology, but it should be noted that not all connectors are required. The demand points for the above technologies are completely different for connectors in different supporting fields and different usage environments.

6. Development direction of connectors

The development of connectors should be towards miniaturization, high-density, high-speed transmission, and high-frequency. Miniaturization refers to the smaller center spacing of connectors, and high-density refers to the realization of large number of cores. The total number of effective contacts for high-density PCB (printed circuit board) connectors reaches 600 cores, and specialized devices can reach up to 5000 cores. High speed transmission refers to the requirement of modern computer, information technology, and networking technology for signal transmission with a time scale rate of up to megahertz frequency band and pulse time of up to sub milliseconds. Therefore, high-speed transmission connectors are required. High frequency is to adapt to the development of millimeter wave technology, and RF coaxial connectors have entered the millimeter wave operating frequency band.

7. Famous connector manufacturers both domestically and internationally

AVIC Optoelectronics, Aerospace Electronics, Sichuan Huafeng, Foxconn Technology, Tyco Electronics, Molex, Amphenol, FCI, JAE (for reference only)

A Complete List of Commonly Used Terminology for Connectors

1. Connector: A detachable component usually installed on a cable or equipment for the electrical connection of a transmission line system (excluding adapters)

2. RF connector: It is a connector used within the RF range.

3. Video: Radio waves with a frequency range of 3Hz to 30MHz.

4. Radio frequency: A radio wave with a frequency range of 3 kHz to 3000 GHz.

5. High frequency: A radio wave with a frequency range between 3MHz and 30MHz.

6. Coaxial: The inner conductor has a dielectric support and can structurally obtain the minimum internal reflection coefficient within the frequency range used in measurement.

7. Triple axis: A transmission line composed of three concentric conductors with a common axis and insulated from each other.

8. Level: The level of mechanical and electrical precision of connectors, especially in terms of specified reflection coefficients.

9. Universal connector (Level 2): A type of connector manufactured with the widest allowable dimensional deviation (tolerance), but still capable of ensuring the minimum specified performance and compatibility.

Note: The requirements for reflection coefficient can be specified or not.

10. High performance connector (Level 1): A type of connector that specifies the limit value of reflection coefficient based on frequency variation. Generally, the specified dimensional tolerance is not more stringent than the corresponding Level 2 connector. However, when it is necessary to ensure that the connector meets the requirements of reflection coefficient, the manufacturer is responsible for selecting the connector