RF Connector expertise Oct 12, 2015

    The basic properties of RF connectors can be divided into three categories: mechanical, electrical, and environmental.Another important mechanical property is the mechanical life of the connector.Mechanical Life is actually a durability indicator, they are referred to as mechanical operation in NATIONAL standard GB5095.It takes one insert and one pull out as a cycle, and judges whether the RF coaxial connector can normally complete its connecting function (such as contact resistance value) after the specified insert and pull cycle.

    1.Mechanical property As far as connection function is concerned, plug and pull force is an important mechanical property.Plug and pull force is divided into insertion force and pull out force (pull out force is also called separation force), the two requirements are different.In the relevant standards, the maximum insertion force and minimum separation force are stipulated, which indicates that, from the perspective of use, the insertion force should be small (hence the structure of low insertion force LIF and no insertion force ZIF), while the separation force if too small will affect the reliability of contact.The plug and pull force and mechanical life of the connector are related to the coating quality (sliding friction coefficient) of the contact part and the dimension precision (alignment) of the contact part. 

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

    (1) High quality electrical connectors should have low and stable contact resistance.The contact resistances of connectors vary from a few to tens of milliohms. 

    (2) Insulation resistance measures the insulation performance between the contacts of electrical connectors and between the contacts and the housing. Its order of magnitude varies from hundreds to thousands of megohm. 

    (3) The electrical strength, or voltage and dielectric resistance, is the ability to withstand the rated test voltage between the connector contacts or between the contacts and the housing. 

    Other electrical properties.Electromagnetic interference leakage attenuation is used to evaluate the electromagnetic interference shielding effect of the connector, which is generally tested within the range of 100MHz~10GHz frequency.For RF coaxial connectors, there are electrical indicators such as characteristic impedance, insertion loss, reflection coefficient, voltage standing wave ratio (VSWR), etc.Due to the development of digital technology, in order to connect and transmit high-speed digital pulse signals, a new type of connector, namely high-speed signal connector, has appeared. Correspondingly, in terms of electrical performance, in addition to characteristic impedance, some new electrical indicators have appeared, such as Crosstalk, transmission delay, and delay. 

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

    At present, the highest working temperature of connectors is 200℃ (except for a few special high temperature connectors), the lowest temperature is -65℃.When the connector works, the current generates heat at the contact point, resulting in the temperature rise. Therefore, it is generally considered that the operating temperature should be equal to the sum of the ambient temperature and the temperature rise at the contact point.In some specifications, the maximum allowable temperature rise of the connector at the rated operating current is specified. 

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

    (3) When the salt spray connector works in an environment containing moisture and salt, its metal structure, contact surface treatment layer may produce electrochemical corrosion, affecting the physical and electrical properties of the connector.In order to evaluate the resistance of electrical connectors to this environment, salt spray tests are prescribed.The connector is suspended in a temperature-controlled test chamber and ejected with compressed air at a specified concentration of sodium chloride solution to form a salt mist atmosphere with an exposure time specified by the product specification of at least 48 hours. 

    (4) Vibration and impact vibration resistance and impact is an important performance of electrical connectors, in special application environments such as aviation and aerospace, railway and road transport is particularly important, it is the test of electrical connectors mechanical structure of the robustness and electrical contact reliability of important indicators.The relevant test methods are clearly specified.Peak acceleration, duration, impulse waveform, and time for interruption of electrical continuity shall be specified in the impact test.


    (5) Other environmental performance according to the requirements of use, other environmental performance of the electrical connector is sealability (air leakage, liquid pressure), liquid impregnation (resistance to specific liquid vice), low pressure, etc.

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