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Good terminals require multiple environmental factors for reliability
AddTime:2017.08.12      Hits:  【Big Middle Small】  Close

Terminals are usually exposed to a variety of environmental factors, such as during transportation and warehousing, during the manufacturing process, during installation, maintenance, and end-user use. These environmental factors can be understood as established conditions, which can be divided into temperature, humidity, corrosion, pollution, internal and external conditions and human factors. It is also necessary to define the duration of exposure to the changing circumstances in these environmental factors.

Warehousing: the storage environment of large current terminals is different, from controllable clean, heated or air-conditioned, wet warehouses, offices or factories to the uncontrollable environment. The service life of terminal can be seriously affected by heat, humidity or corrosion. In these uncontrollable environments, welding life can be greatly reduced due to oxidation, corrosion and metal intercalation. The surface and function of metal devices will be affected by rust, copper and other forms of corrosion; Plastics, as insulating materials, are also affected by the degradation of flexibility, strength and shape.

The terminal storage period can be long and short, the length can be several months, short days and weeks, some need to make long-term inventory plans for the customers, while others will go to the warehouse immediately. By using fifo inventory strategy, the traceability date label system, the appropriate packaging way, anti-corrosion methods, improvement of storage conditions, and the appropriate terminal materials and design, can improve the reliability of terminals and prolong storage life.

Transportation: environmental factors are related to the problems caused by the vibration, impact, road surface and loading and unloading tools of vehicles and other mechanical devices during operation. Extreme temperatures often combine and exacerbate the effects of vibrations and collisions. Marine terminals are often exposed to salt fog. Transit time is usually predictable, and land transportation and airlift usually last a few days, while sea transport can take months or months. In the process of transportation, the terminal and packaging materials must be kept intact and must be decomposed, deformed, corrosion-resistant and anti-extrusion. Usually adopt the following measures can improve the reliability of transportation, the goods can be smoothly to reach its destination: using a reputable carrier, using the appropriate packaging materials, strong inside and outside packing, appropriate anti-corrosion lining or packing, the necessary measures and appropriate terminal materials and design.

Welding: welding conditions vary greatly depending on the type of terminal and the process of welding. It is suitable for welding of wave crest solder. The terminal of PCB board is typical type of perforation mounting. Porous welds must accurately locate, match, balance and weld well, which is good for insertion and welding. During the whole assembly process, the heat in the preheating area must be supported and the temperature of the terminal body is transmitted through the wave peak welding. The discharge must not affect the terminal, must be easy to clear, can not have any residue. The entire assembly process must be cleaned with water. Temperatures are usually as high as 100 degrees Celsius or higher, and the highest temperature of 280 degrees is not uncommon. Sudden increases in temperature tend to lead to terminal melting, distortion, blistering and distortion. Assembly time is generally divided into a few minutes of solder time, several minutes of preheating time, a few seconds of peak time, and a few minutes of cleaning and drying. The selection of suitable metal materials and resin can improve the reliability of welding.

For reflow soldering, large current terminals installed on PCB boards are usually mounted on the surface or through holes. Surface must be correct installation of welding needle positioning, suitable size, and the PCB can completely coplanar or micro float to accommodate all the tin on the PCB, ensure the quality of welding process has sufficient strength, and the reliability of the circuit (without a break, see chart 1). Perforated welds must be accurately positioned, fit, balanced and well solderable, which is good for insertion and welding. In the process of the whole assembly must withstand high temperature shock produced by heat treatment, mainly used in welding ir preheat preheat and convection heat conduction to welding needle and tin interface with molten solder paste. There is no need to require cleaning, but people generally expect it. Preheating zone, a temperature setting of peak of 230 ° C, the higher temperature in a few minutes. As with wave crest welding, sudden high temperature often causes the terminal to melt, twist, foaming and deform. Assembly time typically consists of several minutes of preheating, a few seconds of peak, and a few minutes of cleaning and drying. Of course, choosing proper metal materials and resins can improve the reliability of welding.