STG pcb assembly process--wave soldering
In the process of electronic components assembly, welding has played a quite important role. It relates to the products performance, reliability and quality, etc., and even affect the subsequent each process's step. Also, due to the electronic components are fast development towards to a light, thin, and small ,so it raised a series of problem for weldig process.For this,the electronic manufacture has a fierce competition sourrounding the SMT welding process, which helps to improve the quality of welding, overcome existing in the welding of short circuit, bridge, solder ball and weld defects such as leakage, to improve the quality of products meet the market demand.
At present,in the PCB Assembly, the wave welding is the most commonly used solder eutectic tin lead alloy, tin 63%; Lead 37%, should always keep the solder in solder pot temperature, its temperature should be higher than that of alloy liquid temperature 183 ℃, and make the temperature uniform. In the past, the 250 ℃ temperature of the solder pot is regarded as the "standard". As flux technology innovation, the solder in solder pot uniformity of temperature controlled, and add the preheater, the development trend is to use low temperature solder pot. In the range of 230-240 ℃ set temperature of the solder pot is very common.Uaually,the component does not have a uniform thermal mass, to ensure all the solder reaches sufficient temperature to form qualified solder joints are necessary. Important challenge is to provide adequate heat, all the lead and solder temperature, so as to ensure that the mobility of the solder, wetting on both sides of the joint.
In the wave soldering process, wave soldering is the core. Preheating can be of metal, coated with flux, dirt-free by conveyor belts to the welding station, solder contacts with a certain temperature, then heat flux, it causes a chemical reaction, and solder alloy formed by wave power interconnection, which is the most crucial step. At present, the common symmetric wave called the primary Crest, set pump speed, wave height, depth of infiltration, reporting point, and transfer rate to achieve good soldering properties provides a full range of conditions. Data should make the appropriate adjustments, to leave behind the crest of the (exit) on the solder to run down, and slowly stop working. PCB with the crest running to eventually push the solder to export. Hanging in the most cases, solder surface tension and best Board of Crest run, between the components and the export side of the crest for zero relative motion. This shelling areas is to achieve the removal of solder on the Board. Should provide sufficient inclination, no bridging, burrs, wire and solder joint defects.
Wave soldering after cooling
Usually,Among the PCB fabrication and assembly ,we will add a cooling workstation at the tail end of the crest welder.In order to limit trends in Cu-Sn intermetallic compound formation of solder, another reason is to accelerate the cooling of the component, when the solder is not fully cured, avoiding transposition of Board.Rapid cooling components, in order to limit exposure to high temperature sensitive components. However, consideration should be given to the aggressive cooling system components and solder joints of the dangers of thermal shock. A "stable" soft control good, forced air cooling system should not damage most of the components.There are two reason to using this systerm: to quickly handle plate, instead of a hand holding, and can guarantee the component temperature is lower than the temperature of the cleaning solution.