Wave soldering is the most commonly used eutectic tin-lead solder alloys: tin 63%; 37% of lead
Master solder purity (standard), peak temperature (230 ~ 250 ℃), total peak exposure time (3-5 seconds), PCB peak in the depth of immersion (50 to 80%)
Wave soldering machine in the tail of an additional cooling station
In the process of assembling electronic components, welding plays a very important role. It relates to product performance, reliability and quality, and even affect each subsequent process steps. In addition, electronic components toward the light, thin and small in the direction the rapid development of welding a series of problems, for which all manufacturers of electronic manufacturing industry around the SMT soldering process in a fierce competition to further improve the welding quality, welding to overcome the existing short-circuit, bridging, solder balls, and weld defects, thereby improving product quality to meet market demand. Currently, the most widely used welding processes are wave soldering and reflow soldering. Wave soldering process is mainly used for through-hole components and various types of welding, is a key group of welding processes. Despite the wave soldering process for many years of history, and will continue to follow the go, however, but if we have access to practical, viable wave soldering process must hold time. Because this process must achieve rapid, high productivity and reasonable cost and other requirements. In other words, this process before and welding is closely related to each process step, including capital investment, PCB design, component solderability and pcb assembly operations, flux selection, temperature / time control, solder and crystal structure.
At present, wave soldering is the most commonly used eutectic tin-lead solder alloys: tin 63%; 37% of lead, should always grasp the solder solder pot temperature, the temperature should be higher than the liquid alloy temperature 183 ℃, and make the temperature uniform. Past, 250 ℃ solder pot temperature is considered "standard." With the flux technology innovation, the entire solder pot solder temperature uniformity under control, and the addition of a preheater, the temperature trend is to use a lower solder pot. In the 230-240 ℃ range setting solder pot temperature is very common. Typically, the component is not uniform thermal mass, to ensure that all the joints to achieve sufficient temperature to form a qualifying spot is necessary. Important issue is to provide enough heat to raise the temperature of all the leads and pads to ensure the mobility of solder, solder wetting both sides. Low temperature solder components and substrates will reduce thermal shock, help reduce scum formation at a lower intensity, the flux coating operation and flux compounds working together, can have a peak export enough flux, this can reduce the generation of burrs and ball. Solder pot solder composition is closely related with the time, that change over time, thus leading to the formation of scum, which is removed from the welding of the components of residues and other metal impurities in the welding process causes and causes loss of tin. These factors can reduce the solder flow. In procurement, to the provisions of the trace metal content of the tin solder dross and the highest limits in the various standards, (such as are clearly defined as IPC/J-STD-006). In the welding process, the solder purity standards required ANSI/J-STD-001B is also provided. In addition to the restrictions of the scum, 63% tin; 37% tin-lead alloy in the provision of not less than the minimum content of 61.5%. Wave soldering components on a layer of gold and copper concentration of organic gathered swimming faster than in the past. This concentration, coupled with significant loss of tin, solder can lose mobility, and the welding problems. Looks rough, granular solder joints is often caused due solder dross. Because the accumulation of dross solder pot or component inherent residue bleak, rough grainy solder joints may also be a sign of low tin content, not the local special solder, tin-pot loss is the result of tin. This appearance may be in the solidification process, due to vibration or shock caused. Solder joint appearance will be able to directly reflect the process issues or material problems. To maintain the solder "full pot" process control program in accordance with state and check the solder pot for analysis is very important. As the solder pot with scum and "drained" solder pot of flux, it is usually unnecessary, as required in conventional applications to add solder to tin pot, so that the solder tin pot is always full . In the case of loss of tin, add pure tin helps to maintain the required concentration. In order to monitor the tin pot compounds, should be routine analysis. If you add a tin, sampling and analysis should be to ensure that solder Chengfen correctly proportioned. Scum too much is a troublesome problem. No doubt, there is always scum solder pot there, in the atmosphere is particularly true when welding. Use the "chip wave" component which is helpful for welding high-density, due to exposure to the atmosphere of the solder surface is too large, leaving the solder oxidation, it will produce more dross. Solder pot solder layer covering the surface with the scum, oxidation speed slowed down. In welding, the peak of the tin pot will produce turbulence and flows more scum. Recommended conventional method is to skim the scum, if frequent write-cut, it would generate more scum, and consumed more solder. Scum also may have been mixed in the wave, causing instability or wave turbulence, thus requiring the liquid ingredients to the solder pot to give more maintenance. If allowed to reduce the amount of tin solder pot, then solder the surface of the scum will enter the pump, this phenomenon is likely to occur. Sometimes, the joints will be mixed with granular scum. Initially discovered scum, may peak caused by rough and potentially clogging the pump. Tin pan should be equipped with an adjustable low-volume solder sensor and alarm devices.
In the wave soldering process, the crest is the core. Can be preheated, coated with flux, dirt-free metal to the welding station by conveyor belt to reach a certain temperature solder, and then heated, so the flux will produce a chemical reaction, the peak power through the formation of solder alloy interconnects, which is the most critical step. At present, the commonly used symmetrical peaks known as the main peak, set the pump speed, wave height, depth of invasion, transmission angle and transmission speed, in order to achieve good welding characteristics with a full range of conditions. Should make an appropriate adjustment to the data, leaving behind the crest (outlet) should slow down and make the solder run, and slowly stop the run. PCB with the solder wave to run the final push to exports. Hang in most cases, solder surface tension and the best run of the board of the peak in the components and the export side of the peak can be achieved between the zero relative motion. The shelling the region is to achieve the removal of board solder. Should provide full tilt, no bridges, burrs, wire drawing, and ball and other defects. Sometimes, the peak export demand with a hot air flow to ensure the formation of the bridging rule out the possibility. Mounted on the bottom of the plate surface mount components, sometimes, flux compensation or behind the formation of the "harsh peak" area of ??the bubble, and the leveling of peaks before the peak using the turbulence chips. The high speed peak vertical turbulence helps ensure solder pad contact with the leads. Laminar flow in the entire flat part of the vibration peaks can also be used later to eliminate air bubbles to ensure the solder to achieve a satisfactory contact with components. Basically, welding workstation should be: high-purity solder (standard), peak temperature (230 ~ 250 ℃), the total exposure time of peak (3 to 5 seconds), PCB immersed in the depth of the peak (50 to 80 %), to achieve the transfer orbit and in parallel with the tracks parallel to the wave solder pot state flux levels.
After cooling wave soldering
Wave soldering machine in the tail is usually an additional cooling station. In order to limit the formation of copper-tin intermetallic compounds, the trend of solder joints, another reason is to accelerate the cooling of components in the solder is not completely cured, to avoid the board shift. Rapid cooling components, to limit exposure to high temperature sensitive components. However, taking into account the erosion of the cooling system components and solder joints of the danger of thermal shock. A well-controlled "soft stabilization" and forced air cooling system should not damage most components. Using this system for two reasons: fast processing board without Yongshou gripping and ensure components of the cleaning solution temperature than low temperature. People are concerned about the latter reason, the flux residue may cause some blistering reasons. Another phenomenon is sometimes react with certain scum phenomenon of flux, so that makes the residue "cleaning can not afford." Welding workstation settings to ensure the data meets all of the machines, all design, materials and processes used in all conditions and requirements of materials no established formula to meet these requirements. Must understand the whole process every step of the operation.
In short, to get the best weld quality, to meet the needs of users, must be controlled prior to welding, the welding of each process step, because the entire SMT assembly process every step of interrelated, interacting, any further problems will Shadow of the overall reliability and quality. Welding operation, too, so all parameters should be strictly controlled, time / temperature, the amount of solder, flux composition and transmission speed, and so on. Generated in the welding defects, should try to identify the causes, conduct analysis, to take corresponding measures, will affect the quality of a variety of defects being nipped in the bud. Thus, in order to ensure the production of the products meet the technical specifications.