SMT process

- Oct 20, 2018-


In the wave soldering process, the wave peak is the core.The preheated, flux-coated, non-soiled metal can be sent to the welding station through the conveyor belt to contact the solder with a certain temperature, and then heated, so that the flux will have a chemical reaction, solder alloys through wave peak power interconnection, which is the most critical step.At present, the commonly used symmetric wave crest is called the main wave crest, and the pump speed, wave peak height, infiltration depth, transmission Angle and transmission speed are set to provide all-round conditions for achieving good welding characteristics.The data should be properly adjusted, and the solder should be slowed down after leaving the crest and slowly stopped.The PCB will eventually push the solder to the outlet as the wave crests run.Under the most suspended condition, the solder's surface tension and the crest of the optimized plate run, achieving zero relative motion between the crest of the component and the exit end.This dehulling area is achieved by removing the solder from the plate.Sufficient dip Angle shall be provided without defects such as bridge, burr, wire drawing and soldering ball.Sometimes, the crest outlet needs to have a hot air current to ensure that the possible bridging is excluded.After mounting the top surface at the bottom of the plate to attach the element, sometimes to compensate for the flux or bubbles forming in the "harsh crests" area behind the plate, while the turbulent chip crests are used before the crests are levelled.The high vertical velocity of a turbulent crest helps to ensure that the solder is in contact with the lead or pad.The vibration part behind the levelled laminar wave crest can also be used to eliminate air bubbles and ensure the solder to achieve satisfactory contact components.Welding workstation should be basically: high purity solder (according to the standard), peak temperature (230 ~ 250 ℃), contact crest the total time (3 ~ 5 seconds), depth of PCB in wave (50 ~ 80%), parallel transfer orbit and wave parallel to orbit in the state of flux content in tin pan. 

Cooling after welding of 3 wave crests

A cooling station is usually installed at the end of the wave crest welding machine.The aim is to limit the tendency of copper-tin compounds to form solder joints, and another reason is to accelerate the cooling of the components, avoiding plate displacement while the solder is not fully solidified.Quick cooling module to limit sensitive element exposure to high temperature.However, the hazards of the thermal shock of the erosive cooling system to the elements and solder joints should be considered.A well-controlled "soft and stable" forced gas cooling system should not damage most components.There are two reasons for using this system: it can quickly process the board without holding it by hand, and it can guarantee that the temperature of the component is lower than the temperature of the cleaning solution.People are concerned about the latter cause, which may cause some flux residue to bubble.Another phenomenon is sometimes the appearance of a reaction with some of the flux dross, so that the residue "can not be cleaned out."No formula can meet these requirements in terms of ensuring that the data set up in the welding station meets all machines, all designs, all materials used and process material conditions and requirements.You must understand every step of the whole process.4 conclusion in conclusion, in order to obtain the best welding quality and meet the needs of users, every process step before and during welding must be controlled, because every step of SMT's entire assembly process is interrelated and interacted with each other, and any problem in any step will affect the overall reliability and quality.The same is true for welding operations, so all parameters, time/temperature, solder volume, flux composition, transmission speed, and so on should be strictly controlled.The defects in welding shall be identified as early as possible, analyzed, and corresponding measures shall be taken to eliminate the defects affecting quality in the bud state.In this way, we can ensure that the products produced conform to the technical specifications.