![]() Although it is possible to allow the PCBA to cool in air, it is better to use a temperature control system to control the cooling rate, because the cooling rates too fast may damage components or solder joint peeling Slowly cooling will produce tin-silver-copper-nickel intermetallic compounds and reduce the strength of solder. Components need to stay in the reflow zone for long time enough to wet the solder joints, but if the time too long, devices will be damaged.Īfter the reflow zone, the product undergoes a cooling process, calling the cooling zone, which mainly strengthens the solder joints. The reflow zone is the area with the highest temperature during the reflow soldering process, also known as the Time Above Liquids (TAL), and the temperature is mostly set to be 20-40 ☌ higher than the solder liquefaction temperature. The important role of this area is to maintain a uniform temperature of surface components even though different sizes and materials, so that the PCBA can reach thermal equilibrium before entering the reflow zone. When the solder paste is on the eve of melting, the volatiles is further removed, and the activator will start to act, decomposing oxides on the welding surface. The temperature of RSS usually maintains in the region of 150☑0☌, and the temperature of RTS falls between 150-190☌. In this stage, the volatile solvent in the solder paste will slowly evaporate, and the preheating time depends on the allowable maximum rate of the surface components temperature changing and the solvent volatility of the solder paste. This area is the stage where the temperature of the Printed Circuit Board Assembly (PCBA) raises from normal temperature to 150☌, mainly to allow the printed circuit board and surface mount device components to be gradually preheated to avoid damage during soldering. So the main purpose is to completely fix surface mount device on the printed circuit board by reflow soldering.Ĭommon reflow soldering temperature curves include Ramp-Soak-Spike (RSS) and Ramp-To-Spike (RTS), as shown in Figure 1 and Figure 2, which can be divided into four stages, the preheat zone, soak zone, reflow zone and cooling zone, the following will introduce four stages one by one. ![]() The solder paste is a mixture of flux and tin powder, which is characterized by its viscosity when no soldered, and can stick to the components placed on the surface of the printed circuit board, protecting the surface elements from being slightly shaken and not being offset. This is a material used to solder electronic components to printed circuit board, and functions like tin-wire and tin-powder. This is a common method used in surface mount technology to bond components, which saves large amount of solder, and more suitable for surface mount device. Reflow soldering is to use solder paste to bond electronic components to solder pads, and control the temperature through the reflow oven, solder paste is gradually melted, and then the printed circuit board is cooled and solder solidified to achieve permanent bonding. Exceeding the product specification may cause damage, so reflow soldering must be tested correctly before putting it into use. In practical applications, it must be adjusted according to product specifications and production environment. ![]() The standard of reflow soldering temperature curve refers to IPC/JEDEC J-STD-020E. This article will introduce reflow soldering technology, analyze various temperature curves, and common problems. ![]() Therefore, reflow soldering technology came into being. However, wave soldering is no longer suitable for surface components decreasing volume. The electronic industry is developing rapidly, and surface mount technology is undoubtedly an important invention to promote its growth.
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