![]() The same is true in the reflow phase, because the temperature should be equal to or higher than the required peak temperature within a fixed preset time. It should also be noted that it is ideal that the temperature during the drying or soaking stage is fairly constant. The peak value of lead-containing solder is about 210-220☌, and the peak value of lead-free solder is about 30☌. The temperature shown in the above reflow curve is the typical temperature of solder paste most commonly used by PCB contract manufacturers (CM). The reflow phase of the circuit board assembly is a thermodynamic process in which the circuit board goes through four intervals of temperature ranges, as shown in the figure below. The temperature and time interval of each stage are preset according to the following parameters: circuit board size, number of components, number of layers, type of solder, etc.Īs mentioned above, during assembly, reflow soldering is used to fix the SMD to the circuit board. The process involves running the circuit board through an oven and going through a four-stage profile: preheating, soaking, reflow, and cooling. For double panels, the bottom layer is the same. ![]() Reflow soldering is a surface mount technology (SMT) process that is used to connect components to the top layer of the PCB. For surface mount components, as well as pick and place, reflow is the most important stage.įirst, let us define reflow soldering, and then study how to best design circuit boards to avoid potential reflow-induced failures, which may threaten the successful development of PCBA. By using PCB assembly equipment to place and firmly fix the components, the design embodiment is finally determined. The process starts and depends on a well-defined design, which includes specifying all materials, components and their layout, or stacking and PCB layout. The development of PCBA is a good example of how to realize these four aspects of product generation. However, the quality of the results usually depends on the specific equipment and its efficiency. With these basic elements, almost anything can be achieved or produced. You need time to integrate the first three. Is the knowledge or expertise necessary to execute the plan.ģ. Nitrogen capable reflow ovens and SMT ovens are typically equipped with an automatic gas sampling system and an Oxygen Analyzer.To generate tangible projects of any degree of complexity, there are four basic requirements:Ģ. The Oxygen levels in a Nitrogen reflow process can be as low as less than 10ppm but may be higher than 500ppm for some less critical processes. The use of Nitrogen or Forming Gas is meant to reduce or eliminate oxidation of the assembly during the heating process. A number of specifications are employed including a maximum and minimum peak temperature inside the reflow soldering oven, such as Flux Activation Time (FAT), Time Above Liquidus (TAL), heating and cooling ramp rates, etc.Ī reflow furnace can process circuit boards in air atmosphere or in a controlled Nitrogen or Forming Gas environment. The recipe is optimized to achieve the profile that the solder reflow machine manufacturer has specified for the solder paste that is used on the board. ![]() The temperature that the board “sees” as it is processed through the oven is called “ the profile”. The program with the temperatures for all of the zones, as well as the belt This set point corresponds to the temperature the circuit board should be exposed to as it passes through that zone. During the reflow soldering process, the zones are programmed with a thermal set point. Depending on the length and throughput of the oven there may be few zones, 8 or less, or many zones, 12 or more. Inline reflow ovens are configured with a number of heating zones followed by cooling section(s). The most modern reflow ovens use closed-loop convection. Convection reflow ovens had many advantages including vast improvements in heating uniformity. Later on, the industry, led by companies like BTU International, switched to convection heat transfer. In the early days of electronics manufacturing, infrared (IR) heating technology was employed. For larger manufacturers, an inline or conveyor belt reflow oven is the best choice. An led reflow furnace can be a small batch (box) style oven for very small lab scale operations. Thermal processing of solder for electronics manufacturing takes place in a reflow oven.
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