② As the temperature rises linearly, it is easy to control and the process has good repeatability. ① On the premise of not increasing the total time, prolong the heating time, so as to avoid the damage of components caused by excessive heating rate. Of course, the use of this temperature curve has a prerequisite what is that it must use the reflux furnace with a good heat transfer performance, in order to make the soldering parts in the peak temperature, thus, its surface temperature difference can meet the requirements. However, the total process time is not extended, but can be appropriately shortened the total process time. Its main feature is the elimination of the heat preservation stage, soldering parts from room temperature slowly rose to the peak temperature, thus extending the heating time, so that the heating rate can be reduced to 0.8~2 ℃ /s. This curve is called a "tent" or "triangle" shape. ② As the liquid time of lead-free solder is prolonged, it is beneficial to overcome the wettability of lead-free solder. ① Maintain sufficient time at high temperature to achieve thermal balance of components with large thermal capacity differences and reduce the cavitation of BGA solder joints. This curve is called trapezoidal temperature curve, and its main feature is to extend the peak time of reflow area, so that the time of soldering parts above the liquid phase line is extended from the traditional 40s ~ 60s to 60s ~ 90s, and the time of 30s ~ 60s should be maintained at the peak temperature of reflow soldering. Therefore, many studies recommend the following two types of temperature curves for lead-free solders. However, the melting point of lead-free solder increases obviously, which challenges the optimal process parameter value tested by long-term production practice. And the temperature of reflow process is above 183 ℃, with peaks rising 30 ℃ ~40 ℃. The temperature of “Heat Preservation” is around 140 ℃ ~160 ℃. That is, “Heating” – “Heat Preservation” – “Reflow” – “Cooling”. Typical reflow temperature curves using Sn/Pb eutectic solders are usually divided into four sections. Suitable Temperature Curve of Lead-free Solder: The eutectic solder with a 93% diffusibility range, and the lead-free solder with a 73%~77% diffusibility range. Therefore, we must raise the manufacturing temperature in the manufacturing process, otherwise it will cause a series of adverse consequences.Ģ) Wettability is slightly worse. It has a melting point of about 217 degrees Celsius and a complete melting temperature of 235 degrees Celsius. Compared with the traditional solder, it has two disadvantages in terms of manufacturability as following:ġ) The melting point is high. These results would be useful for R&D personnel in designing and implementing newer applications with finer‐pitch interconnect.Alloy,, is the best solder in the reflowing process. Some factors have main effects across the volumes and a number of interactions exist among them. Mathematical models describe the relationships among VSPD, VSBF and theoretical volume of solder paste. The results from the study show that the percentage change in the VSPD depends on the combination of the process parameters and reliability issues could become critical as the size of solder joints soldered on the same board assembly vary greatly. The study uses a fractional factorial design (FFD) of 2 4−1 Ramp‐Soak‐Spike reflow profile, with all main effects and two‐way interactions estimable to determine the optimal factorial combination. This study investigates the relationship between volume of solder paste deposit (VSPD) and the volume of solder bump formed (VSBF) after reflow, and the effect of reflow profile parameters on lead‐free solder bump formation and the associated solder joint integrity. The deposition of consistent volume of solder from pad‐to‐pad is fundamental to minimizing surface mount assembly defects. At very narrow aperture sizes, solder paste rheology becomes crucial for consistent paste withdrawal. Electronic components and their associated solder joints have reduced in size as the miniaturization trend in packaging continues to be challenged by printing through very small stencil apertures required for fine pitch flip‐chip applications. Increasing global customer demand for miniaturized electronic products is a key driver in the design, development and wide application of high‐density area array package format. The electronics manufacturing industry was quick to adopt and use the Surface Mount Technology (SMT) assembly technique on realization of its huge potentials in achieving smaller, lighter and low cost product implementations.
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