![]() Such a guess work would not be so bad if they went back and checked the profiles using some failed boards because there are plenty of failed boards in such companies. They tend to guess the thermal mass of the board and use guess the oven settings that may work. For example, many companies do not even bother with using loaded board attached with thermocouples. However, this easy task is rarely performed by many companies. In case of BGAs, thermocouples need to be attached to the inner and outer rows of the balls as well.Ĭommercial hardware and software packages, such as MOLE, data pack and many others are available to make thermal profile development an easy task. With this tighter process window the importance of using product specific profile is becomes even more critical.įor developing the profile, you need the loaded board with six to eight thermocouples soldered to solder joints of large and small components across the board. This reflow process window narrows to 15C since the soldering needs to be done between 230C to 245C. Of course, the selection of this temperature curve, mainly based on the melting point of metal composition of the lead-free solder paste, the activity temperature of the flux, the structure and function of the reflux furnace, the heat capacity of the welding object and other specific circumstances, the ultimate goal is not to damage the PCB and components under the premise of reliable soldering quality.With tin lead eutectic composition one could easily get away by maintaining peak temperature between 190C to 225C, a variation of almost 35C and still achieve good reflow soldering results. ⑤ Compared with the traditional reflux furnace, energy consumption is reduced and maintenance is relatively simple. ④ The solderability and bright solder joints can be improved by using solder flux activation temperature matching the paste of lead-free alloy. ③ Due to slow heating, the temperature difference of PCB board surface decreases, which is conducive to overcoming the adverse factors of lead-free solder causing the reduction of process window. 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. Alloy,, is the best solder in the reflowing process. ![]()
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