The main function of the preheating and heating section in the early stage is to remove moisture on the PCB board, prevent foaming, and preheat the entire PCB to prevent thermal damage. The general temperature requirements are: in the preheating stage, the temperature can be set between 60℃-100℃, generally 70-80℃, and about 45s can play the role of preheating. If it is too high, it means that the temperature of the heating section we set is too high, and the temperature of the heating section can be lowered or the time shortened. If it is too low, you can increase the temperature of the preheating section and the heating section or lengthen the time.
The temperature setting is lower than the heating section. The function of this part is to activate the flux, remove the oxide and surface film on the surface of the metal to be soldered, and the volatile matter of the flux itself, enhance the wetting effect, and reduce the temperature difference. Generally, the actual test tin temperature in the constant temperature section should be controlled (lead-free: 170~185℃, lead: 145~160℃). If it is too high, the constant temperature can be lowered. If it is low, the constant temperature can be increased. If the preheating time is too long or too short in our measured temperature analysis, it can be adjusted to solve by lengthening or shortening the constant temperature period.
After the second period of constant temperature, the operation is over, the temperature of the BGA rework station should be kept between (lead-free: 150~190℃, lead: 150-183℃). High, you can set the temperature of this section lower or shorten the time. If it is low, you can increase the temperature of the preheating section and the heating section or extend the time. (Pb-free 150-190℃, time 60-90s; leaded 150-183℃, time 60-120s), the heating setting is slightly higher than the constant temperature setting.
We mainly set the peak soldering temperature to be lead-free: 235~245℃, and lead: 210~220℃. If the measured temperature is too high, the temperature of the fusion welding section can be appropriately reduced, or the time of the fusion welding section can be shortened. If the measured temperature is low, you can increase the temperature of the melting section or lengthen the time of the melting section; because the upper nozzle of the machine is directly heated to the BGA rework station, and the lower nozzle is heated through the PCB board, so the temperature setting of the lower part should be higher than the upper part after the start of the fusion welding section
Reflow can be used as a cooling setting, and the setting temperature should be lower than the melting point of the solder ball. Its function is to prevent the BGA from cooling too fast and causing damage. Generally, the bottom reflow temperature can be set according to the thickness of the board, and it can be set between 80-130°C because the function of the bottom is to preheat the entire PCB board, to prevent the heating part and the surrounding temperature from being too large to cause the board to deform. So this is also one of the reasons for the higher rework yield of BGA rework stations in the three-temperature zone.
The above five steps can be combined with the PCB board to adjust the relevant temperature. For example, the Toshiba and Sony boards are thinner, easier to heat, and more easily deformed. At this time, you can appropriately lower the temperature or heating time. After the adjusted temperature curve is finished, whether the maximum temperature, preheating time, and reflow time meet the requirements. If not, you can adjust it according to the above method and then save the best temperature curve parameters for use.
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