The biggest advantage of a high-precision BGA rework station for soldering BGA is that the temperature curve can be accurately set. The BGA rework station will go through a preheating period of 190°C, and then automatically heat up to 250°C, and then to 300°C, the solder paste can be fully soldered, and then the cooling is decreased, and then the cooling is carried out. The temperature curve setting also needs to be based on whether the chip contains lead, the size of the chip, and the temperature and duration of each stage of the solder paste brand are different.
The temperature rise rate of the lead-free preheating zone can be generally controlled at 1.2~5℃/s (seconds), the temperature in the preheating zone is generally not more than 160℃, the temperature in the holding zone is controlled at 160~190℃, and the peak temperature in the reflow zone is generally It is controlled at 235~245℃, and the temperature is maintained for 10~45 seconds, and the time from the temperature rise to the peak temperature should be maintained for about one and a half minutes to two minutes. The melting point of leaded solder paste is 183 degrees, while the lead-free solder paste is 217 degrees. That is to say, when the temperature reaches 183 degrees, the leaded solder paste begins to melt, and the actual melting point of the solder ball will be higher than that of the solder paste due to its chemical properties.
The rework of high-precision BGA chips needs to be set according to the type of chip, temperature program, etc. Hot air heating is based on the principle of air heat transfer, using high-precision controllable heating controls to adjust the air volume and wind speed to achieve a uniform and controllable heating purposes. During soldering, the body of the BGA chip is transmitted to the tin bead part of the BGA chip due to heat transfer. The temperature will be a certain difference from the temperature at the hot air outlet. When the high-precision BGA rework station is heated at the set temperature, the above factors must be taken into account. We also need to understand the performance of the tin beads and set the temperature segment.
When we need to rework the new BGA chip, without knowing its temperature tolerance, we need to set a value for the high-precision BGA rework station and BGA rework machine, and then monitor the entire heating process. When the temperature rises above 200 degrees At this time, observe the melting degree of the solder balls, and use tweezers to test whether they can move. When the BGA chip solder balls are completely melted, the BGA chip will be clearly observed to sink down. At this time, heat the chip at a constant temperature for 10-20 seconds, that is, the temperature is completed. setting. The ordinary BGA rework station does not have a constant temperature stage setting, which is easy to cause damage.
If the rework of high-precision and fine-pitch BGA chips must be completed using a high-precision BGA rework station, there are two reasons: the ordinary BGA rework station is generally in the second temperature zone, and it cannot desolder the lead-free chips; the high-precision BGA rework station Compared with the ordinary BGA rework station, the advantage is that it has three parts of the heating system for independent temperature control, which can be combined according to different chip spacings to achieve the best temperature heating effect.
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