Above, we mentioned the introduction of BGA repair temperature curve, so let's continue our conversation.
Melt welding and back welding:
The two temperature segments can be used in conjunction with one, and the temperature segment can be set directly to "melt weld". This part is to make a good fusion between tin ball and pcb pad. In this part, we mainly want to achieve the welding peak (no lead :235~245℃, lead :210~220℃). If the temperature is too high, we can appropriately reduce the temperature of the melting welding section or shorten the time of the melting welding section. If the temperature is too low, the temperature of the melt welding section can be increased or the time of the melt welding section can be lengthened. We limit the welding time of common bga chip types to 90 seconds, that is to say, we increase the time when the temperature is low, and choose to increase the melting welding temperature when the temperature is still low over 90 seconds. If the ideal peak is reached after 70 seconds, we can change it to 70 seconds in the fourth period.
The final backweld can be used as a cooling setting that is lower than the melting point of the tin ball. Its role is to prevent BGA from cooling too fast and causing damage.
The upper air nozzle of the machine is heated directly against the BGA, while the lower air nozzle is heated through the PCB board. Therefore, the temperature setting of the lower part should be higher than that of the upper part after the melting welding section begins. At the same time, when the lower part is hotter than the upper part, it can effectively prevent the board from concave due to gravity. So when you set the temperature the upper part stops heating earlier than the lower part.
Bottom temperature, generally can be set according to the thickness of the board, generally can be set between 80-130 degrees Celsius. The function of the bottom is to preheat the whole PCB board, to prevent the heating part and the surrounding temperature difference is too large and cause the deformation of the board. So this is why the general repair platform is now three temperature area. Without the bottom warm-up, the success rate of BGA repair will be reduced and the PCB may be damaged.
Finally, combined with PCB board to adjust the relevant temperature. The board is thinner and more prone to deformation on hot days. At this time, you can appropriately lower the temperature or heating time.
(For some glue filling BGA devices, you can properly extend the heating time, so that it will be easier to dismantle)
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