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BGA device repair (Rework) process, one of the important link is the temperature curve (Themal Profiling) setting. The maintenance process requires more temperature control than normal Reflow temperature curves. In a conventional reflow furnace, there is little temperature loss. For maintenance, the PCB circuit is generally heated in the air for a single component. In this case, the temperature loss is quite serious. Therefore, the temperature compensation cannot be achieved by heating alone. This is because on the one hand, for the device, the excessively high temperature will obviously damage the device itself, and on the other hand, the temperature rise will inevitably cause the uneven heating of BGA, resulting in bending deformation and other negative effects. Therefore, setting the appropriate temperature curve is the key to BGA maintenance. In addition, due to the different material, thickness and heat dissipation of PCB, the temperature sensitivity of corresponding BGA is also different.
In order to achieve better maintenance results, it is necessary to set the most appropriate repair temperature curves for different PCB boards.
The temperature curve of BGA repair can be divided into six parts: preheating, heating, constant temperature, fusion welding, back welding and cooling. But in general, the first five sections are enough. Welding and diswelding can use the same temperature curve, but we can divide the temperature curve into six sections.
1. Preheating: the main function of pre-heating and heating section is to remove moisture on PCB board, prevent bubbling, and preheat the whole PCB to prevent thermal damage. The general temperature requirements are: in the preheating stage, the temperature can be set between 70℃ -110℃, generally set 80-90℃, about 35s can play the role of preheating. At the same time, the preheating time can be extended moderately according to the actual situation, such as PCB board or BGA exposed in the air for a long time.
2. Heating up: At the end of the second constant temperature time, the temperature of BGA should be kept between (lead-free :140~180℃, with lead :140-173℃). If it is too high, it means that the temperature of the heating up period we set is too high, and the temperature of this period can be set lower or shortened. If it is too low, the temperature of the preheating section and the heating section can be increased or longer.
(Lead-free 140-180℃, time 50-80s; There is lead 160-193℃, the time is 70-130s)
3. Constant temperature: We generally set the temperature of this temperature section to be slightly lower than that of the heating section, so as to equalize the internal temperature of the tin ball, make the overall temperature of the BGA average, and make those slightly lower temperatures rise slowly. And the section can activate the flux, remove the oxide and surface film on the surface of the metal to be welded and the volatiles of the flux itself, enhance the wetting effect and reduce the effect of temperature difference. Generally, the actual test temperature of the tin ball in the constant temperature section is required to be controlled between (lead-free :160~175℃, with lead 135~150℃), and the time can be 20-40s.
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