The success rate of SMD components of the BGA rework machine is closely related to the storage environment of the BGA. The BGA must be stored at 20-25°C and <10% RH under normal circumstances, and it needs to be used within 8 hours once opened. Normal PBGA is easy to absorb moisture in the air, so we need to use nitrogen and remove the moisture inside the chip first when welding the patch. Otherwise, it is easy to cause damage to the chip due to moisture vaporization.
If you want to achieve a 100% success rate when patching components on a BGA rework machine, you need to set different temperature curves according to different packaging methods. For example, the composition of CBGA is Pb90Sn10 with a melting point of 302℃, which is attached to a ceramic carrier with a low melting point solder to prevent reflow. In general, the peak temperature of reflow welding is 210~225℃. If the diameter of the solder balls is 0.76mm and the distance is 1.17mm, you should pay more attention to the temperature control to ensure the BGA temperature difference between adjacent.
3. Preheating is also an important link of SMD components of the BGA rework machine
The first step is to use an activated flux to remove the oxides and surface films of the metal to be welded and the volatiles of the flux itself. It aims to enhance the wetting effect, reduce the temperature difference of the PCBA substrate, prevent thermal damage, remove moisture, prevent the substrate from warping, prevent bubbling, and reduce the temperature difference between adjacent BGAs. In this process, you only need to set the temperature of the thermostat to 80~100℃, and then put the PCBA substrate into the box for 8~20 hours.
The solder ball will be in a liquid state when it reaches the melting point. However, an over-long time and an over-high temperature and pressure will destroy the surface tension and support of the solder ball, which will cause the chip to fall off and cause a short circuit on the PCBA pad during reflow. In addition, it is necessary to appropriately reduce the welding time of the last temperature slot and reduce the bottom preheating temperature to ensure there is no short-circuit of SMD components of the BGA rework machine.
The manual alignment will cause an offset between the chip and the pad, so you must use a good automatic BGA rework machine to ensure a 100% success rate of SMD components. The surface tension of the solder ball will cause an automatic correction process between the BGA chip and the pad. If the heating is uneven, the chip will be prematurely switched to the reflow side. If the reflow is stopped at this time, the chip cannot fall down normally and resulting in false welding and empty welding. If we extend the heating time, the preheating temperature at the bottom will be too high so that the solder balls cannot drop evenly. Therefore, it is still necessary to use a BGA rework machine to patch the BGA.
The above information is methods and notes for the success rate of SMD components of the BGA rework machine. SMD components of the BGA rework machine use the bottom solder balls to connect to the circuit board. It is necessary to shorten the signal transmission path to increase the number of devices and have a good heat dissipation function.
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