The BGA rework process described herein is generic in nature to the type of heating system used. The experience BEST has gained in reworking thousands of BGAs on hundreds of different customer PCBs. BEST has expertise on stacked package (PoP) rework as well.
However Ball Grid Array rework is the operation of removing and then replacing with either existing or new a replacement device. This typically occurs when an upgrade is required, the device has failed or has been improperly placed ion to the PCB. By emulating the original controlled manufacturing process the replacement device can be properly seated on to the PCB.
Prior to removal to beginning the removal of the BGA, PCB preheating is necessary. This is especially true in the case of lead free PCBs as the required temperature difference across the package during device reflow is supposed to be very tight. By heating up the bottom side of the PCB, then applying top side of heat to the component to be removed, the heat becomes localized at the component and not distributed throughout the thermally conductive material of the PCB. This help reduce the possibility of the PCB from becoming warped.
By monitoring the PCB at several points on near and within the package the proper profile can be developed. External thermocouples (TC) are used as standard practice to monitor these temperatures. When heating the component from the top side, the generated heat should remain localized at that site until the solder goes in to the liquid state. The BGA component in this part of the BGA rework process can then be lifted from the PCB using vacuum.
After component is removed, the next step in the ball Grid Array Rework process is site cleaning which is referred to as residual solder removal. This process can be done in a multitude of different fashions. One of the methods is with an operator using a hand soldering iron and copper braid. With lead-free solders entering mainstream manufacturing a few years ago, the increased melting point of the solder complicates this process further. Damaging the solder mask, lifting BGA pads during device removal and the damage of solder mask with excessive and uncontrolled heat are just some of the potential problems if the ball grid array rework/repair process is not done correctly.
Once the device has been removed and the site prepped the ball grid array must now be re-soldered to the location. This step is similar to removing the device from the PCB on that the replacement device is subjected to a controlled time-temperature characteristic curve. Prior to placement solder paste can either be re-printed on to the site location or paste flux can be used for attachment.
In any case a well-developed ball grid array rework process needs to be in place to insure a high first pass yield.
