BGA rework is typically performed to remove components that are faulty, damaged, or incorrectly aligned, and to replace them with new components. The basic principle of manual rework is to handle the circuit board and components with care to avoid overheating, which could cause damage to the board’s plated through-holes, components, and solder pads. (I personally do not recommend using a hot air gun for rework). Below is the BGA rework process using a BGA rework station.
I. Desoldering
- Preheating: Preheat the PCB and BGA to remove moisture. Use a constant temperature oven for baking.
- Nozzle Selection: Choose a nozzle size suitable for the BGA chip and install it on the machine. The upper nozzle should completely cover the BGA chip or extend 1-2mm beyond it. The upper nozzle can be larger than the BGA, but it must not be smaller to ensure even heating. The lower nozzle should be larger than the BGA.
- Fixing the PCB: Secure the PCB that needs rework on the BGA rework station. Adjust its position and use a fixture to clamp the PCB and position the lower nozzle under the BGA (for irregular PCBs, use custom fixtures).
- Temperature Curve Setup: Set the corresponding temperature curve. The melting point for leaded solder is 183°C and for lead-free solder is 217°C. Use the standard lead-free temperature curve provided by the rework station and make adjustments as necessary. It’s recommended to use a BGA rework station that allows temperature curve settings through a program for ease of operation and real-time temperature monitoring.
II. BGA Rework
- Cleaning Solder Pads: If the BGA is just removed, clean the solder pads of the PCB and BGA as soon as possible. This minimizes damage to the solder pads caused by temperature differences when the PCB and BGA are not fully cooled.
- BGA Reballing (Requires Silman Tech reballing station, matching solder balls, and steel mesh): Arrange the solder balls on the BGA.
- BGA Soldering: Set the soldering temperature on the heating platform (approximately 230°C for leaded solder and 250°C for lead-free solder). Place the BGA with solder balls on the high-temperature cloth in the soldering area of the heating platform and heat it using a hot air gun. When the solder balls are in a molten state, with a shiny surface and uniform arrangement, move the BGA to the cooling platform to cool down, completing the soldering process.
III. Resoldering
- Applying Flux: To ensure soldering quality, inspect the PCB solder pads for any dust before applying flux. Place the PCB on the workbench and brush an appropriate amount of flux onto the solder pad positions (applying too much flux can cause short circuits, while too little can result in poor soldering, so ensure the flux application is even and appropriate).
- Placement: Align and place the BGA correctly on the PCB. Use the silk screen frame lines for assistance, ensuring the alignment of the BGA solder pads with the PCB pads. Ensure the orientation mark on the BGA surface corresponds to the orientation mark on the PCB silk screen frame lines to prevent misalignment.
- Soldering: This step is similar to desoldering. Place the PCB on the BGA rework station, ensuring proper alignment between the BGA and PCB. Apply the desoldering temperature curve and initiate soldering. Once heating is complete and automatic cooling occurs, remove the PCB to complete the rework process.