Adjustment Strategy When BGA Rework Station Testing Reveals an Inadequate Curve

Usually, the rework curve can be divided into five stages: preheating, ramp-up, soak, reflow, and cool down. Below is an explanation of how to adjust when the curve is found to be inadequate, typically divided into three parts.

1. Preheating and Ramp-Up Stage: This stage aims to reduce PCB temperature differentials, remove moisture to prevent bubbling, and avoid thermal damage. The temperature requirement for testing solder temperature should be between (lead-free: 160175°C, leaded: 145160°C). If the temperature is too high, it indicates that the set ramp-up temperature is too high, so you can decrease the ramp-up temperature or shorten the duration. If it’s too low, you can increase the preheating and ramp-up temperatures or their durations. For PCBs stored for an extended period without baking, you can extend the preheating duration to remove moisture.
2. Soak Stage: This stage activates flux, removes surface oxides and films from the metal surface, evaporates flux volatiles, enhances wetting, and reduces temperature differentials. The practical temperature requirement for testing solder temperature should be controlled between (lead-free: 170185°C, leaded: 145160°C). If the temperature is too high, decrease the soak temperature slightly; if too low, increase it. If the preheating duration is found to be too long or too short, adjust the soak duration accordingly.
3. Reflow and Cool Down Stage: This stage ensures excellent fusion between solder balls and PCB pads. The primary goal is to reach the soldering peak (lead-free: 235245°C, leaded: 210220°C). If the temperature is too high, decrease the reflow stage temperature or shorten its duration. If the temperature is too low, increase the reflow stage temperature or extend its duration. The typical reflow duration for BGA chips is limited to 100 seconds. If the temperature is too low, increase the duration; if it’s still too low after 100 seconds, consider raising the reflow stage temperature.

Adjustment for Shortened Preheating Time:

1. If the temperature does not reach 150°C after the completion of the second stage (ramp-up), increase the target temperature appropriately or extend the soak time in the second stage. The temperature should reach 150°C after the completion of the second stage.
2. If the temperature reaches 150°C after the completion of the second stage, extend the soak time in the third stage by the same amount of time that was short in the preheating stage.

Adjustment for Shortened Cool Down Time:

1. Moderately extend the soak time in the cool-down stage by the same amount of time that was short.
2. If the preheating and cool-down stages are too long, reverse the above methods accordingly.
3. After adjusting the temperature curve, retest it, check if the detected temperatures meet the requirements during heating, and ensure that the maximum temperature, preheating duration, and cool-down time meet the requirements. If not, adjust it again according to the above methods until the curve meets the requirements, then save these temperature curve parameters for later use.