The temperature profile is a crucial factor for successful BGA chip rework on a BGA rework station. Compared to conventional reflow soldering temperature profiles, the temperature control requirements during BGA rework operations are higher. Typically, the temperature profile for BGA rework can be divided into six parts: preheating, heating, soak, melting, reflow, and cooling. Here’s a detailed method for quickly setting the temperature profile on a BGA rework station.
Considerations for Setting the Temperature Profile:
- Type of Solder Used: There are two main types of solder commonly used in SMT (Surface Mount Technology): leaded and lead-free. Leaded solder has a melting point of 183°C, while lead-free solder has a melting point of 217°C. Therefore, the temperature settings should ensure that the solder reaches its melting point effectively. For lead-free chips, the preheating zone temperature ramp-up rate should be controlled between 1.2 to 5°C/second, soak zone temperature should be maintained between 160 to 190°C, and the peak temperature in the reflow zone should be set between 235 to 245°C for a duration of 10 to 45 seconds.
Peak Temperature Setting:
- Temperature Differential: During soldering, it’s essential to consider the temperature differential between the hot air outlet and the solder balls on the BGA chip due to heat transfer. To achieve accurate temperature control, it’s recommended to insert the thermocouple probe between the BGA and the PCB (Printed Circuit Board), ensuring that the probe’s tip is exposed between them. Adjust the airflow and velocity to achieve uniform and controllable heating. This ensures precise temperature measurement, enhancing the accuracy of the heating process.
Setting Temperature Profile for Chip Soldering:
Here’s a step-by-step guide for setting the temperature profile when soldering chips using a BGA rework station:
- Preheating: Preheating helps remove moisture from the PCB, prevents bubbling, and preheats the entire PCB to prevent thermal damage. The temperature during this stage can be set between 60 to 100°C, typically around 70-80°C, for a duration of 45 seconds.
- Heating: The purpose of the heating phase is to raise the temperature of the PCB gradually. If the temperature is too high, reduce the temperature or shorten the duration of the heating phase. Conversely, if the temperature is too low, increase the temperature or extend the duration of the heating phase.
Although setting the temperature profile on a BGA rework station may seem complex, it’s a one-time process, and the saved temperature profile can be reused. Attention to detail and patience are essential during the setup process to ensure the correct temperature profile for soldering BGA chips and to guarantee a high success rate in rework.
