How Chee Mau makes qualified BGA soldering

During PCB assembly, BGA (Ball Grid Array) soldering is a key link in the SMT process, and its soldering quality directly affects the reliability of the product. Chee Mau ensures the effectiveness of BGA soldering through strict process control, multi-level detection methods and professional rework processes.

1. Process control: ensuring soldering quality

Chee Mau takes the following measures to optimize the process and reduce the defect rate during BGA soldering:

1.1 Temperature curve optimization:

- Adjust the reflow soldering temperature curve according to the BGA solder ball material (lead/lead-free) to ensure that the solder ball is completely melted and forms a good solder joint. For example, lead-free solder balls usually require a peak temperature of 235-250°C, while lead solder balls are about 210-220°C.

- Control the heating slope (usually 2-4°C/s) and cooling rate to avoid thermal stress causing solder joint cracks.

1.2 Solder paste printing control:

- Use high-precision stencil (such as laser-cut stencil) to ensure the right amount of solder paste to avoid bridging or cold soldering.

- Use SPI (solder paste inspector) to check the quality of solder paste printing to ensure uniformity of thickness, shape and coverage.

1.3 SMT precision management:

- Use high-precision SMT machines (such as optical alignment systems) to ensure that BGA is aligned with PCB solder pads to reduce the risk of offset.

1.4 Flux selection:

- Use low-residue, high-activity flux to avoid excessive use that causes solder ball voids or residue corrosion.

2. Soldering effectiveness inspection

Since BGA solder joints are located at the bottom of the chip, traditional visual inspection cannot be directly observed, and Chee Mau uses a variety of inspection methods:

2.1 X-ray inspection (AXI):

- 2D/3D X-ray inspection of solder joint shape, bridging, and voids (such as blow holes, tin splashing, etc.) is the main method for BGA inspection.

2.2 Optical microscope/magnifying glass inspection:

- Check BGA alignment, parallelism and peripheral solder overflow.

2.3 Functional test (ICT/FCT):

- Verify the connection reliability of BGA through electrical performance test, such as short circuit and open circuit detection.

2.4 Destructive test (sampling):

- Perform cross-section analysis on some samples to observe whether the internal structure of the solder joint is qualified.

3. Repair method for unqualified welding

When poor BGA soldering is detected, the factory usually adopts the following rework process:

3.1 Rework station desoldering:

- Use BGA rework station (with optical alignment function) to accurately control the upper and lower heating temperatures (such as 300°C for the upper part and 270°C for the lower part) to avoid PCB deformation or chip damage.

- For BGA fixed with glue (such as mobile phone motherboard), the glue must be softened (such as using a solvent or heating to 200-250°C) before removal.

3.2 Tinning and re-soldering:

- Use a tinning plate (such as a small hole tinning plate) and high-quality tin paste to ensure that the size of the tin balls is uniform and avoid poor secondary soldering.

- Apply an appropriate amount of flux paste during re-soldering, adjust the temperature curve, and ensure that the solder joints are fully melted.

3.3 Pad repair:

- If the PCB pad falls off, Chee Mau use scraping the copper layer, tinning or micro copper foil to repair.

4. Additional safeguards we use

- Environmental control: Keep the temperature and humidity in the workshop stable to reduce poor soldering caused by PCB moisture absorption (such as popcorn effect).

- Equipment calibration: Regularly check the temperature accuracy of the reflow oven and rework station to ensure process stability.

- Staff training: Operators need to be familiar with the characteristics of BGA soldering to avoid overheating or mechanical damage during manual rework.

Chee Mau ensures the high reliability of BGA soldering by optimizing the soldering process, multi-dimensional detection (X-ray, functional testing, etc.) and professional rework methods. For unqualified solder joints, they need to be repaired by combining rework stations, tinning technology and pad repair methods. These measures jointly ensure the stable application of BGA packaging in high-end electronic devices (such as mobile phones, servers, etc.).