Why BGA Reballing is Necessary:
The purpose of BGA reballing is to facilitate the soldering of BGA chips. With the increasing application of BGA technology, issues such as BGA chip reflow may arise. Typically, when there are soldering issues under the chip, such as with Northbridge or contact points, BGA equipment can be used for reflow soldering. Only when reflow soldering is ineffective, reballing is necessary. reballing is a patience-testing task. Below are detailed steps for BGA reballing, hoping to assist everyone.
BGA Reballing Method:
- Ensure Flatness of Solder Pads: It is essential to ensure that the solder pads are flat during BGA reballing. If they are not flat, it may cause inconvenience in subsequent work. Therefore, the solder pads need to be leveled. If uneven, clean the pads with board cleaner and ensure there are no burrs by touching them with your hand. The pads should be bright for proper soldering. If the pads appear gray or black, apply flux and reflow until they become shiny. After leveling the pads, clean them thoroughly.
- Apply Flux Evenly: This is a crucial step. Use a flat-tipped brush to lightly apply a layer of flux evenly on the BGA solder pads. The flux must be applied uniformly. A tip to ensure uniformity: after applying, check the reflection under sunlight to ensure the traces of flux are uniform, rather than unevenly distributed. This step is critical because uneven application of flux can lead to problems during the heating process, especially when heating without a steel mesh.
- Mounting Balls onto the BGA Chip: Place the chip on the base of the mounting station, then cover it with a flat steel mesh. Pour an appropriate amount of solder balls into the mesh and gently shake it to ensure each hole is filled with a solder ball. Then, remove the steel mesh. Secure the chip with tweezers onto the heating platform for ball melting. (Note: Pay attention to different temperatures for leaded and lead-free solder balls—typically around 190°C for leaded and 240°C for lead-free solder balls.) When heating the BGA, use a material with small area and slow heat conduction under the BGA to prevent excessive heating, such as high-temperature fabric, which will quickly melt the solder balls, otherwise, prolonged heating can damage the chip.
- Determining Heating Completion: Experienced practitioners suggest that when the solder balls turn from gray to shiny liquid state during melting, it indicates completion. Therefore, good lighting conditions, preferably under sunlight, are necessary for clear observation (Note: The center of the BGA generally heats slower than the surrounding area, so observe the solder balls in the center. If they turn from gray to shiny, stop heating immediately). However, this method may be difficult for beginners since it requires discerning the change with the naked eye. Another method is to lightly touch the center solder ball with the tip of tweezers during heating. If it melts, it will deform into a liquid state; if not melted, it will shift position. However, be careful and gentle when performing this action. If soldering is challenging due to the thickness of the chip, a hot air gun can be used to heat at a fixed height while continuously rotating. Once the center solder ball turns shiny, immediately stop heating and allow it to cool naturally.
Precautions:
Steel Mesh: Ensure that the steel mesh remains undeformed and clean. If deformed, correct it manually. If the deformation is severe, replace it with a new steel mesh.
Selection of Solder Balls: The market offers solder balls in various sizes, ranging from 0.2mm to 0.6mm. When selecting solder balls, ensure they are clean, uniform in size, and differentiate between leaded and lead-free solder balls, as they require different melting temperatures.
Overall, BGA reballing requires precision and attention to detail. Following these steps and precautions can help achieve successful reballing.