The opening of FR4 PCB BGA welding can be caused by several factors, including insufficient solder paste, poor solderability, poor coplanarity, mounting misalignment, thermal mismatch, and exhaust through the solder mask. The effects of various factors are described as follows.
1. Insufficient solder paste
Inadequate solder paste printing caused by opening blockage will cause solder opening, which is very common in CBGA or CCGA, because solder paste collapse will not occur during reflow of these two devices.
2. Poor weldability
Contamination and oxidation of the pad are common causes of wetting issues. Contaminated fr4 pcb pads prevent solder from wetting, causing it to flow towards the interface between the solder ball and component. This results in open welds on the fr4 pcb pad side. Poor weldability of the pad can also lead to weld opening after the PBGA solder ball melts and collapses.
3. Poor coplanarity
Inadequate coplanarity often leads to or directly causes weld opening. The maximum allowable fr4 pcb non-coplanarity is 5mil in a local area or 1% in the entire area, according to IPC-600 standards. During the repair process, preheating should be utilized to minimize non-coplanar deformation of the fr4 pcb.
4. Chip offset
Component deviation during mounting can result in weld opening.
5. Thermal mismatch
The shear force from internal stress can cause weld opening. A large temperature gradient passing through the fr4 pcb can lead to this phenomenon. For example, SMT reflow is often followed by wave soldering, resulting in BGA corner solder joint cracks. This is due to the rapid temperature rise in the top surface of the fr4 pcb during wave soldering, creating stress between the hot fr4 pcb and cold PBGA.
6. Exhaust gas passing through the solder mask
Poor exhaust around BGA pads with solder mask restrictions can also cause weld opening. In this case, volatiles will be forced to discharge from the interface between the solder mask and the packaging pad, blowing the solder away and resulting in weld opening. Pre-drying the BGA patch can solve this issue.
In conclusion, the following measures can be taken to address BGA weld opening:
1) Ensure sufficient solder paste is printed
2) Improve the weldability of fr4 pcb pads
3) Maintain coplanarity of the fr4 pcb substrate
4) Precisely mount elements
5) Avoid excessive temperature gradients
6) Cover through holes before wave soldering
7) Pre-dry elements
1. Insufficient solder paste
Inadequate solder paste printing caused by opening blockage will cause solder opening, which is very common in CBGA or CCGA, because solder paste collapse will not occur during reflow of these two devices.
2. Poor weldability
Contamination and oxidation of the pad are common causes of wetting issues. Contaminated fr4 pcb pads prevent solder from wetting, causing it to flow towards the interface between the solder ball and component. This results in open welds on the fr4 pcb pad side. Poor weldability of the pad can also lead to weld opening after the PBGA solder ball melts and collapses.
3. Poor coplanarity
Inadequate coplanarity often leads to or directly causes weld opening. The maximum allowable fr4 pcb non-coplanarity is 5mil in a local area or 1% in the entire area, according to IPC-600 standards. During the repair process, preheating should be utilized to minimize non-coplanar deformation of the fr4 pcb.
4. Chip offset
Component deviation during mounting can result in weld opening.
5. Thermal mismatch
The shear force from internal stress can cause weld opening. A large temperature gradient passing through the fr4 pcb can lead to this phenomenon. For example, SMT reflow is often followed by wave soldering, resulting in BGA corner solder joint cracks. This is due to the rapid temperature rise in the top surface of the fr4 pcb during wave soldering, creating stress between the hot fr4 pcb and cold PBGA.
6. Exhaust gas passing through the solder mask
Poor exhaust around BGA pads with solder mask restrictions can also cause weld opening. In this case, volatiles will be forced to discharge from the interface between the solder mask and the packaging pad, blowing the solder away and resulting in weld opening. Pre-drying the BGA patch can solve this issue.
In conclusion, the following measures can be taken to address BGA weld opening:
1) Ensure sufficient solder paste is printed
2) Improve the weldability of fr4 pcb pads
3) Maintain coplanarity of the fr4 pcb substrate
4) Precisely mount elements
5) Avoid excessive temperature gradients
6) Cover through holes before wave soldering
7) Pre-dry elements