Basic requirements for BGA pad design
1. The center of the pad of each solder ball on the PCB coincides with the center of the corresponding solder ball at the bottom of the BGA.
2. The PCB land pattern is a solid circle, and the via hole cannot be processed on the land.
3. After the via hole is electroplated, it must be blocked with dielectric materials or conductive glue, and the height must not exceed the height of the pad.
4. Generally, the diameter of the pad is less than 20% to 25% of the diameter of the solder ball. The larger the pad, the smaller the wiring space between the two pads.
5. The number of wiring between two pads is calculated as P-D≥(2N+I)Xr where P is the pitch of the solder balls: D is the diameter of the pad: N is the number of wiring: X is the line width.
6. General rules: The diameter of PBGA pads is the same as the pads on the device substrate.
7. The width of the wire connected to the pad should be the same, generally 0.15~02mm.
8. The solder mask size is 0.1～0.15mm larger than the pad size.
9. The design of CBGA pads must ensure that the template opening is such that the solder paste print volume is greater than or equal to 0.08mm2 (this is the minimum requirement) to ensure the reliability of the solder joints after PCBA processing products. Therefore, the pad of CBGA is larger than that of PBGA.
10. Set the positioning line of the outer frame.
Setting the external positioning line is very important for the inspection after SMT placement. The size of the positioning frame is the same as that of the chip. The line width is 0.2～0.25mm; the 45° chamfer indicates the direction of the chip. There are two types of frame positioning lines: silk screen and copper coating. The former will cause errors. The latter is more precise. In addition, 2 Mark points should be set outside the positioning frame.