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 opening of the template 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 outer positioning line of BGA/CSP is shown in the figure.

The size of the positioning frame is the same as the chip shape. The line width is 0.2～0.25mm; the 45° chamfer indicates the direction of the chip. There are two types of outer 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.

In addition, after the editor of Jingbang Electronics shared the above knowledge with you today, I have a whim today. I am always here to share some knowledge about SMT patch processing with you. Have you thought about it yourself? What problems are often encountered in the PCBA manufacturing process? Below I will take the initiative to share with you some of the problems we encountered in the patch processing at the beginning, and made a brief overview. I hope that friends who know can positively reply and comment!

1. What are the technical requirements for applying solder paste? What are the requirements for environmental temperature, humidity, and environmental sanitation for solder paste?

2. How to select, use and store solder paste correctly? What is the purpose of reheating after taking out the tin tone from the refrigerator before use?

3. Briefly describe the three methods of applying solder paste and the scope of application. Which method is currently the most widely used?

4. What are the principles of solder paste printing and the three key elements for the success of solder paste printing?

5. What printing parameters need to be set for the automatic printing machine? What are the operating steps and requirements for graphic alignment?

6. What are the methods to check the printing quality of solder paste? What are the treatment methods for unqualified products?

7. What are the main factors that affect the quality of solder paste printing? What influence does the degree of solder paste and adhesion have on the quality of printing?

8. How to choose the size of the alloy powder in the solder paste according to the assembly density?

9. What are the advantages and disadvantages of the metal secondary knife and the rubber scraper?

10. Briefly describe the judgment and adjustment methods of the main defects and defective products of the printed solder paste.

11. Briefly describe the main application occasions of the solder paste dispensing process of the manual dispenser. Briefly explain its operation method.

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