Why convert PCB files into GERBER files and drill data before submitting them to PCB factory boards?

Most engineers are accustomed to designing PCB files and sending them directly to the PCB factory for processing. However, a popular international practice is to convert PCB files into GERBER files and drill data before submitting them to the PCB factory. Why bother with this?

Because electronic engineers and PCB engineers have different understandings of PCBs, the GERBER file converted by the PCB factory may not be what you want. For example, when you define the parameters of components in the PCB file during design, and you do not want these parameters to be displayed on the finished PCB product, you did not specify that the PCB factory followed suit and left these parameters on the finished PCB product. This is just an example. If you convert PCB files into GERBER files yourself, you can avoid such events from happening.

GERBER file is an international standard photo format file that includes RS-274-D and RS-274-X formats. RS-274-D is called the basic GERBER format and must be accompanied by a D-code file to fully describe a graphic; RS-274-X is called the Extended GERBER format, which itself contains D-code information. Commonly used CAD software can generate these two formats of files.

How to check the correctness of the generated GERBER? You only need to import these GERBER files and D code files in the freeware Viewmate V6.3 to see them on the screen or print them out through the printer.

Drilling data can also be generated by various CAD software, usually in Excel format, and can also be displayed in Viewmate. Without drilling data, of course, PCB cannot be made

What precautions should be taken when designing impedance circuit boards?

Impedance design and calculation:

The changing relationship between the four elements of impedance control and their mutual influence:

1. H=thickness of the medium between the signal layer and the reference layer;

Thickness ↑, impedance value ↑, thickness ↓, impedance ↓

2. W=wiring width;

Line width ↑, impedance value ↓, line width ↓, impedance ↑

3、 ε R=dielectric constant of the material;

Dielectric ↑, impedance value ↓, dielectric ↓, impedance ↑

4. T=wiring thickness;

Copper thickness ↑, impedance value ↓, copper thickness ↓, impedance ↑

(1) W (design line width): This factor is generally determined by the design. When designing, please fully consider the compatibility of line width with this impedance value. To achieve this impedance value, there are certain restrictions on the use of line width under certain conditions such as H, Er, and usage frequency.

(2) S (spacing): The spacing between impedance lines is mainly determined by the customer, and compensation and production processing control should be fully considered during engineering production.

(3) T (copper thickness): When designing, the influence of electroplating thickening on copper thickness should be considered, and the thickening thickness is generally 18-25um;

(4) H (medium thickness): When designing, consideration should be given to the symmetry of the laminated structure and the inventory of the core plate; There may be differences between the theoretical calculated thickness and the actual thickness formed during operation for boards with low residual copper rate. This factor should be fully considered during design.

Precautions for impedance design:

1. The impedance line must have a corresponding reference plane, and the reference plane must be complete;

2. Different types of impedance lines should be distinguished and labeled;

3. The directions between adjacent wires are set perpendicular to each other or stepped diagonally at 45 °;

4. When the reference planes corresponding to impedance lines with the same width on the same layer are consistent, avoid different impedance requirements;

5. Use standard copper thickness, and the finished copper thickness should not exceed 2OZ;

6. Minimize cross layer impedance lines as much as possible

7. The radiation of coplanar impedance is lower, and the coupling interference of electric and magnetic fields is smaller, which is better than microstrip lines

8. The via itself has parasitic capacitance and inductance. The parasitic capacitance of the via will prolong the signal rise time and reduce the circuit speed. The parasitic inductance of the via will weaken the effect of the bypass capacitance and the filtering effect of the entire power system. Therefore, it is necessary to reduce the grounding PTH via design near the impedance line

9. Similarly unreasonable solder pads and copper point interference can also cause impedance discontinuity, so it is necessary to reduce the spacing between impedance lines that is very small

Design of solder pads and copper dots or blocks

What surface processes are commonly used on circuit boards?

There are usually several surface treatment processes for circuit boards, and for different products and purposes, different treatment methods will be used. Below, Tengchuangda will analyze the characteristics of different surface treatment processes for everyone:

1. ElectropolyticNi/Au

The cost of the gold-plated plate process is the highest among all plates, but currently, it is the most stable and suitable for use in lead-free processes. Especially in some electronic products with high unit prices or requiring high reliability, it is recommended to use this plate as the substrate.

2. OSP board (OrganicSolderabilityReservives)

The OSP process has the lowest cost and is easy to operate, but its popularity is still poor due to the need for assembly plants to modify equipment and process conditions, as well as poor repeatability. Using this type of sheet metal, after high temperature heating, the protective film pre coated on the PAD will inevitably be damaged, leading to a decrease in solderability, especially when the substrate undergoes secondary reflow. Therefore, if another DIP process is required in the process, At this point, the DIP end will face welding challenges.

3. ImmersionAg

Although "silver" itself has strong mobility, leading to leakage, the current "immersion silver" is not simply metallic silver in the past, but "organic silver" co plated with organic matter. Therefore, it can meet the needs of future lead-free processes, and its solderability life is longer than that of OSP boards.

4. ElectrolessNi/Au, ENIG

The biggest problem with this type of substrate is the issue of "BlackPad", so many large manufacturers do not agree to use it in lead-free processes, but most domestic manufacturers use this process.

5. ImmersionTin

This type of substrate is prone to contamination and scratches, and the process (FLUX) can cause oxidation and discoloration. Most domestic manufacturers do not use this process, resulting in relatively high costs.

6. Spray tin plate

Due to its low cost, good soldering performance, reliability, and strongest compatibility, this type of solder spray plate with good soldering characteristics cannot be used in lead-free processes due to its presence of lead.