1. PCB companies commonly used circuit board processing processes are as follows:

2. Single-panel process, double-panel process, multi-layer board process,

3. PCB material selection.

4. PCB material selection:

5. a) The substrate with a higher Tg should be chosen appropriately—glass transition temperature Tg is a key property of polymers, determining material characteristics and serving as a critical parameter for substrate selection. The Tg of epoxy resin typically ranges from 125 to 140 degrees Celsius, while the reflow soldering temperature is approximately 220 degrees Celsius, significantly exceeding the Tg of PCB substrates. High temperatures can lead to thermal deformation of the PCB and, in severe cases, damage components. *Tg should be higher than the operational temperature of the circuit.

6. b) Low CTE is essential—due to discrepancies in thermal expansion coefficients in the X, Y, and thickness directions, PCB deformation is likely, which can cause metallized holes to break and damage components in extreme situations.

7. c) High heat resistance is necessary—generally, the PCB should exhibit heat resistance of 250°C for 50 seconds.

8. d) Good flatness is required.

9. e) Electrical performance requirements: for high-frequency circuits, materials with low dielectric constant and low dielectric loss are essential. Insulation resistance, withstand voltage strength, and arc resistance must meet product specifications.

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**PCB Thickness Design**

1. Allowable board thickness for general placement machines: 0.5~5mm.

2. The typical PCB thickness ranges from 0.5~2mm.

3. Only low-power components, such as integrated circuits, low-power transistors, resistors, and capacitors, should be assembled under conditions with no strong load vibrations, using a thickness of 1.6mm and a board size within 500mm x 500mm.

4. Under load vibration conditions, it is necessary to either reduce the plate size or reinforce and increase the support points based on the vibration conditions; a 1.6mm plate may still be used.

5. When the plate surface is large or unsupported, consider increasing the thickness to 2~3mm.

6. For higher levels, the thickness of each layer must meet additional requirements (e.g., withstand voltage requirements).

7. If the PCB size is smaller than the minimum mounting size, a boarding method must be employed.

**Design of Laminated Structure**

8. In laminated structure design, we focus on creating structures that meet customer needs. The basic design principles include: if the customer specifies a structure, it must be designed accordingly. If impedance requirements exist, a suitable laminate structure must be utilized. If no specific structure is provided, the dielectric layer thickness and pressing thickness must meet the customer’s requirements. The inner layer should preferably use a thicker core plate; the minimum dielectric thickness is 0.06mm, and a single PP structure should be used whenever possible. Surface PP can only discharge 1080, 2116 laminate structure design software.

9. Misunderstandings regarding laminate structure due to Protel series software can lead to incorrect media thickness requirements, as depicted in the accompanying image. If layers are obtained without special settings, the pressure structure equals the medium thickness. Consequently, a smaller core board thickness may result, increasing PP quantity and costs. If there are no requirements, specifying them in the processing instructions is recommended.

**Inner Graphic Design**

10. The distance between inner holes and lines should be maximized; the higher the level, the greater the distance. (For 4-layer boards, maintain a minimum of 7mil; for 6-8 layers, a minimum of 8mil is required.) The higher the level, the greater the distance between inner holes and copper, typically exceeding 10mil, improving reliability. In areas with dense holes, lines should ideally be placed between two holes. Elements on the board should be at least 15 mils from the board’s edge; for higher levels, consider increasing this distance. Spread copper beneath golden fingers to prevent thin areas.

**Frequently Asked Questions**

11. The inner network may appear unclear due to: A) Holes tangent to the inner graph, making the network indeterminable. B) Hole designs on isolation lines with incomplete PAD designs, preventing network determination. C) Quincunx pads on isolation lines that also hinder network identification.

**Drilling Design**

12. Thickness-to-diameter ratio: The preferred ratio of hole to plate thickness is less than 1:8; processing becomes difficult at 1:8 or more.

13. When using the reflow soldering process, via hole settings should include: A. Generally, the via hole diameter should be no less than 0.3mm; the minimum hole diameter to board thickness ratio should not be less than 1:8. A smaller ratio complicates metalization and increases costs. B. Vias should not be directly placed on pads or at the corners of pads. C. A thin wire coated with solder mask should be present between the via and the pad, with a length greater than 0.5mm and a width greater than 0.1mm.

14. The minimum hole diameter is 0.2mm. Larger holes should be used where possible, with the distance between hole edges exceeding 12mil; via holes should not be drilled on solder pads.

15. PCB aperture tolerance control range: normal aperture tolerance follows IPC 2 standards, with crimp hole diameter tolerances within ±0.05mm. PTH tolerances can be controlled within ±0.08mm, while NTPH tolerances remain within ±0.05mm.

16. Hole position tolerance is ±0.075mm.

17. Hole copper requirements: IPC 3 standard controls average hole copper at 25um, with single points exceeding 20um. Common drilling file issues often arise during the design of the outer circuit.

18. Limit line width spacing to 3/3mil; typical finished product requirements include 1OZ minimum line width/spacing of 4.5/4.5mil, and 2OZ minimum line width/spacing of 6/6mil. Copper thickness increases require corresponding line width and spacing adjustments, with a recommendation to increase by 1mil separately if circumstances allow.

19. The current-carrying capacity of line width varies at different temperatures (1OZ). Reference the line width current-carrying capacity comparison table.

20. Teardrops should be added to PCB pad traces to prevent pad detachment during wave soldering.

21. No vias should be placed on SMD pads; maintain a distance of at least 0.2mm between vias and pads.