Let me introduce the following 5 aspects:
1. Introduction to Circuit Boards
2. Introduction to Circuit Board Materials
3. Basic Structure of Circuit Boards
4. Circuit Board Manufacturing Process
5. Circuit Board Case Sharing
1Introduction to Circuit Boards
1. Flexible Printed Circuit Board
The flexible printed circuit board (Flex Print Circuit, abbreviated as “FPC”), is a printed circuit board made of flexible substrates, which can be single-sided, double-sided, or multi-layered. It features light weight, thinness, short length, small size, high density, high stability, and flexible structure. It can not only bend statically but also dynamically bend, roll, and fold.
2. Rigid Printed Circuit Board
The rigid printed circuit board (Printed Circuit Board, abbreviated as “PCB”), is made of rigid substrate materials that are not easily deformed. It is flat during use and has advantages such as high strength, resistance to warping, and secure installation of surface-mounted components.
3. Rigid-Flex Boards
The rigid-flex board (Rigid Flex) is a special flexible printed circuit board formed by selectively laminating rigid and flexible substrates together, creating a compact structure with electrical connections formed by metallized holes. It features high density, fine lines, small hole diameter, small volume, light weight, and high reliability. Its performance remains stable under vibration, impact, and humid environments. It can be bent and mounted in three dimensions, effectively utilizing installation space, and is widely used in portable digital products such as mobile phones, digital cameras, and camcorders. Rigid-flex boards are often used in packaging reduction, especially in consumer electronics.
2Introduction to Circuit Board Materials
1. Conductive Medium: Copper (CU)
﹣Copper Foil: Rolled Copper (RA), Electrolytic Copper (ED), High Ductility Electrolytic Copper (HTE)
﹣Thickness: 1/4OZ, 1/3OZ, 1/2OZ, 1OZ, 2OZ, these are common thicknesses
﹣OZ (ounce): Unit of copper foil thickness; 1OZ = 1.4 mil
2. Insulating Layer: Polyimide (PI), Polyester, Polyethylene Naphthalate (PEN)
﹣The most commonly used is Polyimide (abbreviated as “PI”)
﹣PI Thickness: 1/2mil, 1mil, 2mil, these are common thicknesses
﹣1 mil = 0.0254mm = 25.4um = 1/1000 inch
3. Adhesive: Epoxy Resin, Acrylic System.
﹣The most commonly used is epoxy resin, thickness varies depending on different manufacturers
4. Copper Clad Laminates (CCL):
﹣Single-sided Copper Clad: 3L CCL (with adhesive), 2L CCL (without adhesive), as illustrated below.
﹣Double-sided Copper Clad: 3L CCL (with adhesive), 2L CCL (without adhesive), as illustrated below.
5. Covering Film (Coverlay, abbreviated as “CVL”): Composed of insulating layer and adhesive, covering the conductor, providing protection and insulation. The specific layering structure is as follows
2. Conductive Silver Foil: Electromagnetic Wave Protection Film
﹣Type: SF-PC6000 (Black, 16um)
﹣Advantages: Ultra-thin, good sliding and bending properties, suitable for high-temperature reflow soldering, and good dimensional stability.
The common type is SF-PC6000, the layering structure is as follows:
3Rigid-Flex Structure Display
4Circuit Board Manufacturing Process
1. Cutting: Cutting
2. Mechanical Drilling: CNC Drilling
3. Plating Through Hole
4. DES Process (Five Steps)
(1). Film Application (Dry Film)
(2). Exposure
Working environment: Yellow light
Purpose: Through UV light exposure and film blocking, the transparent areas of the film and dry film undergo optical polymerization reactions, while the brown areas of the film cannot be penetrated by UV light, preventing optical polymerization reactions with the corresponding dry film.
(3). Development
Working solution: Na2CO3 (K2CO3) weak alkaline solution
Purpose: To wash away the parts of the dry film that did not undergo polymerization reactions using a weak alkaline solution.
(4). Etching
Working solution: Acidic oxygen water: HCl + H2O2
Purpose: To use the chemical solution to etch away the copper exposed after development, forming a graphic transfer.
(5). Film Stripping
Working solution: NaOH strong alkaline solution
5. AOI
Main Equipment: AOI, VRS System
The copper foil with formed circuits must undergo scanning detection for circuit defects through the AOI system. The standard circuit image information is stored in data format in the AOI host. The CCD optical imaging head scans the circuit information on the copper foil into the host and compares it with the stored standard data. If there are anomalies, the positions of the anomalies will be numbered and recorded for transmission to the VRS host. The VRS will magnify the copper foil 300 times and sequentially display according to the previously recorded defect positions. The operator will determine whether it is a true defect. For true defects, markers will be made at the defect locations with a water-based pen for the convenience of subsequent personnel to categorize and repair the defects. The operator utilizes a 150x magnifying glass to determine the defect type, categorize, and form a quality report, which is fed back to the previous process for timely improvement measures. Since single-sided boards have fewer defects and lower costs, AOI interpretation is difficult, so manual inspection is used.
6. Fake Paste
Protective film functions: 1) Insulation, anti-soldering; 2) Protect circuits; 3) Increase flexibility of soft boards, etc.
7. Hot Pressing
Working conditions: High temperature and high pressure
8. Surface Treatment
After hot pressing, surface treatment is required for the exposed copper foil.
The method depends on customer requirements
9. Silk Screen Printing
Main equipment: Screen printing machine, oven, UV dryer, screen plate making equipment. Through the principle of screen printing, ink is transferred to the product, mainly printing product batch numbers, production cycles, text, black shading, simple circuits, etc. The product is aligned with the screen plate using positioning pins, and the ink is pressed onto the product through the pressure of the squeegee. The screen plate is divided into parts with text and patterns, while the non-text or pattern parts are sealed with photosensitive emulsion, preventing ink leakage. After printing, it enters the oven for drying, and the printed text or pattern layer tightly bonds to the product surface. Some special products require additional special circuits, such as adding a few circuits on a single-sided board to achieve double-sided board functionality, or adding a shielding layer on a double-sided board must be realized through printing. If the ink is UV-drying ink, then a UV dryer must be used. Common issues: ink leakage, contamination, gaps, protrusions, peeling, etc.
10. Testing (O/S Inspection)
Testing fixture + testing software for full functionality inspection of the circuit board
11. Punching
Corresponding outer shape film tools: knife film, laser cutting, etching film, simple steel mold, steel mold
12. Processing and Assembly
Processing and assembly refer to assembling materials according to customer requirements, such as suppliers assembling:
A. Stainless steel reinforcement
B. Beryllium copper sheet/phosphor bronze sheet/nickel-plated steel sheet reinforcement
C. FR4 reinforcement
D. PI reinforcement
13. Inspection
Inspection items: Appearance, dimensions, reliability
Testing tools: Two-dimensional, micrometer, caliper, magnifying glass, soldering furnace, tensile testing machine
14. Packaging
Operation methods: 1. Plastic bag + cardboard
2. Low-adhesion packaging material
3. Standard vacuum box
4. Special vacuum box (anti-static grade)
Double-sided PCB Manufacturing Process Flow Chart
Rigid-Flex Board Manufacturing Process Flow Chart
5Circuit Board Case Sharing
1. Design Scheme
1. Scheme Description:
• The new COF scheme integrates reinforcement and chip attachment areas on a single steel plate, as shown in the FPC schematic.
• Main Uses:
• 1. To minimize the sensor’s contact with the uneven surface of the circuit board, the sensor is directly attached to the flat steel plate, ensuring that the sensor is perpendicular to the optical lens axis, reducing image blurriness.
• 2. In the ≤0.3mm scheme, the new COF flatness is superior to that of rigid-flex boards, achieving a reduction in module height while ensuring flatness.
• 3. Direct contact between the sensor and the steel plate enhances thermal conductivity.
2. Design Scheme
1）.P8V12G-621-00 Circuit Board (Structural Diagram Below:)
The design thickness of the circuit board is 0.3mm, with a steel plate protrusion height of 0.02mm.
2）.P8V12G-621-00 Circuit Board (Wiring Diagram Below:)
3）.P8V12G-621-00 Circuit Board (Layering Diagram Below:)
4）. Circuit Board Scheme Design Limitations Assessment:
1. The purple small box in the figure indicates the steel plate support area;
2. The support area is distributed diagonally with respect to the SENSOR;
3. The minimum window area of the support area is 0.5*0.5, the larger the area, the better the flatness;
4. The module head size ≥8.5*8.5;
5. The number of SENSOR pins ≤80;
6. MIPI 2Lane output is more conducive to routing than 4Lane output;
7. Routing is more favorable when MIPI is near the connector (as shown in the right image, the MIPI routing is below the pad);
3. Comparison of Advantages and Disadvantages
Comparison of flatness data for P8V12G under different types:
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