**Overview of PCB High-Frequency Board Selection and Production Methods**
1. **Definition of PCB High-Frequency Board**
A high-frequency board is a specialized circuit board designed for elevated electromagnetic frequencies. It is utilized for high-frequency applications (frequencies exceeding 300MHz or wavelengths shorter than 1 meter) and microwave applications (frequencies over 3GHz or wavelengths less than 0.1 meter). The copper board is produced either through conventional rigid circuit board manufacturing techniques or specialized processing methods. Generally, a high-frequency board is defined as one operating at frequencies above 1GHz.
2. As technology rapidly advances, an increasing number of equipment designs are implemented within the microwave frequency range (>1GHz) and even extending into the millimeter wave domain (up to 30GHz). This trend signifies a continuous rise in frequency, leading to heightened material requirements for circuit boards. For instance, substrate materials must exhibit superior electrical properties, robust chemical stability, and minimal signal loss as power signal frequencies increase, underscoring the critical importance of high-frequency boards.
2. PCB High-Frequency Board Application Field
Mobile communication products, intelligent lighting systems, power amplifiers, low-noise amplifiers, and passive components like power splitters, couplers, duplexers, and filters are all part of the high-frequency board application landscape. Additionally, automotive anti-collision systems, satellite systems, and radio systems exemplify the growing trend toward high-frequency electronic equipment.
3. Classification of High-Frequency Boards
1. **Processing Method of Powder Ceramic Filled Thermosetting Material**: This method is similar to that used for epoxy resin/glass woven cloth (FR4), but the sheets tend to be more brittle and susceptible to breakage. Consequently, the lifespan of drilling and routing tools may decrease by 20%.
2. **PTFE (Polytetrafluoroethylene) Material Processing Method**:
– **Material**: It is essential to maintain the protective film to avoid scratches and creasing.
– **Drilling**: Utilize a brand-new drill bit (standard 130), and single drilling is recommended. The presser foot pressure should be set to 40 psi. An aluminum sheet acts as the cover plate, with a 1mm melamine backing plate used to secure the PTFE plate. After drilling, clear any dust from the holes using an air gun. Employ the most stable drilling machine with optimized parameters (generally, smaller holes require faster speeds, lower chip loads, and reduced return speeds).
– **Hole Treatment**: Plasma treatment or sodium naphthalene activation is beneficial for enhancing hole metallization.
– **PTH Copper Sinking**: Following micro-etching (maintaining a 20 micro-inch control), the plate is processed from the de-oiling cylinder when PTH is initiated; if needed, a second PTH cycle can be employed.
– **Solder Mask**: Pre-treatment involves acid washing—mechanical grinding should be avoided. After pre-treatment, bake the board at 90 degrees Celsius for 30 minutes, then apply green oil for curing. The baking process consists of three stages: 80 degrees Celsius, 100 degrees Celsius, and 150 degrees Celsius, with each stage lasting 30 minutes. If any oily residue is observed on the substrate, it should be washed and reactivated.
– **Routing**: Place white paper on the circuit surface of the PTFE board, clamping both sides with FR-4 substrate boards or phenolic base plates (1.0MM thick) that have been etched to remove copper. Ensure a substantial sulphur-free paper separates the base material from the copper surface, and conduct a visual inspection. Effective routing processes are crucial to minimizing burrs.
4. Process Flow
1. **NPTH PTFE Plate Processing Flow**: Cutting → Drilling → Dry Film → Inspection → Etching → Corrosion Inspection → Solder Mask → Characterization → Tin Spraying → Forming → Testing → Final Inspection → Packaging → Shipping.
2. **PTH PTFE Plate Processing Flow**: Cutting → Drilling → Hole Treatment (plasma or sodium naphthalene activation) → Copper Immersion → Board Electricity → Dry Film → Inspection → Diagram Electricity → Etching → Corrosion Inspection → Solder Mask → Characterization → Tin Spraying → Forming → Testing → Final Inspection → Packing → Shipping.
Challenges in high-frequency board processing include: copper sinking, where achieving copper coverage on hole walls can be difficult; managing map transfer, etching, line width, and gap control; and overseeing the green oil process to prevent issues like poor adhesion and blistering. It is crucial to rigorously control scratches on the board surface at every stage of processing.
In the realm of high-frequency board manufacturing, PCB factories must consistently maintain efficient multi-variety rapid delivery capabilities. The goal is to establish the strongest PCB prototype and small to medium batch manufacturing plant in China, integrating high-quality lean production management with robust R&D and manufacturing capabilities. This approach, combined with continuous innovation and the company’s core PCB technology, empowers Chinese enterprises with independent intellectual property rights to accelerate their technological advancements.
