Microwave Tech - PCB high-frequency board selection and production and processing

The definition of high-frequency board for circuit board production High-frequency board refers to the special circuit board with higher electromagnetic frequency, which is used for high frequency (frequency greater than 300MHZ or wavelength less than 1 meter) and microwave (frequency greater than 3GHZ or wavelength less than 0.1 meter). PCB is a circuit board produced on microwave base copper-clad boards using part of the process of ordinary rigid circuit board manufacturing methods or using special processing methods. Generally speaking, a high-frequency board can be defined as a circuit board with a frequency above 1GHz!

With the rapid development of science and technology, more and more equipment is designed for applications in the microwave frequency band (>1GHZ) or even in the millimeter wave field (30GHZ). This also means that the frequency is getting higher and higher, and the circuit board is The requirements for materials are getting higher and higher. For example, the substrate material needs to have excellent electrical properties, good chemical stability, and the loss on the substrate with the increase of the power signal frequency is very small, so the importance of the high-frequency board is highlighted. 2. PCB high-frequency board application fields: mobile communication products; power amplifiers, low-noise amplifiers, etc.; passive components such as power splitters, couplers, duplexers, filters, etc.; automotive anti-collision systems, satellite systems, radio systems, and other fields, The high frequency of electronic equipment is the development trend.

2. PCB high-frequency board application fields: mobile communication products; power amplifiers, low-noise amplifiers, etc.; passive components such as power splitters, couplers, duplexers, filters, etc.; automotive anti-collision systems, satellite systems, radio systems, and other fields, The high frequency of electronic equipment is the development trend.

Classification of high frequency board powder ceramic filled thermosetting material
A. Manufacturer:
4350B/4003C from Rogers
Arlon's 25N/25FR

Taconic's TLG series
B. Processing method:
The processing process is similar to epoxy resin/glass woven cloth (FR4), except that the sheet is relatively brittle and easy to break. When drilling and gongs, the life of the drill tip and gong knife is reduced by 20%. PTFE (polytetrafluoroethylene) material

A. Manufacturer: RO3000 series, RT series, TMM series from Rogers
Arlon's AD/AR series, IsoClad series, CuClad series
Taconic's RF series, TLX series, TLY series
Taixing Microwave's F4B, F4BM, F4BK, TP-2

B. Processing method: 1. Cutting: The protective film must be kept for cutting to prevent scratches and creasing

2. Drilling
1. Use a brand new drill tip (standard 130), one by one is the best, the pressure of the presser foot is 40psi
2. The aluminum sheet is the cover plate, and then the PTFE plate is tightened with a 1mm melamine backing plate
3. After drilling, use an air gun to blow out the dust in the hole
4. Use the most stable drilling rig and drilling parameters (basically the smaller the hole, the faster the drilling speed, the smaller the Chip load, the smaller the return speed)

3. Hole treatment
Plasma treatment or sodium naphthalene activation treatment is conducive to hole metallization

4.PTH copper sink
1 After the micro-etching (the micro-etching rate has been controlled by 20 microinches), in the PTH pull from the de-oiler cylinder into the board
2 If necessary, go through the second PTH, just start the board from the expected cylinder

5. Solder mask

1 Pre-treatment: Use acidic plate washing instead of mechanical grinding plate
2 Baking plate after pretreatment (90 degree Celsius, 30min), brush with green oil to cure
3 Baking plates in three stages: one section of 80 degree Celsius, 100 degree Celsius, 150 degree Celsius, each for 30 minutes (if you find that the substrate surface is oily, you can rework: wash off the green oil and reactivate it)

6.Gong board
Lay the white paper on the circuit surface of the PTFE board, and clamp it up and down with the FR-4 substrate board or phenolic base plate with a thickness of 1.0MM etched to remove the copper, as shown in the figure: high-frequency board lamination method

The burrs on the back of the gong boardneed to be carefully trimmed by hand to prevent damage to the substrate and copper surface, and then separated by a considerable size of sulfur-free paper, and visually inspected. To reduce burrs, the key point is that the gong board process must have a good effect.

Fourth, the process flow NPTH's PTFE plate processing flow

Cutting-Drilling-Dry Film-Inspection-Etching-Erosion Inspection-Solder Mask-Characters-Spray Tin-Forming-Testing-Final Inspection-Packaging-Shipment

PTH's PTFE plate processing flow


Cutting-drilling-hole treatment (plasma treatment or sodium naphthalene activation treatment)-copper immersion-board electricity-dry film-inspection-diagram electricity-etching-corrosion inspection-solder mask-character-spray tin-molding-test-final Inspection-Packaging-Shipping Five

V. Summarize the difficulties of high-frequency board processing
1. Immersion copper: the hole wall is not easy to be copper
2. Control of line gaps and sand holes of map transfer, etching, line width
3. Green oil process: green oil adhesion, green oil foaming control
4. Strictly control board surface scratches in each process.