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1. The definition of PCB high frequency board
High-frequency board refers to a special circuit board with a higher electromagnetic frequency. It 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). The copper board is a circuit board produced by using part of the process of the ordinary rigid circuit board manufacturing method or using a special processing method. 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 field
2.1 Mobile communication products
2.2 Power amplifier, low noise amplifier, etc.
2.3 Passive components such as power splitters, couplers, duplexers, filters, etc.
2.4 Fields such as automobile anti-collision systems, satellite systems, and radio systems. The high frequency of electronic equipment is the development trend.
Three. Classification of high-frequency boards
3.1 Powder ceramic filled thermosetting material
A. Manufacturer:
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%.
3.2 PTFE (polytetrafluoroethylene) material
A: Manufacturer
1Rogers' RO3000 series, RT series, TMM series
2Arlon's AD/AR series, IsoClad series, CuClad series
3Taconic's RF series, TLX series, TLY series
B: Processing method
1. Cutting: the protective film must be kept to prevent scratches and creasing
2.Drilling:
2.1 Use a brand new drill (standard 130), one by one is the best, the pressure of the presser foot is 40psi
2.2 The aluminum sheet is the cover plate, and then the 1mm melamine backing plate is used to tighten the PTFE plate
2.3 After drilling, use an air gun to blow out the dust in the hole
2.4 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
4.1 After the micro-etching (the micro-etching rate has been controlled by 20 micro inches), the PTH pulls the plate from the de-oiler cylinder
4.2 If necessary, pass the second PTH, just start the board from the expected cylinder
5. Solder mask
5.1 Pre-treatment: Use acid washing plate instead of mechanical grinding plate
5.2 Baking plate after pretreatment (90 degree Celsius, 30min), brush with green oil to cure
5.3 Three-stage baking: one section is 80 degree Celsius, 100 degree Celsius, 150 degree Celsius, and the time is 30min each (if you find that the substrate surface is oily, you can rework: wash off the green oil and reactivate it)
6.Gong board
Lay 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 copper.
High-frequency board gong board stacking method
The burrs on the back of the gong board need 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.
Four: process flow
1. 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
2. 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: Summary: Difficulties in 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
