PCB high frequency board board selection and production processing

Circuit board production of high frequency board definition High-frequency board refers to the electromagnetic frequency of the higher special circuit boards for high-frequency (frequency greater than 300MHZ or wavelength of less than 1 meter) and microwave (frequency greater than 3GHZ or wavelength of less than 0.1 meters) in the field of PCB, is in the microwave substrate copper cladding board on the use of ordinary rigid circuit board manufacturing method of some of the processes or the use of special treatment methods to produce the circuit board. Generally speaking, high-frequency board can be defined as the frequency of 1GHz or more circuit boards.

With the rapid development of science and technology, more and more equipment design is in the microwave band (> 1GHZ) or even with the millimeter wave field (30GHZ) above the application, which also means that the frequency is getting higher and higher, the substrate of the circuit board requirements are also getting higher and higher. For example, the substrate material needs to have excellent electrical properties, good chemical stability, with the increase in the frequency of the power signal in the substrate loss requirements are very small, so the importance of high-frequency boards came to the fore.

 PCB high frequency board applications Mobile communication products; amplifiers, low-noise amplifiers, etc.; power dividers, couplers and couplers, duplexers, filters and other passive components;automotive collision avoidance systems, satellite systems, radio systems and other fields, electronic equipment, high-frequency is the development trend.

Classification of high frequency boards powdered ceramic filled thermoset materials:

A. Manufacturer.

4350B/4003C from Rogers Corp;

Arlon's 25N/25FR;

TLG series from Taconic.

B. Processing Method.

Similar process as epoxy resin/glass woven fabric (FR4), except that the sheet is more brittle and prone to plate breakage, and the life span of drilling and gonging nozzles and gong knives is reduced by 20% when drilling and gonging, PTFE (polytetrafluoroethylene) material.

A. Manufacturer:

Rogers' RO3000 series, RT series, TMM series;

Arlon's AD/AR series, ISO Clad series, CuClad series;

Taconic's RF series, TLX series, TLY series;

F4B, F4BM, F4BK, TP-2 of Taconic Microwave.

B. Processing Methods: 

A) Opening: 

Protective film must be retained for opening to prevent scratches and indentations.

B) Drilling

 a, Use brand new drilling nozzle (standard 130), a piece of one stack is the best, pressure foot pressure is 40psi

 b, Aluminum sheet for the cover, and then use 1mm miamine gasket, the PTFE plate to tighten the

 c, After drilling, use the air gun to blow out the dust in the hole.

 d,Use the most stable  drilling machine, drilling parameters (basically the smaller the hole, the faster the drilling speed, the smaller the Chip load, the lower the return speed)

C) Hole Treatment

Plasma treatment or sodium naphthalene activation treatment is good for hole metallization.

D) PTH Copper Immersion

 a, After micro-etching (micro-etching rate of 20 micro inches control), in the PTH pull from the degreasing cylinder into the plate.

 b, If necessary, a second PTH will be performed and the plate will only be fed from the pre-oil cylinder. Starting from the expected cylinder.

E) Solder Mask

 a, Pre-treatment: Acid wash, no mechanical abrasion.

 b, Bake the board after pre-treatment (90℃, 30min), brush green oil for curing.

 c, Three sections of the baking plate: a section of 80 ℃, 100 ℃, 150 ℃, time 30min each (if found on the substrate surface to throw the oil, you can rework: wash off the green oil, re-activation of the treatment)

F) Gong Plate

The white paper will be laid in the PTFE board line surface, the top and bottom with a thickness of 1.0MM etched copper FR-4 substrate plate or phenolic base plate clamping, as shown in Figure: high-frequency board gong plate stacking method

After the gong plate plate edge burrs need to be carefully scraped by hand to prevent damage to the substrate and copper surface, and then separated by a considerable size of sulfur-free paper, and visual inspection to reduce burrs, focusing on the gong plate process to Shaw the effect should be good. 

C. Process Flow NPTH PTFE Board Processing Flow

Cutting-drilling- dry film - inspection -etching- etching inspection - solder resist - character - tin spray - molding - testing - final inspection - packaging - shipping

PTH PTFE board processing flow.

Cutting - Drilling - Hole treatment (plasma treatment or sodium naphthalene activation treatment) - Copper immersion - Plate electrodes - Dry film - Inspection - Graphic electrodes - Etching - Etching inspection - Soldermask - Characters - Spraying tin - Molding - Testing - Final inspection - Packaging - Shipping

D. Summarize the Difficulties of High Frequency Board Processing

 a, Copper immersion: the hole wall is not easy to copper;

 b, Figure turn, etching, line width of the line notch, sand hole control;

 c, Green oil process: green oil adhesion, green oil blistering control;

 d, Each process appears to strictly control the board surface scratches.