Some electronic products need special signals for which you have to make a high-frequency PC Board. Such a circuit board can provide 500 MHz to 2 GHz frequency that is ideal for microwaves, a radio frequency, and certain mobile applications that involve high-speed designs.
Several electronic components and switches are complex and need to transfer signals at a fast speed which is provided by high-frequency PCBs. Such boards need special materials because ordinary materials can affect signal transmission due to a poor Er value. Designers have to consider certain factors while designing the high-frequency Printed Circuit Board that we will discuss below.
Understanding a High-Frequency PCB
PCB involves connections of different components through conductive paths to run a specific electronic item. Designers use copper to develop a conductive path in a PCB. Circuit boards also help in signal transmission in the case of Wi-Fi and other satellite systems. In other words, you need a high-frequency circuit board to connect multiple objects through signals.
Which Factors Affect The High-Frequency PCB?
The design of a high-frequency PCB is not that easy because certain factors influence it and you have to consider them. Such boards have complex fabrication due to high-frequency laminates. Besides, the circuit board has to manage different applications’ thermal heat transfer.
You can’t use any material for high-frequency PCBs because it influences signal transmission that can be fast or slow, depending on the material. Moreover, the change in a material’s Er value also affects a PCB’s impedance.
Similarly, the dielectric material also plays a role in the design of high-frequency boards. Manufacturers use different dielectric materials as mentioned below:
The Roger’s is not expensive, and its DF and DK values are also less than other materials. Besides, it is ideal for prototyping manufacturing and applications. Moreover, there is a minimum chance of signal loss due to this material.
Whereas Teflon is used due to its high frequency that is up to 5 GHz that enhances the speed of signals between different parts and objects.
On the other hand, the FR4 is ideal for RF applications that need a frequency from 1GHz to 10 GHz. But, the electric products having FR4 have certain drawbacks due to their limitations.
The best material for high-frequency PCBs is Teflon due to factors like water absorption, DK, and DF. Teflon is more expensive than other materials, but it is ideal for products that need more than 10 GHz frequency of signals.
What Are The Standard Specifications Of a High-Frequency PCB?
You have to consider certain materials to have a high-frequency board as mentioned above. Moreover, the change in a material’s Er value also affects a PCB’s impedance. PCBs are available in different frequencies and have certain specifications that we will discuss below.
PCB Size: It should be at least 6 mm x 6 mm, and can go up to 457 mm x 610 mm.
PCB Thickness: It ranges from 4 mm to 5 mm.
Type of Material. Generally, it should be RO4003C, Ro3003, RT5880, and Ro3010
Weight of Copper: It ranges from 0.5 oz. to 2 oz.
PP: It includes Domestic-25FR, Domestic-6700, and Roger’s 4450F.
Min Spacing: It should be at least 3 mils.
Solder Mask Colors: Some common colors, in this case, are yellow, red, white, green, and blue.
Sides of Solder Mask. They are according to the design files.
Silkscreen Colors and Size: The colors are mostly white, black, and yellow, whereas the sides are according to the files.
Impedance Clearance: It is either plus 10% or minus 10%, depending on the design.
High-Frequency PCB Finish: It can be immersion tin, gold, silver, or electroless nickel. All these finishes should be RoHS certified.
Annular Ring: It should be min 4 mil.
Diameter of Drilling Hole: It is a minimum of 6 mils.
All the above species are standard and may change according to the board design. Besides, most circuit boards are customized and designed according to your needs. It is hard to recognize the best high-frequency circuit board, however, the material and specifications can help you in this case. You can also get professional help from a qualified PCB designer and/or a circuit board manufacturer.
Top Tips To Develop The Best High-Frequency PCB
As you know high-frequency PCBs have a high density and integration than other PCBs, they need a thoughtful design and fabrication. Such boards are more scientific than traditional circuit boards, and we have some tips to help you create a reliable PCB.
1. The pins that exist between various layers of a high-frequency PCB should have minimal leads as an alternate. Besides, the lead between different pins should be small.
2. When it comes to high-frequency devices, there should not be more bends between their pins.
3. Make sure that loops don’t develop while wiring.
4. The impedance of signals should be compatible.
5. The power pins of an integrated PCB should have a high-speed decoupling.
Meeting the Challenges of A High-Frequency PCB
No matter how well-designed is your high-frequency circuit board, you have to face some challenges during its fabrication and assembly. Let’s discuss some common issues in this case.
A professional fabricator knows that the thickness of internal layers decreases during the lamination of a multi-layered PCB made if FR4. So, the manufacturer should evaluate the percentage of such a loss. This helps printed circuit boards manufacturers get the right dimensions after the lamination process is over.
Besides, the laminate material is not hard like FR4, so it reacts differently. You should know the behavior of each material. Besides, you should scale each thickness separately or it will affect the registration from drill to pad and layer to layer. The fabricator should know all the statistics in this regard.
Preparing Different Layers
A board with several layers is complex, as you have to prepare each layer to have a strong bond, especially in the case of Teflon. Soft material can get deformed during the aggressive preparation of a surface. Such a deformation results in wrong registration, turning a PCB into a scrap.
Replacing the Teflon becomes expensive and causes delays in fabrication. So, you must prepare the surfaces carefully to avoid such challenges.
Preparation of Holes
You need to prepare the hole before plating. Like, it should be free from debris or epoxy attached to its walls. A smooth surface helps have a well intact copper plating. However, ceramic or Teflon involves a different kind of hole preparation.
This process involves a lot of care like you should consider various parameters of the drill machine to avoid the smearing of the substrate. After drilling, the hole is treated through plasma that involves gases. Poor preparation of the hole before copper plating might result in poor signal transmission. Hence, a PCB should have clean holes to perform better.
Considering the CTE Rate
The designer also has to consider the CTE or coefficient of thermal expansion of different materials. Different materials have different expansion rates, besides this expansion can occur in any direction like x, y, or z, depending on the heat. You can have well-finished holes if the CTE is less.
The factor of CTE can cause issues during a hybrid PCB of several layers when you join the high-frequency materials with FR4. So, the CTE of the materials should be compatible, or different layers or materials will expand differently, creating an issue.
Other than layers, vias also have to face this issue. Hence, the plugging material of the vias should be compatible with other materials.
Some FR laminates are similar to the RF materials in terms of behavior, and you should understand it. For example, the ceramic impregnated boards are hard when you drill through the drill bits. The hit counts should be less, besides, the RPM and spindle settings should be customized.
Sometimes the holes have fingers, which are hard to remove, so the adjustment of drilling parameters is essential to reduce fiber.
So, you can meet all the above challenges if you design and fabricate a PCB carefully by approaching a prototype pcb manufacturer to verify your design.
Importance of a High-Frequency PCB
A high-frequency PCB is widely used in different industries, such as military, interchanges, gadgets, vehicles, PC, instrumentation, clinical, and other such fields. These circuit boards are more in demand than before, and 15% of circuit boards in the market come up with high frequency.
Sometimes the electronic components and switches are complex and need to transfer signals at a fast speed which is provided by high-frequency PCBs. Such boards need special materials because ordinary materials can affect signal transmission due to a poor Er value.
You can’t use any material for high-frequency PCBs because it influences signal transmission that can be fast or slow, depending on the material. Moreover, the change in a material’s Er value also affects a PCB’s impedance. PCBs are available in different frequencies and have certain specifications.
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