It has become impossible for printed circuit board enthusiasts to think of, design, or fabricate printed circuit boards without material substrate consideration. PCBs and PCB materials go hand-in-hand. So yes, you have to factor in the conductive, silkscreen, and surface finish materials. Equally, you will also have to determine what non-conductive material between FR4, Arlon, Ceramic, etc., you will use for your printed circuit board.
If you want an FR4 PCB, based on the type of PCB desired, then picking an FR4 material becomes non-negotiable. However, the FR4, which makes the FR4 PCB comes as a world of its own. It has plenty of aspects that you must consider during your design phase, especially if you want a top-quality PCB for your application. But to help you understand the FR4 PCB, we will canvass all the relevant details to help you decide. So hold on for the ride.
FR4 PCB: The Material
The characteristics and properties of an FR4 material make it ideal for use in diverse application areas. You can always bank on its versatility and cost-effectiveness, making it popular across the board for PCB production. It forms the backbone of most rigid electronic circuit boards.
FR4 comes as a common denotation of the glass-reinforced epoxy resin substrate or laminate, as defined by NEMA. It not only denotes the name but the standard rating as well in circuit board manufacturing. The name rates the grade deployed in making the epoxy sheets which also indicates the base quality of the sheet (laminate). The FR is flame-retardant and indicates whether the material complies with plastic material inflammability requirement or UL94V-0 standard, while the “4” distinguishes it from other materials within a similar case.
In almost every instance, you will use the FR4 material to provide the printed circuit board’s structure, circuit integrity, and safety. It prevents the spread or propagation of fires while also extinguishing the fire whenever the material begins burning. FR4 comes as a fiberglass composite that gets woven into the thin, cloth-like laminate sheet. The fiberglass inner layer gets bounded by the flame-resistant and non-conductive epoxy resin.
The fiberglass provides structural integrity, while the epoxy resin offers material rigidity, flame retardance, among other essential material attributes. As a result, the FR4 proves popular as a printed circuit board base material. You not only take advantage of their versatility and affordability but their insulating and high dielectric strengths. Further, the FR4’s moisture and temperature resistance, high strength-to-weight ratio, besides their lightweight nature can serve you a treat.
Types of RF4 PCB and their Corresponding Attributes
Different types of RF4 PCB exist, and this mainly stems from the diverse array of attributes each possesses. Understanding the specific attributes of the glass-reinforced epoxy-resin becomes necessary owing to its role as the backbone for all forms of RF4 PCBs. The typical RF4 PCB types come as a result of the different characteristics each possesses. It can stem from the glass transition temperature, dielectric constant, coefficient of expansion, etc. Therefore, you can do well to begin by understanding the various material attributes besides their corresponding RF4 PCB types.
But firstly, it is crucial to understand that an FR4 PCB can come in different layers. Single-layered copper-clad FR4 most apply for circuit boards with simple applications. A double-sided copper-clad board or a multilayer copper-clad board becomes instrumental for more advanced PCBs applications. Such a glass epoxy PCB will come with the FR4 fiberglass of varied thickness and other vital properties based on the PCB design.
RF4 PCB Types Based on Classification
FR4 printed circuit boards can get classified differently based on attributes. It includes the following.
Size or Thickness
FR4 PCBs come at different thickness sizes, though the standard fr4 thickness is 0.78mm. However, the double and triple thicknesses come at 1.57mm and 2.36mm, respectively. FR4 PCBs can also be remarkably thinner at just 0.5mm. For the copper-clad FR4 board, the copper thickness can range from 18µm to 140µm. However, you cannot take away the importance of the FR4 1.6 mm when it comes to developing your FR4 PCB.
Source of FR4 Material
The classification determines the type of RF4 PCB based on the source of the FR4 material. Here, you will find FR4 PCBs like Isola FR4, Rogers FR4, etc. Such FR4 PCB board boards get fabricated using glass epoxy FR4manufactured by Isola and Rogers, respectively. You can therefore come across PCB types as Rogers FR4 PCB, FR4 Isola PCB, etc.
If you have come across PCB types with names such as an FR4 circuit board, then it touches on the material attributes of the PCB. It could have gotten developed by FR4 epoxy substrate, a derivative of the FR4 like TG170 PCB material that makes a high TG PCB, PCB fiber FR4, fr4 94v0, etc. Below, some of the FR4 PCB material attributes.
Glass Transition Temperature
The glass transition temperature comes as an essential aspect of every PCB substrate. It denotes the temperature upon which the polymer substrate transforms from the rigid glassy substrate to the soft and un-melted material. Glass transitional temperature, TG, gets measured as modulus or stiffness. It is the TG point where the material will have significant changes to its thermal properties, above which it expands in an isotropic manner.
The glass-transitional temperature ranges from 140 °C to 370 °C with specific categorizations of low, standard, and high TGs. Glass transitional temperature. The standard FR4 material possesses a glass transition temperature of 130 to 140 centigrade. You will likely find this type of FR4 out there. However, other factors such as coefficient of expansion, dielectric value, among other considerations, come to play in determining its standard nature.
Standard FR4 comes in various subcategories. The type offered depends on the contract manufacturer hired for the PCB manufacture. For instance, RayMing PCB and Assembly will offer FR4 VENTEC (VT 481) and FR4 SHENG YI (1000H) families, while others might only offer one standard type or distinct ones like the xw228dk fr4. However, most of the attributes will have the standard range of values as stipulated by the industry. The thickness of the FR4 SHENGYL group ranges from 0.2mm to about 3.2mm. On the other hand, the FR4 VENTEC comes with a thickness of 0.2mm to about 3.2mm.
FR4 High TG in Perspective
Most FR4 substrates do not exceed the 140-degree centigrade mark – low TG. It is a critical aspect to comprehend, especially for newbies who might not know better. The glass-transitional temperature for RF4 epoxy, often inferred as the FR4 TG is an important aspect of the RF4 laminate.
The TG ranges rank from low, moderate to high, with low ranging from 130 to 140 degrees centigrade. Values ranging from 150 to 160 degrees centigrade are classified as moderate TG, while high TG materials have TG values above 170 degrees centigrade. Most standard RF4 PCBs fall under the low TG materials though recently, the advent of the FR4 high TG material has become useful in developing multilayer PCBs. It is no wonder you will find FR4 TG 130, RF4 TG 150, FR4 TG 155, RF4 TG 170, and RF4 TG 180. High TG FR4 materials encompass better heat, moisture, and chemical resistance, besides enhanced stability to their standard counterparts.
The glass transition temperature value of an RF4 material determines the type of application that can apply. An FR4 with a high glass transitional temperature implies the ability to withstand higher frequencies and heat without damaging the circuit. Here, you will find examples like the FR4 SHENG YI family with a thickness range of 0.6mm to 3.2 mm. an FR4 VENTEC family (VT47) has a thickness range of 0.6 mm to 3.2 mm. The RF4 thickness influences the glass-transitional temperature and is thus a critical factor to consider.
It refers to the temperature upon which the FR4 PCB sheet gets permanently decomposed. The FR4 PCB decomposition temperature comes at the highest TG value of 180 degrees centigrade. Beyond this point, the FR4 changes its chemical properties permanently.
CTE or Coefficient of Thermal Expansion
An FR4 PCB material has an excellent CTE because it comes low. Such a low CTE makes it perfect for deployment in diverse heat-emitting applications. CTE also relates closely with the thermal conductivity, which means a low thermal conductivity for an RF4 material. CTE and thermal conductivity also correlate with the FR4 PCB thickness. It would help if you considered these aspects when designing your FR4 PCB.
Some of the most important electrical properties you must consider for an RF4 material include the following: dielectric constant, surface resistivity, volume resistivity, and relative permittivity. Such elements beyond the FR4 PCB thickness influence the functionality and suitability of the FR4 for specific applications.
The Layer Number
It considers the number of layers, though other factors such as FR4 Dk (dielectric constant), FR4 board thickness, FR4 substrate thickness also play a role. An FR4 standard board will therefore require that you search for the right FR4 circuit board material regardless of whether you want to develop a double-sided copper-clad PCB board or a single-sided one.
How does FR4 Gets Used in Printed Circuit Boards?
The properties of an FR4 material make it perfect for developing quality printed circuit boards at low costs. Your PCB manufacturer relies on this FR4 board, alongside its properties as the insulating backbone for developing the circuitry. Immediately the FR4 board is completed, the board is laminated with copper foil layers using an adhesive under heat. The copper will form the circuitry on the completed PCB (either on one or both sides based on the design).
However, if you intend to make a complex printed circuit board from an FR4 substrate, you may have to deploy it over one layer. Further, the layer number may also need to increase for more complex circuits. However, from this point, etching of the circuitry gets completed before covering with solder mask and prepping it with the silkscreen layer. All that remains now entails soldering before getting your FR4 PCB product.
Aspects to Consider in Picking a Suitable FR4 PCB Thickness
Often, you have to specify the FR4 PCB thickness desired when ordering for an FR4 laminate board—as an electrical engineer or designer, understanding the various specifications of the FR4 thickness becomes pivotal. For instance, the thickness can get measured in inches or other inches-derivatives like millimeters, etc., based on suitability to the existing setting. Further, the FR4 PCB material thickness will also vary based on the project’s needs. But the most common measurements range between ten-thousandth to about three inches.
You, like most people, may consider the board’s thickness an insignificant factor in the printed circuit board design. However, it proves essential as it affects numerous aspects of the functionality of the board. Because of this, you need to consider some of the critical factors that influence the FR4 PCB board’s thickness.
If you have concerns regarding the space when designing your FR4 PCB, a thinner board may prove the best solution. It comes as a significant factor in manufacturing smaller electronic devices such as USB connects and other Bluetooth accessories. Additionally, smaller FR4 PCBs, when used in a larger electronic project, tend to save more space within the device, a desirable aspect. So always go for a thinner FR4 PCB when the situation allows you to.
The type and amount of connections can determine the success or failure of your FR4 PCB. For instance, an incorrect connection can easily result in damages. Therefore, if you have a two-sided printed circuit board design, it becomes necessary to consider joining both sides with an edge connector. However, an edge connector might prove to limit when it comes to the final printed circuit board size. Edge connectors solely fit specific sets of printed circuit board thickness. Therefore, the mating segment of the connector needs to snugly fit the side of the printed circuit board to avoid risking damage or slippage of the PCB. Because of this, it is prudent to figure out the circuit design before picking the materials to deploy for the circuit board.
The significance of impedance matches when it comes to maintaining the board’s function cannot get underestimated. Multilayer boards function as capacitors on the neighboring layers. Because of this, the board’s thickness becomes vital. Remember that the FR4 substrate’s thickness determines the dielectric thickness, which then influences the capacitance value.
You must consider this aspect when developing high-frequency printed circuit boards like microwave or RF designs. Why should impedance figure prominently? High-frequency designs concentrate on impedance matching as part of maintaining optimal functionality of the FR4 circuit board. Therefore, getting the correct impedance for every circuit board layer becomes crucial.
In most cases, your FR4 PCB board’s flexibility will depend on your specific application area. For instance, thinner circuit boards are capable of flexing to some extent. Based on the circuit board’s application, it may prove unusual as an attribute but significant either negatively or positively. Some applications need more flexible circuit boards, especially if it needs regular flexing or stressing. For instance, boards for automotive and medical applications experience constant flexing or stressing of the PCB.
You can also find the flexibility aspect of the PCB detrimental to the printed circuit board manufacturing process. Such problems then translate to serious challenges during assembly. For instance, when you deploy a machine to handle an extra flexible board, it may get soldered at an angle. Further, the flexing can result in connections or components on the board breaking.
The FR4 thickness often gets influenced by the type of application the PCB needs to get deployed. However, thin boards generally prove undesirable due to the limitations the thinness causes to the printed circuit board. It is impossible to get or ensure grooves on a thin FR4 PCB besides averting the risk of fractures when enlarging the surface. However, thicker boards ensure this possibility. Therefore, always account for this during the design phase – especially the PCBs thickness, during the PCB design phase.
Like most PCB designers, you will find the board’s thickness as a critical influencer of the compatibility between the board and the components. However, note that a smaller thickness range works a treat for most components. For instance, it works perfectly for through-hole components.
Like most of us, lighter products prove more attractive. Since the FR4 PCB’s weight gets influenced by the thickness of the FR4 sheets, it needs to get considered. Weight does not necessarily prove an issue for some applications, though crucial to consider for consumer electronics. Lighter rigid flex PCB products will result in more lightweight electronic products, making it cheaper to ship and afford for a large carder of customers.
Situations that Require an RF4 PCB
Plenty of electronic applications may opt for an epoxy-based RF4 circuit board. The reliability, low cost, and strength make the material ideal for making PCBs. But an FR4 cannot apply to every situation, especially in situations that feature high-frequency designs. You might have to rely on high-frequency laminates in such cases.
Picking a suitable laminate type from such a plethora of options may prove daunting. You, therefore, need to consider the following in ensuring you make the best decision for your printed circuit board needs.
The cost of developing your printed circuit board plays a key role. You need to abide by a budget, and this may at times demand an RF4 PCB material due to their considerably low costs. Other laminate materials like ceramic or Arlon, which act as high-frequency materials, fetch markedly higher prices. You may find the cost of the alternative laminates too steep, especially if costs play a significant part in your PCB design decision.
The aspect of signal loss always proves critical for your PCB design, primarily in high-frequency scenarios where the loss of signals proves problematic. In such designs, you need to avoid an FR4 material because of its high dissipation compared to its high-frequency counterparts. It implies that such FR4 PCB will suffer signal losses at a higher frequency than identical circuits on high-frequency laminates.
An RF4 material has a dissipation factor of 0.02, whereas the dissipation factor for plenty of high-frequency laminates ranges around 0.0004. A lower dissipation factor implies a lesser overall signal loss. However, the RF4 laminate’s dissipation factor tends to increase with the signal’s frequency. It, therefore, means that an increase in signal frequency will increase the loss of the signal. Further, high-frequency laminates have DF attribute stability, thus, experiencing minor loss at elevated or higher frequencies.
The impedance stability represents a critical factor that you need to consider during the design of your FR4 PCB. It portends extra predictability when it comes to performance, especially for high-frequency designs or larger electronic circuits. Predictably, the FR4 also differs from other high-frequency laminates in the results they offer. Maintaining a stable impedance needs a dielectrically stable material across its entire surface. Because of this, an RF4 material proves unsuitable for sustaining stable impedance because of its widely fluctuating dielectric constant.
Another crucial factor you must consider in your FR4 design entails the FR4’s temperature performance. Only pick a laminate (either an RF4 or high-frequency material) with acceptable temperature performance for your PCB. The dielectric constant’s thermal coefficient proves ideal when comparing the material’s performance based on temperature management. It will measure the material’s Dk changes as the temperature changes. In most instances, an RF4 has about 200 ppm/ Δ ͦC. High-frequency laminates have about 40 ppm/ͦC.
While relatively small for each laminate type, the outcome often proves significantly varied. For instance, the RF4 significant coefficient will result in a varied Dk across its surface.
You must pick the right dielectric constant to ensure a properly functioning PCB. The DK influences the size of the transmission lines within the circuit, especially for high-frequency PCBs. Therefore, selecting the right DK becomes essential based on the size of the printed circuit board required.
You have to consider the operational surrounding or environment of the electronic circuit before opting either for an RF4 or a laminate board suitable for higher frequencies. It should include aspects like temperature and moisture. For instance, high-frequency laminates offer more heat and moisture resistance than FR4 laminates. As a result, the environment (operating) has no or lesser impact on the circuit’s functionality, whereas the opposite proves the case for an RF4 material.
You can always enjoy plenty of benefits when utilizing an FR4 board material to develop your FR PCB. You enjoy the varied attributes that accompany RF4 materials and the cost-effectiveness of such boards, especially for standard applications. If you wanted to understand the FR4 PCB, now you know.