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What Is Multilayer Fr4 PCB Substrate Material?

FR4 serves as a name and a reference rating, &  it is also written as FR-4. For high-quality PCB manufacturing operations, FR4 is the perfect default substrate material because of these characteristics. These characteristics can also serve as the basis for PCBs that are both high-quality and affordable when employed properly.

FR4 serves as the main insulating backbone of a PCB. This serves as the foundation upon which the circuit is built by the manufacturer. The FR4 board is prepared and then heated and coated with one or many folds of copper foil applying adhesive. Depending on the board’s design, this copper may wrap one or either side and create the connectors in the final version.

To create more complex circuitry, complex PCBs may layer the electronic circuit or use more than one side. From here, the board is prepared for the last touchscreen layer and the following soldering process by having the circuits designed and filed off before being coated with a modified surface layer.

Ceramic vs. FR4 PCB : When to Use?

multilayer pcb manufacturing
multilayer pcb manufacturing

When most people hear the phrase “ceramics,” they immediately think of their primary or secondary school art class when they proudly made their parents a misshapen coffee cup. When you were an engineer, ceramic materials were essential to the creation of electronic components. Knowing how to design a different substrate PCB with transistors can be helpful.

Ceramic PCBs are advantageous for industries that need faster-speed amplitude boards that can survive challenging environments. By transitioning from FR4 to ceramic Boards, heavy industrial and aerospace equipment can experience significant improvements in reliability. The main disadvantage is the price, which can add up in large manufacturing runs.

· Ceramic vs. Multilayer FR4 PCB 

Compared to FR4 boards, ceramic boards have several unique features that can be used in specific applications. There is no one “ceramic” substance; rather, the term applies to a class of substances that share a similar chemical makeup and set of physical characteristics. Aluminum oxide, aluminum nitride, and beryllium oxide are ceramic materials utilized as substrates for circuit boards. Other ceramics with comparable properties include those made from substrates like silicon carbide and boron nitride.

The heat conductivity of FR4 and porcelain materials is a significant distinction. Comparatively to the ceramic materials employed for a circuit, FR4 has an appallingly low thermal conductivity. FR4 is roughly 20 times more thermally conductive than aluminum oxide. Beryllium oxide always has greater thermal conductivity than aluminum nitride, which is around 100 times more thermally conductive than silicon carbide. The material with the greatest thermal conductivity is boron nitride.

High thermal demands on FR4 Boards frequently need the use of metal structures to convey heat in order to make up for their poor thermal conductivity. Heat is transferred away from the surface layers through thermal connectors, metal surfaces on the inner surface, active cooling components like blowers, and thermal landings. Except for extreme circumstances, porcelain boards do not need these components, and heat can be simply transferred to a mechanical landing, an effective cooling feature, or device packaging.

Chemistry and physics majors may be aware that materials that carry heat well also make excellent electrical conductors. Ceramics defy this tendency a little. Thus these boards can still be utilized as PCB substrates because their conductivity is so low. Doping, which is also how ceramic resistors’ resistance is set, can be used to change the electrical properties of ceramic boards.

· Multilayer FR4 PCB Ceramic Boards

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Further advantages of ceramic boards make them particularly beneficial for multilayer boards. Due to more consistent heat transport across the board, the high degree of thermal conductivity helps minimize the development of critical areas on the base and inner circuit layers. Heat waves are more prone to emerge on an FR4 PCB because it depends on metallic structures or aggressive cooling to move heat away from specific areas of the circuit or between layers.

Vias on FR4 boards are prone to fracture during temperature cycling and are used by multilayer boards to access the interior layers of a circuit. Deficiencies in the thermal expansion ratio between copper and FR4 cause the possibility of fracture to exist. These boards experience stress from thermal cycling along the chamber and butt connections within vias. Designers must take additional precautions to prevent failure since these spots are prone to fracture.

Because the thermal expansion coefficients of ceramic circuit boards are closer to those of their conductor structures, less stress builds up during thermal cycling in these structures. The ceramic board’s better overall thermal conductivity guarantees that heat capacity is also more consistent, preventing significant stress from being placed on any vias in a specific area of the board.

Ceramics possess a desirable level of mechanical strength and are capable of withstanding high mechanical loads, such as powerful vibrations and shock. A porcelain board will often distort less than an FR4 for just that applied stress since they have smaller Young’s moduli.

· Manufacturing Multilayer FR4 PCB Ceramic Boards

Silver or gold conductive pastes can be used throughout the ceramic board manufacturing process to lay trace connections in each layer. A coat screen printing procedure is commonly used to insert these metal components or substrates in each layer. Furthermore, micro vias can be laser-drilled or physically hammered in an unfired layer.

The complete stack of printed and stacked ceramic layers is then baked in an oven. The ceramic board must be baked at a temperature below 1000 °C, which is the same as the temperature at which gold and silver paste sinter. Gold and silver can be used on ceramic Boards thanks to this cooling bake method.

It is simple to incorporate analog elements directly into the inner layers of a ceramic PCB thanks to the compression molding and sintering process for multilayer PCBs. In a PCB constructed of FR4 material, this is not feasible. Designers are now able to enhance the density of connections and components on inner layers.

How To Select Multilayer Fr4 PCB Thickness?

multilayer circuit board

The designer or electrical engineer should specify the FR4 thickness when placing an order for a laminate board for a PCB project. Based on which is most suitable for the environment, this is determined in inch-based quantities, like a 1,000th of an inch, thou, or millimeters. FR4 sheets can be any thickness. However, they often span from ten through to three inches depending on the project’s requirements.

Although board thickness might not appear to be a crucial element in a PCB’s design, it actually is. In order to determine the width of a plank for design, numerous criteria are taken into account because board thickness impacts a number of the board’s functional characteristics. The following are some of them.

1. Space

If the designer is concerned about space, a smaller FR4 board is typically preferred. This is a key component in the creation of numerous Bluetooth accessories and USB connectors, which are tiny devices. Smaller FR4 PCBs are typically preferred to reduce space inside the device, even for bigger applications.

2. Connections:

An edge connector is necessary to link the two sides of a two-sided PCB design. Since PCB edge connectors can only fit a specific range of PCB thicknesses, this might be a significant limiting factor for the PCB’s final size. To avoid slippage or PCB damage, a connector’s mating component must fit tightly against the edge of the Board. That’s one of the main explanations for why choosing the material for the circuit comes before designing the circuit.

3. Impedance Matching

Each multi-layered board serves as a capacitor for the layers below it. Because the width of the PCB FR4 substance impacts the width of the insulator, which significantly influences the capacitance value, the width of this panel is crucial.

This is a particularly important consideration for some elevated PCB designs, such as Rf/microwave ones. Getting the proper inductance for every layer is vital in high-frequency designs because impedance matching is a crucial element for maintaining good board performance. 

 

 

 

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