PCB core Vs. Prepreg – Which Material to Choose

Printed circuit boards are the heart of electronic devices. You can get a lot of information regarding PCB on google. If you are a PCB manufacturer or designer, then material selection is very important when it comes to PCB cores. You can say that the core is the basic substrate. It has copper traces to make rigid base material. Many new designers may confuse PCB and prepreg materials. Sometimes they use these terms interchangeably. Let’s dig deeper into what a PCB core is. What is the difference between Prepreg and core material?

 What is a PCB Core?

A printed circuit board (PCB) Core is the foundation of PCB. This core is an essential part of every type of PCB. Whether it is a single-sided or double-sided board, they all have a core as base material. One or both sides have a copper coating.

Core also has different names, like FCCL, or laminate. Usually, The Core consists of the FR4 material. You can find titanium epoxy laminate, fiberglass epoxy laminate, and copper traces in the FR4 core. Prepreg helps in connecting the layers. In multilayer printed circuit boards, there are different layers.

Prepreg material help to connect these layers. It provides support and connects all the layers. Properly connected layers provide better conduction. Multilayer board is a mixture of Prepreg and Core.

In multilayer PCBs, there is a cooper layer and core between prepreg material to provide better insulation. After the layers are stacked up, all layers undergo some pressing and heating to get the required thickness.

For example, If you have a four-layer PCB, then it has two top and bottom layers. Prepreg and core are present between the top and bottom layers. copper foil is the initial copper thickness applied on the external and inner layers of a multilayer PCB board.

Similarly, in six-layer PCB, top layer, prepreg layer, and internal ground plane. The core is present between inter ground plane and the inner power plane. Again, there is a prepreg layer and then a bottom layer.

What is Prepreg Material?

Prepreg is an abbreviation for “pre-impregnated” materials. Prepreg is a fiberglass fabric. It has a coating of resin to provide its strength. Prepreg is also known as the dielectric material. It acts as glue and helps to connect the layers. Material is a sandwich between two layers of the core. That’s why when the board undergoes some heat and pressure, the resin of prepreg material melts and settles with the layers.

 Nowadays, the three types of Prepreg are available based on resin concentration. For example, the high resin has the maximum number of resins. Standard resin and medium resin have some lower concentrations. 

Prepreg Preparation Process

Not all Prepreg is equal. Resin glass weave and material properties define its characteristics. That’s why the production procedure for this glass fabric is quite similar to the weaving of yarns. Similarly, glass wearing is tight or loose according to requirement.

Therefore, resin amount and variety also affect the prepreg material’s refractive index. As a result, hardened resin provides strength to the layers. Phenolic resins also proved strength to PCB core material. It is an inexpensive material.

The typical prepreg preparation process involves the following simple step

  • Thermoplastic resin helps to make prepreg material.
  • the second step is the Removal of Excess Resin from Prepreg. B-stage materials are essential components of prepreg PCB. for example, B-stage materials include epoxy and resin.
  • The third step involves curing at low and high temperatures. In other words, you want to know about endurance.

Important Things to Keep in Mind for PCB Core Materials

What materials can provide you with ideal thickness? Controlling the thickness is very important when it comes to PCB functionality. Materials must provide the ideal thickness in multilayer PCB.

· Understand What Core Materials Go Well with What Prepreg Materials

PCB core and Prepreg work together. In some cases, certain core materials do not go well with those of Prepreg. So, it is important to understand what materials go well with what materials in core layers. As a result, you may mess up things.

· Copper Foil Thickness

If you are manufacturing multilayer PCB, then copper foil thickness plays an important role. Copper foil thickness can range from one ounce to four ounces, depending upon different factors. If the copper foil has a good thickness, then there is a better flow of charges. It means that thick copper foil provides better conduction.

· The Number of Layers

The number of layers also plays an important role in the selection of core material. Multilayer sheets are present in PCBs. These sheets should be thin sheets to control the thickness. Adjacent layers must have different dielectric constants. Therefore, you must focus on the number of layers. For example, if you neglect the thickness of layers then you have to compromise the efficiency of the board.

How To Choose Core and Prepreg Materials for Printed Circuit Boards?

 How to choose core and prepreg materials for the printed circuit boards? It’s a tricky question. Both have different properties. That’s why it is critical you have a clear circuit design. Similarly, you must know the exact value for the electrical conductivity and the return loss. Both core and prepregs have clear structural differences. Therefore, you have to understand the signals and their strength.

That’s why it is important you should know what laminate density you need. The thickness of the board also affects the conductivity and signal propagation throughout the printed circuit board. Therefore, you must know the exact dielectric constants. Precise impedance matching is also necessary.

Your work enables you to adjust your design to your particular applications. The layer stack manager in design tools is helpful for selecting PCB and prepreg materials. They give you access to a materials library.

Library gives you access to important data on a broad range of standardized materials. It also helps you to know more about materials for substrates. These features increase your productivity while still allowing you to adapt your design to highly specific applications.

 Conclusion

Core and prepreg are different from each other. Both play important roles in the manufacturing process of PCBs. I hope the above-mentioned information will help you to know more about PCB core. At this point, you will have a better understanding of PCB core and Prepreg. What their roles are in multilayer PCBs? The best core material must be heat and temperature resistant with conductive filaments.