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Difference between PCB Core and Prepreg Materials

Prepreg Core is the isolating material of the PCB, often referred to as before laminating. Manufacturers mostly use Prepreg as a binding substance. Not just that, experts also employ it as a multifunctional PCB inner conduction material. Thus, once the user laminates the Prepreg & extrudes the half-healed epoxy, it solidifies and runs and binds the multilayer panels together to create a dependable insulator.

When the distinction between both Core and Prepreg is evident, what specific property should you use? When plate, etching, and drying, how do crucial electrical characteristics change? As more manufacturers are aware of the work at GHz frequency range, these principles are vital to size traces of these materials appropriately and prevent difficult signal integrity difficulties.


We have to grasp what a PCB is until we can comprehend Core vs. Prepreg PCB. The printed circuit board (PCB) is the source of all today’s technologies. It’s a set of electrical components linked to a tiny gadget. Our devices would not be able to work as designed without the PCB.

A PCB consists mainly of several substratum sheets, copper layering, tiny holes, a welding mask, a coating (typically in the tin-boiler), several components before fusion. However, when it is done, it doesn’t appear like building a PCB entails too much. The actual construction procedure is rather long since each computation must be correct to prevent malfunction.


Prereg PCB is a conductive substance that planners pack to provide the appropriate insulate between the copper and a core or dual Core of a PCB. Prereg is a level of isolation. Since a copper sheet and a core may be bonded, it may be called a binding material safely. Users may also customize Prereg as special insulators to their demands. A chemical technique may also be used to turn a given section of a Prereg into a conducting zone by combining appropriate catalytic substances and additives.



The PCB core is a hard foundation material coated on one or two aspects with copper. The CORE is employed in the fabrication of single-sided and two-sided boards and in the manufacture of PCBs of sharing arrangements.

The PCB center consists of the FR4 elements of titanium epoxy laminates and copper traces. The Prereg connected the layers and the PCB core when users heated there.

Experts responded to the Core as the core panel and also to the Core of PCB production. It has a certain copper, width, and firmness of double bread. Its multilayer board is a mixture of Prereg and Core.


Prepreg is a fiberglass fabric/towel coated with a resin preservative, as the name implies. The glass strands are knitted into a glass tissue. This glass fiber fabric is half-dried into material from the B-stage.

Most prepregs are substances of the B-stage. It is vital to track the volume fraction of the material used throughout the production process Prepreg, as it enables the material to be adjusted according to the demand. The number of repetitions of warp and fill affects the epoxy the glass weave can hold.



Depending on the size and other needs, many kinds of prepregs are integrated into PCBs. According to its resin composition, Prepregs are compatible with standard resin (SR), mid resin (MR), or high resin (HR). The more and more resin it holds, the more costly it becomes.


With clear structural differences in the core prepreg materials, it is critical from a circuit design perspective to get an exact value for the electrical conductivity and the return loss. If your signals have minimal growth time, you can usually get away using a user information sheet value. Once your knee and analog signals have reached the GHz range, attention must be taken with the datasheet values, particularly when modeling interconnect behavior and employing resistance-controlled routing.

The difficulty with data source numbers is that the true electrical conductivity determined is based on the test technique, geometric routing, particular frequencies, convention on the law, and the thickness of the material. John Coonrod spoke extensively about this subject in a recent interview. The fabric pattern of PCB core/prepreg components renders them inhomogeneous and anisotropic, meaning that the main material qualities change in space and various directions. This is why we get fiber weaving phenomena such as excitation of the skew and fiber cavity.

You could wonder, why should a laminate density define the material characteristics? The reason is that the important parameter characterizing the signal behavior is a useful electrical conductivity, which relies on your material’s trace size and layer thickness. 

Finally, copper texture on a particular laminate is the second key characteristic to be considered. The above two studies Will present efficient dielectric constant calculations for the geometries of microstrip and strip lines without the assumption of copper ruggedness. There is, however, a straightforward linear approach to compensate for copper rawness:

Suppose you are working at really high speeds and high frequencies and want very precise connection characterization. In that case, the best choice is to produce a test coupon and utilize standard measurements to calculate the functional dielectric constant. A topology that roughly resembles your anticipated interconnection geometry should be used in your test procedure. This requires some effort at the front, but precise testing and measuring might save you needless prototype runs in the rear.

Suppose you pick from a variety of PCB core versus prepreg material, the Altium Designer.   You will have access, or you may define special material characteristics for exotic substrates, to a component library that offers crucial information on various standardized materials. These capabilities enhance your efficiency and enable you to adjust your design to very particular applications.


PCB cores and coatings are comparable yet extremely distinct in certain aspects. Your Core is one or more prepreg panels crushed, hardened, and heat-cured, and the Core is covered on each side with a copper foil. The resin is injected with the prepreg material, wherein the resin is solidified but left untreated. Many companies define Prepreg as the duct tape that ties the core components together; the exposure to heat allows the resin to start binding to the next layers when 2 cores are placed at either edge of a prepreg lamellate. The solidified resin cures slowly bypass, and its resultant material characteristics approximate the core layers.

The resin substance contains a glass fabric. The production procedure for this glass fabric is quite similar to that for the fabrication of yarns. The glass fabric may be pretty narrow (e.g., 7638 prepreg) or flexible (e.g., 1081 prepreg), manufactured by the weaver. Any flaws and general yarn uniformity will decide the magnetic characteristics responsible for the scatter, loss, and fiber tissue impact of the signals in the circuit.

According to the resin amount, resin variety, and glass fabric, core PCB vs. prepreg materials may have a slightly differing refractive index. This may be a concern if boards need to be designed that match extremely exact impedances since the absorption coefficient observed on a track relies on the dielectric constants of the material resulting. Not even all prepreg and core materials are mutually compatible, and core/prepreg stacks with widely varying dialectal constants make predicting accurate dielectric constants and inefficiencies in an interconnection problematic.

Every PCB core or prepreg material has a problem with high voltage creeping and leakage current. Copper electromigration and further expansion of conductive filaments are a cause for the FR4 material creeping criteria. This difficulty drove a move to – anti (Non-DICY) in FR4 Prepreg and coatings, albeit with a want to improve the transition of the glass and breakdown temperatures. Phenolic resins offer greater breakdown and transition temperatures than DICY resins and increase isolation resistance upon complete curing.

We can interpret it this way, and The Prepreg is a PCB isolating material. Prepreg shall not be Prepreg before encapsulation, also known as Prepreg. It shall be utilized mainly as a connecting material and an isolating material for a multilayer integrated circuit board’s inner guiding pattern. After lamination, the semi-curated epoxy is ejected, starts to flow, reinforces the multilayer sheets, and produces a durable insulator.

The Core is the essential material for the production of PCB. The Core is also referred to as the core panel, which has some toughness, depth, and double copper bread. Therefore, Core and Prepreg are a mixture of the multilayer board. The distinction between the two:

  • PCB material prepreg and the older material is semi-solid, cardboard-like, the later hard, copper-like,
  • Prepreg is a sticky + dielectric, and the Core is the fundamental PCB material; two functions are entirely distinct;
  • The Prepreg may be curved, not bent to Core;
  • Prepreg is not capacitive; the copper layer between both sides of the Core is a permeable print board.

Final Thoughts

Prereg is a must and not simply a key aspect of the PCB production process when multilayer is included. Without Prereg, manufacturers will have no substance to hold the multiple layers together. The Core and Prereg are the other two elements of the PCB. This Core contains traces of copper as a substance FR4 prepreg. The Core, meanwhile, holds the PCB via Prereg.

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