What Exactly is Prepreg in a PCB?

What is a Prepreg PCB?

Prepreg is a part of untreated FR4. The FR4 is utilized in the PCB manufacturing process, where it performs the function of binding the etched cores together. It can also be useful in gluing the copper foil with the etched core. Thus, the prepreg in a PCB can vary in thickness in accordance with the height of the etched boards. If we compare prepreg vs. core, the latter is FR4 coated with copper either side and is made in a core factory. But the prepreg is sort of virgin FR4 that gels itself into the structure of a PCB board.

What is the prepreg PCB preparation process? A typical prepreg process involves:

• Reinforcing with resins which can be either thermoplastic or thermoset.
• Removal of excess resin
• Preparation of curing with high and low-temperature settings

Application in the PCB Manufacturing Process

The common application of prepreg in a PCB’s manufacturing process lies in bonding the copper realms of a copper-plated laminate with copper foils applied in a multi-layer rigid type PCBs. Besides, it is used in a flexible circuit or rigid-flex circuit board manufacturing process too.

Multi-Layered Boards

The multi-layered PCB of rigid type employ prepreg in bonding the CCL or copper-coated laminate with copper foil.

Complex PCBs

Complex PCBs are categorized as – Flex Circuit with Stiffener PCB and Rigid-flex board.

In the flex circuit with stiffener PCB type, the PCB layer achieved is single-sided to multi-layer style. The prepreg application lies in bonding the FPC with a stiffener in this case.

In the rigid-flex board type, the PCB layer is double-sided to multi-layer type. This structure is achieved by using Prepreg for bonding CCL with copper foil and also by bonding FPC with stiffener.

How is it used?

Advanced fabricating experts use prepregs to achieve the purpose of minimizing the weight of the part they are preparing. The low weight parts are needed where the devices or products are supposed to work against any flow or resistance. For example, the aerospace needs lightweight parts; so, does the racing and sporting materials. The pressure vehicles and a few commercial products also fare well in terms of cost-efficiency when they weigh less. It becomes possible to achieve with prepreg. Fabricators need to have experience in processes like vacuum bagging and hand layup to use prepreg in their work.

Primary industries where prepreg finds its application are:

• Construction
• Defense and ballistic
• Marine
• Transportation
• Infrastructure
• Wind energy/power and a few others.

Why is it Important?

Prepreg is an integral part of the PCB manufacturing process because:

• These are easy to apply and to learn to work with. Getting accustomed to it does not require much technical expertise. With regular use, even a less tech-savvy person can become familiar with prepregs. Thus, the cost of labor does not shoot up when the prepregs are used.
• PCB prepreg material is very less messy as compared to the wet style layups. Thus, these contribute to waste management during the manufacturing process better, followed in PCB making units.
• These are available in various types, such as Kevlar, fiberglass, and hybrid as well. Thus, you name the purpose, and there is a suitable prepreg available for it.
• To top it all, the possibility of reducing the weight of the device becomes higher, which is quite essential in some particular types of equipment required for working in unique conditions.

It is worth learning that the PCB prepreg material displays a better shelf life when these are stored in colder temperatures. It is because its resin part remains deactivated, allowing it to remain intact and usable beyond a chosen timeframe.

What Role Does It Play?

Prepreg plays a very crucial role in the PCB development process. It offers a trusted gluing material that can stick or bind the layers of PCB together. Its purpose is that of securing the copper foil to an etched core or of fusing the two etched cores. 

A prepreg is a sheet that can work as an insulating agent in a PCB. So, apart from working as binding material, the prepreg is also used to introduce insulation in inner conducting parts of a multi-layered PCB board.

Prepreg PCB is also proving its utility in reducing the weight of the components, which means achieving better use of the device or equipment minus the troublesome transportation cost and functionality hassles.

Conclusion

Prepreg is an abbreviated term that can be expanded as pre-impregnated. It forms a receiving substrate on which the copper coils can be appropriately fused. It is an FRP reinforcement, which technically speaking is fiberglass impregnated with resin. Thus, it does the job of holding the layers together to achieve a desired thickness of the PCB board. It is mainly responsible for the correct binding of layers, the insulation between them, and also for reducing the overall weight.