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 Everything You Need to Know About Inner Layer PCB

Everything You Need to Know About Inner Layer PCB


The inner layer processing is an essential step in the production of multilayer PCBs. As a PCB factory with over 20 years of expertise in the production of circuit boards. we will go over the knowledge and production process of the inner layer. in the production of multilayer circuit boards in this article.

pcb inner layer

What is the Inner Layer PCB?

A multilayer PCB consists of multiple layers of copper traces and insulating material. such as fiberglass epoxy resin, stacked together. Each copper layer in a multilayer PCB referred to as an inner layer. These inner layers are typically etched with circuit patterns. and serve as the conductive pathways for electrical signals within the PCB. The inner layers are then laminated together with insulating material. and the outer layers added to enclose the structure.

The number of inner layers in a multilayer PCB can vary depending on the complexity of the circuit design. and the requirements of the application. A multilayer PCB can have as few as four layers or can extend to dozens of layers, depending on the specific needs.

In summary, the inner layer in the context of a PCB. refers to one of the copper layers within a multilayer PCB structure. which carries the circuit patterns and provides the electrical interconnections between components.

The Importance of PCB Inner Layer

Understanding and discussing the inner layer PCB. That is important to comprehend the overall structure, functionality. and performance of the circuit board. It helps engineers, designers, and manufacturers make informed decisions. during the PCB design and manufacturing process.

The inner layer of a PCB is an important aspect to consider and discuss for several reasons:


The inner layers of a PCB are where the majority of the circuit traces and connections located. These layers carry the electrical signals and provide the necessary interconnections. between components, ensuring the proper functioning of the circuit.

Layer Stackup:

PCBs constructed using multiple layers of conductive material and insulating material. The arrangement and configuration of these layers. including the inner layers, well known as the layer stackup. The layer stackup affects various aspects of the PCB design. such as signal integrity, power distribution, and impedance control.

Signal Integrity:

The inner layers play a crucial role in maintaining signal integrity within the PCB. Proper placement and routing of signals on the inner layers help minimize noise. crosstalk, and interference, ensuring reliable communication between components and preventing signal degradation.

Power and Ground Planes: Inner layers are often dedicated to power and ground planes. These planes provide a stable reference for signals. help distribute power throughout the circuit, and minimize electromagnetic interference (EMI). They also aid in heat dissipation and can enhance the overall performance and reliability of the PCB.

Design Considerations:

When designing a PCB, engineers need to carefully plan and allocate the components. and traces, signals on the inner layers. This includes considering factors such as signal routing. thermal management, electromagnetic compatibility (EMC), and manufacturability. Discussing inner layer PCBs allows for a deeper understanding of these considerations.

The Steps of PCB Inner Layer Process

The process of manufacturing inner layers for a PCB typically involves the following steps:

Preparing the Substrate:

The first step is to prepare the substrate material. which is usually a thin sheet of fiberglass epoxy resin known as a core. The core cleaned and inspected for any defects or irregularities. that could affect the PCB’s performance.

Applying Copper Foil: Copper foil laminated onto both sides of the core material. The copper foil is typically available in rolls and has adhesive on one side. It is carefully aligned and bonded to the core material. using heat and pressure to create a uniform copper layer.


A layer of photoresist, a light-sensitive material, applied onto the copper layer. The PCB designer’s digital artwork, known as the inner layer Gerber file, used to create a photomask or a film. The photomask or film aligned and exposed to UV light. which transfers the pattern onto the photoresist.


The exposed photoresist developed using a chemical solution. which removes the unexposed areas, leaving behind the desired pattern of resist. The areas of copper covered by the developed photoresist. protected during the subsequent etching process.


The PCB etching process where the unprotected copper is chemically dissolved. leaving only the copper traces and pads that covered by the developed photoresist. The etching solution typically used an acidic solution that selectively removes the copper.

Stripping the Photoresist:

Once the etching process is complete. the remaining photoresist stripped off using a chemical solution or a plasma process. leaving behind the desired copper traces and pads on the inner layer.

Inspection and Testing:

The inner layer inspected for any defects. Such as incomplete etching or over-etching. and tested for electrical continuity and resistance to ensure the integrity of the copper traces.

Prep for Lamination:

After inspection and testing, the inner layers cleaned and prepared for lamination. This includes applying an adhesive layer, known as prepreg. onto the copper surface to help bond the inner layers. with the outer layers of the PCB during the lamination process.

These steps are typically followed for each inner layer in a multilayer PCB. Once all the inner layers processed. they laminated together with the outer layers. and the PCB goes through additional processes such as drilling, plating. solder mask application, and component assembly to complete the fabrication of the final PCB.

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