PCBs are a vital part of modern electronics, forming the core for links and attachment of electronic components. 6-layer PCBs form part of almost all complex devices like mobiles, computers, and sophisticated industrial equipment.

This article discusses manufacturing a 6-layer PCB. Generally, it will be the careful steps one has to take in the entire electronic backbone process.

Conceptualization and Design

Initial Design Considerations

• Functionality and Performance Requirements : Define the electrical performance, signal integrity, and power distribution needs.
• Size and Shape Constraints: Defining physical dimension and shape based on the device’s housing and application.

Software Tools for PCB Design

• PCB can be designed and simulated using industry-standard tools such as Altium Designer, Eagle, and KiCad.

Making of Schematic Diagram

• Choice of components: The selection shall be based on the component’s function and shall be compatible to a certain extent.
• Schematic Drawing: Create a full schematic drawing that shows all electrical connections in the circuit.

PCB Layout Design

• Stack-up design: Design the six-layer arrangement encompassing signal, power, and ground layers.
• Component Placement: Positioning the components so that the signal interference among them is minimized and space is best utilized.
• Trace routing would mean routing all electric connections between the components, considering signal path length and cross-talk.

Verification and Simulation of Design

• Validate the design individually with simulations and obtain all performance requirements and reliability parameters for the design.
• Perform Design Rule Checks (DRC) to find and correct potential problems.

This way, the design process ensures the 6-layer PCB performs properly and works effectively.

Material Selection

Materials used in 6-layer PCB

• Substrate: FR4 is a general-use substrate due to its proper performance-to-cost ratio. FR4 is a laminate that combines good electrical insulation with mechanical strength.
• Copper Foils: The conductive layers are made of copper. The copper thickness varies to suit different current-carrying needs.

Making Material Selection Based on Properties

• Electrical Properties: A dielectric constant and loss tangent are selected for each material, which will directly impact signal integrity and impedance control.
• Thermal Properties: Thermal properties, expressed as thermal conductivity and the glass transition temperature (Tg), are very important in dissipating heat and maintaining thermal cycle stability.

The selection of the right material for the 6-layer PCB ensures the best possible performance is achieved.

Manufacturing of PCB Layers

Base Material Preparation

• Substrate Cutting to Size: The FR4 substrate is cut into fine panels for 6-layer PCB manufacture.
• Surface Preparation: The substrate is thoroughly cleaned of all contaminants to provide a smooth, adhesive surface on which something can be poured without fear of it not sticking.

Creating the Inner Layers

• Photoresist: A light-sensitive material is applied on the copper-clad substrate. The coating will protect selected areas during the etching process.
• The photoresist-coated substrate is exposed, and UV light is passed to it using a photomask with a circuit pattern. The photoresist material hardens with the intensity of UV light irradiated in the exposed areas.
• Developing: A developed solution finally washes out any residual unexposed photoresist and reveals the bare copper in regions where it needs to be etched away.
• Etching the copper: The substrate is immersed in an etchant solution. The etchant eats out the uncovered copper, leaving in place only the desired copper traces that pattern the inner layer circuitry.

Layer Alignment and Stacking

• After the individual  inner layers are made, they are aligned and stacked in a very tight arrangement. This forms a single structure for the multilayer PCB, where one layer is prepreg bonded (pre-impregnated with resin).

The inner layers must be manufactured accurately and reliably during the process, which is especially crucial with a 6-layer PCB.

Drilling and Plating

Drilling Holes for Vias and Through-Holes

• Precision drilling is done from a CNC machine to create vias (inter-layer connection) and through holes (for component leads).

Plating Through Holes With Copper

• Electroplating: The drilled PCB is cleaned and placed in a chemical bath to electroplate, thereby plating a thin layer of copper inside the holes. Great care is also taken in this stage since the holes are through, connecting one layer to the other.
• Reliable Connection: Several good quality checks, such as visual inspection and electrical tests, ensure the uniformity of the copper plating and its proper adhesion to provide a reliable electrical connection over the entire PCB.

This step must be cautious regarding the structure and electrical integrity of the 6-layer PCB.

Imaging and Etching of the Outer Layer

Applying Photoresist on the Outer Layer

• The outer surfaces of the PCB would then be covered with a layer of photoresist. This light-sensitive coating would define the circuit pattern for the outer layers.

Exposing and Developing the Outer Layer Pattern

• The photoresist-coated PCB is exposed to UV light. This step hardens the coating in areas exposed to the light. The unexposed photoresist is developed and cleaned, revealing the copper beneath.

Etching Away Unwanted Copper

• The PCB is immersed in an etching solution that corrodes the exposed copper. What remains is the desired circuit pattern, protected by the hardened photoresist. This is the process by which complex conductive pathways are created out of the outer layers.

This step is used to complete the circuit patterns on the outer layers of the PCB.

Solder Mask and Surface Finish

Solder Mask Application to PCB

• A solder mask is deposited over the PCB. This protects the copper traces from impurities and avoids solder bridges.

Techniques for Applying Solder Masks

• Some of the popular techniques include silkscreen printing and photo imaging.

UV Curing Process

• The returned mask is then subjected to UV curing to harden the applied solder mask for protection.

Surface Finish Application

• Types of Surface Finish: Hot Air Solder Leveling (HASL) finish, and the Electroless Nickel Immersion Gold (ENIG) finish are the most common types. 
• Purpose: These finishes protect the exposed copper and improve the copper surface, which is essential for the reliable attachment of components and to avoid oxidation.

This stage ensures PCB safety and preparedness for assembly.

Electrical Testing and Quality Control

Visual inspection for Defects

• Inspect the PCB for any visible imperfection, such as layer misalignment, cracks, or blemishes on the surface.

Electrical Testing Techniques

• Flying Probe Testing: Probes are electrically tested by automation without needing a custom fixture, which is great for small batches.
• In-circuit testing (ICT): This method tests whether every component on the PCB is functional, using a bed-of-nails checking fixture to ensure correct placement and operation.

Visual and electrical tests are done before the 6-layer PCB is shipped so that it will meet the agreed design and industry criteria for functionality and reliability.

Final Assembly and Packaging

PCB Assembly with Components

• The components are then mounted onto the PCB by the pick-and-place machines.

Soldering Techniques

• Wave Soldering: This is where through-hole devices are soldered as the PCB flows over a molten solder wave.
• Reflow soldering: Solder paste is melted in a reflow oven. This melted paste is then used to hold the components together.

Final Check and Test

• Carry out final inspection and functional testing for each assembled PCB to ensure that components are in their proper positions and functioning.

This final step is to make the PCBs ready for electronic instruments.

Viasion: Excellence in 6-Layer PCB Manufacturing

As one of the leading companies in 6-layer PCB manufacturing, Viasion can deliver world-class, premium-quality PCBs. Its high-end capabilities ensure leading performance and reliability.

• Precision Engineering: We apply sophisticated technology to develop complex multilayer designs.
• Quality Materials: We use high-quality substrates and copper foils to continuously be durable and efficient.
• Rigorous Testing: We thoroughly inspect and electrically test the parts to ensure they are in perfect working condition.
• Committed to Environment: Eco-friendly practices are followed during manufacturing.

Use our services for the production of 6-layer PCBs. You can trust us with the assurance of excellence, reliability, and innovation.

Conclusion

All that the 6-layer PCB manufacturing goes through, with its detailed design, material selection, precision in layering, drilling, plating, and careful testing, is done to ensure that quality control and precision remain at the top of the list. In addition, it ensures that advancements keep coming in PCB technology to offer more sophisticated and efficient solutions to the electronics industry.

Related articles:

• What are Printed circuit boards (PCBs)?
• How Artificial Intelligence is Revolutionizing PCBs
• What Is the Aluminium Layer of a PCB?