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A Comprehensive PCB Lamination

PCB lamination is one of the most crucial steps in the PCB manufacturing process. It helps to create high-quality PCBs. If your PCB is manufactured without lamination, it would be too fragile to operate properly. It makes the overall functionality of your device inefficient and unstable.
At FC, we carried out the PCB lamination process using a special PCB laminator, following every standard and protocol. We will discuss PCB lamination and its basics, including types, materials, and processes.

What is a PCB Laminator?

The device that is used to create the PCB by boning the material’s layer together under high pressure and heat is the PCB laminator. The material used for manufacturing printed circuit boards (PCBs) is called PCB laminate. It is a composite material with structural stability and electrical insulation on the PCB. The PCB laminate comprises several layers, copper foil, and a substrate.
The main elements of a PCB laminate are as follows:
 
Substrate: The PCB laminate’s core material is called the substrate. Usually, it is constructed from a non-conductive substance. FR-4 provides better mechanical strength, heat resistance, and dimensional stability.
 
Copper Foil: Copper foil is laminated onto the substrate to generate conductive paths for electrical impulses. Typically, copper foil comes in various thicknesses, like 1 oz (35 µm) or 2 oz (70 µm). In the lamination process, pressure and heat are used to attach the copper foil to a substrate.
 
Prepreg: Pre-impregnated resin is a resin material impregnated with a curing agent. It is employed to fuse the PCB laminate layers. Prepreg layers are made of fiberglass fabric infused with epoxy resin. During lamination, the prepreg layers serve as an adhesive by sandwiching the copper-clad substrate between them.
PCB laminates involve stacking different layers in the substrate, copper foil, and prepreg. The layers are then bonded in a lamination press using pressure and heat. Single-layer PCBs have a single copper layer on a substrate, and multi-layer PCBs have multiple copper layers divided by prepreg. Advanced electronics and computer systems are two typical applications that use multi-layer printed circuit boards (PCBs) because they require a high circuit density.

Types of PCB Laminator

There are different types of PCB laminators. They are described below:

FR-4 laminate

FR-4, also called fiber-reinforced epoxy resin, is widely used today. This material is better in performance, price, and availability. FR-4 provides mechanical rigidity and durability to the board.

CEM-1 laminate

CEM-1 laminates are less expensive than FR-4. Rather than using fiberglass, CEM-1 uses a composite epoxy resin reinforced with cellulose paper. The mechanical qualities of CEM-1 get worse, since cellulose paper fibers are not as robust as fiberglass. It requires more moisture as well. However, the cost of the materials is much lower, which can save some PCB costs when performance standards are not as strong.

Polyimide laminate

Kapton and other polyimide films offer superior chemical resistance and thermal stability, making them appropriate for adaptable PCB applications. Polyimide films’ glass transition temperatures are over 300°C, indicating their extreme temperature resistance. Because of their heat tolerance, polyimide-based flexible circuits can be used in high temperatures.

High Frequency/High Speed

High-frequency and high-speed digital printed circuit boards employ specialized laminates designed for maximum electrical performance. Important parameters, including loss tangent and dielectric constant, are minimized to preserve signal integrity at higher speeds. Microglass fiber-reinforced PTFE (Teflon) composites are a common high-frequency/high-speed laminate material. PTFE blends packed with ceramic are also utilized.

Metal Clad Laminate

In metal-clad laminates, thin copper or aluminum foil layers are attached to one or both sides of the dielectric substrate. The ability to disperse and diffuse heat permits the production of PCBs with a metal core.
 
Aluminum-clad laminates provide the highest thermal conductivity for heat dissipation. Additionally, copper-clad laminates have good thermal characteristics. These metal-based boards are perfect for high-power applications where proper thermal control is essential.

Advantages of PCB Laminate

The advantages of PCB laminate are as given below:

1. Electrical insulation

The laminate separates the conductive copper layers. It guarantees better signal flow and protects against short circuits. It facilitates the maintenance of electrical integrity. Furthermore, it reduces the possibility of interference or signal coupling.

3. Environmental protection

The lamination serves as a barrier of defense. It protects the PCB from impurities like dust and moisture. It aids in avoiding oxidation, corrosion, and harm to the electronic parts. Likewise, it guarantees the circuit board's durability and dependability.

5. Signal integrity

Maintaining signal integrity on the PCB is mostly dependent on the lamination. Managing the impedance and spacing of copper wires helps reduce signal loss, reflections, and electromagnetic interference. This is particularly important in high-speed analog and digital circuits, where signal quality is critical.

2. Mechanical stability

The PCB gains structural strength from the lamination. It hardens and prevents it from bending or warping. The circuit board's integrity depends on this mechanical stability. It is applied to mechanical stress, shocks, or vibrations that could affect the PCB.

4. Miniaturization and high-density

 Laminate makes the production of multilayer PCBs, higher circuit density, and miniaturization possible. When multiple layers of copper and insulation are stacked together, a smaller footprint can accommodate more components and functions.

6. Ease of manufacturing

It is simple to work with laminate materials because they are made to operate with the PCB fabrication process. It offers a sturdy surface for soldering and attaching components.

Process of PCB Lamination

If you want to learn about PCB lamination technology, please watch the video below first.

Step One: Surface Preparation

This process includes thoroughly washing the panels, rinsing them with pure water, removing fingerprints and corroded copper surfaces, and removing pollutants.

Step Two: Micro-Etching

In micro-etching, an acid is used to oxidize previously plated copper foil. This procedure guarantees the consistency of the copper layer and protects critical regions from exposure, including pads and channels necessary for the transmission of electrical impulses.

Step Three: Surface Treatment

The PCBs get careful surface treatment using a black oxide bath. It improves epoxy resin adherence and successfully prevents delamination problems.

Step Four: Inner Layer Stack-up

At this stage, a worker manually arranges the prepregs and inner layers in their proper order and uses the riveting machine to fuse them gently.

Step Five: Full Stack Assembly

The stack is kept between stainless steel plates and sheets of copper foil. During lamination, the steel plates guard against damage and warpage. This entire assembly fills the laminating press.

Step Six: PCB Lamination

A hydraulic laminating press heats the sandwich assembly. The prepreg layers flow and soften under pressure and heat while the epoxy cures. As a result, the layers fuse to form a sturdy laminated circuit board. Usually, PCB lamination requires one to two hours of pressure and heat.

Step Seven: Cooling

Following lamination, the cured assembly is placed in a cooling press. As temperatures drop, cooling under pressure avoids forming internal tensions and warpage.

Step Eight: Detaching

When the laminated board reaches to room temperature, the stainless steel plates separate from it. This makes the outer layers of copper foil visible.

Step Nine: Hole-Alignment

After lamination, X-rays verify the alignment of the inner layer hole. During the high pressure, a moving layer is identified. Deburring and reemerging holes continue until all layers realign in the layers.

Factors to Consider When Choosing PCB Laminate Materials

There are different factors to consider when choosing the PCB Laminate materials. They are illustrated below:

Loss Tangent

The loss tangent determines signal loss at high frequencies due to absorption in the laminate material. A lower value in the loss tangent improves overall signal integrity by reducing signal loss.

Thermal Conductivity

It shows the rate at which heat passes through the laminate. More thermal conductivity encourages hot components on the board to dissipate heat more effectively. It guarantees the control of temperature.

Coefficient of Thermal Expansion (CTE)

This coefficient represents the expansion of the laminate with each degree of temperature increase. Aligning the CTE between the copper and laminate layers improves the PCB’s durability by reducing thermal stresses.

Flame Retardancy

The PCB laminate material should possess strong flame retardant qualities to maintain the circuit board’s safety and prevent fire incidents.

Glass transition temperature (Tg)

Tg is the temperature at which the material used to make PCB laminates changes from a vitreous to a flexible condition. The stability of the board and heat resistance can be improved by selecting a material with a suitable high Tg value.

Electrical properties

The laminate should have strong electrical insulation properties to prevent leakage or short-circuit problems. The PCB needs to have a lower loss tangent and dielectric constant to guarantee signal integrity. Due to their ability to reduce signal distortion and attenuate losses within the PCB, these features are essential for preserving the integrity of transmitted signals.

Chemical resistance

Materials should be resistant to solvents, including fluxes, cleaning solutions, and environmental contaminants to ensure better performance of products.

Dielectric constant

The quality and speed of signal transmission on a circuit board depend on the dielectric constant of the PCB laminate. Choosing a material with a lower dielectric constant helps reduce interference and signal attenuation.

Conclusion

The laminate of a printed circuit board is a composite structure consisting of a prepreg layer, a copper foil layer, and a core material. It provides structural stability to the printed circuit board. As the foundation of the circuit board, it enables the electrical connections to work properly.

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