Printed Circuit Boards (PCBs) provide a mechanical support for the placement of components in an electronic device or equipment. As such, these boards require as much factors that would enhance the performance.
Copper clad laminates have become a favorite among designers and this is for several, good reasons. In this article, we explain the meaning and copper clad laminate uses.
What is a Copper Clad Laminate?
It can be interpreted to be the laminate with a copper covering. Ideally, a CCL copper clad laminate is a thin sheet of copper that is bonded either on both of the sides or just on one side.
The reasons for the bonding include to provide the required mechanical support for the PCB, as well as to make it the core or primary foundation for the development of the circuit board.
What Constitutes the Copper Clad Laminates?
These laminates are made up of two constituents and despite the fact that they function differently, they also unify at the end.
The following are the constituents:
The substrates or the core is the primary constituent. It is notable for the wide range of functionalities it introduces to the PCB. Examples of these are thermal conductivity, improved rigidity/mechanical strength and electrical insulation.
The function of the CCL copper clad laminates’ substrate is to provide the aforementioned functionalities. It is designed as a thin board with flattened surfaces.
These foils are used to provide additional electrical functionalities to the Printed Circuit Board. They are also responsible for the bonding of the substrate with the foils.
For the bond to be established, the copper foils need to bond or be joined to the substrate/core either on one or two sides.
The following are some of the provisions of the copper foils for the PCB:
- The provision of the ground and power planes.
- Electrically-conducting traces.
- Electrically-conducting Plated Through Holes (PTH) and;
- The pads for mounting the PCB components.
Types of Copper Clad Laminate Laminates
Different kinds of laminates can be utilized to create the best laminates, made out of sheets of copper.
The following are some of the options:
1. Epoxy Glass Fiber Cloth Substrate
Also called the glass epoxy copper clad board, it refers to the type of laminate laminates comprising of reinforcement and adhesion. On the one hand, there is the electronic glass fiber cloth that acts as the reinforcing laminates and on the other hand is the epoxy resin, acting as an adhesive.
The laminates properties include:
- Up to 55ppm/˚C Coefficient of Thermal Expansion before Tg and up to 285ppm/˚C after Tg.
- UL-94V0 flammability
- Up to 0.8w/mK of thermal conductivity.
- A dielectric constant of 1MHz – ~4.7
The characteristics of the epoxy glass fiber substrate include not more than 15% weight percentage of water and moisture absorption rate (hygroscopicity). The attributes also include low thermal conductivity, and excellent sound insulation and absorption properties.
2. Paper Substrate
The two major types of paper substrates used with copper clad laminates are epoxy paper substrates and paper phenolic copper clad laminates.
For the epoxy variant, it features improved mechanical and electrical properties, especially when compared to the FR-1 laminates.
The attributes of the phenolic paper laminate include:
- Higher anti-silver ion migration ability.
- Low relative density and;
3. Metal Base Copper Clad Laminates
These are also called the aluminum-based copper clad laminates. Noted for the higher heat dissipation and high thermal conductivity capabilities, these laminates enable the use of PCBs in a wide range of applications.
Among the benefits of aluminum copper clad laminates are:
- Tri-Structure: this supports the integration of three different layers. The first, the circuit layer, is capable of conveying higher current with the same line width and thickness as the FR-4 laminates. The metal base/layer takes care of the thermal conductivity and thermal expansion coefficient, while the insulation layer improves the power output and increases the module’s power load by being more conducive towards the diffusion of heat.
- It has an extensive usage or application in hybrid Integrated Circuits (ICs), high-current pieces of equipment and office automation solutions.
4. Polyimide (PI) Flexible Copper Laminates
Also called Polyimide (PI) for short, it refers to the type of copper clad laminates made from the heat-resistant high molecular organic polymers.
The attributes include:
- It can be used for the following: folding, dynamic bending and crimping.
- It is soft and efficient.
- The heat-resistance is at its best.
- Thin, light and flexible structure denote it.
Types of Polyimide (PI)
The two major types of Flexible Copper Clad Laminates (FCCLs) are the two-layer FCCL (2L-FCCL) and the three-layer FCCL (3L-FCCL). The difference is that the former doesn’t use an adhesive, while the latter does.
5. Poly Tetrafluoroethylene (PTFE)
This is one of the “special resin glass fiber cloth substrates.” They are so-called because of the higher heat-resistance and improved dielectric properties they offer.
The PTFE copper clad laminates have the following attributes:
- They are mostly used with the Radio Frequency (RF) and microwave applications.
- The synthetic polymer laminates provide improved dielectric properties, especially when it is compared to some high-frequency PCB laminates.
Types of Materials to Use for Copper Clad Laminates
The following are some of the materials you can use for the CCL copper clad laminates:
It is essentially a fiberglass impregnated with resin. It doubles as an additional layer used for building up the multilayer PCB’s extra layers.
The properties of a prepreg include:
- Different variants, which are based on the amount of resin it contains. Examples are High Resin (HR), Medium Resin (MR) and Standard Resin (SR).
- After the fiberglass is reinforced, the adhesive is then applied to strengthen the reinforcement.
2. FR-4 Material
This refers to the Fire Retardant (FR) copper clad laminate material used for higher glass transition temperature. The other features include a lower coefficient of thermal expansion and good thermal conductivity.
3. Copper Foil
This is yet an important material for the copper clad laminate sheet. As an electrolytic copper (cathoid material), it is made as a deposit on the thin layer located on the PCB’s base.
A successful bonding of the copper foil to the PCB’s base charts the way for the application of a protective material to enhance the circuit board’s surface’s protection.
4. Composite Epoxy Material, Grade 3 (CEM3)
This is a type of copper clad laminate material used in place of the Fire Retardant 4 (FR-4) material.
It is prioritized for the following reasons:
- It is a cost-effective alternative to the FR-4 material.
- CEM3 materials are preferred due to the lighter design.
On the flipside, using the FR-4 material may seem a better option, considering that it offers a higher endurance when compared to the CEM3.
The Basic Requirements for Copper Clad Laminates
You can choose a copper clad laminate if it meets certain basic requirements, such as the appearance, chemical composition and physical attributes.
Here are some of the considerations to make before deciding:
1. Physical Requirements
This refers to the physical properties of the laminates. Considering that they tend to be subjected to a lot of physical usage, you want to verify the punching quality, bending strength and the Peel Strength (PS).
Other physical characteristics worth considering are:
- The heat-resistance. This should include the following thermal stresses: T288, Td, T300 and T260).
2. Appearance Requirements
These refer to what happens to the laminates if they are overly exposed to “danger.” For example, and depending on the handling process during processing, the board could be exposed to some manufacturing defects, such as:
- Dented copper surface
- Resin points
- Pinholes and;
Others are scratches and wrinkles.
3. Chemical Performance
Do the chemical characteristics meet the standard specifications? The key considerations to make here are:
- Dimensional stability
- The ability of the chemicals to resist or stand up to the chemical reagents.
- The ability to withstand flammability
- Meeting the Z-CTE or Z-axis coefficient of the thermal expansion.
- The glass transition (Tg) temperature.
4. The Electrical Performance
This requirement is important, as it helps to balance the different electrical properties of the copper clad laminates.
For context, the electrical performances of the different parameters should be at the best, if the laminate is to be used with high-electronic circuits.
The following are some of the most important parameters for adjudging the electrical performance:
- Comparative Tracking Index (CTI)
- Insulation resistance
- Dielectric Loss Tangent (Df)
- Volume resistance
- Dielectric Constant (DK)
- Electric strength
- Surface resistance
- Arc resistance
5. Environmental Considerations
It is also important to determine if the copper clad laminates can thrive when exposed to certain environments. You want to check the water resistance rate and the ability to resist corrosion.
Choosing the right copper clad laminates require an eye for details to pick out the size, environment, chemical and physical requirements.
The tips shared in this article should you get you started and point you in the right direction as to what to look for when working with these laminates.
Last but not least, endeavor to reach out to a professional copper clad laminate manufacturer to customize the laminates that will not only specify the PCB’s characteristics, but also define the performance and give the desired shape to the circuit board.