What is Copper Clad Laminate Used for PCB

What is Copper Clad Laminate

Copper clad laminate, abbreviated to CCL is a type of PCB material with glass fiber or wood pulp paper as reinforcing.

With the innovation and development of high-density electronic assemblies, the integration and assembly density of components on the boards are more and more power dissipated. If the substrates have poor dissipation, it will lead to the unreliability of the whole assembly.

The Printed circuit board (PCB) substrates are one of the most widely used to fabricate boards. They are kinds of material that soaks in resin, with the electronic glass fiber or other reinforcing material to contribute to the copper-clad on either of the sides of the board or even both. Copper clad laminate finds applications in radio, computers, television, mobile devices, and many electronic assemblies.

Types of Copper Clad Laminates

Each of the PCBs has its own requirements and specifications - designers or engineers responsible for the development of the assembly take into consideration all of these requirements. This is why we are going to review the different kinds of copper clad laminate used in the development of PCB.

There are two general types of copper clad laminate (CCL):

Kinds of Copper Clad Laminate

Keep in mind that the two major types we’ve revealed above are the most commonly met in PCB electronics. The copper-clad laminates are not limited just to these two types. Now we are going to review more widely applied types of CCLs over the world.

We will also review some of their general properties such as flammability, flexural strength, coefficient of thermal expansion, Tg, and more.

1. CEM-3 (Composite Epoxy Materials Grade-3) is a fiberglass composite material developed on the FR0-4 basis, with a combination of woven glass fiber and non-woven glass plus core raisin filling. The color is usually milky white. The properties of CEM-3 are that it has lower mechanical endurance but is a cost-effective replacement for other copper-clad laminates such as FR-4.

2. FR-4 is the most popular copper-clad laminate used around the world. FR-4 has an impressive performance and is cheaper than some special materials. In the meantime, this material has been fully identified and studied, so it can now be modified to produce a variety of different helpful boards such as halogen-free types.

3. Aluminum is another common material used for the manufacturing of printed circuit boards. It is popular and widely used in high-power and LED products due to its impressive dissipation capabilities.

4. Polyimide (PI) is one of the top heat-resistant high molecular organic polymers. It is efficient because of its softness, and it is the main material used for the manufacturing of flexible printed boards.

5. Poly Tetrafluoroethylene (PTFE) or "Teflon" is a synthetic polymer material that has better dielectric properties when compared to conventional high-frequency materials. It is an excellent solution for special or demanding microwave/RF products. The only concern here is the expensive price that the manufacturers have to consider carefully.

In general, electronics have a lot to do with each copper-clad laminate, and they also include FR-½, 22F, CEM-1, and other substrates.

Copper Clad Laminate Materials

Prepreg- A prepreg (comes from pre-impregnated) is basically fiberglass impregnated with resin. The raisin has to be dried beforehand but not too hardened so that it will be able to flow and completely immerse as heating. In general, prepregs are fiberglass reinforced and strengthened by an adhesive similar to the FR4 material that we reviewed earlier in the article.

Different manufacturers have different requirements when it comes to thickness and specific types of prepreg. Furthermore, there are the versions "SR" Standard Resin, "HR" High Resin, and "MR" Medium Resin that are based on the resin content. The best possible material used depends on the desired final layer of structure, thickness, and impedance.

Copper Foil - Copper foil is an electrolytic cathodic material. It is deposited on a thin and continuous layer of metal foil on the base of a PCB. It is easy to bond to an insulating layer, which will lead to the creation of a printed protective layer to protect the board from corrosion.

What makes the Best Copper Clad Laminate?

Size - Since the copper clad laminate is the base material of a PCB, they have to meet some size requirements accurately as per the desired end design. All parameters are taken under careful consideration including width, length, diagonal deviation, and warpage. All these requirements have to be met to be exact for a successful application.

Appearance - There is a wide range of possible issues that can occur on the copper foil due to unexpected elements during the manufacturing process. Some of these issues could be scratches, dents, resin points, pinholes, wrinkles, bubbles, and more. If any of these issues occur, this will lead to the poor performance of the copper-clad laminate and it will then reflect on the printed board.

Electric Performance - The electric performance has to be carefully designed as this is one of the essential aspects. Again, here we have some strict requirements including dielectric loss tangent (Df), dielectric constant (DK), surface resistance, insulation resistance, volume resistance, arc resistance, electric strength, and Comparative Tracking Index (CTI).

Environmental Performance - It has to be ensured that simple requirements such as water absorption and corrosion resistance are met. Otherwise, the production process may encounter serious failures in performance.

Chemical Performance - The chemical performance of copper-clad laminate is extremely important and it has to meet the strict requirements for flammability, Tg, chemical regents resistance, Z-axis coefficient of thermal expansion (Z-CTE), and dimensional stability.

Physical Performance - Requirements related to physical performance include peak strength (PS), dimensional stability, bending strength, heat resistance (with thermal stress, Td, T260, T300, T288), and punching quality.

The Future of Copper Clad Laminate

There are two major potential leads we have that are directly related to the higher and newer requirements that have been brought concerning reliability and heat resistance.

Halogen-Free Copper Clad Laminate - This refers to copper-clad laminates with a content of bromine (Br) and chlorine (Cl) that is controlled within 900ppm when their overall content is below 1500ppm.

To illustrate it better here is a comparison table of halogen-free copper-clad laminate vs FR-4 CCL.

Lead-Free Copper Clad Laminate - The lead-free copper-clad laminate refers to CCLs whose surface mounting is carried out without the application of lead-free solder. According to the regulations of RoHS, six substances such as PBDE and PBB are no longer in use for copper-clad laminate. If we compare it with the DICY curing system (with a curing agent, dicyandiamide) applied in ordinary FR-4 copper-clad laminates, lead-free CCLs take advantage of the PN curing system). To visualize refer to the below table:

Here are also the terms of peel strength on halogen-free copper-clad laminates and lead-free CCLs that have been accepted by the printed circuit board and copper-clad laminate industries.

How Copper Clad Laminates are Classified?

Copper clad laminates are usually classified by a few essential aspects and standards that allow us to sort them into 5 categories:

Learn More about PCB fabrication and CLL

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When working us them you can expect:

PCBONLINE’s capability:

• Layer: 1 ~ 42
• Laminate: normal Tg/high-Tg/lead-free/halogen-free
• Surface finishing: OSP/HASL/LF HASL/immersion ENIG/immersion tin/immersion silver
• Board thickness: 0.15 ~ 3.2 mm
• Max board size: 500 × 580 mm
• Copper thickness: (inner finish copper) 1-4oz, (outer finish copper) 1-7oz
• Min. line width/spacing: 0.0635 mm/0.0635 mm
• Min. CNC drilling size: 0.15 mm
• Min. laser drilling size: 0.075 mm
• HDI stack up: 1+N+1, 2+N+2, 3+N+3

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Conclusion

This article gives comprehensive research on copper clad laminate, including its types, and how to classify and choose them, and recommends a good PCB manufacturer, PCBONLINE, who can customize boards made of any materials.