According to PCB Trace Technologies Inc, each Printed Circuit Board or PCB has its own requirements and specifications. Their usage conditions guide product development engineers in selecting the best options for PCBs. The PCB industry divides copper clad laminates into various categories, such as:
Mechanical Rigidity—There are rigid copper clad laminates and flexible copper clad laminates. Some examples of rigid copper clad laminates are CEM-1 and FR-4. An example of flexible copper clad laminate is Polyimide.
Insulating Materials and Structure—There are copper clad laminates with organic resins such as CEM-3 and FR-4. Others are ceramic-core copper clad laminates, and metal-core copper clad laminates.
Laminate Thickness—There are thick laminates with thicknesses of 0.8 to 3.2 mm, and thin laminates with thicknesses of less than 0.78 mm.
Reinforcement Material—There are copper clad laminates with glass fiber base, such as FR-4 and FR-5. There are copper clad laminates with paper base, such as XPC. Other copper clad laminates are with composite base, such as CME-1 and CME-2, and phenolic base.
Insulating Resins—Copper clad lamination classification is also based on different insulating resins the PCB use. There are polyester resin based copper clad laminates, epoxy resin based ones, and cyanate resin based copper clad laminates.
Flame Retardant—There are two types of copper clad laminates, such as flame retardant type and non flame retardant type. Based on the UL standards, rigid copper clad laminates can be of four different flame retardant grades, such as UL-94V0, UL-94V1, UL-94V2, and UL-94HB types.
Based on the above classifications, the PCB industry uses six popular copper clad laminates:
Aluminum based copper clad laminates with high thermal conductivity are the most common among resin-based metal-insulating types available. These are most suitable for manufacturing PCBs with high heat dissipation. Metal-based heat dissipating substrates are mostly useful in applications involving hybrid integrated circuits, office automation, automobiles, power equipment, high-power electrical equipment, high-current equipment, power equipment, and many other fields. Their most widespread application involves high-power LED products. Although aluminum is the most common type of metal base, there are copper clad laminates that use copper cores also.
The industry uses aluminum as the most common type of metal base copper clad laminate because of its superior heat dissipating function. Typically, a single board will have a triple-layer construction, consisting of a layer of copper foil circuit, a layer if insulator, and lastly, a layer of metal base.
High-end applications may have a double-sided construction, consisting of a layer of copper foil circuit, a layer of insulator, an aluminum base followed by a layer of insulation, and another layer of copper foil circuit.
Some applications need multi-layer metal base boards. Typically, these consist of ordinary multi-layer boards bonded with insulating layers on an aluminum base. High-power products like LED lights make extensive use of metal-based copper clad laminates because of its superior heat dissipation capabilities.
Copper clad laminates with metal base typically use electrolytic copper foil for the circuit layer. During fabrication, the operator etches this layer to form the printed circuit for anchoring and connecting electronic components. In comparison with regular FR4 laminates, copper layers on an aluminum substrate can carry higher currents even when of the same width and thickness.
The insulating layer is the most important layer of the aluminum substrate, as it performs the triple functions of bonding, insulating, and heat conduction. This insulating layer forms the largest thermal barrier in the aluminum substrate. The higher its thermal conductivity, the better it is at removing and diffusing heat that any component on the circuit layer generates when operating.
As better heat removal results in reducing the operating temperature of the board, this leads to the board being able to carry more power load. This can result in reducing the product volume, or in prolonging the service life while improving its power output.
Several factors govern the choice of the metal part of the substrate. These include the thermal conductivity, thermal expansion coefficient, mechanical strength, hardness, weight, cost, and surface condition. Aluminum offers a good balance of all the above properties, making it a popular choice.
Copper clad laminates with epoxy reinforced glass fiber cloth has epoxy resin as the adhesive and glass fiber cloth as the reinforcing material. The glass fiber cloth offers better mechanical properties, impact resistance, dimensional stability, and moisture resistance as compared to copper clad laminates with a paper substrate.
Epoxy reinforced glass fiber cloth provides a good electrical performance, high working temperature, and remains largely unaffected by the environment. Fabrication of multi-layer PCBs requires an adhesive layer between the glass fiber cloth substrate and the copper clad laminate of the inner core.
Because of its greater benefits over other types of resin reinforced glass fiber cloth substrates, the epoxy reinforced glass fiber cloth copper clad laminate is popular for manufacture of double- and multi-layered PCBs.
Among the popular epoxy reinforced glass fiber cloth copper clad laminates, the PCB industry uses FR4 as the most popular and widely used. For applications with special requirements, there are FR4 material with high glass transition temperature of Tg characteristics. FR4 is also cheaper than most special materials available in the market. Therefore, the electronic industry uses FR4 for producing many types of useful circuit boards.
FR4 is the code name for flame retardant materials. FR4 uses a resin material that can extinguish itself on combustion. Therefore, there are other varieties of fire retardant materials that the industry uses for manufacturing general PCB. Typically, most of these fire retardant composites consist of Tera function epoxy resins, fillers, and glass fibers.
Most epoxy reinforced glass fiber cloth copper clad laminates have unique technical properties like high thermal insulation. This is because glass fiber has low thermal conductivity, especially when it is of small diameter. It also has low bulk density, which makes it suitable for use as heat insulation, heat preservation, and as general insulation in industrial and construction sectors.
Characteristics of the composite copper clad laminate falls between epoxy reinforced glass fiber cloth and paper base copper clad laminates. These include its mechanical properties and the cost of manufacturing. The composite substrate uses cotton pulp fiber, paper, or wood pulp fiber as the core substrate, glass fiber paper as the core material, and glass fiber cloth as the surface substrate. With flame retardant epoxy resin for impregnation, the color of composite copper clad laminates is usually milky white.
Typical examples of composite copper clad laminates are CEM-1 and CEM-3. Of the two, CEM-3 has lower mechanical durability. The industry uses CEM-1 and CEM-3 in place of FR4 for double-sided boards because of their lower cost performance.
There are two types of paper based copper clad laminates—phenolic and epoxy paper based copper clad laminates.
These are insulation laminates with phenolic resin as binder and wood pulp fiber paper as reinforcement. It is possible to drill or punch phenolic paper-based copper clad laminates. These are often cheaper and have lower density. However, paper phenolic copper clad laminates cannot withstand high operating temperatures, and their moisture and heat resistance are lower than that of the epoxy reinforced glass fiber cloth types.
Most PCBs built from paper phenolic copper clad laminates are of the single-sided type, although double-sided PCBs for silver paste vias are also available. Examples of paper phenolic copper clad laminates are XPC (non flame retardant) and FR1 (flame retardant) type.
The epoxy paper copper clad laminates use epoxy resin as adhesive. The mechanical and electrical properties of epoxy paper copper clad laminates are slightly better than those of FR1. Example of epoxy paper copper clad laminate is FR3.
Polyimide is a high molecular organic polymer with very high heat resistance. The PCB industry uses polyimide widely for manufacturing flexible printed circuit boards because of its flexibility and softness. Flexible copper clad laminates are the most popular substrates for flexible PCBs, rigid-flex PCBs, and substrates for tape packaging.
Polyimide flexible copper clad laminates are thin, light, and flexible. They are amenable to bending, folding, and crimping, but not static bending. It is possible to divide them into three-layer flexible boards with adhesive, and two-layer flexible boards without adhesive. Polyimide flexible copper clad laminates exhibit high temperature resistance, good dimensional stability, and higher bond strength. They can be made thin for better fold resistance.
Advanced technology is making various and diversified demands on PCB manufacturers. Accordingly, they have produced various copper clad laminate substrates with many special resin glass fiber cloth for achieving higher dielectric properties and higher heat resistance. Most manufacturers use resins that exhibit high thermal resistance, high Tg, low water absorption, low dielectric loss, and low dielectric constant.
Special resin glass fiber cloth copper clad laminates are an excellent solution for special applications like RF/Microwave products. However, these laminates are expensive.
PCB Trace Technologies Inc has been making valuable contribution to the PCB industry with our extensive experience spanning two decades and more. For any details of top quality PCBs and copper clad laminates, please visit our website or contact our professionals for consultation.