In PCB processing, several key characteristics of Copper Clad Laminate (CCL) are critical. These include dimensional stability, thermal resistance, surface smoothness, adhesion between copper foil and substrate, flatness (warping and twisting), drillability (resin contamination), electroplating performance, chemical resistance, and moisture absorption. Recent years have also introduced requirements for UV shielding and CO2 laser drillability. The performance of CCL in these aspects closely correlates with the quality of PCB manufacturing. If the selected CCL fails to meet PCB processing requirements, it can lead to substrate defects or even waste products.
For instance, poor dimensional stability in CCL negatively impacts inter-layer alignment during multilayer board manufacturing, resulting in inadequate connections for through-holes and circuit patterns. Low thermal resistance can lead to warping and twisting of substrates during drying and the application of etchants in the PCB manufacturing process. Additionally, poor surface smoothness—stemming from uneven glass fiber interweaving—can compromise the quality of fine pattern formation on the PCB. Significant warping and twisting during lamination can lead to low precision in micro-pattern positioning.
Furthermore, during drilling, cutting heat can cause resin contamination if the CCL has poor drillability, negatively affecting the quality of hole processing. If the resin is too brittle or interlayer adhesion is weak, it can result in rough hole walls and exposed glass fibers, directly impacting electroplating quality. Additionally, if additives in the resin leach during electroplating, it can contaminate the plating solution, leading to abnormal precipitation of certain components.
Throughout the PCB manufacturing process, CCL must withstand exposure to acids, alkalis, and organic solvents. Therefore, it must possess high chemical resistance and low moisture absorption; otherwise, the substrate's surface may discolor, and performance may degrade.
To ensure high-quality installation of components on PCBs, CCL must meet various performance requirements. These requirements mainly focus on dimensional stability (low thermal expansion coefficient), solder heat resistance, flatness, copper foil peel strength, and bending strength.
If the dimensional stability of CCL is inadequate, it will lead to reduced accuracy in component placement. Low solder heat resistance can cause quality issues such as substrate bulging, delamination, and copper foil blistering during wave soldering or reflow soldering due to thermal shock. Excessive warping can further decrease the accuracy of component installation, leading to poor connectivity in soldered joints. If the copper foil peel strength decreases after thermal shock, it may cause the copper foil to detach along with the mounted components. Additionally, a low bending strength can result in excessive deformation (commonly referred to as "sagging") under the weight of heavier components.
Recent trends towards smaller SMC chip components require CCL to have even higher surface smoothness.
When it comes to the operation of complete electronic products, greater emphasis is placed on CCL's electrical insulation properties, dielectric constant, dissipation factor, thickness precision (especially for connector applications), reliability (including low thermal expansion coefficient, moisture and heat resistance, and thermal resistance), mechanical strength, flame retardance, environmental characteristics, and thermal conductivity.
To ensure the normal and stable operation of complete electronic products, insulating substrates must not exhibit ionic migration, as this phenomenon directly impacts insulation reliability, dielectric strength, and can even lead to short circuits between circuit lines.
For precise control of characteristic impedance and high-speed signal transmission, CCL must demonstrate excellent dielectric properties (including low dielectric constant). Especially under high-frequency and high-humidity conditions, the dielectric properties must remain stable.
The quality of electroplated through-holes is directly related to the long-term reliability of complete electronic products. Thus, the quality of through-hole production is closely tied to the dimensional stability of CCL in the thickness direction (Z-axis) and the surface direction (X and Y axes). As complete electronic products trend towards miniaturization and lightweight design, the demand for high-density wiring, fine traces, and small apertures in PCBs increases, leading to heightened requirements for CCL dimensional stability.
Overall, the performance requirements for CCL across these three aspects highlight different priorities. In PCB processing, the focus is primarily on dimensional stability, drillability, electroplating quality, warping, twisting, and chemical resistance. In component installation, key concerns include thermal expansion coefficients, thermal shock resistance, copper foil peel strength, and flatness. For the operation of electronic products, emphasis is placed on electrical insulation reliability, dielectric constant, dissipation factor, moisture and heat resistance, flame retardance, and environmental characteristics.
Different substrate materials exhibit unique properties. Below is a comparative analysis of various types.
Phenolic paper-based laminate uses phenolic resin as a binder and wood pulp fiber paper as reinforcement. It is cost-effective and lightweight, making it suitable for punching. However, its working temperature, moisture resistance, and thermal resistance are lower compared to epoxy glass fiber laminates. Predominantly, single-sided copper clad laminates are produced, but there have been dual-sided products developed for silver paste via-hole applications that exhibit improved silver ion migration resistance.
Common product models include FR-1 (flame-retardant) and XPC (non-flame-retardant).
Epoxy paper-based laminate uses epoxy resin as a binder. It exhibits improved electrical and mechanical performance over FR-1. The main product model is FR-3, which is more prevalent in Europe.
Epoxy glass fiber-based laminate employs epoxy resin as a binder and electronic-grade glass fiber cloth as reinforcement. It is an essential substrate for multilayer printed circuit boards due to its mechanical properties, dimensional stability, impact resistance, and moisture resistance.
This type of laminate is widely used, with FR-4 being the most common product model. Recent developments have seen the introduction of high-Tg FR-4 products to meet evolving electronic installation and PCB technology demands.
Composite laminate includes CEM-1 and CEM-3 types, which use wood pulp fiber or cotton pulp fiber paper as core materials reinforced with glass fiber cloth and treated with flame-retardant epoxy resin. These are currently among the most common composite laminates.
CEM-1 and CEM-3 offer a balance between mechanical performance and manufacturing cost, allowing for punching and drilling. Some CEM-3 boards manufactured abroad have surpassed standard FR-4 in terms of leakage resistance, thickness precision, and dimensional stability, leading to their widespread use in double-sided PCB production.
Specialty resin glass fiber-based laminates focus on high electrical performance and heat resistance, including types such as polyimide (PI), polytetrafluoroethylene (PTFE), cyanate ester (CE), bismaleimide triazine (BT), and thermosetting polyphenylene oxide (PPE or PPO). These materials typically exhibit high heat resistance (high Tg), low moisture absorption, and low dielectric constants. However, they tend to have higher manufacturing costs and slightly reduced rigidity, resulting in poorer PCB processability compared to FR-4 substrates.
Flexible copper clad laminate is crucial for flexible printed circuits (FPC), rigid-flex PCBs, and strip packaging substrates. Its standout features include being thin, lightweight, and structurally flexible. FCCL can be dynamically bent, curled, and folded. There are two main types: three-layer FCCL with adhesives (3L-FCCL) and two-layer FCCL without adhesives (2L-FCCL). Compared to 3L-FCCL, 2L-FCCL exhibits better temperature resistance, dimensional stability, bond strength, and thinner profiles.
The most common type of metal-based laminate is high thermal conductivity aluminum-based laminate. Metal-based laminates serve as essential materials for high thermal conductivity PCBs. The exceptional thermal performance, mechanical processing capabilities, electromagnetic shielding, dimensional stability, and multifunctionality make them increasingly popular in mixed integrated circuits, automotive, motorcycle, office automation, high-power electrical equipment, power devices, and high-current devices, especially in LED packaging applications.
This professional overview provides a comprehensive understanding of the essential properties and performance characteristics of various types of Copper Clad Laminate in PCB manufacturing.
