Within the vast realm of printed circuit boards, various types of substrate such as aluminum, ceramics, FR4, and composite epoxy resins play a role in constructing the PCB’s core, serving as the foundation for supporting and interconnecting circuits. When engineers face different projects, they often choose PCB substrate that match the project’s characteristics. In this article, TechSparks will delve into an ancient substrate material – CEM-1 – and explore its advantageous features.
What is CEM-1 Material and Why Use It
CEM-1 is a type of fiber-based composite material recognized by NEMA standards, reinforced with a layer of glass fiber laminate. Its primary composition includes paper substrate, epoxy resin, and various additives, which give the board a milky-white appearance. The full name of CEM-1 is Cotton-Epoxy-Methyl Ester-1, with the “1” indicating the grade or type of laminate, suggesting it falls within a lower classification in terms of general performance and characteristics. In the modern electronic world, as circuit complexity increases, the demand for multi-layer boards rises, directly promoting the development of FR4 materials, leaving CEM-1 in the background. However, even so, it still finds its place in specific applications. The following content outlines its characteristics:
- Incompatible with plated through hole and can only be used for constructing single-layer circuit structures;
- Priced at around 70% to 80% of similar products, considered a cost-effective alternative to FR4;
- Capable of maintaining stable electrical performance within a temperature range of 100°C to 130°C;
- CEM-1 PCB possesses a robust physical structure capable of supporting large components.
CEM-1 vs. CEM-3 vs. FR-4
| Features | CEM-1 | CEM-3 | FR-4 |
|---|---|---|---|
| Material | Cellulose substrates, epoxy and methyl ester resins | Same as CEM-1 but different material ratio | Fiberglass Cloth and Epoxy |
| Appearance | Not the smoothest but its surface is relatively flat | Milky white appearance and smooth texture | Appearance green, smooth surface without obvious fiber texture |
| Available Layer | Single Layer | Single and Double Layer | All structure types |
| Mechanical Strength | Relatively brittle, with lower mechanical strength | Superior to CEM-1, influenced by material ratios | Substrates with higher mechanical strength can accommodate impact resistance, bending resistance, and crack resistance |
| Electrical Properties | Due to higher dielectric constant and dielectric loss, electrical performance is often poorer | Similar to CEM-1, there might be signal loss in high-frequency applications | Typically exhibits good electrical performance, particularly in the low-frequency and mid-frequency ranges |
| Machinability | Prone to cutting or fracturing during the manufacturing process | Despite improved mechanical properties, some issues persist | Compatible with various intricate processes such as fine circuitry, small vias, and narrow traces |
| Flame Retardant | Level of flame retardancy varies based on the manufacturer and product specifications | Similar to CEM-1, it falls slightly short of FR-4 | FR stands for Flame Retardant, with 4 indicating the grade, and it can self-extinguish in flame tests |
| Cost | Cheapest | Moderate | Most Cost Effective |
| Application | Applications with simple circuits and low performance requirements such as calculators, remote controls, digital clocks, etc | Can be used in applications requiring heat resistance and mechanical strength such as industrial control equipment, automation equipment, etc | Most commonly used substrate materials can be used whether it is high-performance servers, communication base stations or aerospace equipment |