What is the difference between CEM-1 and FR 1?

Overview of CEM-1 vs FR-1

CEM-1 (Composite Epoxy Material) and FR-1 (Flame Retardant) are two types of materials used in printed circuit boards (PCBs). Both provide electrical insulation and mechanical support for electronic components. However, there are some key differences between CEM-1 and FR-1 in terms of their composition, properties, applications, and cost.

Comparison Table

Property	CEM-1	FR-1
Base Material	Paper/glass fiber composite	Paper
Resin System	Epoxy	Phenolic
Flame Retardancy	Lower	Higher
Moisture Resistance	Higher	Lower
Thermal Performance	Higher Tg	Lower Tg
Typical Applications	Consumer electronics, Telecom	Low-end consumer products
Relative Cost	Higher	Lower

Composition and Manufacturing

CEM-1

CEM-1 is a composite material made from a non-woven fiberglass mat substrate that is impregnated with an epoxy resin system. The fiberglass provides mechanical reinforcement while the epoxy offers good electrical insulation properties. CEM-1 is manufactured using the following process:

1. A non-woven fiberglass mat is produced using chopped glass fibers that are randomly oriented and bonded together with a chemical binder.

2. The fiberglass mat is impregnated with an epoxy resin system, typically using a hot roll lamination process.

3. Copper foil is bonded to one or both sides of the impregnated mat using heat and pressure.

4. The laminate is cured in an oven to crosslink the epoxy resin.

The resulting CEM-1 laminate has a nominal thickness of 1.6mm and can be further processed (drilled, plated, etched) to create circuit patterns.

FR-1

FR-1 is made from multiple plies of cellulose paper that are bonded together with a phenolic resin system. The paper provides the mechanical backbone while the phenolic resin provides flame retardancy and electrical insulation. FR-1 is manufactured as follows:

1. Kraft paper sheets are impregnated with a phenolic resin.

2. The impregnated paper sheets are dried to remove solvents.

3. The B-staged sheets are cut and stacked in the desired thickness.

4. Copper foil is placed on one or both sides.

5. The stack is laminated under high temperature and pressure to bond the layers.

6. The laminate is post-cured to fully crosslink the resin.

FR-1 is available in thicknesses ranging from 0.8mm to 3.2mm. The paper-phenolic construction makes it less expensive than glass-epoxy laminates.

Properties

CEM-1

Key properties of CEM-1 include:

• Good mechanical strength and stiffness from the fiberglass reinforcement
• Higher moisture resistance than FR-1 due to the use of epoxy resin
• Better thermal performance (higher Tg) than FR-1
• Moderate flame retardancy, but lower than FR-1
• Good electrical insulation properties (Dk of 4.2 @ 1 MHz)
• Can be used in multilayer PCB designs

FR-1

Important characteristics of FR-1 are:

• Moderate mechanical strength, but lower than CEM-1
• Excellent flame retardancy due to phenolic resin
• Lower moisture resistance compared to epoxy
• Lower thermal ratings than CEM-1
• Good electrical insulation (Dk of 4.6 @ 1 MHz)
• Typically used for single-sided or double-sided PCBs
• Punching ability allows it to be used in pin-in-hole designs

Applications

CEM-1

CEM-1 is commonly used in applications such as:

• Consumer electronics
• Computer peripherals
• Telecommunications equipment
• Industrial controls
• Automotive electronics

It is suitable for products that require good mechanical strength, moisture resistance, and thermal stability at a lower cost than high-performance glass-epoxy laminates. The ability to use CEM-1 in multilayer designs allows for higher interconnect densities.

FR-1

FR-1 is mainly used in low-end, cost-sensitive applications including:

• Consumer appliances
• Toys and games
• Low-power electronics
• Single-sided and double-sided PCBs

The excellent flame retardancy of FR-1 makes it suitable for products that may be exposed to high temperatures or sparks. It is also a good choice when punched hole designs are required for through-hole component mounting.

Cost Comparison

In general, CEM-1 is more expensive than FR-1 due to the use of fiberglass reinforcement and epoxy resin. The raw materials and processing costs are higher for CEM-1.

FR-1 is one of the lowest cost PCB Materials available. The use of cellulose paper and simple phenolic resin keeps the material cost down. FR-1 is often used in high-volume, low-cost products where performance requirements are not as demanding.

However, the total cost of a PCB depends on many factors beyond just the laminate material, such as number of layers, size, complexity, and special processing requirements. In some cases, using a higher-performance material like CEM-1 can allow for a smaller, simpler design that reduces overall cost.

Frequently Asked Questions

1. Can CEM-1 be used for high-frequency applications?

While CEM-1 has good electrical properties, it is not suitable for high-frequency (above 1 GHz) applications due to its relatively high dielectric constant and loss tangent. For high-speed digital or RF designs, engineer ing materials like Rogers or Teflon laminates are a better choice.

2. Is FR-1 suitable for lead-free soldering?

FR-1 has a relatively low glass transition temperature (Tg) around 130°C, which makes it marginal for use with lead-free soldering processes that require peak temperatures above 240°C. The phenolic resin system can soften and degrade at these temperatures, leading to delamination or other defects. It is best to use FR-1 with traditional SnPb solders.

3. Can CEM-1 be used in high-voltage applications?

CEM-1 has good electrical insulation properties, with a Dielectric Breakdown strength of 20-50 kV/mm depending on thickness. This makes it suitable for use in many low to medium voltage applications. However, for high voltages (> 1 kV), specialized materials like FR-4 or ceramic-filled laminates provide better insulation and arc resistance.

4. How do CEM-1 and FR-1 compare in terms of machinability?

Both CEM-1 and FR-1 can be machined using standard PCB processing methods like drilling, routing, and punching. However, FR-1 tends to be more brittle and prone to chipping or cracking due to its paper-based construction. CEM-1 is more forgiving and produces cleaner edges when machined.

5. Are CEM-1 and FR-1 environmentally friendly materials?

Neither CEM-1 nor FR-1 would be considered environmentally friendly by today’s standards. Both contain halogenated flame retardants and use non-renewable resources like petroleum-based resins. However, there are initiatives underway to develop more sustainable PCB materials based on natural fibers, bio-based resins, and non-toxic flame retardants. As these eco-friendly materials become more widely available and cost-effective, they may start to displace traditional materials like CEM-1 and FR-1 in some applications.

Conclusion

In summary, CEM-1 and FR-1 are two types of PCB base materials that differ in their composition, properties, and applications. CEM-1 is a composite made from fiberglass and epoxy resin, offering good strength, moisture resistance, and thermal stability. FR-1 is a paper-phenolic laminate that provides excellent flame retardancy at a low cost.

CEM-1 is often used in consumer electronics, telecommunications, and automotive applications where performance and reliability are important. FR-1 is commonly used in low-end consumer products and single/double-sided PCBs where cost is the primary concern.

When selecting between CEM-1 and FR-1, engineers must carefully consider the specific requirements of their application in terms of electrical, mechanical, thermal, and environmental performance as well as cost targets. In some cases, a hybrid stack-up that uses both materials in different layers may provide the optimum balance of properties and cost.

As PCB technology continues to evolve, we can expect to see new materials emerge that offer improved performance, sustainability, and value. However, traditional materials like CEM-1 and FR-1 will likely remain important options for many applications in the near future.