Why Choose CEM PCB? CEM Benefits and Applications

Several qualities make a CEM PCB worth considering. One of them is cost-effectiveness, which perfectly suits many low-cost electronic products. This post explores the benefits of CEM in PCB production. Learn why it replaces popular materials like FR4, its downsides, and typical applications.

What is CEM PCB?

CEM is “composite epoxy material” in full. It refers to a milky white or yellowish PCB substrate made of more than one material. In this case, it combines cellulose, glass fibers, and an epoxy resin in its structure.

Various additives improve its properties, such as flame retardation. On the other hand, the glass materials are either woven or non-woven, depending on the desired characteristics.

CEM or composite material laminates are inexpensive and lightweight, among other benefits. These make them popular in low-cost applications with less strict requirements.

However, they have lower properties than most other substrates today, as we will see shortly. Before that, let’s examine their two primary versions.

CEM PCB Types

CEM circuit boards exist in two main types, 1 and 3. These variants differ in material composition and structure. As a result, they have varying characteristics and applications that fit them best.

CEM 1 PCB

CEM 1 consists of woven glass fabric surfaces enclosing a cellulose/paper core and bonded with resin. It has fewer benefits than CEM3 but performs better than paper-based laminates.

Its main attribute is cost-effectiveness, which makes it suit cheaper electronics. On the down side, you can only use it to produce single layer printed circuit boards.

CEM 3 PCB

A CEM 3 PCB is a higher grade. It uses non-woven glass fibers and epoxy, making them studier and more resistant to ingress and damage. Although pricier, it has more advantages, with properties that make it more usable. The section below compares the two materials.

CEM 1 vs. CEM 3 PCB

The two PCBs fall in the same composite epoxy group. However, they use varying material amounts and structures. These give rise to specific properties. The following table shows the difference between the two substrates.

Feature	CEM-3	CEM-1
Mechanical Strength	Sturdier	Less strong and brittle
Physical appearance	Smooth surfaces	Less smooth
Electrical properties	Moderate performance	Comparable to CEM-1
Flame retardation	moderate	Slightly higher
Number of layers	Single and double-sided	Single-sided only
Machinability	Fair	Better
Temperature range	Up to 110 degrees Celsius	Up to 130 degrees Celsius

We mainly use the CEM 1 PCB material for lower performance needs. It has inferior qualities compared to grade 3 types. However, it costs less, making it an affordable solution for many consumer electronics.

CEM 3 PCB material is almost comparable to FR4. It has a robust structure and high glass transition temperature, among other characteristics. As such, it suits harsher applications, sometimes even replacing FR4.

Why Choose CEM PCB Material

PCB materials have come a long way. Today, users can choose from many advanced categories and subtypes. Despite that, composite substrates remain popular choices. Various reasons explain why, including those listed below.

Benefits

• Cost Benefit: it costs much less than higher-grade materials like FR4 and metal substrates. This benefit makes the circuit board excellent for many low-budget projects.
  
• Electrical Performance: it has decent electrical properties, which make it suitable for various uses and electronic products.
  
• Mechanical Properties: the material has good mechanical characteristics. These make it reasonably sturdy and resistant to different forces.
  
• Weight Advantage: it weighs less and fits smaller portable devices like remote control modules and toys.
  
• Versatility: it comes in two versions. These increase its application options, meeting lower and higher needs.
  
• Eco-Friendliness: composite substrates do not use brominated flame retardant epoxy resins, making them safe for the environment.
  

Limitations

• Lower Heat Resistance: it has a lower thermal performance with a working temperature of less than 130 degrees Celsius.
  
• Low Thermal Conductivity: it offers reduced thermal conduction and heat dissipation, which limits its usage.
  
• Moisture Absorption: it’s also less usable in highly humid conditions, with a water absorption rate of up to 0.3%.
  
• Reduced Mechanical Strength: it has a lower ability to resist damage than its FR4 counterpart, making it liable to damage by cracking, breakage, or other ways.
  
• High Dielectric Losses: it has a high dielectric constant. This property makes it experience losses at higher frequencies.
  
• Reduced Durability: it has a reduced lifespan, which limits its use to lower-end electronics with lenient longevity requirements.
  
• Less Suited for Higher Applications: its lesser properties make it unsuitable for high-performance applications. These include high-heat uses like military and aerospace or high-speed telecommunication circuits.
  

CEM PCB Design Considerations

Composite material PCB design has a few requirements, given its unique properties, just like other materials, such as FR4 and ceramics. The following considerations are worth noting when considering a PCB of this type.

Board and Copper Thickness

The material can make boards between 0.8 and 2.0 mm to ensure mechanical strength while keeping electrical and thermal performance within desired limits.

The thickness of the copper foils varies from 35 to 70 microns. Again, the exact value depends on the board’s application. For instance, a thicker size carries more current.

Trace Width and Spacing

Trace width and spacing are critical in composite epoxy boards and other materials. The designer ensures appropriate sizes to control impedance, reduce crosstalk, and other needs.

Ideal spacing varies from 0.20 mm to but can exceed that if the board will carry high-frequency signals. This requirement mainly applies to the grade 3 type. This version supports slightly higher frequencies than grade 1.

Via Distribution and Size

The number of vias and their placement affect the board’s performance. As such, the designer must ensure they remain within limits. The material supports 0.5 mm via sizes. This size varies depending on performance requirements.

CEM Material PCB Applications

We generally use composite glass mat PCBs in lower-end electronics. These are low-stress uses with no complex electronic circuits and components. However, given the material’s varying characteristics, the application depends on the board type or grade.

Consumer Electronics: it’s a good choice for general-purpose electronics like remote controls, kid toys, calculators, and various household devices.

LED Lighting: you can also use it in low-cost and low-heat LED fixtures, given their affordability and qualities like decent thermal resistance and dimensional stability.

Automotive Electronics: some automotive parts contain the PCB due to its inexpensive nature. They include power windows, door locks, sensors, and infotainment system components.

Computer Parts: the board acts as a thermal component in computer parts that experience excessive heat, such as the CPU. It also produces keyboard PCBs and those of other peripherals.

Medical Industry: high-quality versions also have helpful applications in the healthcare sector. You’ll usually find them in thermometers, monitoring devices, and other devices.

Industrial Applications: it has applications in various electrical and electronic device components, such as actuators, sensors, power supplies, converters, and controllers. The boards in these applications are typically CEM-3 PCBs.

Conclusion

The CEM substrate is a lower-end circuit board material. Despite that, it still has helpful use in various industries, from consumer electronics to industrial applications. It presents a low-cost alternative to the popular FR4 and other materials, making it usable in applications where property requirements are low and less strict.