Introduction

Printed circuit boards (PCBs) are made from insulating substrate materials that provide the foundation to mount and interconnect electronic components. While FR-4 glass-reinforced epoxy is the most common PCB material, there are lower cost options that serve well for some applications.

This article provides an overview of low-cost PCB materials, their properties, trade-offs, and applications where they make sense to consider over higher performance substrates.

Low Cost PCB Materials

Here are some of the cheapest options for PCB substrate materials:

FR-1 Paper Epoxy

• One of the original PCB materials made from paper and phenolic resin
• Low dielectric constant and loss for stable electrical performance
• Low glass transition temperature limit of 105°C
• Very low cost but less durable than FR-4
• Used for simple, low layer count PCBs where high reliability not required

CEM-1 Cotton Paper Epoxy

• Made from cotton paper reinforcement and epoxy resin
• Low moisture absorption properties
• Low thermal conductivity for good insulation
• Low cost, but inferior electrical and mechanical properties compared to FR-4
• Typically used only for single or double sided boards

Polyester

• Made from polyester film bonded with acrylic adhesive
• Isotropic properties due to lack of fiberglass reinforcement
• Low cost option for simple double sided PCBs
• Limited temperature range and prone to stretching
• Used for inexpensive consumer electronics

PEN

• Substrate made from polyethylene naphthalate resin
• An economical alternative to polyimide flex PCB materials
• Good dimensional stability under temperature variations
• Low moisture absorption characteristics
• Thin flexible PCBs, RF/microwave antennas

Polyimide

• Kapton and similar polyimide films widely used for flex PCBs
• High chemical resistance, stable dielectric properties
• Withstands high temperatures up to 400°C
• Low cost compared to advanced flex materials like LCP
• Single, double, and multilayer flex circuit boards

Cost Factors

Some of the factors that make these materials less expensive PCB options:

• Lower material costs – Wood pulp paper, cotton, and generic resins are cheaper than glass fabric and advanced epoxy resins used in FR-4. Polyester films also low cost.
• Less processing – Does not require advanced resin flow, precise pressure and temperature control of high Tg FR-4 materials.
• Standard manufacturing – Uses typical PCB fabrication processes so does not require specialized equipment.
• Relaxed tolerances – Dimensional stability and electrical properties not as critical as FR-4.
• Lower layer counts – Costs rise significantly for multilayer boards, so kept to 1-2 layers.
• Smaller sizes – Generally used for smaller PCB sizes which improves yields and utilization.
• Limited testing – Less electrical testing required compared to complex, high reliability boards.

Tradeoffs and Limitations

The limitations and downsides to using the cheapest PCB materials include:

• Lower temperature ratings – Typically limited to 105°C max continuous use.
• Inferior mechanical properties – More prone to cracking, delamination, and damage compared to FR-4.
• Reduced dimensional stability – Greater thermal expansion and more prone to warpage.
• Lower reliability – Not suitable for long term use in harsh conditions.
• Limited layer counts – Rarely used beyond 2-4 conductive layers.
• Restricted circuit density – Larger lines and spaces due to material movement.
• May require thicker boards – To compensate for lower mechanical strength.

Applications

Some example applications where these low cost PCB materials may be acceptable:

• Simple electronics hobbyist projects
• Non-critical consumer electronics – toys, basic devices
• Prototyping short lifetime boards where cost is priority
• Education and training printed circuit design
• Temporary boards for testing and evaluation
• Low complexity circuits without need for multilayers or small features
• Non-safety critical assemblies where reliability is not an issue

Material Selection Criteria

Here are some of the criteria to consider when selecting low cost PCB materials:

Electrical Properties

• Dielectric constant
• Loss tangent
• Leakage current
• Breakdown voltage
• Insulation resistance

Mechanical Properties

• Flexural strength
• Tensile strength
• Compressive strength
• Glass transition temperature
• Coefficient of thermal expansion

Physical Properties

• Moisture absorption
• Thermal conductivity
• Density
• Flammability rating

Fabrication Factors

• Layer count
• Line width/spacing
• Via sizes
• Tolerances
• Soldering and assembly processes

Cost Saving Tips

Some ways to reduce PCB costs, even with higher performance materials:

• Use smallest board size possible for circuit
• Minimize holes and vias
• Standardize on a few board thicknesses
• Reduce layer counts where possible
• Use slightly relaxed design rules when able
• Order larger panel sizes for better yield
• Work with fabricators to optimize pricing
• Take advantage of any volume discounts
• Consider slightly longer lead times for batches
• Reuse proven designs when feasible

Summary

• Paper epoxy, polyester, and polyimide are among the cheapest PCB materials.
• Mainly used for simple, low layer count, non critical circuits.
• Performance and capabilities limited compared to FR-4.
• Important to match electrical, thermal, and mechanical needs.
• Consider cost tradeoffs – higher cost material may pay off long term.
• Opportunities to reduce cost even with FR-4 or advanced materials.

Frequently Asked Questions

Q: What are typical thicknesses for low cost PCB materials?

A: Typical thickness range:

• Paper Epoxy: 0.8mm to 1.6mm
• CEM-1: 0.8mm to 2mm
• Polyester: 0.05mm to 0.5mm
• Polyimide: 12μm to 75μm
• PEN: 25μm to 250μm

Q: What are the maximum operating temperatures?

A: Max temperature range:

• Paper Epoxy: 105°C
• CEM-1: 120°C
• Polyester: 125°C
• Polyimide: 400°C
• PEN: 150°C

Q: How many layers can these materials support?

A: Typical layer counts:

• Paper Epoxy: 1-2 layers
• CEM-1: 1-4 layers
• Polyester: 1-2 layers
• Polyimide: Unlimited
• PEN: 1-6 layers

Q: What types of resin systems are used?

A: Typical resins include:

• Paper Epoxy: Phenolic
• CEM-1: Epoxy
• Polyester: None, only adhesive
• Polyimide: N/A
• PEN: Proprietary formulations

Q: What are some key electrical properties?

A: Electrical properties:

• Dielectric constant: 3.5 to 10
• Loss tangent: 0.02 to 0.1
• Volume resistivity: 1012 to 1015 Ohm-cm
• Dielectric strength: 150 to 400 V/mil

Article Highlights

• Paper epoxy, polyester, and polyimide are among lowest cost PCB materials.
• Primarily used for simple, prototype, non-critical disposable circuits.
• Maximum temperature ratings limited to around 105°C-150°C.
• Mechanical strength, layer counts, circuit densities restricted.
• Important to match material properties to application needs.
• Opportunities to lower cost through design optimization and fabrication process.