What is PCB Thickness and Why Does it Matter?
PCB thickness refers to the overall height of a printed circuit board, measured in either inches or millimeters. It is a critical design specification that impacts many aspects of the PCB’s performance, manufacturability, and end use.
The thickness of a PCB affects:
- Mechanical strength and rigidity
- Thermal management and heat dissipation
- Impedance control and signal integrity
- Compatibility with components and connectors
- Manufacturing processes and costs
Choosing the appropriate PCB thickness is essential to ensure your board functions reliably in its intended application while balancing design requirements and budget constraints. Thinner boards offer space and weight savings but may be more fragile, while thicker boards provide sturdiness at the expense of size.
Standard PCB Thickness Options
PCBs are available in a range of standard thicknesses to suit different needs. The most common options are:
| Thickness (inches) | Thickness (mm) | Layers | Applications |
|---|---|---|---|
| 0.003″ | 0.07 mm | 1 | Ultra-thin flex circuits |
| 0.005″ | 0.13 mm | 1-2 | Thin flex circuits |
| 0.010″ | 0.25 mm | 1-2 | Rigid-flex, wearables |
| 0.016″ | 0.40 mm | 2-4 | High-density interconnect |
| 0.020″ | 0.50 mm | 2-4 | General purpose |
| 0.032″ | 0.80 mm | 4-6 | Heavy copper, power |
| 0.062″ | 1.57 mm | 6-10+ | Backplanes, servers |
| 0.093″ | 2.36 mm | 8-16+ | Ultra-thick, military |
| 0.125″ | 3.18 mm | 10-24+ | Extremely rugged |
Most standard PCB designs use a thickness between 0.062″ (1.57 mm) and 0.093″ (2.36 mm). 0.062″ is the default thickness for many 4-6 layer boards, while 0.093″ provides extra durability for 8+ layer counts. Thin boards under 0.020″ are used for flexible or space-constrained applications.
Factors Affecting PCB Thickness Choice
Number of Layers
The layer count is one of the primary drivers of PCB thickness. Each additional copper layer adds roughly 0.0035″ to the total board thickness, while insulating prepreg and core materials contribute extra height based on the Layer Stack-Up design.
Typical thickness ranges for common layer counts:
- 1-2 layers: 0.005″ – 0.020″
- 4 layers: 0.020″ – 0.050″
- 6 layers: 0.032″ – 0.062″
- 8 layers: 0.062″ – 0.093″
- 10-12 layers: 0.093″ – 0.125″
High layer count PCBs over 0.125″ thick are used for extremely complex boards like backplanes and supercomputers. The maximum practical thickness is around 0.250″ (6.35 mm).
Copper Weight
The weight or thickness of the copper foil used for each layer also contributes to overall PCB thickness. Standard copper weights include:
- 0.5 oz (18 μm)
- 1 oz (35 μm)
- 2 oz (70 μm)
- 3 oz (105 μm)
- 4 oz (140 μm)
Heavier copper weights over 2 oz are considered “heavy copper” and are used in power delivery or high current applications. Heavy copper can add substantial thickness to a board compared to using standard 1 oz weights.
Material Choice
The choice of laminate material used in the PCB stack-up affects thickness as well. Standard FR-4 epoxy-glass is the most common dielectric and is available in thicknesses from 0.002″ to 0.059″.
Thicker laminates provide more rigidity and mechanical strength. Thinner materials allow higher layer counts and density. Using a mix of thick and thin laminates allows optimizing the stack-up.
Other high-performance laminates like polyimide, PTFE, or hydrocarbon ceramics come in varying thicknesses that may differ from FR-4. Specialized materials may be required for applications that demand extra thickness.
Application Requirements
The end use and operating environment of the PCB are key factors in determining thickness requirements. Rugged applications exposed to vibration, impact, or harsh conditions often demand thicker boards for durability:
- Industrial controls, robotics, machinery
- Automotive and transportation
- Aerospace and defense
- Outdoor telecom and infrastructure equipment
Thickness is also important for PCBs that generate significant heat, such as power electronics. Thicker boards have more thermal mass to absorb and spread heat. Very thin boards may warp or deform under high heat loads.
On the other hand, some applications prioritize size and weight savings over thickness:
- Wearable devices
- Smartphones and tablets
- Laptops and thin clients
- Instrumentation and test probes
Thin, lightweight PCBs are ideal when space is limited or the product needs to be as compact as possible. Flexible circuits also demand very thin laminates.
Manufacturing Considerations for PCB Thickness
Aspect Ratio
The aspect ratio is the proportion of a PCB’s thickness to its smallest surface dimension (length or width). If the board is too thick relative to its size, it becomes difficult to manufacture reliably.
Most PCB Fabricators recommend an aspect ratio below 1:25 for best yields. For example, a 2″ x 2″ board should not exceed 0.080″ thick, while a 1″ x 1″ board should stay under 0.040″.
Exceeding the aspect ratio can cause issues with:
- Plated through-hole reliability
- Drill wander and breakage
- Resin starvation and lamination defects
- Warping and bowing
When designing very thick boards, make sure the overall board dimensions provide a manufacturable aspect ratio. Slim, pencil-like form factors are not feasible beyond a certain thickness.
Minimum Hole Size
The PCB thickness limits the minimum drilled hole diameter that can be reliably formed and plated. Very small holes become increasingly difficult to drill and plate as the aspect ratio of the hole’s depth to diameter increases.
Typical minimum Finished hole sizes for standard thicknesses:
| Thickness | Min. Hole Diameter |
|---|---|
| 0.020″ | 0.008″ |
| 0.032″ | 0.010″ |
| 0.062″ | 0.014″ |
| 0.093″ | 0.018″ |
| 0.125″ | 0.020″ |
Smaller vias and thicker boards require progressively more advanced drilling and plating capabilities that may increase cost or limit fabricator options. Consult with your manufacturer on their specific capabilities.
Routing and Profiling
Mechanical routing is commonly used to separate individual boards from a fabricated panel. The router bit diameter must be smaller than the narrowest cut to be made.
Thicker PCBs require larger router bits and more powerful routing spindles to cut through the material. This limits the minimum rout widths and spacing that can be achieved.
Typical minimum rout widths for different thicknesses:
| Thickness | Min. Rout Width |
|---|---|
| 0.020″ | 0.025″ |
| 0.032″ | 0.031″ |
| 0.062″ | 0.062″ |
| 0.093″ | 0.093″ |
| 0.125″ | 0.100″ |
When the cut width is too narrow for routing, specialty cutting methods like v-groove scoring or stamping may be used instead. This can add time and cost to fabrication.
How to Specify PCB Thickness
When ordering your PCBs, you will need to specify the desired thickness to your fabricator. Provide the thickness callout in your fabrication drawing, PCB Stackup diagram, or design data package.
The most common ways to specify thickness are:
- Finished board thickness in inches (e.g. 0.062″ ±10%)
- Finished board thickness in millimeters (e.g. 1.57mm ±10%)
- Layer count and copper weights (e.g. 4 layers, 1 oz/1 oz copper)
For standard layer counts and copper weights, specifying the layer count is usually sufficient for your fabricator to build to a default thickness. If you have specific requirements, call out the exact finished thickness.
Always include an acceptable tolerance on your thickness callout. PCB thickness can vary due to material availability, plating thickness, and lamination processes. A typical tolerance is ±10% of nominal thickness.
Frequently Asked Questions
What is the most common PCB thickness?
The most common PCB thickness is 0.062″ (1.57 mm), which is the default for many 4-layer boards. 0.093″ (2.36 mm) is also very common for 6-8 layer boards.
How thick can a PCB be?
PCBs can be fabricated up to about 0.250″ (6.35 mm) thick, but thicknesses over 0.125″ (3.18 mm) are rare. Very thick boards are used for specialized military, aerospace, and industrial applications.
Can PCBs be made thinner than 0.003″?
Yes, extremely thin PCBs down to 0.001″ (25 μm) or less are possible using advanced materials and fabrication techniques. These ultra-thin boards are used for high-density flexible circuits in compact electronics.
Are thinner PCBs cheaper?
In general, thinner PCBs are less expensive than thicker ones, as they use less material. However, very thin PCBs may require specialized processing that increases cost. The most cost-effective thickness depends on the complexity and layer count of the design.
Does PCB thickness affect signal integrity?
Yes, PCB thickness can affect signal integrity and impedance control. Thinner dielectrics between layers allow for finer trace widths and spacings, but may increase crosstalk. Thicker dielectrics provide more isolation but limit routing density. The stack-up must be carefully designed to optimize SI.
I hope this in-depth guide to PCB thickness provides a useful reference for your PCB design and manufacturing needs. By understanding the key factors and tradeoffs involved in PCB thickness, you can make informed decisions to optimize your board’s performance, reliability, and cost.
