Understanding PCB Thickness: An Expert Guide

What is PCB thickness?

PCB thickness refers to the total height of the board from its top surface to the bottom surface. It is determined using the height of the substrate and other layers, like copper, as well as other coatings, like the solder mask and silkscreen. PCB thickness is typically measured in millimeters or mils (thousandths of an inch).

The thickness of the PCB that is most common is 1.57mm or 62mil. Its typical tolerance is around ±10% or ±0.1 mm, depending on material and stack-up. 1.57mm has become the industry standard due to historical reasons when the PCB was made manually without computer-aided design programs. When electronics shifted to using transistor technology and integrated circuits, the boards were designed using breadboarded techniques on wooden benches, and the wood on the top would be removed, replacing it with Bakelite plastic.

Although 1.57mm thickness has become the most commonly used standard, it is certainly not the only alternative offered by manufacturers, as there is a wide range of standard thickness options available. Other standard thickness increments typically appear as 1mm or 1.5mm multiples, which are also available in stackup form from manufacturing companies, including PCB manufacturers. Mechanical design engineers who use metric systems will find that the round units of 1mm multiples are a good choice for design projects since they also have familiar tolerances associated with them.

Certain types of products and PCB designs do not adhere to standard stackup thicknesses. Examples include flex PCBs and rigid-flex PCBs, ceramic core PCBs, metal core or metal-backed PCBs, PCBs with thick dielectric layers on backplanes, PCBs with numerous dielectrics laminated together sequentially, printed ink electronics, and additively manufactured PCBs; these types of products could theoretically have any thickness, provided that the material to produce them is available commercially. On the thinner end of the scale are printed ink electronics and flex PCBs, which typically use thin substrates as the base material. On the opposite end of the scale are backplanes that often have very large thicknesses, particularly when high-density daughter board connectors are used.

Copper Thickness Conversion Chart (oz-mm)

The weight of copper in the production of PCBs is usually represented in ounces. The thickness that will be obtained by spreading out 1 oz (or 28.35 grams) of copper over an area of 1 square foot is 1.37 mils or 0.0348 mm. This convention arose from the way copper foil suppliers referred to their products.

The conversion between copper weight and actual thickness follows a consistent mathematical relationship across all values. Here's the conversion chart showing copper thickness across different measurement units:

Converting between these measurements requires simple formulas. To convert thickness in mils to copper weight: Copper Weight (oz) = Thickness (mils) / 1.37. Conversely, converting copper weight to thickness in mils: Thickness (mils) = Copper Weight (oz) × 1.37.

Most PCBs use 1 oz copper thickness as the standard specification. For instance, if you need to determine a 4-oz thickness, multiply the 1-oz baseline by four: 1.37 mil × 4 = 5.48 mils. This calculation method applies to any copper weight value you encounter in your designs.

Common Standard PCB Thickness

Industry specifications define thickness ranges based on the number of PCB layers. Although 1.57 mm continues to be widely used regardless of the number of layers, different boards have their own thickness ranges.

Single-layer PCB thickness

A single-layer PCB has a limited number of core material options, thus creating limited choices in regard to board thickness. A PCB with a very low thickness will only have one core layer; therefore, it will only be able to have a maximum of two copper layers. For the majority of circuit boards, the minimum achievable thickness for a PCB will be 0.2mm. However, ultra-thin applications may extend the ability to produce even thinner boards.

2-layer PCB thickness

The most common thicknesses of 2-layer PCB are between 0.6 and 1.6 mm, although they can also be manufactured in thicker options like 2.0 mm and 2.4 mm. The majority of PCB substrates will have a final thickness of 1.6 mm (0.063 inches) for 2-, 4-, and 6-layer boards. A typical 2-layer board at 0.062" to 0.063" final thickness features a 0.057" core, and copper foil on the outer layers that are 0.0014" thick each.

4-layer PCB thickness

The four-layer stackups are typically between 0.8mm and 2.4mm. The standard thickness is still 1.6mm, although 1.2mm is widely used. In a typical 1.6 mm four-layer stackup, the core layer might be around 0.8 mm to 1.0 mm, with the remaining thickness made up by two prepreg layers (e.g., 0.4 mm + 0.4 mm or 0.3 mm + 0.3 mm). For example, a 0.062" stackup can use either a 0.037" core with two 0.0091" prepreg layers, or a 0.047" core with two 0.0075" prepreg layers. Actual thicknesses vary based on copper weight, impedance, and what the fab can do.

6-layer PCB thickness

The thickness of a 6-layer PCB typically ranges from 0.8 mm to 3.2 mm, with 1.6mm being the most commonly used standard. Different thicknesses suit different applications: 0.8mm to 1.0mm for thin and light devices like laptops and tablets; 1.2mm for compact enclosures and modules; 1.6mm for general-purpose boards; 2.0mm for higher mechanical strength or heavier components; and 2.4mm for applications requiring extra rigidity or high-voltage isolation. PCB thickness tolerances generally follow industry standards: ±10% for boards 1.0 mm and thicker, and ±0.1 mm for boards thinner than 1.0 mm. While thinner boards use less material, they don't always cost less. Extremely thin boards (e.g., below 0.8 mm) require tighter process control and have higher scrap rates, which can increase cost. However, common thicknesses like 1.0 mm and 1.2 mm are typically priced the same as the standard 1.6 mm.

Importance of PCB thickness

Selecting an appropriate thickness affects multiple design dimensions beyond basic mechanical considerations. The thickness choices you make cascade through electrical, thermal, and production variables.

Devices performances

Signal integrity also becomes increasingly sensitive to thickness when dealing with fast speeds. Thick boards ensure an increased spacing between layers and impact impedance management. The necessity for uniform impedance of usually 50 ohms when working with high speeds is important for avoiding reflected waves and data corruption. Impedance mismatch results from changes in dielectric thickness, leading to signal distortion.

Properties related to mechanical stability vary drastically according to thickness variations. Increased thickness in printed circuit boards enhances the structural strength of the boards, and this quality makes such boards ideal for manufacturing boards with larger sizes, connections that require constant insertions, and extreme operating conditions common in automotive, industrial, and aerospace industries. Thin PCBs offer more flexibility and low weight, thus being used in manufacturing small devices and flexible/rigid boards. While 1.6 mm thickness offers stability against bending, thin boards can crack easily without protection.

Manufacturing process

Standard 1.6mm thick printed circuit boards (PCBs) are still the least expensive and quickest to manufacture; custom-thickness PCBs increase the cost and turnaround time of manufacture. Thicker printed circuit boards require more accurate tooling to drill the holes for the vias and through-holes. Non-uniform panel thicknesses or values outside of expected tolerances will create non-uniform pressure on the boards during lamination, thus leading to either separation of the laminations or poor inter-layer adhesive bonding. The reflow soldering profiles must be adjusted for the thickness differences between printed circuit boards; for example, the reflow conditions for a 2.0mm thick printed circuit board will require a longer preheat period than those of a 1.0mm thick printed circuit board.

Heat dissipation

Thicker boards dissipate more heat, benefiting power electronics applications. A 2.0mm thick board can reduce component temperatures compared to thinner alternatives, assuming other factors remain constant. Copper thickness directly correlates with thermal performance. Increasing the inner layer copper from 1 oz to 2 oz can drop the temperature rise from 50°C to 30-35°C above ambient in power-dissipating components.

Characteristics and Applications of Different PCB Thickness

Different thickness categories serve distinct application requirements based on space constraints, power demands, and environmental conditions.

Ultra-thin PCB

Ultra-thin boards are made with a thickness of 0.2–0.4 mm using flexible materials such as polyimides. As a result, they ensure the highest level of flexibility possible. Ultra-thin boards are ideal for use in wearables, medical devices, and microelectronics because they occupy a tiny area. Some boards are only 0.1mm thick. The smartphones, tablets, and wearables will find the ultra-thin boards beneficial in saving space and making them lightweight. For instance, in smartwatches, their boards are made up of 0.4mm thickness. Likewise, medical devices and diagnostics use the thin boards when fitting into catheters, pacemakers, and endoscopes. However, the thin boards may be vulnerable to bending pressure.

Mid-range thin PCBs

Mid-range thicknesses of 1.0mm to 1.2mm suit applications needing moderate durability and layer counts of 4-6. Industrial controls and communication devices frequently use these boards. They offer improved mechanical stability compared to thinner options while maintaining reasonable compactness.

Thicker PCBs

Thick copper PCBs feature copper thickness ranging from 100 to 500 μm or more, defined as boards with copper thickness of 70 μm (2 oz) or more. These boards excel in automotive battery management systems, power supply converters, inverters, aerospace avionics, solar inverters, and industrial automation. Their high current capacity and effective heat dissipation make them suitable for renewable energy systems and high-performance computing in data centers.  

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Key Factors Affecting PCB Thickness

Multiple engineering variables combine to determine final board dimensions. Understanding how each component contributes helps you make informed design decisions.

Layer Stack-up Configuration

The stack-up architecture determines how cores, copper layers, and prepreg will be assembled. Between the two designs, the 4-layer asymmetrical and symmetrical, the difference in both board thickness and stability can be quite large.

Layer number

Additional layers increase overall dimensions. Each added layer requires extra core or prepreg material, directly expanding total thickness. Moving from 2 to 4 layers typically adds 0.4mm to 0.8mm.

Substrate Thickness

Core material forms the foundation of your board. FR-4 substrates come in discrete thicknesses, with each manufacturer offering specific options that constrain your total thickness choices.

Prepreg Thickness

When laminated, the prepreg layers assist in gluing the cores together. Prepregs are offered in many different thicknesses, which gives you the ability to fine-tune the spacing between the copper layers, thereby controlling impedance.

Solder Mask Thickness

Solder mask usually results in adding 0.5-1.0 mils for each side. Although this amount is very small, it is a coating that adds to the final dimensions, so it needs to be included when calculating tolerances.

PCB Copper Thickness

Copper weight affects overall dimensions. Standard 1 oz copper adds 1.37 mils per layer, while 2 oz copper doubles this contribution, impacting total thickness accordingly.

Signal and Impedance Requirements

High-speed signal operation will require specific spacing between dielectric layers to maintain the minimum impedance value specified by each signal layer. Often, the minimum spacing needed between the signal area and reference planes will be dictated by these requirements.

Operating Environment

Rugged mechanical characteristics are often associated with increased thickness of material due to needing to withstand a harsh environment, whereas portable electronics require thinner materials to reduce weight and optimize space.

Design-Specific Constraints

However, there are certain PCB designs that present their own set of constraints that affect the choice of thickness. Constraints such as the height of the components used, connectors, and the type of via used (blind, buried, etc.) can limit the range of thicknesses possible. Moreover, certain designs where a higher density of components is required might necessitate thinner PCBs, while those with bulky components would need thicker ones.

Challenges in PCB Thickness

Manufacturing boards outside tolerance specifications creates problems that extend beyond simple dimensional errors. Warpage and cost implications represent the primary obstacles designers and manufacturers face.

Warpage Issues

Warpage refers to the bending and twisting of boards from their natural straight shape. The main reason behind thermal stresses developed during various production activities, such as soldering and curing, is different material expansion rates. In the case of reflow soldering done at 260°C, the difference in the materials used for FR-4 substrates creates internal stress due to the different expansion rates. The imbalance in copper can also lead to further warping as the side that has greater copper creates different expansion rates.

Any form of warping affects the production process in a significant way. Even if there is any warpage amounting to only 0.1mm on a 100mm wide board, solder joints will be difficult to make, and proper components cannot be assembled. With regards to BGA components, any amount of warping exceeding 0.75% of the board diagonal dimension results in assembly defects. Pick-and-place automated machines need flat surfaces, and therefore any form of warping leads to misaligned components.

Tolerance and Hidden Costs

Deviation from the required tolerance of thickness results in high monetary costs. Nonconformity in terms of quality leads to increased costs of labor and material. If 100 units are produced at $500 and half are rejected due to tolerance, then the cost of producing each unit effectively becomes double. The nonconformity may cause production line delays in sectors such as the automobile or aerospace, resulting in fines. Projects that may initially cost $10,000 may end up costing $15,000.

Ignoring tolerances will result in reduced yield. Yield for the normal production process is normally around 95%, whereas ignoring tolerance will bring it down to as low as 80%. For example, for projects involving the production of 1,000 units, reducing the yield by 15% would reduce the yield by 150 pieces.

How to Choose Appropriate PCB Thickness

Balancing competing design requirements requires a methodical selection process. Following a structured approach ensures your thickness choice supports both performance goals and manufacturing realities.

Define Application and Performance Needs

First, determine the specifications of performance, use case, and loading required for your board's components. Consumer electronics would be better served by using 1.6 mm since it offers a good balance between manufacturing efficiency and durability. High-powered uses require thicker copper, such as 2 oz or higher, to ensure effective heat dissipation. On the other hand, high-frequency uses require thin PCBs to enhance speed and reduce transmission loss.

Evaluate Component and Assembly Specs

Board-edge connectors require a particular thickness for specific connector models. The connector will not significantly influence layout, but adjustments must account for changes to the board itself. Verify compatibility with automated assembly equipment, as some lines have constraints on board thickness.

Assess Signal Integrity and Impedance

The thickness of the PCB can affect the impedance of the traces, which is an important factor in high-speed (or RF) designs. The dielectric material can help improve the integrity of the signal, but a thicker dielectric will require wider traces in order to maintain controlled impedance.

Review Manufacturability and Standards

Typical thicknesses such as 1.0mm and 1.6mm are processed without difficulty by most manufacturing facilities. However, ultra-thin boards less than 0.40mm and extra-thick boards greater than 2.0mm may require specialized machinery. As such, 1.60mm is the most cost-effective option as it is commonly available and can be produced on an efficient production line.

Optimize Cost and Lead Time

Standard thicknesses require shorter lead time as the material is readily available. Non-standard thicknesses result in higher costs for the material and might even entail some setup charges. It is advisable to maintain standard thicknesses to avoid incurring unnecessary expenses.

Conclusion

The choice of PCB thickness will influence every aspect of the design process, including signal performance, thermal performance, manufacturing costs, and assembly efficiency. As we've seen above, a thickness of 1.6mm is good enough for most applications, along with the ability to be flexible when other conditions call for it. The choice of PCB thickness must always involve balancing performance criteria with manufacturing criteria. Factors like the environment of the application, component types, and impedance requirements need to be considered. For high-power applications, thicker copper layers work well, while thinner boards are preferred in space-constrained devices.

FAQs

What is the standard PCB thickness?

The most frequently used thickness of FR-4 substrates is 1.6 mm (around 62 mil). The use of this specification is quite common in the case of consumer electronics, smart home technologies, and control systems in industries.

When should I choose an ultra-thin PCB below 0.6mm?

The ultra-thin circuit boards can be used where there is limited space or weight constraints, such as smartphones, tablets, wearables, laptops, UAVs, and robotics. But the disadvantage is that they do not offer much mechanical strength to withstand heavy components.

Does PCB thickness affect cost?

Yes, increasing PCB thickness generally increases cost due to higher material usage and manufacturing complexity.

Can I freely choose a non-standard thickness?

Non-standard thicknesses require custom stackups, which may decrease yield and raise costs. It is always recommended that you verify manufacturability with your PCB manufacturer prior to specifying any thicknesses.

What is the typical tolerance for PCB thickness?

The tolerance allowed by most PCB manufacturers on standard thickness is ±10%. If the thickness is extremely thin (<0.6mm), then the tolerance allowed would be about ±0.075mm.

Which thickness should I choose for edge-card connectors?

A thickness of 1.57–1.6 mm is typically recommended unless otherwise specified in the connector datasheet, as it ensures proper contact and insertion performance.