Standard PCB Thickness – Determine the Right Standards

Many factors come into play when purchasing and manufacturing a printing circuit board (PCB), such as profile, weight, and components. However, among the essential factors is the PCB thickness. Why? The thickness affects its conductivity and resistance, significant considerations that have to match your PCB requirements. Typically, the PCB thickness has a significant role in its functionality.

Typically, a customer or a designer has to provide scant information about where and how it will be used. It helps determine a specific thickness that is appropriate for its application and the area it is used.

In turn, let us look at the various levels of thickness available and how you can determine the right standards for your requirements.

1、Standard PCB Thickness

During the 20th century, the standards of PCB were defined, starting from a sheet frame to when Albert Hanson developed flat foul conductors insulated in multiple layers. The boards had a simple design with a single panel with many layers placed together. Today, PCBs are either single-sided (with one copper layer), two/double-sided (two copper layers with a substrate layer between them), or multilayer (multiple layers of the two-sided PCB).

The typical PCB thickness is 0.063inches or 1.57mm; it is a standardized level defined from the past. That is because, during the plywood industry, 0.063" was the thickness of the plywood sheets used as substrates for electronic devices, which included PCBs.

Image 1: PCB Thickness

When multiple layer PCBs started developing, the thickness of the connectors between the boards had to match. Therefore, the level of consistency became a significant variable, and there was a requirement for a standard deck of the copper used as layers on the plate edges. In turn, 0.063" became the Standard PCB Thickness.

Nevertheless, there is a broad thickness range of 0.008 inches to 0.240 inches, between which you can choose depending on the application or usage area. It is, therefore, essential that you communicate requirements for the appropriate PCB thickness size.

1.1 PCB board thickness

The width of the board is reliant on the insulating layer and the content of its material. Early in the development of PCBs, the layers, top, and bottom were made of Bakelite, and the resultant thickness was 0.0065".

Over time, the use of better substrates other than plywood started being used. For instance, epoxy or paper reinforced phenolic resin are among the substrates used between layers of copper foil. Consequently, the use of lighter materials in addition to the lack of use of the edge connectors, the board thickness is at times below 0.0065".

1.2 PCB copper thickness

Copper being the dictator of a PCB's functionality and application area, its thickness has an essential role in achieving the standard PCB thickness. Its measurement is usually an ounce (oz). It is achieved by spreading an ounce of copper evenly over a square foot area, which results in 1.37 mils (1.37 thousandths of an inch).

Usually, PCBs are manufactured with 1 oz of copper. Also, it is the presumed thickness by manufacturers when the designer does not give them specific measurements.

However, if the current that is to pass through the PCB will require more than an ounce of copper, a manufacturer can add the weight of the copper or the width of the trace. However, price increases not just because of the increased copper but also that processing thicker copper are more challenging and require more time.

1.3 PCB trace thickness

The PCB trace thickness is the thickness determined by the designer, and it is one of the essential parameters in PCB designing. It is specified in the designer Garber files to prevent overheating or damaging the PCB. When the current flows or increases, the copper traces start heated, and ultimately, PCB temperature rises. When the temperature exceeds the limit of the PCB, it starts getting damaged. Therefore, the path should be thick enough to allow higher current passage without affecting the average temperature of the PCB.

So how is the PCB trace thickness determined? The amount of current passing through the PCB is compared to the increase in temperature. The width that can handle the increase in temperature from the average operating temperature to the maximum operating temperature is the trace thickness.

The task of calculating the trace width would be tiresome. Designers, therefore, use a PCB width calculator that provides the appropriate width for current to pass through without causing any damage to the PCB. The resultant thickness has broad internal layers due to more heat storage as the external layers transfer their heat through convection to them.

It is recommendable to use internal trace width for all traces.

2、Standard PCB Fr-4 Thickness

Also known as FR-4 or FR4, Fr-4 stands for flame retardant, and the four indicate a class of the materials used. Fr-4 is a name, as well as a rating. It is used as a name during the manufacture of a PCB and the fiberglass-reinforced with epoxy-laminated sheets. As a rating, the Fr-4 is used to grade the epoxy laminate sheets to indicate their quality.

If you often deal with PCBs, you are likely familiar with the Fr-4 material. It is a popular PCB base material as it is the main ingredient used to manufacture rigid circuit boards.

The Fr-4 material is a structure mainly composed of fiberglass weaved to a thin and cloth-looking sheet. The fiberglass gives the Fr-4 popularity as a solid base for the manufacturing of rigid circuit boards. It is enclosed with a fire-resistant epoxy resin, and it is where the rigidity comes from.

Image 2: Standard PCB Fr-4 Thickness

Among other reasons, the Fr-4 is popular is due to the low cost of its materials and its versatility. The FR-4 sheets have an immense dielectric strength as electrical insulators. Besides, they are lightweight, water, and heat-resistant; in short, they are suitable for various environmental conditions.

The Fr-4 standard PCB thickness is measured in millimeters or inches.

It is usually from 3" to 10". The use of either calibration depends on what the designer or manufacturer prefers. Due to the widespread use of the Fr-4 substrate, the range of its subsequent board thickness can go to some extreme.

So with such a wide range of Fr-4 thickness, what factors would a designer consider in manufacturing a PCB?

Component Compatibility: Even though the Fr-4 can be used to manufacture almost any printed circuit board, its thickness affects the board component compatibility. For instance, sizeable through-hole PCB parts differing from most components as they have through-holes that require small PCB thickness.

Space: Space is an indispensable factor when designing PCBs, especially during small devices such as USB connectors and Bluetooth Accessories. In turn, thinner boards are fitting, where saving space is vital.

Design Requirements:

Most manufacturers prefer thicker boards to thinner ones. Why? With Fr-4 substrate, narrower boards are more likely to get broken when they are too big. Also, they lack groove features. On the other hand, thicker boards are spectacularly flexible and have groove features. Therefore, it would be wise to consider the extra weight of a PCB.

Flexibility:

It is debatable whether flexibility arises from thinner or thicker boards, but the right answer is where the PCB is being used and its application. Let us take an example of applying the Electronic Control Unit in the medical field; thinner boards ensure you encounter less stress. In this situation, narrower boards result in very flexible PCBs.

However, when a PCB is being manufactured, using thinner boards can be troublesome, especially during soldering. Due to their flexibility, the panels are likely to bend when soldered, causing the other components to curve at an undesired angle. In the process, the members and their connections can also break, resulting in a damaged board.

Impedance Matching:

The thickness of the board is essential when dealing with multilayer boards since impedance matching is crucial. That is, as the layers create the dialectic, which facilitates impedance control.

Image 3: 4 Layer Thickness

A manufacturer is usually aware that with high-frequency signals, components like in a microwave impedance matching are vital, and the capacitance ought to be taken into account on each layer. Without impedance matching, adequate board functionality amounts to almost zero.

Connections: Another significant factor that affects the customer's desired width of a PCB design is the edge connector. During the manufacture of a PCB, a manufacturer ought to be careful with the Fr-4 thickness. If the connector's mating part does not match, the results will damage the PCB.

To avoid such accidents, the materials used in making a PCB are decided after the circuit design is complete.

It acts as a template or blueprint of a PCB that accurately fits the mating part of a connector or component.

Weight: Obviously, the thickness of the board will have an impact on the value of the PCB. A manufacturer might not be keen on the importance of the PCB, but it is of great significance to the customer. A lighter board means saving on shopping costs as the final product is more lightweight.

In summary, even with such a wide range of thickness, a thinner layer is more suitable for a device. Nonetheless, a designer is never sure whether a small board would match your mating parts of connectors and through-holes of devices. Therefore, the wise choice is usually to go for the standard PCB thickness.

3、Standard PCB Core Thickness

PCB core is the layer containing the Fr-4 substrate sandwiched by copper foils as manufactured in a core factory. In the making of a standard PCB core, some items have to be put in place. The copper foils used to form the Fr-4 core layer should be smooth and exact.

Two is the pre-preg, a layer used to laminate the core should be in check. This layer is made of fiber mesh saturated with a resin bonding agent manufactured to bind etched hearts. It also contains uncured Fr-4, whose thickness is different from the height of the etched boards on either side.

Image 4: Popular Cores

Manufacturers have a problem in choosing the standard PCB core thickness when making a multilayer design PCBs. The issue lies with the fact that the information on the exact material requirements is usually partly stated or not given. As a result of the lack of such vital information, the performance of the resultant PCB is downgraded.

Nevertheless, a manufacturer may call fortunate situations while the thickness requirements are still not met, and the PCB works just fine. That means the PCB core materials are not critical to performance, and all along, the customer does not notice.

However, today the quality of a product is its excellent performance, and to achieve this, the core thickness needs to be as accurate as possible. Consequently, designers must provide comprehensive as well as precise requirements of the PCB core to the fabricator.

PCB core thickness range

The weight of the measurements of the core thickness range from half an ounce to 3 ounces, in between which an exact size is made based on the PCB desired functionality. Note that the resultant weight includes the copper foils, which are of similar value on either side.
So what happens if a manufacturer has different copper weights on both sides? It usually leads to extra charges of current and, thus, poor PCB performance.

However, if you can have a core thickness with a suitable copper weight, you can use some pre-preg sheets in dielectric positions to achieve your final consistency. That is not necessarily provided during the design, especially where there is no need for impedance control.

However, if the impedance requirement is not essential, you can always correctly state it on the documentation that you will provide to the manufacturer. They then can make modifications of the pre-preg between the cores.

4、Standard two-layer PCB Thickness

Multiple board-layered designs have developed over time and are now a popular type of board used in PCB making. They are popularly composed of epoxy-based glass fabric material but with copper covering. Thanks to the development of technology, the various layers allow for more loads and still have a thickness of 63mm.

Due to the wiring requirements of complex circuits, the PCBs layer counts were added. In turn, the circuit boards that were also produced have higher layer counts, and the result is the increase of the PCB thickness from 63mm to 93mm.

Using Isola's 370HR materials, inner layer cores are available, including 5, 8, 9.5, 14, 18, 21, 28, 35, 39, 47, 59, and 93 mil cores. However, there are Isola's 370HR cores of 8, 10, 14, 22, and 39 mils provided for high-temperature materials.
The standard PCB thickness also depends on the layers of the foil lamination. If the foil lamination is for a four-layer PCB, the standard thickness would be 0.031". For a 6-layer foil lamination, the most appropriate standard would be 0.062".

Eventually, for an 8-layer and a 10-layer board, the standard PCB thickness is provided as 0.062, 0.093, and 0.125 inches. You can also choose ½, one, or a 2-ounce inner layer of copper foil, depending on your requirements for your board. You can also use either of our provided dielectric builds or your controlled stack-up.

4.1 standard two-layer PCB thickness

Image 5: Standard two-layer PCB thickness

4.2 Four-layer PCB thickness standard

Image 6: Four-layer PCB Thickness Standard

5、PCB Thickness Tolerance

PCB thickness tolerance is defined as the allowance of the substance used in PCB manufacturing. This could be either lower or more than the standard amount of the material.

Image 7: PCB Thickness Tolerance

The manufacturer uses the IPC guideline and rules as a party line that provides a different specification created with in-house tolerance parameters. These parameters have adequate variations for a manufacturer to create a board and function correctly in its application area.

6、Conclusion

By now, it is crystal clear of the immense importance the PCB thickness holds in the PCB functionality. It, therefore, requires designers to be keen to deliver accurate results for the best performing PCBs and that is where we, OurPCB, come in.

We understand that getting a PCB is an investment, and we value our customers, putting their confidence in us to provide nothing less than the best. In turn, we put our experience over the years to work and use the latest technology in creating every PCB, thus bringing out proper standard thickness as per our client's requirements.

If you have any questions about PCB, PCB manufacturing, or the PCB assembly process in your project, feel free to contact us as we are available 24 hours. Most importantly, if you want to make an order, we will always be glad to deliver critical, high-performance PCB and PCBA solutions at your doorstep.