Many factors come into play when purchasing and manufacturing a printing circuit board (PCB) such as profile, weight and the components. However, among the essential factors, is the PCB thickness. Why? The thickness affects its conductivity and resistance which are major 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 of where and how it is going to going be used. It helps in determining a specific thickness that is appropriate for its application and the area it is used.
In turn, let us have a 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 is when 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 board with many layers placed together. Today, PCB's are either single-sided (with one copper layer), two/double sided (two copper layer with a substrate layer between them) or multi-layer (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 PCB's.
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 thickness became a significant variable and there was a requirement for a standard level of the copper used as layers on the plate edges. In turn, 0.063” became the Standard PCB Thickness.
Nevertheless, there is a general 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, use of better substrates other than plywood started being used. For instance, epoxy or the paper reinforced phenolic resin, are among 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 area of application, 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 square foot area which this results to 1.37 mils (1.37 thousandths of an inch).
Usually, PCBs are manufactured with the 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, increases in price and not just because of the increased copper but also, processing thicker copper is more challenging and requires 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 of 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, trace 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 wide internal layers due to storage of more heat 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 indicates a class of the materials used. Fr-4 is a name as well as a rating. It is used as a name during manufacture of a PCB and the fiberglass-reinforced with epoxy-laminated sheets. As a rating, the Fr-4 is used in the grading of the epoxy laminate sheets as an indication of their quality.
If you often deal with PCBs, it is likely that you are familiar with the Fr-4 material. It is a popular PCB base material as it is the main ingredient used in the manufacturing of rigid circuit boards.
The Fr-4 material is a structure mainly composed of fiberglass weaved to a thin and cloth-looking sheet. It is the fiberglass that gives the Fr-4 popularity as a solid base for 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, it is a material suitable for various environmental conditions.
The Fr-4 standard PCB thickness is measured in millimeters or inches. The use of either calibration depends on what the designer or manufacturer prefer. Due to the popular use of the Fr-4 substrate, the range of its subsequent board thickness can go to some extreme. It is usually from 3" all the way to 10".
So with such a wide range of Fr-4 thickness, what factors would a designer consider in the manufacturing of a PCB?
Component Compatibility: Even though the Fr-4 can be used in the manufacturing of almost any printed circuit board, its thickness has effects on the board component compatibility. For instance, large through-hole PCB parts differing with most components as they have through-holes that require small PCB thickness.
Space: Space is an indispensable factor when designing PCBs especially during manufacture of 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, thinner 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 of whether flexibility arises from thinner or thicker boards but the right answer would be- it depends on where the PCB is being used and its application. Let us take an example of the application of the Electronic Control Unit in the medical field; thinner boards ensure you encounter less stress. At this situation, thinner boards result to very flexible PCBs.
However, when a PCB is being manufactured using thinner boards can be troublesome especially during soldering. Due to their flexibility, the boards are likely to bend when they are soldered causing the other components to curve in an undesired angle. In the process, the components and their connections can also break resulting to 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. In case the connector's mating part does not match, the results would be damage of the PCB.
To avoid such accidents, the materials used in the making of 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 weight of the PCB. A manufacturer might not take keenness on the weight of the PCB, but it is of great significance to the customer. A lighter board means saving on shopping cost as the final product is lighter.
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. One, the copper foils used to form the Fr-4 core layer should be smooth and with a very exact thickness.
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 together etched cores. 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 at all. As a result of lack of such vital information, the performance of the resultant PCB is downgraded.
Nevertheless, there are situations a manufacturer may call fortunate 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, it is essential that designers 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 the PCB desired functionality. Note that the resultant weight is inclusive of the copper foils which are of similar weight 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 thickness. That is not necessarily provided during the design especially where there is no need for impedance control.
However, if the impedance requirement is not much of an 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. Thanks to the development of technology, the multiple layers allows for more loads and still have a thickness of 63mm. They are popularly composed of epoxy based glass fabric material but with copper covering.
Due to the wiring requirements of complex circuits, the PCBs layer counts were added. In turn, the circuit boards were also produced have higher layer counts, and the result is the increase of the PCB thickness from 63mm to 93mm.
Using the Isola's 370HR materials, there are inner layer cores available including 5, 8, 9.5, 14, 18, 21, 28, 35, 39, 47, 59 and 93 mil cores. However, for high-temperature materials, there are Isola’s 370HR cores of 8, 10, 14, 22 and 39 mils provided.
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 to be used would be 0.031”. For a 6-layer foil lamination, the most appropriate standard to be used 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, 1 or 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 of 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 for it to function correctly in its area of application.
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 the technology in creating every PCB thus bringing out proper standard thickness as per our client's requirements.
In case you have any questions about PCB, PCB manufacturing or PCB assembly process in your project, feel free to contact us as we are available 24 hours. Most importantly, in case you want to make an order, we will always be glad to deliver critical, high-performance PCB and PCBA solutions at your doorstep.