Guideline

The Ultimate Guide to Understanding PCB Thickness

pcb layup

The total thickness of the prepreg, solder mask, silkscreen, and CU layers together is referred to as the PCB thickness. Regular PCB boards are typically between 62 mils (1.57 mm) to 93 mils (2.4 mm) thick. With increased complexity and number of layer counts, the thickness of PCB also varies. In recent developments, fabrication firms are constructing certain new standard thicknesses of 125 mils(3.175mm) and 250 mils(6.35) thick boards respectively based on clients’  requests.

A vital component of PCB design is thickness, which influences the board’s functionality, robustness, and dependability in a variety of environmental settings.

The Design Elements that Impact PCB Thickness

The following design elements have an impact on PCB thickness. So PCB design engineer should understand the elements which will affect the circuit board thickness. 

  • The thickness of copper

The typical thickness of copper is 1-2 ounces (1.4 – 2.8 mils). However heavy copper PCBs can be designed with 50oz (70mils) or more. The amount of copper on board is determined by the current that must be carried through the PCB. The thicker the board, the more the process involved in manufacturing, which in turn increases the cost of PCBs.

The overall cost of the PCB is also determined by the thickness of the copper used on board.

  • Prepreg or dielectric material

Prepreg and dielectric materials are non-conductive materials that are used to improve insulation between two foils or copper layers. These are typically composed of epoxy resin. The most often utilized prepregs are FR-4.  The base material is the most critical factor that affects printed circuit board thickness. 

The selection of prepreg depends on several aspects such as dielectric constant(Dk), dissipation factor(Df) and glass transition temperature(Tg).

  • Number of layers

As the circuit becomes more complicated, the number of layers on the PCB increases. The addition of more prepregs and CU foil results in an increase in PCB thickness as the number of layers grows.

  • Operating environments

Environmental factors such as temperature, humidity, pressure, mechanical stress, and other external situations might affect the performance of the printed circuit board.

Maintaining the right thickness of the board is essential to prevent problems in the electronic device, especially when it needs to endure all of these and perform in such tough conditions. 

  • Through-hole types

The opening created by through-holes allows component leads or wires to go from one side of the board to the other. There are various types of through holes, such as plated through holes (PTH) and non-plated through holes (NPTH).

As the density of the component increases on the board, HDI drills comes into action. There are three types of HDI drills available: Micro via, Buried via, and Blind via.

Selecting the appropriate sort of drill hole can affect the PCB board thickness and manufacturing process.

Standard 6 Layers PCB Thickness

Standard 6 Layers PCB Thickness

Manufacturing Factors that Affect the PCB Thickness

PCB manufacturers should also understand the factors which will affect the PCB thickness very well. Then, they can make sure the finished PCBs can meet the customers’ requirements. So very experienced CAM engineers are needed to design the stack up in DFM state, especially for HDI circuit boards with blind and buried via. 

  • Core and prepreg thickness

PCB base material take the biggest partition in PCB board thickness. For example, a standard 2-layer PCB with 1.6mm thickness. The base material thickness is around 1.5mm.  standard 4-layer PCB with 1.6mm thickness, the thickness of core and prepreg is around 1.4mm. So PCB manufacturers need to make sure the base material (including core and prepreg) is used correctly.

  • Copper thickness

Copper thickness is one of the manufacturing parameters that affect the PCB thickness. Copper is plated on the board through a process called copper plating. A thicker copper layer requires more copper material to be plated on the board which leads to process complexity and increased manufacturing cost. This can also impact the overall thickness of the PCB.

  • Drilling Equipment used

The largest holes that can be drilled are restricted by the board’s thickness. The diameter and depth of the holes are likewise restricted by the drilling machine.

The capacity of the drilling machine and the drill’s aspect ratio determine the thickness of the PCB.

  • Number of layers

Single side and double side PCBs are relatively thin, while multilayer PCBs with three or more layers are thicker due to the additional copper weight and the prepregs. It is ovisou that more layers means more printed circuit board thickness.

  • The depanelization method

It is the process of separating the PCBs from array format to indithe vidual board using scoring or routing methods.

The ideal technique for depanelizing the PCBs from the array format depends on the thickness of the board.

Classification by PCB Thickness

PCBs can be classified according to their layer counts, materials, surface finishes, technologies., etc. Here, we try to classify PCBs according to their thickness: thin PCB, thicker PCB and extremely thick PCB.

  • Thin PCB

Boards with reduced thickness ranging from 15.7mil (0.4mm) to 39.4mil (1.0mm) are referred to as thin PCB. These boards are light in weight & flexible, making them suitable for applications where space and weight are critical factors. These PCBs are commonly used in portable electronic devices, wearables and devices where flexibility is required.

  • Thicker PCB

Boards with thickness ranging from 62mils(1.6mm) to 93mils (2.4mm) and more are referred to as thick PCB. These boards have enhanced mechanical strength and durability compared to thin PCBs, making them suitable for applications where robustness is crucial. Thicker boards are commonly used in industrial applications, power electronics devices and consumer electronic devices where the board needs to withstand mechanical stress.

  • Extremely Thick PCB

Some printed circuit boards can be thicker than  93mils (2.4mm), and backplane PCBs are as thick as 400mils (10.16mm). These kinds of PCBs are usually backplane boards or testing boards that contact many thousands of components with extremely large dimensions.

PCB Board

Standard PCB thickness

After knowing the main factors of circuit board thickness, we talk about the standard PCB thickness or typical PCB thickness. Generally speaking, the most commonly used PCB board thickness is 62 mils (1.57 mm), but there is a slight difference according to the PCB materials and PCB types. 

PCB TypePCB Thickness (mil)PCB Thickness (mm)
FR4 PCB62 mils1.57 mm
Aluminium PCB39 mils1.0  mm
Power PCB93 mils2.4  mm
Backplane PCB250 mils6.35 mm
Semi-flex PCB8 mils0.2 mm
1 layer Flex PCB4  mils0.11 mm
2-layer Flex PCB8 mils0.195 mm

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