How Thick is a Flex PCB?

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Designers are fond of using ‘standards’ when working with flex PCBs, often preferring certain dimensions of the circuit board for their applications. While there is no regularized standard dictating flex PCB thickness, certain industry trends have emerged in order to minimize costs and simplify costs.

 

The thickness of the flex PCB will directly bear the resistance and connectivity of the application.

How Thick are Flex PCBs?

The preferred flex circuit thickness in the industry is about 0.062 inches or about 1.57 mm. But most designers will end up with a range of numbers: from 0.7 mm all the way to 6.40mm and even higher. A standard 2-layer flex PCB is about 0.32 mm thick while a 4 layer flex PCB is 0.42  mm thick. The more layers you have, the greater the overall thickness of the flex PCB. 

 

The width of the flexible PCB depends on a number of factors. These factors influence the board's functionality and properties. Let’s cover them in more detail below to help you figure out the most appropriate flex PCB thickness for your application.

Size and Weight

By definition, Flex PCBs are required to be thin to achieve their flexibility. However, certain applications that do not require flexible boards can utilize a thicker board for improved structural integrity. It goes without saying that thicker PCBs are heavy and also take up more space. This can become a problem in applications where real estate is at a premium.

 

The desired application of the flexible circuit will determine its size and weight, which will be one of the first parameters that the designers will define before assembly.

Thickness of the Copper

Copper will play a pivotal role in the functionality of the flex PCB and its application. The thickness of the copper will play an essential role in achieving the target thickness of the flex PCB. The copper layer is generally only 1.4 to 2.8 mils wide. This is the default thickness that manufacturers stick to unless the designer tells them otherwise. With that said, designers can alter the thickness based on their requirements.

 

It is worth noting that thicker copper boards will be more expensive due to the processing challenges involved.


Note: Flexible boards are thin but susceptible to breaking easily. However, thick boards are less flexible and don't break as easily.

Flex PCB Layer Count

Flex PCBs can be single-layered, double-sided, or multi-layered. For obvious reasons, the more layers you have, the greater the thickness of the flex PCB. 2 to 6 layer flex PCBs are easier to comply with standard thicknesses. Things get more complicated once you go above eight layers.

 

In general, you should allow for more PCB thickness if your application needs more layers. If the design does not require several layers, but needs to fall under a certain threshold of thickness, then lowering the number of layers may be a better option.

Flex pcb Board Materials

PCB applications depend on the materials used in its construction. These choices will also determine the thickness of the board. Fabrication of a PCB consists of laminate, substrate, silkscreen, and solder mask. The substrate and laminate greatly impact the overall thickness of the board.

 

Materials commonly used for flex PCB substrates include PET, FR-1, and alumina, depending on the dielectric constant. Laminates consist of polyimide, BT epoxy, or Teflon. Both substrates and laminates feature a range of thermal, electrical, and mechanical properties that have bearing on the flex PCB’s thickness.

PCB Trace Thickness

PCB trace thickness lies in the range of 0.008 inches to 0.240 inches. Why is this important? Because PCB trace thickness has a direct impact on the board's impedance. Moreover, designers perform many complicated calculations based on PCB trace thickness.

 

Even the smallest inaccuracies in the calculations can have devastating consequences for the application and damage the components attached to the PCB board. Most designers use a PCB width calculator to determine the appropriate thickness to prevent any damage to the PCB board.

Type of Signal

Flex PCBs carry various signals that have a bearing on the materials to be used, which can determine the overall thickness of the board. For instance, a flex PCB operating in a high power environment will require wider traces and a thicker layer of copper, which means that it will be much thicker than boards carrying low power signals.

 

HDI flex PCBs carry more complex signals, but they utilize thin traces, laser microvias, and thinner materials, which are thinner than most flex PCBs.

Vias Used

Flex PCBs route traces through boards instead of through their surface, which plays a role in creating a more compact design. Designers can use various types of vias, including:

  • Micro via
  • Through via
  • Buried via
  • Via-in-pad
  • Blind via

 

The density and type of vias used will influence the final thickness of the board. Micro vias, in general, are used on flex PCBs that are thinner since they are used for high-density connections.

Operating Environment

The thickness of the PCB will affect the resistance and conductivity of the flex pcb board. This is why designers prefer certain thicknesses in different environments. For example, a thin PCB may not be ideal in extreme operating environments. 

 

On the other hand, thicker copper traces are not very thermally stable when exposed to higher current, making them a bad choice or use in high current environments. The components used on the flex PCB are also important because they enhance the board’s operations.

Wrapping Up

As you can imagine, designers have several choices regarding PCB thickness. While sticking to a standard flex PCB thickness will lower costs, custom thickness nesses will ensure that your application gets all the functionality it needs.

 

Regardless of your preferences for the flex PCB thickness, you need to partner with a supplier that can meet your goals. Hemeixin PCB is an industry leader that offers the best flex PCBs to its customers every time. If you want to discuss flex PCB thickness options, contact us today.

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