Guide, PCB Manufacturing

Flex PCB Material: Construction, Classification, and Advantages

Flex PCB

What is Flex PCB?

Flex PCB is referred to as a flexible printed circuit board. It is made of flexible insulating material. The common insulating materials are polyimide or polyester like KAPTON and MYLAR.

Flexible PCB boards can be folded, bent and wrapped to fit any place as per requirement and three-dimensional. Due to this flexibility, We can fit flexible PCB board in any mechanical place where rigid PCB does not work.

Flexible PCB boards are widely used in lots of high-tech electronic devices, such as:

  • Flexible display- smartphone, folded mobile phone
  • Wearable devices like smartwatches, fitness belt
  • Medical devices
  • Aerospace, Automotive products, Military, etc.

 

Construction of Flex PCB

  • Flex PCB Laminates

Adhesive less material, Adhesive material and FR and Non-FR laminates, cover layers and the bond ply.

See the below adhesive flex core Vs. Adhesive less flex core

adhesive flex core Vs. Adhesive less flex core

Both adhesive core types are used as per the desired application of the circuit. However, the designer can contact their PCB manufacturer based on their specific needs.

  • Copper Type and Thickness Callout

There are different metal foils available for the flexible circuit, Copper Foil is the common foil used in the Flex circuit. Copper is highly conductive than any other metal. Also, it’s inexpensive to plate and etch. The RA copper foil type is used in the flex circuit. RA stands for Rolled and Annealed copper. In any flex application, copper type and thickness should be matched.

Thick copper is required in high-power applications. Thin copper is used in general applications like bendable and flex requirements. Common flexpcb uses H Oz copper and 1Oz copper in the PCB. Also, the additional copper plating is added to the circuit as well.

  • Cover layer and Solder mask

The cover layer is an insulating material that covers the copper circuitry in the flexpcbs. The solder mask is not used in the flexpcb due to its hardness but the cover layer is the most suitable for the dynamic flex PCBs. The adhesive material is used to join the copper traces and cover layer.

Cover layer and Solder mask

The cover layer comes in a different thickness of 0.5mil to 5mil of polyimide and for adhesive, the range is 0.5mil to 3mil. Heavy copper weight PCB consumes the more adhesive material.

While Ordering the Flex PCBs, customers need to specify their requirements to the PCB fabricator which is very suitable.

 

Classification of Flex PCB

  • Simple Single Sided Flex PCB

Simple Single Sided Flex PCB

Simple single sided Flex PCBs have a one-sided copper foil. In the flex, the solder mask covers the copper circuit. Instead of a solder mask, there may be a cover layer. The cover layer and the solder mask have the same function.

Same single side flex with Stiffeners see the example below:

single side flex with Stiffeners

cover layer pcb

  • Double Sided Flex PCB

A double-sided flex PCB has a flexible polyimide core with a common thickness range from 1-5 mil thick.

See the example below for double-sided flex with the different stiffeners:

double-sided flex

The manufacturing process for double sided Flex PCBs and multilayer Flex PCBs is the same as the Rigid PCB manufacturing process.

  • Multilayer Flex PCB

Multilayer flex PCB is a complex advanced circuit board, whose structure includes flexible substrates, copper layers, adhesive layers, coverlays and overlay films. It has the flexibility advantage of flexpcb and the high space efficiency of the multilayer PCB. It can realize more complex circuits in a smaller space while adapting to various small spaces and unconventional shapes. Therefore, this type of board is mainly suitable for wearable devices such as smartphones, tablets, etc. that can have compactness and complex functionality.

The specific structure diagram is shown below:

Multilayer Flex PCB

Advantages of the Flex PCB

  • Three-Dimensional Solution: The finished product is flexible to use and allows the electronic components to be in an optimum location in the product used by the consumer.
  • Reduce Assembly Cost: Before the flexible PCB boards, the different circuits and components need to be purchased and assembled. In the flex circuit, the number of interconnections is reduced to only one.
  • Eliminate Human Error: When there is a different interconnection of wire, it creates human error. It is especially true that flexpcb eliminates human error.
  • Reduce Weight and 3Volume: Flex circuits are light in weight, so the final product reduced the weight and saved space compared to the rigid boards.
  • Dynamic Flex: The flex circuits are designated to be flex and fold. It can be banded in three dimensions. This PCB has a more banding cycle and improves the product’s appearance.
  • Improve Thermal Management: A flexible PCB board is suitable for high-power devices because its materials are suitable for high temperatures, which is beneficial to increase the service life of electronic products.

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