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Multilayer Flex PCBs

Multilayer Flexible Circuits

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The multi-layer flex circuit (Multilayer Flex PCB, Multi-Layer PCB,Multilayer FPC) pertains to a flex circuit featuring more than two circuit layers. Three or more flexible conductive layers, with flexible insulating layers in between each one, are interconnected by means of metalized holes via vias/holes and plating to form a conductive path among the different layers, and the external layers are polyimide insulating layers.


Typically, a multilayer flexible circuit is a combination of several double-sided flex circuits and single-layer flex circuits, thus there is no pre-existing flexible copper-clad laminate. During the entire production process, the multiple layers may or may not be continuously laminated together. If your design requirements call for maximum flexibility, continuous lamination might not be suitable.


The multi-layer flexible circuit made of polyimide is at least one-third lighter than the rigid FR4 PCB. However, as there are multiple layers, it loses the flexibility of single-sided and double-sided flexible PCBs, yet the majority of these products do not have a demand for flexibility. The most prevalent multi-layer circuits are 4L, 6L, and 8L. 10L or circuits with more than 10 layers are seldom utilized in the market.


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Multilayer Flexible Circuits（Multilayer FPC,Multilayer Flex PCB)

 

When to use & Feature of Multi-Layer Flex

Eliminating the need for complex welding processes, multi-layer flex circuit boards have significant functional differences in terms of higher reliability, better thermal conductivity, and more convenient assembly performance. They also have excellent electrical properties such as a low dielectric constant. Therefore, multi-layer flexible circuits are an effective solution when the following purposes and characteristics are required:

  • Unavoidable crossovers

  • Elimination of crosstalk

  • Ground and power plane applications

  • Used for EMI, RF shielding applications

  • Through-hole assembly

  • Specific impedance controlled

  • Up to 10 or more conductive layers

  • Unbonded regions to increase flexibility in bend region

  • Increased circuit density: Multilayer high circuit density system can handle multiple conductive layers to save space

  • High components density

  • Other customer-specified electrical requirements

  • Ideal for the aerospace and defense markets

 

Multi-Layer Flex Circuit Structure / Stack up


Here is stack up of a normal 14 layers Rigid +4-layers flexible circuit:
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There are more complex interconnections, layer design surface mounting. Contact us  to see more stacked multi-layer flex circuits.

Multi-layer flexible printed circuit boards can be further classified into the following types:


  1. Normal stack up: All the layers are laminated to one another, without any separation between each layer. It loses its inherent flexibility after lamination. The more layers the circuit has, the less flexible the circuit becomes.

  2. Unbonded/Separated stack up: Each layer or several layers are separated from one another in the central portion. Thus, they are unbonded in the center area and electronically connected at both ends of the flexible circuit. The flexibility is much better than that of the normal stack-up. Which is also called "Air Gap".


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Multi-Layer Flex Circuit Materials:


Multi-layer flex also allows for localized areas where stiffeners, pins, connectors, and components may be added, so the material is the same as double-sided flex circuits, all have core material, coverlay, stiffeners, PSA EMI/RF shielding.

 

 

Key Capabilities:  

 

  1. Multilayer circuits-from 1 to 10 layers

  2. Min LW/LS: 4mil/4mil

  3. Adhesive-based and adhesiveless constructions, including thermoplastic and thermoset stiffener attachment.

  4. Polyimide substrates: 1/2mil – 4mil

  5. Copper: 1/3OZ – 2OZ, RA or ED type

  6. Stiffeners include Polyimide (0.075-0.20mm), FR4 (0.15-2.0mm), and punched or formed metal parts (0.075-1.0mm)

  7. Low-cost, conventional fabrication and lamination completed with PTH based plating

  8. Screened inks, photo-imageable soldermasks, or laminated coverlay dielectrics

  9. Surface finishes: ENIG, electroplated nickel/gold, immersion silver, tin,

  10. EMI Shielding

As a professional manufacturer of a multi-flex circuit(Multilayer FPC,Flexbile PCB,Rigid-flex PCB), boards in China, I-TECH can always make your circuit board dreams come true. Welcome to contact us anytime for inquiries about multi-layer flexible circuits.




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