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Multilayer Flexible Circuits

The multi-layer flex circuit refers to a flex circuit with more than 2 layer circuit layers. Three or more flexible conductive layers with flexible insulating layers between each one, which are interconnected by way of metalized holes through the vias/holes and plating to form a conductive path between the different layers, and external are polyimide insulating layers.

Normally a multilayer flexible circuit is a combination of several double-sided flex circuits and single-layer flex circuits, so there’s no already existing flexible copper-clad laminate. The multi-layers may or may not be continuously laminated together throughout the production process. If your design needs require maximum flexibility, continuous lamination may not be appropriate.

The multi-layer flexible circuit made of polyimide is at least 1/3 lighter than rigid FR4 PCB, but as there’re several layers, it loses the flexibility of single-sideddouble-sided flexible PCB, but most of these products are not required for flexibility. The most popular multi-layers circuit are 4L and 6L and 8L. 10L or a circuit of more than 10L is seldom used in the market.

Multilayer Flexible Circuits

Multilayer Flexible Circuits

When to use & Feature of Multi-Layer Flex

Eliminating the need for complex welding processes, multi-layer flex circuits board have tremendous functional differences in terms of higher reliability, better thermal conductivity, and more convenient assembly performance. And also, has excellent electrical properties such as a low dielectric constant. So multi-layer flexible circuits are an effective solution when the following purpose & characteristics are needed:

  • 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 4-layer flexible circuit:
 

There are more complex interconnections, layer design surface mounting. Click to see more stacked multi-layer flex circuits.

 stack up of multi-layer flex circuits

Multi-layer flexible printed circuit boards can be further divided into the following types:
1) Normal stack up All the layers are laminated to each other, without separating between each layer, it loses its inherent flexibility after lamination. The more layers circuit has, the less flexible circuit will be. 

2) Unbonded/Separated stack up:  Each layer or several layers are separated from each other in the center portion, so they are unbonded in the center area and electronically connected at both end of the flexible circuit. The flexibility is much better than normal stack-up.
 

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:  

  • Multilayer circuitry-from 3 to 14+ layers
  • Min LW/LS: 4mil/4mil
  • Adhesive-based and adhesiveless constructions, including thermoplastic and thermoset stiffener attachment.
  • Polyimide substrates: 1/2mil – 4mil
  • Copper: 1/3OZ – 2OZ, RA or ED type
  • Stiffeners include Polyimide (0.075-0.20mm), FR4 (0.15-2.0mm), and punched or formed metal parts (0.075-1.0mm)
  • Low-cost, conventional fabrication and lamination completed with PTH based plating
  • Screened inks, photo-imageable soldermasks, or laminated coverlay dielectrics
  • Surface finishes: ENIG, electroplated nickel/gold, immersion silver, tin,
  • EMI Shielding

As a professional manufacturer of a multi-flex circuit boards in China, Best Technology 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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