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6 Layer PCB Manufacturing - How is a 6-layer Circuit Board Made

PCBONLINE Team

Tues, Mar 29, 2022

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A PCB layer refers to a copper layer, and the PCB layer number means the copper layer number. A 6-layer printed circuit board, by its name, means the circuit board has 6 layers of copper circuit layers. 6-layer PCBs have a compact component layout and reduce manufacturing costs. Usually, consumer electronics and cost-effective products apply 6-layer PCBs.

How is a 6-layer PCB manufactured? This post reveals 6-layer PCB manufacturing from the below content.

Part1: Basic Structure of 6 Layer PCBs

A 6-layer PCB is composed of a PCB core that has two PCB layers, and two layers on its two sides. It belongs to multilayer PCBs.

A PCB core consists of a substrate material layer and two copper layers. It is cut from a double-sided copper-clad laminate. Between the copper layers and the PCB core is the prepreg. Prepreg and PCB substrate are the same materials, but only that prepreg is semi-cured, while the substrate is cured. An external PCB layer consists of a prepreg riveting with a copper foil.

The 6 layers include signal layers, ground (GND) layers, and power layers. The top layer (layer-1) and bottom layer (layer-6) must be signal layers. The four internal PCB layers include 2 signal layers, 1 ground layer, 1 power layer, or 1 signal layer, 2 ground layers, 1 power layer. So there are 4 6-layer PCB stack-ups.

6-layer PCB stackup 1

6-layer PCB stackup one: signal1-GND2-signal3-signal4-power5-signal6

6-layer PCB stackup 2

6-layer PCB stackup two: signal1-signal2-GND3-power4-signal5-signal6

6-layer PCB stackup 3

6-layer PCB stackup three: signal1-GND2-signal3-GND4-power5-signal6

6-layer PCB stackup 4

6-layer PCB stackup four: signal1-GND2-signal3-power4-GND5-signal6

Part 2: 6 Layer PCB Manufacturing

A 6-layer PCB is manufactured by laminating PCB layers on the PCB core. Once the circuit is etched on the PCB core and the third and fourth layers are done, the second and fifth layers are laminated on the core under high temperatures and high pressures. Then the circuit is etched on the second and fifth layers. And the top and bottom layers are also laminated on the 4-layer board and the circuit is etched. And the solder mask is spayed on the top and bottom layers and the surface finish is processed on the PCB pads.

You may ask, how about drilling on the 6-layer PCB, and how is the circuit etched on the copper layer?

Two circuit etching methods can be the PCB layers. Choosing which methods depends on whether the layer requires to be drilled with HDI vias. The two circuit etching methods are:

  • Positive plane etching - the etching liquid is lye, and this method is used on PCB layers that don't require HDI via drilling. Its process - the UV light casts the circuit pattern on the copper layer that has been printed with a UV-sensitive film. The film on copper under the circuit pattern shadow is still liquid, and the film on unwanted copper hardens. Then the liquid film is washed away. And then tin is plated on the exposed copper as a protective layer. Next, the dry film is peeled off. Finally, the exposed unwanted copper is etched away with lye, and only copper in the circuit pattern remains.
  • Negative plane etching - the etching liquid is acid, and this method is used on PCB layers that require HDI via drilling. Its process is - the UV light casts the circuit pattern shadow on the copper layer that has been printed with the other type of UV-sensitive film. The film on copper under the circuit pattern shadow hardens, and the film on unwanted copper is still liquid. Then the liquid film is washed away. And the exposed unwanted copper is etched away with acid. Finally, the dry film is peed off, and only copper in the circuit pattern remains.

For the PCB core, both circuit etching methods can be used; for the top and bottom layer, only positive plane etching can be used.

If PCB holes of the 6-layer PCB are only PTH holes, the PCB board is mechanically drilled after lamination, and then the PTH holes are electroplated with copper for circuit layer connection.

For the 6-layer HDI PCBs, the top layer, bottom layer, second layer, and fifth layer are laser-drilled and electroplated before lamination. The PCB core is plated-through laser-drilled and electroplated before lamination.

Part 3: 6 Layer PCB Manufacturer - PCBONLINE

PCBONLINE is a reliable 6-layer PCB manufacturer founded in 1999, with two large PCB manufacturing bases and one PCB assembly factory. We can manufacture and assemble advanced PCBs from 1 to 60 layers, so 6-layer PCB manufacturing is also available to order.

Here are reasons for you to work with the 6-layer PCB manufacturer PCBONLINE:

    • Our 6-layer PCB manufacturing capability can meet HDI requirements, and high-speed or high-frequency circuit design demands.
    • We have rich experience in manufacturing 6-layer PCBs, such as 6-layer FR4 PCBs, 6-layer Teflon-based PCBs, 6-layer flexible PCBs, 6-layer rigid-flex PCBs, etc.
    • Free and professional one-on-one design/engineering support for your 6-layer PCB project.
    • ISO 9001:2015, IATF 16949, IPC, REACH, UL, RoHS-certified one-stop 6-layer PCB manufacturing.
    • Free DFM, DFT, DFX for 6-layer PCB manufacturing and assembly, with no minimum order limit.

If you want 6-layer PCB manufacturing or assembly, or if you have any concerns about 6-layer PCB design or manufacturing, please feel free to send your Gerber/IPC-2581 and messages to PCBONLINE by email at info@pcbonline.com.

Conclusion

6-layer PCBs can contain 4 signal layers, 1 ground layer, 1 power layer, or 3 signal layers, 2 ground layers, 1 power layer. And there are 4 types of 6-layer PCB stack-ups. After introducing the structure, this post reveals the 6-layer PCB manufacturing process. If you have any words about the content in this post, welcome to leave your comments.