JLCPCB 4 layer pcb stack mentions a copper core as the image attached. Is this a error or the layer 2 and 3 are wittingly in short?

This image makes no sense...

Taken from: https://cart.jlcpcb.com/impedance?_ga=2.35895136.1315427483.1592868937-1547839306.1592059153

enter image description here

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    \$\begingroup\$ That is a bit confusing. I've ordered "metal core" and "copper core" PCBs that had a signal layer, then a dielectric like FR4, then a thick metal layer for rigidity or heat dispersion. In this case "core" means a rigid FR4 with copper on top and bottom. Then they press prepreg on top and bottom and then copper on top and bottom of that to get 4 separate layers (that's simplified). I'm sure you're getting a 4 layer board but I would double check directly with the board house to be safe. I've been surprised before with this kind of thing, especially when language translation is involved! \$\endgroup\$
    – 65Roadster
    Jun 23, 2020 at 0:13
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    \$\begingroup\$ Note that in general, core, prepreg, and b-stage layers do not count towards your layer count. So what you've shown I would call a 4-layer PWB. \$\endgroup\$
    – SteveSh
    Jun 23, 2020 at 0:33
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    \$\begingroup\$ The Orange is meant to be a separate 2 layer board while the other layers are prepreg and Cu foil and probably bad english translation. rearranged say (copper with core) \$\endgroup\$ Jun 23, 2020 at 2:15

3 Answers 3


The ‘close parentheses’ is in the wrong place, which why this is confusing.

It should say “1.1 mm (with copper) core”, which is exactly the total of the two 17.5um copper layers and the 1.065mm FR-4 core.


It may help to visualize how PCB stackups are produced

Internal Copper layers are actually provided to your PCB manufacturer as raw material in the form of unatached sheets of copper, they are etched and cut before being glued onto a fiberglass substrate (known as " prepreg layer ") and these are glued together to create a stackup.

Copper layers come in several standard "weights" which dictate the thickness, which is on the order of 0.5-2 thousandths of an inch.

Prepreg comes in a variety of standard thicknesses , typically on the order of 1-20 thousandths of an inch.

To create rigidity, a solid "core" of thicker fiberglass is also used, with several , slightly thicker , standard thicknesses. This material may have copper pre attached for e.g. 2 layer applications which resembles proto PCB material. It is more or less "fat prepreg"

Typically a core is 20-60 thousandths of an inch. And it forms the bulk of the material of a PCB.

A 2 layer board is all core.

A 4 layer board can either use 2 cores and one prepreg but typically 2 prepreg layers and one core. It is somewhat easier to produce in this arrangement. . This results in close spacing between layer 1-2 and layer 3-4 vs close spacing between Layer 2-3 (2 cores)

A good MFG allows you the freedom to select your stackup, maybe for a premium if it requires special steps or "nonstandard" material for them.

There are sometimes reasons, dictated by application, to pick one vs another but it is normal to have such small spacing between layers in a multi layer board.


The core is just that - the core of the PCB. It's not made out of conductive material. The total width of core and inner layers is shown for your reference only.


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