No-copper PCB means there is no circuitry on the board but there is base material and optional presence of holes, solder mask, and silkscreen. That means the PCB is without a copper layer (no track and no copper area). No-copper PCB is never used to perform any electrical functions. No-copper PCB should be used for mechanical supports; sometimes it is used for providing height and width; sometimes it is used for decorative purposes; there may be many uses, but it is never used to provide electrical connections or circuitry as there is no copper on the board.
Let's see how a no-copper PCB is constructed and what kind of layer forms on a no-copper PCB.
Vid.1: No copper PCB construction
As we saw in the no-copper PCB construction video, there are a few unfamiliar terms for you: solder mask and silkscreen. We must know about solder masks and silkscreens (also known as overlays and legends).
Solder mask is nothing, but it is nonconductive INK, which is used to provide isolation between two open nets or pads. Moreover, solder mask protects our whole circuits (the copper area) on the PCB from external damage as it covers most of the copper area. We can usually provide solderable pads open from solder mask INK to provide connection with components. See the image below for a better understanding of solder masks.
Fig. 3: Solder mask layer on single layer PCB
In Fig. 3, we saw a solder mask layer on a single-layer PCB. Now, in your mind, the question should be, "Why did the customer require a solder mask on the no-copper PCB? —as there is no copper present and no component needs to be soldered on a no-copper PCB ". The answer should be to protect the base material or to colorize the PCB to make it look better.
Silkscreen (also known as legends or overlay):
Silkscreen is used for adding some text, symbols, and component naming (also known as designators) to the PCB. The naming of components on the PCB will aid the engineer during the assembly process. At the time of assembly, engineers watch component designators on the PCB and make sure their location is correct while installing that component on the PCB. Furthermore, there is a polarized component marking on the silkscreen that indicates the correct component direction. Some customers add their own company logo, date code, and drawing to the silk screen layer. For a better understanding of what silk screening is, see the diagram below. I have added both sides of the silkscreen to the single-layer PCB. Generally, silkscreen should be on one side and always on the opposite side of the copper layer for single-layer PCBs.
Fig. 4: Silkscreen layer on single layer PCB