Single-sided to multilayer: how many layers does your board have?
The number of copper layers is the single most important factor for how easily an old board can be recaptured. Here is how the common types are built and how you can tell them apart.
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Single-sided boards (1 layer)
Copper on one side only, components usually on the other side with their leads pushed through holes. Typical for older consumer electronics, power supplies and simple controls. Often made of phenolic paper (FR-2, recognisable by its brown colour and the smell when heated) rather than glass-epoxy.
For reverse engineering, single-sided boards are the easiest case: everything is visible.
Double-sided boards (2 layers)
Copper on both sides, connected through plated holes (vias). This is the most common type in industrial electronics from the 1980s onwards. Base material is usually FR-4 glass-epoxy.
Both sides can be scanned; the vias tell us where the layers connect. Components on both sides or under large parts need extra care, but the data can be captured completely without destroying the board.
Multilayer boards (4, 6 and more layers)
Additional copper layers are laminated inside the board, often as continuous ground and supply planes, sometimes with signal traces. A four-layer board looks like a double-sided board from the outside – the inner layers are invisible.
To capture inner layers you need X-ray imaging or controlled grinding of a sacrificial board layer by layer. That is why we handle 1–2 layer boards as standard and multilayer boards on request, together with a specialised partner.
How to tell how many layers a board has
- Hold the board against a strong light: on a 1–2 layer board you see light through areas without copper; inner planes block the light.
- Look at the edge of the board or at a cut-out with a magnifier: thin copper lines inside the laminate indicate inner layers.
- Vias that do not connect to any visible trace on either side usually go to an inner layer.
- Old fabrication drawings or a layer number printed near the edge (e.g. L1, L2, L3, L4) give a direct answer.
Not sure? Send us sharp photos of both sides and the edge. We tell you in the assessment.
Base materials at a glance
| Material | Typical use | Note for rebuilds |
|---|---|---|
| FR-2 / phenolic paper | Old single-sided consumer boards | Rarely offered today, usually replaced by FR-4 or CEM-1 |
| CEM-1 / CEM-3 | Cost-optimised single and double-sided | Still available, mechanically weaker than FR-4 |
| FR-4 | Standard for 2 layers and multilayer | Default choice for most rebuilds |
| High-Tg FR-4, polyimide | High temperature, lead-free soldering, aerospace | Specified in the fabrication drawing when needed |
Questions
Can you rebuild a 4-layer board?
Yes, on request. Inner layers need X-ray or destructive analysis of a second board, so effort and price are higher than for a double-sided board.
Does the rebuilt board have to use the same material?
Not necessarily. Old materials such as FR-2 are hard to get. We specify a current equivalent and document the change.