1. The meaning of the solder mask layer is to open a window on the green oil of the entire solder mask, in order to allow welding!

　　2. By default, areas without solder mask must be coated with green oil!

　　3. Paste mask layer for SMD packaging! SMT encapsulation uses: toplayer layer, topsolver layer, toppaste layer, and the toplayer is the same size as the toppaste layer, but the topsolver is one circle larger than them. DIP encapsulation only uses the top layer and multi layer layers (after some decomposition, I found that the multi layer layer is actually the top layer, bottomlayer, top layer, and bottomlayer layers with overlapping sizes), and the top layer/bottomlayer is one circle larger than the top layer/bottomlayer.

　　Question: Is the statement 'tin or gold plating only occurs when the copper layer corresponding to the solder layer has copper' correct? This sentence is from a person who works in a PCB factory. His meaning is: to make the effect of tin plating on the part painted on the solder layer, the corresponding solder layer part should have copper skin (i.e., the area corresponding to the solder layer should have a toplayer or bottomlayer layer part)! Now: I have come to a conclusion: "The copper layer corresponding to the solder layer is only tin or gold plated when there is copper in the copper layer" is correct! The solver layer represents an area that does not cover green oil!

　　Different layers of PCB

　　1 Signal layer

　　The signal layer is mainly used for arranging wires on the circuit board. Protel 99 SE provides 32 signal layers, including Top layer, Bottom layer, and 30 MidLayer.

　　2 Internal plane layers

　　Protel 99 SE provides 16 internal power layers/grounding layers. This type of layer is only used for multi-layer boards and is mainly used for arranging power and grounding wires. We refer to double-layer boards, four-layer boards, and six-layer boards, which generally refer to the number of signal layers and internal power/grounding layers.