The advantages and disadvantages are obvious:

　　Advantages: Low cost, flat surface, good weldability (without oxidation).

　　Disadvantages: It is easily affected by acid and humidity and cannot be stored for a long time. It needs to be used up within 2 hours after opening the seal, as copper is prone to oxidation when exposed to air; It cannot be used on double-sided boards because the second side has already oxidized after the first reflow soldering. If there is a Test point, solder paste must be printed to prevent oxidation, otherwise it will not be able to contact the probe well later.

　　Pure copper is easily oxidized when exposed to air, and the outer layer must have the above protective layer. And some people believe that the golden color is copper, which is a wrong idea because it is the protective layer on top of copper. So it is necessary to extensively gild the circuit board, which is the gold deposition process that I have previously introduced to everyone.