The purpose of tin plating on PCB circuit boards is to prevent bare copper from reacting directly with oxygen in the air, causing oxidation of the board surface. In addition, tin plating is also helpful for PCBA surface mounting, which can be directly melted and used for plug-in, accelerating welding efficiency. So what is the reason for the PCB circuit board not being soldered? Let's take a look below.

　　There are several reasons why PCB boards are not soldered:

　　1. PCB circuit board oxidation, PCB board not tin coated.

　　2. The temperature of the furnace is too low or the speed is too fast, and the tin has not melted.

　　3. If there is a solder paste issue, you can try changing to another type of solder paste.

　　4. The most common issue with battery cells is that they are usually made of stainless steel and require electroplating with a layer of chromium before tin can be applied. If there is oil or poor electroplating on this electroplating layer, it may not be able to solder. You can try using a soldering iron to see if it can be soldered, or put some solder paste on the battery cells, and then use a soldering or electric heating table to heat up and see if the battery cells can be soldered.