PCB Technical - What is the reason why the solder pads are not tinned on the PCB circuit board

Our common computer boards are basically double-sided PCB circuit boards based on epoxy glass cloth, one side of which is for inserting components and the other side for component soldering.

We can see the solder joints very regularly. The discrete soldering surfaces of these solder joints are called PCB pads. Why is the copper wire pattern not tinned?

Because in addition to the soldering pads and other parts, the surface of the other parts has a layer of solder mask that is resistant to wave soldering. Most of the surface solder resist ink is green, and a few use yellow, black, blue, etc., so solder resist oil is often called green oil in the PCB circuit board industry. The role of green oil is to prevent bridging during wave soldering, improve soldering quality and save solder.

It is also the protective layer of the PCB printed board, which can prevent moisture, corrosion, mildew and mechanical scratches.

From the appearance point of view, the surface is smooth and bright green solder mask, which is photosensitive and thermally cured green oil for film on the board.
Not only does the appearance look better, it is also important that the pad has a higher accuracy, which improves the reliability of the solder joint.

There are several situations where the PCB board cannot be tinned.

1. The PCB circuit board is oxidized, and the PCB board is not tinned.

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

3. For solder paste problems, you can try another solder paste.

4. The battery problem, this is the most common problem, because the battery is generally stainless steel, and it needs to be electroplated with a layer of chromium to be tinned.

If the plating layer is oily or the plating is not good, it will not be tinned. You can try to solder with a soldering iron. Or put some solder paste on the battery, and then use a desoldering station or electric heating station to heat it to see if the battery can be tinned.

The above is the double-sided PCB circuit board introduced by the editor. What causes the pad to not be tinned.