The definition of moisture is containing more water than that in the normal condition. Thus, the circuit board used in the moist environment, because the air contains comparatively large moisture, when the moisture is too large, it will turn into drops of water and fall off to the board. When the drops of water fall off to the board and disperse on the board, they will attach to each pin or line of the electronic component or PCB.
Because the applied electronic components at present are all SOP or SSOP SMT components, and the distance between pins is quite tiny, especially the SSOP packaged integrated circuit, so when moisture turns into drops of water and drops into the pins of the integrated circuit, if the circuit board is in an operating state at the moment, it will add an invisible resistance between the pins of the integrated circuit (Because water is conductive), and even leads to circuit-short and causes the circuit board in running to malfunction status.
If the drops of water turned by moisture drops into the pins of the electronic components in the circuit board, and the circuit board is just in the state of non-work or power-off, though it will not cause damage immediately, after the pins or printed lines are soaked by the drops of water, the pins of the components will rust, and over time, the pins will break and give rise to the circuit boards malfunction because of the rusting. When the printed lines are soaked by the drops of water, especially that the signal-convey lines are comparatively fine and after they are soaked for a period of time, there are situations that the printed lines will mould and break, which will result in such situation that the circuit board can’t work after being in use again.
For the reasons for malfunction of the circuit board caused by moisture, here are three pieces of conclusion:
1. The changes of circuit parameter will give rise to malfunction of circuit board;
2. The short of circuit board will result in malfunction of circuit board;
3. The break of signals handling lines of circuit board will lead to malfunction of circuit board.
You could make related measures according to the three pieces of conclusion for reducing or avoiding the situations that malfunction of circuit board you are in charge of caused by moisture.