It’s fair to say that printed circuit boards’ UK existence isn’t an ideal one as they and moisture are not happy bedfellows. The UK has plenty of moisture it can throw at anything with a PCB in and we all have a tale or two of a much loved but deceased mobile phone that had an argument with a raincloud/puddle/toilet. With every year in Britain seemingly getting damper and more of our lives involving electronic equipment that we take outdoors, it’s important to be aware of the problems circuit boards can suffer with.
If a printed circuit board surface becomes contaminated with moisture, the resistance between the tracks and pads can be lowered and this can in turn lead to metal corrosion. Furthermore, it could result in metal filaments forming, growing between tracks on both rigid and flexible circuits and between the oppositely charged metal terminations or between connector pins. This is very likely if you have water, applied voltage and ionic contamination.
It becomes an electrochemical process with the metal dissolving at the anode and then electro-deposited at the the cathode. This resultant metal deposit usually forms as dendrites.
These dendrites can form rapidly as silver or copper, tin or lead or even a combination of metals and, once formed, can cause short circuit. These circuit failures can be rapid – from just half an hour, depending on the voltage applied , the contamination level, and amount of moisture. At the other end of the scale, it can take a few months.
The short circuits occur when they bridge tracks or between pads. Occasionally this can be serious, causing arcing and fires.
Ionic contamination can be caused by the fluxes used in the soldering processes. These could be from grubby hands or even just from atmospheric dust. There are however tests developed back in the 1970s that will measure the contamination level. Basically, washing the printed circuit board in a solvent and measuring the ionic conductivity across the total board area. The contamination result is the average value over the whole PCB surface.
UK Printed circuit board manufacturers are frequently asked to make sure their products meet contamination specifications as cleanliness testing becomes a routine procedure.
Despite the fact that electronics used in dry conditions shouldn’t suffer from the above issues, there can be times when the temperature fluctuates wildly that condensation can appear on the PCB surface. It’s fair to say that the UK suffers from variable weather. Even if it was constantly dry (summer of 76?) there can be problems caused an increased risk of static discharge.
Because of this, highly sensitive electronic equipment is only used in closely controlled environments, monitoring the temperature and humidity. Fortunately, the printed circuit boards UK consumers most often use are not that sensitive and so our daily lives aren’t interrupted too much by the vagaries of our climate.
Unless you have an iPhone that is.