Microscopy - Thermal Damage of PCB at 40x Magnification
Thermal Damage of PCB at 40x Magnification

How microscopy help you to identify thermal damage of PCB in time.

Thermal degradation is not always a result of too high a temperature. We can see the reasons for this if we take a closer look at the process of heat transfer. When something needs to be heated, several factors play an important role. Firstly, the temperature, which has to be transferred to the object. Secondly, the heat transfer. The heat transfer in the oven is better with circulating air than without and in the pot with boiling water even better. Third factor is the duration of the temperature effect. The longer the temperature can act, the more homogeneous the heat distribution.

Heat Transfer: Oven wihtout Convection, Oven with Convection, Pot with Boiling Water

So far, so good. Now let’s have a look at a thermally damaged printed circuit board. If the temperature is right, the heat transfer is guaranteed and the duration of heat exposure is correct, how does thermal damage happen?

This is where heat transfer comes into play. A PCB theoretically consist of the substrate – a relatively good insulator, circuit paths that conduct heat excellently and solder resist – a relatively good insulator. In practice, however, there are also voids, contaminations, non-reacted components from the PCB substrate and solder resist, as well as embedded moisture.

A closer look at a microscopic image of the circuit board clearly shows that the thermal damage occurs at the contact area between the circuit board substrate and the circuit path. Why is this so? The reason is areas with voids, which provide excellent insulation and ensure that the heat cannot spread any further. This results in thermal damage at the interface. At this point, the contact area is too small and the heat cannot spread.

Critical Areas between Solder Resist and Circuit Path at 100x Magnification

What usually remains hidden to the eye can be very easily observed with microscopy at a 100x magnification. Critical areas can also be quickly identified before the soldering process. So, if thermal damage occurs in the PCB, the quality of the PCB must be analyzed more closely, in addition to the soldering process, as a possible cause.

After all, the causes of quality problems usually start with small deviations in the production process and can be easily avoided by early identification. So, look closely, identify in time, act!