Reasons for PCB failures
A populated PCB is a highly complex electronic assembly. Due to its complexity and non-redundancy, an error on just a single component can lead to complete system failure. PCB failure can arise from excessive mechanical, thermal, or electrical stresses, weaknesses created during production, and the natural aging of the components. It is also relatively common for components with insufficient specifications to be selected during product development.
The original fault may cause further damage to other system components, either immediately or over time, as a result of characteristic shifts, voltage peaks, and local overloading in other parts of the circuit.
Errors that only present sporadically for no apparent reason can be especially troublesome. Locating this type of error by a conventional repair process may be very difficult or even impossible.
crack in SMD capacitor;
Source: TechnoLab GmbH; Link:www.technolab.de
In rare cases such as bursting or burning, defective components can be identified visually by obvious external damage. However, it is much more common for the damage to occur at a microscopic level within the component. Damage can for example be caused by mechanical or electrical overloading of the PCB during operation. Mechanical weak points are often introduced during the manufacturing process of the circuit board if excessively large mechanical stresses are created during soldering when joining components with different expansion coefficients. The electrical properties of components also vary according to a natural aging process. For example, electrolytic capacitors lose their electrical capacity over time, and components traversed by strong currents experience “electrical wear”.
Cracked via due to mechanical stress;
Source: TechnoLab GmbH; Link:www.technolab.de
Defects on the PCB itself are usually caused by thermal or mechanical stresses which arise during operation. This can create microscopic cracks in the traces, pads, or vias. These defects can be especially difficult to identify, because they can sporadically alternate between working and not working on the circuit board for no apparent reason (“loose contact”).
Many electrical circuit boards now feature microprocessor or microcontroller systems managed by control software. This software is stored either in the processor or controller itself or separately in a memory chip. Early generations of rewritable memory drives such as EPROMs and flash EPROMs were based on MOSFET memory cell technology, which typically has a data lifespan of 10 to 20 years. In older memory chips, it is not uncommon for individual memory bits to switch state and stop the entire program code from functioning properly.