What is PCB failure
To begin with, PCB, or simply “board,” is a laminated structure that comprises conductive and insulating layers. In nearly any electronic device, PCBs are needed to connect components by conductive pathways and signal traces. This foundational building block is rather not-sustainable at all and can fail because of numerous reasons.
But what’s actually PCB failure? It is simply malfunctioning of this component, resulting in the inadequate working of a device. You may spot refusal to fulfill some functions or difficulty operating in any other way. In the worst-case scenario, an electronic device cannot be activated. Thus, you may know that is PCB failure.
What Causes PCB to Fail?
It is frequent that poor component design is associated with bad placement of parts, overheating of boards, etc. We detailed it further in the text. But there are two more nuances that are rarely discussed.
The printed circuit board is a widespread piece of electronics any manufacturer knows how to approach. Conductive lines, resistors, diodes, pads, and other parts of a PCB are typically well-designed to function effectively.
However, it happens that this layered structure made of various electronic components does not work well. Causes are multiple and hard to predict. Sometimes, design issues are associated with certain modifications of PCBs. Good news: this problem is almost always detected before the board has already been used as parts of numerous devices.
Appropriate selection of materials and the type of solder paste significantly affect the sustainability of the board. It is vital to consider the properties of any substance needed in PCB manufacture. Typically, lower strength, flexibility, and conductive properties result in the production of entire batches of boards of poor quality.
This defect is closely linked to the choice of materials done on the stage of design. A typical consequence of such a defect is the premature failure of a PCB. It is commonly accompanied by any other factors, gradually deteriorating electrical components.
As such, board materials with a low coefficient of thermal expansion (CTE) can be easily degraded if exposed to excessive heat during operation. Alternatively, it is the solder that may cause a defect. Thus, lead-free solder is due when an extreme temperature is predicted.
Assembly of a PCB is a complex process due to the need to align multiple layers perfectly. Issues that may occur are opens, shorts, or crossed signal lines. The manual or automated optical inspection often finds such deteriorations. But, there is still a chance for a finished device to start malfunctioning because of the defect in its PCB.
Well, from the name of the problem, it is evident that an issue with the shifting of components of a board may occur. Typically, workers do not place electrical micro components manually. However, any CNC machine for assembling is not deprived of errors that may happen with a certain probability due to the following reasons.
- Exposure to vibration.
- Deterioration of the software
It is rare that components moved because of the vibration are placed further incorrectly. Typically, they are rejected by a CNC machine assembling a board. However, an error in the software that is responsible for checking the correct positions of a part may allow component shifting.
- Excess of solder paste
It is crucial to deposit a sufficient amount of solder paste on the pads of PCB. Excess of paste typically makes a component float and move. Recommended pasta deposition is 6 mils (thousandth of an inch in length) for small components. You will find more information about soldering issues further in the text.
Physical or mechanical stress is another frequent reason for an electronic component to not function well. PCBs are not an exception. Not necessarily it should be a direct physical impact. Repeated shock or vibrations applied to a device containing a PCB within may easily cause a board to break. Flex boards are more sustainable but still may be deteriorated if their strength ratings are exceeded.
This one is simple. It happens when laminate applied to a PCB’s layers detaches from the material. The typical cause is inadequate CTE of material used. It is commonly accompanied by the unsuitable thermal requirement of the environment in which a board was installed. Such an issue is never a user’s blame unless physical interference has taken place.
This term is typically attributed to biotechnology or any other related discipline. But in engineering, contamination is referred to as the presence of substances/particles/liquids that interfere with a component’s normal functioning.
About 15% of PCB failures occur because of ionic contamination, e.g., negatively or positively charged atoms or molecules. Some other substances may also residue on a PCB.
- Both organic and inorganic acids.
- Flux activators.
Typically, contamination is a result of lack of board cleanliness or, in contrast, application of aggressive chemistry to a device’s surfaces.
Sounds impressive, isn’t it? Typically, exposure to direct flame results in complete deterioration of the entire board. PCBs are comparatively sustainable to heat until it exceeds 170°C. However, long term operating of a board at 145°C or above may also cause components to burn.
Direct extreme heat is not the only cause of burnt components. Thus, in the case components are placed close together (see component design above), they may heat up each other. It impacts the performance of adjacent parts, causing heat-related defects.
Finally, components may not be protected from the voltage correctly. As a consequence, chances for the component to burn from the power surge are greatly increased.
It is not about the weather outside but rather the operational environment within which a PCB is operated. Not only on the stage of fabrication but during its exploitation, any electronics is highly vulnerable to any stresses. The crucial of factors are the following:
- Temperature Fluctuations
This problem arises because of exposure of a device to sunlight and outdoor temperatures. Alternatively, electronics may be heated by external sources nearby. Add to it the inner temperature, caused by heating, in the process of working, components of a board. Solder joints can be cracked and electronic melted if a PCB is impacted.
Moreover, rapid changes in the external temperature are even more destructive than heating a board up. If a device is brought from outdoors during the warm season and, abstractly, put into the refrigerator, the temperature difference would deteriorate electronics even faster.
We all were told in physics classes about the inverse dependency between temperature and relative humidity in the air. Moisture is the drops of water resulting from rapid change in the temperature of the environment. The condensed liquid can easily deposit inside an electronic device. And, as you may know, water is the primary hazard for components, one of which is PCB.
Dust is presented with microparticles of different nature. It may contain contaminants mentioned above or just deteriorate solder paste. Both issues lead to PCB failure because of inadequate flow of signal via connections. Manufacturers of electronics expect users not to sink devices in the sand, but in contrast, clean them from dust from time to time
Solder paste was mentioned above multiple times. Basically, this substance is needed to create electronic connections between a PCB’s pads and surface mount devices (resistors, capacitors, etc.). Paste is typically made from powdered solder, and applied in a controlled environment in a precise measure amount. Let’s look at the types of defects raised from inadequate soldering.
- Opens of PCB that make components lose connections to mount devices.
- Excessive solder that leads to the floating of PCBs, and once again, to the loss of connections to other components.
- Previously described component shifting is another explanation to the way how soldering paste can be applied inappropriately and deteriorate a PCB’s functioning.
- Lack of solder paste causes “cold joints,” i.e., not covering all the routes and connections, making them malfunction.
- Solder bridges, or in other words, connection via solder paste between two components that are not designed to be connected.
- Webbing and splashes of solder paste reduce the quality of a PCB functioning in many ways.
- Finally, pads may be lifted because of the mistake in solder paste applying, which results in sub-quality elect
Well, we could have written here “people make mistakes,” and that’s it. Indeed, even great professionals involved in the manufacturing of PCBs can be a reason for a defect to occur. Let’s review the ways labor can interfere with the normal production of boards.
- Misreading a schematic. In other words, a sequence of layers and positioning of components may not arise from a CNC machine’s error. Sometimes, an engineer plans the production cycle incorrectly, causing near to all component design and burn defects.
- Incorrectly installed components. It is not common to position parts manually, but some such steps may be involved and may be done with an error. Alternatively, a CNC machine could have been programmed by a specialist inappropriately.
- Placing traces too close to each other. This mistake is also attributed to the design of a PCB by a specialist.
- Poor soldering. In case this procedure is done by labor, the risk of improper soldering raises exponentially. You already know the consequences by far.
Aging of Equipment
Now, consider it this way. Any equipment unit has a limited lifespan. As a rule of thumb, manufacturers expect their primitive electronic devices to work for a year or two. More expensive and well-protected pieces of electronics have up to 5 or even 10 years warranty. However, sooner or later, every top-quality component will fail and will require replacement.
All the points mentioned above can also be seen as factors lowering the lifespan of a PCB.
At this point, it is likely that you already have an established insight into PCB failure caused by excessive heat. But since those explanations were related to other factors, let’s just summarize everything and add a bit more. Exposure to heat and moisture (conceived by excessive humidity in the air) is a cause of thermal stress. Already heated components would become overheated, and thus, almost certainly would fail.
And the kicker is the expansion of materials under thermal stress. It is just that some materials can be deformed by heat and humidity working collaboratively. Even a minor deterioration may lead to losing some connections, and consequences of which you are aware.
It seems like the range of factors that lead to multiple defects is so broad that it is hard to expect any electronic to function well long-term. However, the optical examination can allow a rare sub-quality component to the next stage. In most cases, PCBs are the least problematic parts.
In their turn, a user can often prevent PCB failure, helping their electronic devices to function well for a longer period.