PCBA Fault Analysis and Defect Resolution Measures
The assembled PCB board (PCBA board) is the most important component in all electrical equipment and the global demand for PCBA has increased in the past few decades. With this increase in demand, the main focus of many PCB manufacturers now is to minimize faults within PCBs. Hence, an extensive understanding of common PCB faults is needed, specifically to target the root cause(s) and to have the appropriate knowledge to prevent these defects. This understanding is what ensures that high-quality PCBs are produced and eventually, a high-quality PCBA product. It is important to take notice of these points because they have a direct impact on the functionality and quality of the final PCB assembly. As with current advancements in technology, the complexity of PCBs is constantly increasing, which means that there is a higher probability of PCB assembly failure to occur. These failures can be categorized into four groups:
- PCB Design Defects Lead to PCBA Failure (e.g., insufficient clearance)
- Failure related to PCB manufacturing (e.g., over-etching, drilling errors and improper soldering)
- Damage caused by improper use of circuit boards (e.g., excessive use and cumulative damage/fatigue)
- Defects related to the PCBA storage environments (e.g., humid and/or dusty environments)
With great fortune, most PCBA failures can be prevented by having the right knowledge of PCB failures. Therefore, FS Technology recommends that you do not panic after discovering the fault of a circuit board and instead, give priority to fault analysis and troubleshooting. If you are a PCB designer or a PCB manufacturing industrialist, it is critical that you understand how a PCBA can fail under certain conditions. This blog post from FS Tech will discuss PCB assembly failure analysis techniques in detail and list some common PCBA failures while also analyzing the causes to find solutions.
PCBA Design Error Analysis and Remedies
Missing Solder Mask between Pads
A PCB copper layer typically has a thin, specific layer on the topmost surface known as the solder mask. The main purpose of this layer is to essentially act as a shield and form a protective layer between the environment and the conductive traces located in the copper layers of the PCB. It prevents these traces from interacting with other materials like metal or solder and thus, protects the assembled PCB from corrosion and electrocution.
If there is no solder mask between the pads (the portions of metal left exposed intentionally for soldering purposes) on a PCB, then there is a high probability of solder bridges occurring and a circuit board short between two adjacent pads on a PCB. There will also be less protection from corrosion on the PCB.
Remedy
This problem can be prevented by double-verifying the PCB design before sending it to turnkey PCBA fabricators. In some cases, oversight of design may occur but it is important that you give your design to fabricators who have a good track record of proper DFM checking protocols so that any problems can be detected before the design is materialized.
Electromagnetic Problems
Electromagnetic interference (EMI) and electromagnetic capability (EMC) are two different factors to consider in PCB design. EMI is considered noise in electromagnetism, such as unwanted or damaging effects of electromagnetic capabilities, while EMC is the production, propagation and perception of electromagnetic energy. If EMI increases past a certain limit, this could result in a defective PCBA board, which can happen due to flaws in circuit design.
Remedy
EMI can be minimized by increasing the ground plane of the PCB. Most 90-degree-angled components on PCBs produce more EMI so they must be avoided. On the other hand, shielded wires are best in the harness of assemblies as they absorb EMC and eventually can work to reduce EMI.
Module density is too high
After the fabrication of a PCBA board, a very high temperature is used to solder electronic components onto the PCB but during this process, other surrounding components could be burned if the PCB is too densely packed with components. Another problem with highly dense PCBA is that if the PCBA has to run faster, it will produce more heat and can become problematic. With tightly packed components, heat can remain trapped inside the PCBA, which then increases the probability of the overall PCBA burning or overheating. This sort of problem is usually the most difficult to handle because it destroys the electronic nature of other components along with the problematic, faulty component(s). There is a direct relation between overheating and damage to the circuit as an increase in heat results in more damage to the circuit and if heating damage is ignored in a PCBA, it becomes much more difficult to diagnose the board problems.
Remedy:
Any printed circuit board can absorb heat up to certain limits before its total failure and if the heat exceeds that threshold limit, it can create serious consequences down the line and make the PCBA permanently unusable. This problem can be mitigated by using proper size and structure to lower the component density on a PCB and allow more heat to dissipate instead of trapping heat inside the board. Having knowledge of the PCB component orientation guide can eliminate the root cause of the problem of a high density of PCB components.
PCBA Manufacturing Defect List and Solutions
Improper Soldering
Solder bridging or improper soldering is one of the most common among all defects in PCB assembly. Sometimes, solder bridging is referred to as “shorts”. Solder is a critical component of the PCB assembly manufacturing process as it is what keeps a component and its circuit electrically connected. However, it can occasionally become polluted and cause a PCBA failure. Solder can short circuit if it becomes conductive due to excessive moisture in the solder. Some frequent solder flaws, such as excessive solder used and/or lifted pads, all have various effects on the board. In addition to this, when there are abnormal connections between adjacent pads or traces, short circuits can result. Such bridges are mostly very small and thin so it can be difficult to detect them and if remained undetected, they can cause damage to PCB assemblies at a catastrophic level like the burn-up/blow-up of some electronic components. Improper soldering generally includes solder bubbles, dry soldering and cold soldering. All these defects can cause PCB failure and eventually lead to PCBA failure.
Remedy
X-ray visual inspection is one of the best precautions to detect improper soldering and solder bridges, which is even difficult to detect with the naked eye. In most cases, these soldering failures can be resolved by desoldering the PCB components and resoldering them properly.
Uncleaned PCB
Neglecting to clean PCBs is a common mistake made by most PCB manufacturers. There is no doubt that metal PCBs will be affected by various environmental conditions. Oil on the surface of the human body, sweat, oxygen in nature and humid environments can all be potential causes of PCBA damage. Thus, cleaning PCBs as required can reduce a lot of potential risks so most turnkey PCBA companies not only have advanced assembly equipment and perfect quality control systems but also attach great importance to PCB cleaning. The following are the PCB cleaning processes utilized and organized by FS Technology:
- water based cleaning
- Semi-aqueous cleaning
- Solvent cleaning process
- No-clean process
Plating Voids
Plated through-holes in a printed circuit board are copper-coated holes where electricity can pass from one layer to other layers of the PCB with the help of these holes. PCB fabricators usually create these holes through a specific drilling method to make holes pass through all layers of a PCB. After drilling, an electroplating procedure is followed to coat the outer exposed surface of these holes with copper to make them conductive.
Through the process of deposition, a thin layer of conductive copper is deposited to the PCB which, in some cases, is not perfect and can produce voids during plating. These plating voids are gaps in the copper plating which becomes problematic because such gaps in vias or holes are unable to conduct current between layers of the PCB. This results in improper functioning of the PCBA or even entire failure of the PCBA.
The main reason for such plating voids includes insufficient cleaning of drilled holes, contamination of plating material, rough drilling of holes and the formation of air bubbles while plating.
Remedy
Contamination of the plating material and rough drilling can be avoided by properly cleaning the holes and also purifying the plating material. To get a proper hole in the PCB, just make sure to fulfil manufacturer instructions at all times, like the recommended drill speed or required number of drill hits.
Damage caused by improper use of circuit boards
Cumulative Damage/Fatigue
The most common reason for PCBA failure is the presence of defects. During the process of assembling PCBs, flaws frequently manifest themselves.
PCBA damage can be caused by electrostatic damage (ESD) as PCBAs are particularly susceptible to ESD, and even though we can only feel ESD in the thousands of volts, the slightest discharge may cause a PCBA component failure. This failure may be hidden, in which case the PCBA will continue to work but will have decreased dependability, or it may be catastrophic. Reputable PCBA manufacturers such as FS Tech use a number of safety measures to prevent the risk of electrostatic discharge on the production floor. This consists of smocks that are resistant to ESD.
Component burning is also a sort of PCBA damage, which is why it is important to highlight this as it is a leading cause of PCBA failure. A burned component can necessitate replacing the entire circuit board rather than just a single component, depending on the severity of the damage. The following are the three primary reasons for burned components:
- Intense Heat: If a machine becomes too hot or if a circuit board is burned directly by flame, then there is an increased risk of a heat-related problem occurring.
- Improper Spacing of Components: On the PCBA, the performance of nearby electronic components could suffer if some components are packed too closely together since this could cause them to overheat. To prevent heat-related flaws, it is essential that PCBs are designed with the optimal amount of space. Of course, if you know how to choose a PCB manufacturer, this kind of problem is unlikely to arise. Take FS Technology as an example, when you choose our turnkey service, our PCB designers will provide you with professional design guidance, which can eliminate this problem from the root.
- Technical Faults: If the connections on a PCBA are not made properly or the voltage safeguards are not enough, there is a greater possibility that the PCBA will overheat and catch fire. Having specific instructions on how to connect something can help reduce the likelihood of a technician making a mistake.
Excessive Use
PCBAs have a lifespan that is more similar to that of humans than that of great wine. They start to deteriorate as they become older because of their advanced age. In contrast, a turnkey PCB assembly company can extend its lifespan through a rigorous PCB quality control process.
When components near the end of their projected life cycle, they begin to fail, at which point the PCBAs either need to be repaired or replaced with a new one. Implementation failure analysis involves gradually stressing the PCBA until failure (thermally, mechanically, and environmentally), followed by studying the PCBA to discover and explore the specific failure. It takes considerable expertise to spot flaws in each of these different categories.
PCBA failure caused by storage environment
PCBAs are very vulnerable to the effects of environmental variables. Circuit boards are susceptible to expansion when exposed to heat and humidity, which can lead to warping and might potentially damage soldered junctions. Because of this, the production of PCBAs is almost always carried out in an area that has its temperature and humidity carefully controlled so that they remain within acceptable parameters.
Dust affects printed circuit board work
When the PCBA board is working, it will generate a small amount of magnetic and electromagnetic fields, and these magnetic and electromagnetic fields will attract fine dust in the air. If the PCBA is stored in poor conditions and has not been cleaned for a long time, the accumulated dust will corrode the printed lines in the PCB, the pins of the components, and even mildew on the printed lines if it is serious. Mildew usually occurs in signal lines and circuit board vias and the failure or malfunction of many common electronic products may be caused by mildew. If it is a partial runaway phenomenon, it may be due to corrosion of the metal pins. Also, have you ever encountered the phenomenon of good and bad electronic equipment due to various weather conditions? If your electronic device works fine in sunny weather, but malfunctions in wet weather, this may be because of dust in the PCB combined with the moisture in the air to form an invisible resistive network, resulting in a runaway phenomenon.
The effect of humidity on the PCB
The impact of moisture on circuit boards is self-evident, and even a finished electronic product will suffer a lot in a moist environment. Excessive moisture can cause common PCB problems. Excessive moisture saturation in the air will cause water droplets to drip on the circuit board and attach to the pins of the components. The PCB components that are mostly used by many turnkey PCBA assembly companies are SOP or SSOP SMD components. The biggest feature of this chip component is that the distance between the pins is small, which provides a good platform for the attachment of water droplets. If the SSOP packaged integrated circuit runs in the presence of water droplets, an invisible resistance will be added between the pins of the integrated circuit, which will easily cause a short circuit, resulting in circuit board failure, signal processing or transmission lines. In addition, even when not working, prolonged exposure to this environment can cause the pins to corrode and break, resulting in overall board failure.
Remedy
The best remedy is to avoid wet conditions as much as possible. If it cannot be avoided due to the particularity of the project, FS Technology recommends that you choose to use a ceramic PCB, which has the characteristics of 0% water absorption. This article mainly focuses on the circuit board failure analysis and does not focus too much on the various PCB types.
The latest detection method to prevent PCB assembly failure
As PCBA manufacturing technology is progressing day by day, various PCB assembly inspection technologies have gained success. The last technologies being used for this purpose are discussed below.
Optical inspection
In this inspection method, high-powered optical microscopes are used to examine the surface layer of a printed circuit board (PCB). Failures that need to be detected include corrosion, failed solder joints, shorts or openings, build-up of solid impurities (like corrosion), or damage to the surface layer. These failures can be found by inspecting the surface layer.
Microsection inspection
In this inspection technology, a small section of the PCBA is analysed using either an optical microscope or a scanning electron microscope (SEM). Lamination, plating migration, reliability, and roughness inspections are among the most common applications of this technology.
X-ray inspection
Everything that cannot be observed visually or through a test using a scanning electron microscope, is inspected using X-ray technology. In-plane failure inspection, examination of BGA failure, and inspection of other in-plane failure mechanisms are all applications for this.
Now that you know what may go wrong with a PCBA, hopefully you also know how to prevent future malfunctions. Working with PCBA often requires rewriting designs and swapping out components, as necessary. This is simply the nature of the industry. Time and money may be saved by working with a business partner like FS Tech, who is well-versed in the testing, assembly, and manufacturing of PCBA.
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