PCBA fault analysis and defect resolution measures

The PCBA board is the most important component in all electrical equipment. The global demand  for PCBA has increased in past decades. With the increase in demand, PCB  manufacturers’ main focus is to minimize PCBs’ faults. An extensive understanding of PCB common faults, knowing their root cause, and knowing how to prevent these defects ensures high quality PCBs and eventually PCBAs product. It is important to take care of these points because  they have a direct impact on the functionality and quality of the final PCB assembly. As with the advancement in technology, the complexity of PCBs increases which means there is  more probability of failure of PCB to occur. All these failures can be categorized into four: 

Failure related to PCB designing like insufficient clearance. 

Failure related to manufacturing of PCB like over-etching, drilling errors and improper soldering. 

Damage caused by improper use of circuit boards like excessive use and cumulative damage/fatigue.

Defects related to the PCBA storage environments like humid environment and dust environment.

Repairman with faulty circuit board

With great fortune, most PCBA failures can be prevented by having knowledge of PCB failures. Therefore, FS Technology recommends that you do not need to panic after discovering the fault of the circuit board, and give priority to fault analysis and troubleshooting. If you are a PCB Designer or PCB manufacturing industrialist, it is critical for you understand that how a PCBA can fail under certain condition. This FS Tech blog article discusses the PCBA failure analysis. Some PCBA failures and their causes and preventive measures is jotted down as:

PCBA Design Error Analysis and Remedy

Missing Solder Mask between Pads

PCB copper layer has a specific layer on top of it usually known as the “Solder Mask”. The  main purpose of this layer is to make a shield and form a protective layer on conductive traces in  the copper layer of PCB, to prevent traces from interacting with other materials like metal or solder. In short, a solder mask act as a barrier between copper traces and the environment, protecting PCB  from corrosion and electrocution. 

If there is no solder mask between pads (a portion of metal left exposed intentionally for  soldering purpose) of PCB then there is a high probability of solder bridge and PCB short-circuiting  between two pads of PCB, which also reduces corrosion protection of PCB. 

Remedy

This problem can be prevented by double-verifying the design before giving it to Turnkey PCBA fabricators. In some cases, oversight of design might happen but make sure of giving design to  such fabricators who have a good track record of proper DFM checking protocols so they detect  any sort of problem before making the design materialize. 

Electromagnetic Problems

Electromagnetic Interference (EMI) and Electromagnetic Capability (EMC) are two different  things in PCB design. EMI is considered to be noise in electromagnetism like unwanted or  damaging effects of electromagnetic capability, while EMC is the production, propagation, and  perception of electromagnetic energy. If EMI increased after a certain limit, this could result in a  defective product, which can happen due to flaws in circuit design.

Remedy

EMI can be minimized by increasing the ground plane of PCB. Mostly 90 degrees angled  components on PCB produce more EMI, so, they must be avoided. Shielded wires are best in  assemblies’ harness which absorbs EMC and eventually reduces EMI. 

Module density is too high

After fabrication of PCBA board, a very high temperature is used to solder electronic components on  PCB which could burn other components out in the surroundings if the Printed Circuit Board is  densely packed with components tightly together. Also, there is one more problem with highly dense PCBA if PCBA has to run faster, it will produce more heat and become problematic. With  tightly located components heat remain trapped inside that PCB and increases the probability of  PCB burning or overheating. This problem is the most difficult one to handle because it destroys  the electronic nature of other components along with the problematic, faulty component. One can  relate a direct relation between overheating and damage to the circuit, more overheating results in  more damage to the circuit. If heating damage is ignored in the circuit board then it becomes much  more difficult to diagnose the board. 

Computer power motherboard burned out due to high component density

Remedy: 

As any Printed Circuit Board can absorb heat up to certain limits before its total failure. If heat exceeds that limit then it can produce some serious consequences and make PCB unusable permanently. This heat problem can be mitigated by using proper size and structure to lower  components density and allowing more heat to dissipate instead of trapping inside the board. Knowing the PCB component placement orientation guide can eliminate the root cause of the problem of high density of PBC 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. It’s what keeps a component and circuit 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 and 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 difficult to detect them and if remained undetected they can cause damage to PCB assemblies  at a catastrophic level like burn-up or blow-up of some electronic components. Improper Soldering  generally includes solder bubble, dry soldered, and cold soldered. 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-bridge  which is even difficult to detect with the naked eye. In most cases, these soldering failures can be resolved by desoldering the PCB components.

Uncleaned PCB

Neglecting to clean PCB is a common mistake made by most manufacturers.

There is no doubt that metal PCBs will be affected by various environments. Oil on the surface of the human body, sweat, oxygen in nature, and humid environments are all causes of PCBA damage. Cleaning PCBs as required can reduce a lot of potential risks, so most turnkey PCBA companies not only have advanced assembly equipment, perfect quality control systems, but also attach great importance to PCB cleaning. The following are the PCB cleaning processes 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. Electricity can pass from  one layer to other layers of PCB with the help of these holes. PCB fabricators create these holes  with the help of the drilling method, making holes through all layers of PCB. After drilling, an  electroplating procedure is followed to coat the outer exposed surface of the hole with copper to  make it conductive.

With the help of deposition, a thin layer of conductive copper is deposited to PCB which, in some  cases, is not perfect and produces voids during plating. These plating voids are gaps in copper  plating which become problematic because such gaps via or hole are unable to conduct current  between layers of PCB and results in improper functioning of PCB or even in the entire failure of  PCB. 

The main reason for such plating voids includes insufficient drilled holes cleaning,  contamination of plating material, rough drilling of hole, and air bubbles while plating. 

Remedy

Contamination of 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 PCB just make sure to fulfill  manufacturer instructions like recommended drill speed or required number of drill hits. 

Damage caused by improper use of circuit boards

Cumulative Damage/Fatigue

The most common reason of PCBA failure is the presence of defects. During the process of assembling PCBs, flaws frequently manifest themselves.

PCBA damage can be caused by electrostatic discharge (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 a 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 sort of PCBA damage, which is why it is important to highlight, and 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,

1.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.

2.Improper Spacing of Components:  On the PCBA, the performance of nearby electronics components could suffer if some components are packed too closely together, since this could cause them to overheat. It is essential, to prevent heat-related flaws, which printed circuit boards (PCBs) be 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.

3.Technical Faults: If the connections on a PCBA aren’t made properly or the voltage safeguards aren’t 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. 

The implementation failure analysis involves gradually stressing the PCBA till 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 the 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. The failure or malfunction of our 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. If your electronic device works fine in sunny weather, but malfunctions in wet weather. This is because the dust in the PCB combines 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 this environment. 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 most used by most 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 board failure.

Circuit boards corroded by water

Remedy

The best thing to do 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 introduce too much on the type.

Latest PCBA Failure Inspection Technologies

As the PCBA manufacturing technology is progressing day by day, the 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 in order 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, through reliability, and roughness inspections are among the most common applications for this technology.

X-ray inspection

Everything that cannot be observed visually or through a test using 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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