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- December 29, 2022
- PCB knowledge
- (0)
- 06 mins
What causes PCB defects
The manufacturing of Printed Circuit Boards has the aim of delivering complete functional and assembled boards in less time and at the best possible price. For accomplishing the goal, numerous pieces of puzzles are needed to be coordinated right from the selection of material to design, and from design to assembling components, and then till quality assurance techniques application to delivery to the market.
However, sometimes during the fabrication process, several PCB defects incur which are needed to be traced and troubleshot. This article explains some common causes of PCB defects, tracing the defects and preventing them to happen.
What is PCB?
PCB can be defined as the assembling process of electronic and electrical components having metal copper layers used as conductive paths for creating physical connections between components mounted on it. The purpose is also to provide mechanical support for the components mounted over it.
What cause PCB defects?
There are numerous reasons to question what causes PCB defects. However, the defects most occur because of the failure of PCB and sometimes PCB defects occur while the assembly process is underway. PCBs have extreme sensitivity towards the ESD (electrostatic discharge). Even though ESD is only felt at a higher voltage but the smallest discharge is enough to cause PCB defects. Many other causes comprise the misalignment of layers, the crossing of signals, and short circuits within PCB.
How to find defects on a PCB?
Performing different inspections is of great importance during every stage of manufacturing to find PCB defects. The following are some important ways to find defects on a PCB.
- Visual Inspection: This is the most common kind of inspection to find PCB defects. A prism is utilized for finding any defect in reflow solder joints on PCB. Incident light rays are reflected on PCB joints using prism spectroscopy for understanding the problems within PCB.
- X-Ray Inspection: Utilizing this state-of-the-art technology, X-Rays are directed onto PCBs producing images through the absorption of the rays. This helps in identifying various PCB defects that exist within voids, solder joints, wiring, packaging, etc.
- PCB AOI test: The automated optical inspection is for scanning the PCBs through cameras. Images are stored in a camera taken at different angles which are later analyzed by engineers to find PCB defects.
Can PCB be repaired?
There is the possibility of remanufacturing or repairing the PCBs having defected to make them new again. For repairing defective PCB, either it is returned to the supplier for repair to make it function again or, is recycled and redesigned for making it work.What are solutions to fix defects?
The PCB defects can be solved in several ways. PCBs make use of various materials and chemicals. For example, sodium persulphate, ammonium persulphate, ferric chloride, etc. are utilized for the creation of pathways for the conduction of electrical current. These chemicals sometimes get trapped within causing acid pathways resulting in disruption of the electric current. Therefore, the solution is to apply etching for removal of unwanted copper from the circuit board. Photo-activated etching technique is useful in the process.
EMI (electromagnetic interference) causes PCB defects in the electromagnetic compatibility of PCBs. This issue is caused because of flaws in the design of the PCB and is rectified by lowering the ground area of the PCB. Higher temperature is also sometimes affecting the PCB. Therefore, for avoiding PCB to burn it is necessary to place components in the right places at having significant distance between them. Heat sinks may be utilized for ensuring less temperature within PCB.
How much does it cost to fix a PCB?
The cost involved in repairing PCB defects is depending on the kind of application, the design of the PCB, and the nature of the issue with the PCB. Generally, the costs range from $5 and can range up to a few hundred dollars depending on the application or device in which the PCB is used.
What to do if PCB stops working?
Numerous PCB defects cause it to stop working. The following are some major causes and are needed to be checked.
- Physical Damage: It is one of the most common causes of PCB failure. This is related to anything that may apply shock or physical pressure to the PCB. Physical damage may happen when PCB falls from a height and it may get damaged when smacked or get hit with any solid object. Therefore, physical damage is the first thing to check when PCB stops working.
- Failure of Components: Any faulty component may cause PCB defects. When there is no apparent physical damage, but the still PCB stopped working, then the most probable reason is that any of its components have got faulty. Therefore, it is necessary to check all of the components mounted on to PCB one by one to detect and then replace them to make it work again.
- Damage of Traces: As discussed earlier, there are several traces on the PCB for the conduction of electric current. Usually, faults in traces can be noticed through visual inspection but sometimes they can be overlooked. If any of the traces are damaged then it may cause a short circuit or incomplete conduction causing PCB defect. Therefore, traces must be checked and ensured to be correct.
- Design Problem: A poor design may result in PCB defects and cause it to fail. Therefore, the design must be cross-verified.
- Failure of Power: Power failure is somehow similar to the failure of components. When any of the components on the PCB is not getting essential power, or any of the components are getting more power than required may result in PCB failure. Therefore, it is needed to ensure that every component must get the required power level.
How can you prevent PCB damage?
The following are some ways through which PCB defects can be prevented.
- Soldering bridges are needed to be checked. Solder bridges are also known as shorts. Soldering bridges are formed whenever solder is crossing one lead to another creating an abnormal connection among adjacent traces.
- Plating voids are necessary because these are responsible for carrying electric current within the board through holes. Therefore, ensuring there is no copper deposition around the holes to allow current to flow smoothly through the circuit can result in avoiding PCB defects.
- De-wetting or non-wetting occurs to the solder joints that have no extension to the PCB pads. This occurs solder is partially covering the surface of the board and copper is exposed behind. This has a direct impact on the PCB and must be avoided to prevent PCB damage.
- Acid traps must be checked within via positioning that brings the risk of leakage of solder when the assembly process is underway. The issue is resolved through the utilization of epoxy that is non-conductive or through the application of a soldering mask through the holes.
There are numerous reasons to question what causes PCB defects. However, the defects most occur because of the failure of PCB and sometimes PCB defects occur while the assembly process is underway. PCBs have extreme sensitivity towards the ESD (electrostatic discharge).
There is the possibility of remanufacturing or repairing the PCBs having defected to make them new again.
The cost involved in repairing PCB defects is depending on the kind of application, the design of the PCB, and the nature of the issue with the PCB.
Conclusion
The PCB design is requiring outstanding technical skills and precision. A single mistake can lead to PCB defects that may cause huge risks and losses. This is the reason why greater care should be taken while designing the PCB. Furthermore, during the manufacturing process, different inspection techniques must be applied to ensure the smooth fabrication of the PCBs.
