A collection of common PCB problems
Even experienced engineers or professional PCBA manufacturers cannot avoid facing PCB defects. The emergence of these issues will cause numerous irreversible adverse consequences, such as: delaying the delivery time, damage to the manufacturer’s reputation, additional time and money costs, etc. In this article, FS Technology will comprehensively list common PCB problems, and hope to have a positive impact on your project through this article.
What are the factors that cause PCB failure?
As an important and fragile electronic component, any slight error can cause the PCB to malfunction. As a professional turnkey PCBA company, FS Technology strictly controls every link of design, manufacturing, and assembly to ensure that there are no common-sense mistakes. The following is the classification of PCB defects by FS Technology:
Common PCB Manufacturing Defects
With the increase in the number of layers and structures, the manufacturing difficulty of circuit boards becomes more difficult, and manufacturers need to go through more steps to realize the construction of multi-layer PCBs. In this series of processes, the probability of manufacturing PCB errors has skyrocketed due to a combination of factors, including:
PCB Short Circuit Problem
PCB Short circuit is one of the most common defects, and it is typically confused with open circuit. FS Technology hereby gives the definition and difference between the two. An open circuit refers to the disconnection of the connected line due to a break in the middle of the line. A short circuit is when excess copper or other impurities appear between lines that should have a distance, causing the lines to fail to transmit properly. In short, an open circuit is a little less “thing” and a short circuit is a little more “thing”. There are many reasons for the short circuit problem, and it is necessary to know what is caused by a rigorous PCBA failure analysis. FS Technology lists 3 reasons that can cause short circuits on circuit boards and provides corresponding solutions:
Short circuit due to scratches
- Improper operation during alignment will cause scratches on the film surface. In order to avoid this situation, the operator should control the spacing between the boards, use both hands during the whole process, and strictly implement the alignment operation specifications.
- The failure of the connecting board of the developing machine causes the collision and scratches between the board and the board. The PCB manufacturing factory should adjust the spacing distance of the board according to the operator’s ability, and the board should not be placed when there is no one to connect the board at the exit port.
- Improper removal of the plate during electroplating, improper operation when placing the splint, etc., resulting in scratches. Enterprises should remind employees to pay attention to operating specifications when electroplating, and avoid laminating two boards together for splinting.
Short circuit caused by film
- The anti-coating layer is too thin, and the coating exceeds the thickness of the film during electroplating, forming a sandwich. The thickness of the plating resist needs to be increased, and if wet film is used, the thickness can be increased by multiple printings.
- The distribution of the lines is uneven. During the pattern plating process of the isolated lines, due to the high potential, the coating exceeds the film thickness and forms a sandwich. In order to avoid this situation, FS technology generally reduces the current, using a current of 1.7~2.4A, can make the plating height on the isolated area exceed the film thickness.
Short circuit caused by tin loss
- Due to improper operation, the loss of tin in the stripping potion tank is caused. When this happens, it is necessary to control the concentration, temperature, and soaking time of the potion according to the needs. Isolate the boards with a board rack.
- The stacking of the stripped boards causes the loss of tin. The PCB factory needs to dry the stripping solution in time after stripping and check it carefully.
PCB Soldering Defect Problem
Soldering defects are an easy-to-avoid circuit board problem, but because of their variety, they can be easily overlooked in the production process for companies without strict specifications. If this problem occurs, it can be solved by desolder PCBA components. FS Technology briefly lists the most common concentrated welding problems here:
- Destruction of solder joints: Before the solder joints solidify, they are easily affected by external factors and cause the solder joints to move. This is relatively common, and it is only necessary to reheat the solder joint, fuse and correct it.
- Cold welding: Due to insufficient solder fusion, the surface is rough, and the connection is not firm. When this problem occurs it is necessary to reheat the joint to remove excess solder.
- Welding bridge: When the two leads are welded together and the current is greater than the rated voltage, it is easy to cause the components to be burned or the wires to be burned. Ask the PCB manufacturer to review the manufacturing process after receiving the order and control the amount of solder when soldering.
Particle contacts appear on the board
- Solder is contaminated: Contamination of the solder can change its composition, and when this is found, a large amount of pure tin needs to be added or the solder replaced.
- Oxide excess: Too much oxide in tin can make the solder joint structure more fragile, requiring higher tin content and lower preheat and soldering temperatures.
- Poor wettability of solder: The reason for this phenomenon may be due to the improper setting of the reflow temperature. When the board enters reflow soldering, the temperature in the preheating zone rises too fast or the time is too short, so that the moisture inside the solder paste is not completely volatilized. When the reflow soldering temperature zone is reached, the water boils and tin beads appear.
Discoloration of solder joints
- Temperature issues: The color of the PCB solder joints is generally silver-gray, but occasionally some gold solder joints appear. The reason for this phenomenon may be that the temperature of the tin furnace is too high because the frequency of using the tin furnace is too high.
- Different kinds: If the discoloration occurs after cleaning the circuit board, there is no need to worry too much. It may be caused by different types of cleaning agents, fluxes and solder alloys.
We know that cleaning circuit boards is an important part of the PCB manufacturing process, but many small workshops omit this important step in order to save time and cost, which is the main cause of blistering. After the PCB is produced, there are many stains on its surface, such as oxidation, oil stains and glue marks. These alkaline pollutants will corrode the surface of the circuit board and cause blistering. In addition to the first time, the reasons for this bare board defect are as follows:
- Insufficient curing time: If you find that the front and back sides of a certain corner of the bare board are foaming and oiling off after HASL, it is caused by insufficient curing time.
- Tin stripping is not clean: There is a thin layer of tin on the surface of the board. After spraying tin, the tin on the surface of the board will be melted at high temperature and will push up the ink to form a bubble.
- There is water vapor in the hole: the operator does not operate in a standardized manner, and the ink is printed to ensure that the water vapor in the hole is dry.
- Reflow soldering: Reflow soldering is an essential part of SMT assembly, and circuit boards with moisture are very prone to air bubbles when they enter the reflow soldering furnace.
Copper is oxidized and corroded
The PCB layer includes a silk screen layer, a solder mask layer and a copper layer, each of which has its role. The role of the solder mask layer is to protect the copper from oxidation and corrosion, and to prevent the formation of gaps and bridges between electronic components. As a commonly used material in the electronics industry, copper has natural advantages in current transmission, but its ability to resist corrosion and oxidation is extremely poor. Common pcb defects occur when copper oxidizes and corrodes. Some PCB manufacturers use solder mask that is too thin, or wears out from prolonged use, which can easily expose wires.
In the PCB manufacturing process, it is not uncommon for workers not to operate in accordance with the company’s code of conduct, resulting in circuit board problems. The probability of this human error leading to a product defect is as high as 31%. In order to avoid this situation, FS Technology has formulated strict quality control standards and incorporated workers’ operating norms into performance appraisals.
Common PCB design defect issues
Printed circuit board common problems not only occur on bare PCB boards, but also often during the design process. As the first step in PCB production, in order to ensure that the manufactured circuit board is error-free, designers need to strictly enforce the design specifications.
The copper wire is too close to the edge of the board
After designing the circuit, the designer carefully checks the distance between the copper wire and the edge of the base layer and separates the components. Copper spacing issues are often the result of incorrect PCB design for manufacturing (DFM) specifications. This layout risk is minimized due to strict adherence to design specifications.
Misuse of the Graphics Layer
- Too many useless connections make the circuit board more complicated. Only six layers are required to complete the PCB design, but many more are used.
- Speed over quality. In order to save trouble, the designer uses the Board layer to draw the lines on each layer, and uses the Board layer to mark the lines, which may cause the Board layer to be missed, and the connection will be missed and the circuit will be broken.
Design without guidance
A foolproof design solution and a high-quality turnkey PCB assembly service standard are the lifelong pursuit of FS Technology. As an EMS company that includes mechanical assembly, PBC manufacturing, and PCB assembly, we do not blindly assemble components, stack components together, and start welding. We have a first-class sales team, expert-level PCB designers, and top-notch PCB component procurement capabilities. When you place an order at FS Technology, our service begins, from guiding design, to production and assembly, to delivery, in one go, complete the perfect order with the fastest speed.
Common PCB Assembly Problem
Components are loose or misaligned
When the PCB assembly is in the reflow stage, small parts can float on the solder, causing the target solder joints to fall off. At this time, the factory needs to strengthen the support force of the circuit board and design the procedure of the reflow oven according to the specification.
No cleaning flux
In the PCB soldering process, a chemical substance is used – PCB Flux. Its function is to remove oxides on the surface of metal materials and destroy the surface tension of welding materials. When we have long-lived electronics, flux residues on the surface of circuit boards can absorb moisture from the air, causing the exposed metal surfaces to oxidize and corrode over time. In order to provide customers with a better service experience, FS Technology has specially added the work index of cleaning flux in the quality assurance process, and the operators of our production line also complete this work conscientiously and responsibly.
The influence of temperature and humidity
Circuit boards have different advantages and characteristics. Therefore, it is necessary to select the type of circuit board according to the needs of the project, such as: IMS PCB with stronger heat dissipation capacity, flexible multi-layer PCB that makes electronic equipment more miniaturized, and high-frequency PCB focusing on signal integrity. Many customers believe that temperature and humidity will adversely affect the circuit board, so when choosing a PCB manufacturing company, they will also focus on the ventilation of the manufacturing workshop. I believe that most people think this is necessary, but in the opinion of FS Technology, there is no need to worry too much about the impact of temperature and humidity in the manufacturing plant on the circuit board. In the short term, the damage caused by temperature and humidity to the bare PCB board is minimal, and we should pay more attention to the PCBA board, that is, the assembled circuit board.
For the assembled PCBA, the effects of temperature and humidity are fatal. Due to the structure of the PCB itself is relatively fragile, and it runs in electronic equipment after assembly, it is easy to damage the circuit board in a long-term extreme environment (high temperature, large temperature difference, large humidity). When in a high temperature environment: the solder joints of the circuit board are easily damaged, causing the circuit board to be deformed and bent, and in severe cases, the copper wire will be broken. When in a humid environment: The metal substances on the surface of the circuit board (copper traces, pads, component leads) are oxidized and rusted, resulting in overheating and performance degradation of the PCB during operation. In addition to paying attention to the use environment of the PCBA, the review of the assembly factory is also necessary.
In addition to paying attention to the use environment of the PCBA, the review of the assembly factory is also necessary. During PCBA processing, some electronic components have extremely high requirements on the temperature and humidity of the environment. Therefore, in order to ensure the quality of PCBA processing, you need to pay attention to the following issues when choosing a PCB assembly company:
- Temperature and Humidity: The temperature is kept in the range of 24±2℃, and the humidity is kept in the range of 60±10%.
- Professional testing equipment: choose Pt100 platinum resistance temperature sensing instrument; measure temperature by ventilated dry and wet bulb measurement method.
How to Diagnose Common PCB Problems
Through the above we have learned about most PCB problems. Many mistakes can be avoided by understanding design, manufacturing and assembly issues, but if a board fails, how do we identify them?
In fact, it is difficult to find the cause of PCB failure without professional equipment and methods. Some faults can be perceived by human eyes, touch, and smell, such as PCB short circuit, board surface is corroded, etc. However, most of the faults are difficult to detect, and they need to be detected by professional equipment, including multi-phase integrated circuit testing and multimeters. After finding the problem and finding the location of the fault, experts will judge whether to desolder the components or replace the circuit board.
Microsectioning, also known as cross-sectional analysis, is a method used to identify PCB faults by testing individual layers and components with controlled variables to find the location of errors. This method is the most reliable method, but requires a broken circuit board. Microsection analysis is best suited for the following perceived PCB issues:
- System Shorts
- Material Evaluation
- Thermomechanical Failure
- Reflow Soldering Failure
- Holistic Handling of Failures
Solderability analysis focuses on solder and mask related damage. Through solderability analysis, your team will find out whether the components soldered with solder are in good condition, whether there are missing soldering, missing soldering, or weak soldering, so that you can quickly make adjustments.
Solderability testing is a way to test the professionalism of technicians, and the factory needs to have professional testing tools. Technicians must be aware of any PCB failure issues and how certain conditions can affect failure of soldered components, such as PCB storage, aging, and other environmental controls that affect the overall quality of the PCB. Consider solderability testing for the following features:
- Component and Track Polymer/Paint Evaluation
- Solder and Solder Mask Analysis
- Flux and Pad Evaluation
- Overall PCB Coating Health and Durability