Since PCB form the basis of electrical circuitry, it is crucial to maintain their mechanical functionality at all times. Additionally, PCBs provide proper connections between components and various circuit elements, which is crucial for performing tasks like sending and receiving data, calculating electrical parameters, amplifying electronic signals, etc.
When producing PCBs in large quantities, PCB makers make sure they are of the highest quality. PCBs can occasionally be flawed or defective for a variety of reasons, though. As they impair the functionality of multiple circuit components, these flaws cause a variety of issues and challenges with the electronic circuit’s operation.
The desired output in a circuit might be negatively impacted by a variety of problems or flaws. Among them are:
Defects Occurring During Production and Storage
PCBs are susceptible to several environmental conditions, such as temperature, humidity, pollution, etc., just like other electrical components. Throughout production and storage, PCBs can have a number of flaws. Among them are:
Temperature: PCBs are impacted by temperature both during storage and during the installation of components. Numerous temperature variations that occur under extreme circumstances have the ability to contribute to the breakdown of joints or components.
The PCBs’ maximum and minimum working temperatures must be taken into account during the designing process. Temperature fluctuations can cause the PCBs to expand and compress, which can lead to premature PCB failure.
Moisture: Exposure to moisture during PCB fabrication and storage can result in shorts and may cause flaws in a number of circuit components. Airborne moisture and humidity both have the potential to harm solder, which will then lead to corrosion.
Contaminants: Contaminants cause flaws both in the manufacturing process and in the storage locations for PCBs. PCBs eventually lose some of their functionality when exposed to things like dust, insects, pollution, etc.
Impact: When PCBs are manufactured, stored, or transported, impact on the boards has the potential to be disastrous. PCBs produce excessive vibrations when dropped violently or when they are improperly made. As a result, PCBs become less flexible, which in turn causes damage to the PCBs’ tracks.
Defects in Soldering
A soldering defect that results in PCB tracks being traced back because of a poorly placed solder connection can be reduced throughout the design and soldering processes.
The following are some typical soldering flaws:
Open joints, also known as dry joints, happen when the solder does not make direct contact with the PCB pad. Open joints are typically brought on by bending or physical movement, the wrong solder temperature, or vibrations in the PCB while being transported.
Excessive Soldering: During the soldering process, there may be an excessive build-up of solder caused on the components as a result of a late removal of the soldering iron. Due to the increased possibility of solder bridge creation, the circuit connections may suffer as a result.
Figure 1: Excessive Solder
Shifting of Components: This occurs when the components installed on the PCB are not properly aligned during soldering. Open joints and crossed signal lines that are caused by component displacement might cause discrepancy in the electrical circuit. Component shifting can happen for a number of causes, such as heat sinks, changes in solder temperature, manufacturing errors, incorrect designs, etc.
Figure 2: Component Shifting
Webbing and Splashes: This term refers to the phenomenon that occurs when various air contaminants interfere with the soldering of a PCB. These flaws may result in short circuit risks and have an impact on the PCB’s aesthetics.
Lifted Pads: Lifted Pads are pads that have been disconnected or separated from the PCB surface. This leads to anomalies in the circuit connection, which in turn causes the PCB board to malfunction. This problem typically occurs in single-sided PCBs that have no through-hole plating and a thin copper layer.
Figure 3: Lifted Pads
Solder Balling: This is caused due to poor conditions like gassing from the flux or excessive turbulence as the solder flows back. While keeping in mind the no-clean process, numerous solder balls in the PCB can make a fake bridge between two adjoining traces causing malfunction to the circuit.
Figure 4: Solder Balling
Equipment Errors: During the PCB manufacturing process, CNC milling machines are utilized to route, cut, and outline the board. The CNC machine’s robot must be unloaded, and the yard lumber must have holes that are outside the tolerance range in both the horizontal and vertical directions. A collision ensues from this, and a PCB board’s edge collapses as a result. CNC machines can overheat during manufacturing with extremely high throughput. Deteriorated board quality, erroneous alignments, incorrect edging, etc. may result from using machines at temperatures above 150 degrees Celsius.
Figure 5: Machinery Defects
Defects Caused by Electrostatic Discharge
Electrostatic discharge damage on a PCB is very difficult to detect. The electrostatic discharge causes multiple shorts which soften the solder. They can be caused by humans as well as machines and should be minutely detected during the manufacturing and assembly process. Electrostatic discharge is one of the largest reasons for PCB failure and they make components less resistant to short bursts of high voltage.
Figure 6: Electrostatic Defect
Techniques for Detecting PCB Defects
Inspections should be carried out at each stage of the PCB manufacturing process. This ultimately aids in discovering and correcting PCB problems. A few techniques to do this include:
Visual Inspection: During PCB construction, visual inspection is the most typical method of inspection. On the basis of the inspection targets, specific equipment for visual inspection might be chosen. A prism is frequently used to inspect the reflow solder joints on a PCB, which aids in spotting various manufacturing flaws. In order to identify issues with the PCB’s design and layout, incident light rays can be reflected on the PCB or PCB joints using prism spectroscopy.
Figure 7: Visual Inspection
Figure 8: Prism Spectroscopy
X-ray Inspection (AXI): After mass production, soldering, component misalignment, and other issues may arise. X-rays are focused on the PCB components using AXI technology, which uses X-ray absorption to create an image. The use of X-rays in inspection can help find flaws in wiring assembly, solder connections, semiconductor packing, and other areas.
Figure 9: X-ray Inspection
Automated Optical Inspection (AOI): Using one or more video cameras, PCBs are scanned during the automated optical inspection. Images of various parts taken by the camera from various angles and positions are stored. During PCB assembly, these images might then be examined by designers or engineers to find issues like scratches, stains, markings, and other dimensional flaws. Using this technique, we can also spot components that are off-balance or inaccurate. In order to identify the height and width of PCBs as well as the many micro components used on the PCB, systems can use a variety of 3D AOIs.
Figure 10: AOI camera system
Options for Correcting Errors
Engineers and technicians must use soldering tools to reconnect the separated joints in order to fix problems that result from soldering. By checking for small PCB fractures and making sure that the components are not coming loose from the circuit, engineers must be able to determine whether the solder joints or other components are broken. The typical workaround for problems during soldering in a PCB is to place a solder mask between pads. This guarantees that there won’t be any space between the PCB and the stencil.
PCBs are made from a variety of substances and compounds. During production, acids such sodium persulfate [Na2S2O8], ammonium persulfate [(NH4)2S2O8], and ferric chloride [FeCl3] aid in creating routes for electricity to reach the board. The flow of the circuit may be disrupted if these acids occasionally become caught at an angle and create acid paths. When making PCB tracks, PCB etching solutions are used to remove unnecessary copper from the PCB and leave behind only usable copper. Precision metal components can be created using the photo-reactive resist method by using photo-activated etching, which guarantees that acid traps are kept to a minimum.
Electromagnetic energy is produced and transmitted through electromagnetic interference (EMI). The Electromagnetic Compatibility (EMC) of the PCB can occasionally be harmed by EMI. This results from poor design and can be fixed by decreasing the PCB-ground area. Designers can get rid of the electromagnetic compatibility issue by lowering the contact area of the circuit. Additionally, adopting sophisticated PCB production techniques will result in improved manufacture, improving quality and eliminating a variety of PCB flaws.
When high temperatures occur during production, there are some instances where a PCB is exposed, which causes the boards to burn. It is crucial to ensure that components are positioned on the board with enough space between them to allow for good air circulation and to clear heat sinks in order to prevent PCB burning. High-power-consumption components like processors and microcontrollers must be positioned in the center of the PCB for optimum heat dissipation. By dispersing heat throughout the PCB surface in all directions, these devices guarantee that the board’s surface temperature will be reduced.
Chemical fluid leakage that occurs during the PCB manufacturing process might cause the PCB boards to corrode prematurely. After production, the boards must be properly cleaned because minute corrosion remnants can cause short circuits.
The dielectric constant in an electronic circuit must be as low as possible to ensure smooth transmission.
Low hygroscopicity is desirable in substrate materials used in PCBs that are designed to withstand high frequency and speed.
There should be a change in PCB substrate size for the following reasons:
1. The substrate shrinks in size as a result of the release of shearing effects.
2. The base of the PCB plate changes as a result of substrate strain.
3. There is a potential that the dimensions of a multilayer PCB will alter during lamination.
The simultaneous manoeuvrings of the CNC machine’s yard lumber and unloading robot are separated by adjusting the tolerance level accuracy.
Before mass production, it is essential to evaluate the grinding wheel’s functionality and the process’ geometrical parameters to identify and prevent machine flaws.
Locating and spotting flaws in a PCB during production is crucial. If PCB flaws are not discovered in time, they could have disastrous effects on the circuit as well as the person using the circuit in the future. These flaws may take the following forms:
faults resulting from electrostatic discharge, machine faults, manufacturing and storage defects, and more.
The following flaws can be inspected using a variety of techniques. Through X-ray inspection and Automated Optical Inspection (AOI), which makes use of 3D imaging to detect the PCB’s height, width, and other dimensional faults, standard processes to inspect a PCB for flaws or for material damage are carried out.