Printed circuit board defects are frustrating, especially if they are preventable but go unnoticed until after they fail during consumer use. Depending on the application, a printed circuit board failure can be extremely costly and even dangerous.
Printed circuit board defects may damage your reputation, and many issues are easily avoided by choosing a reputable printed circuit board manufacturer. Other defects can be prevented by being mindful of the environment in which you store your circuit boards or assemble your products. Most printed circuit board defects can be attributed to soldering issues, manufacturing or storage conditions, and damage caused by electrostatic discharge.
The bulk of printed circuit board defects can be traced back to a soldering issue. Soldering is a technical skill that becomes even more difficult when dealing with the extremely small components on a printed circuit board. Soldering defects can be minimized both during the design process, and during the soldering process. Some of the most common soldering defects include:
Open joints, sometimes called “dry joints,” occur when the solder doesn’t bond correctly with the point of contact, typically the pad. Open joints do not always cause your circuit to fail, since there may be solder there that makes poor or occasional contact. Open joints are caused by physical movement or bending, incorrect solder temperature, design or manufacturing errors, as well as impact and shifting during use or transport. Occasionally, open joints are caused by using too much solder, which causes the component to lift.
Shifts occur when the printed circuit board or component is not aligned correctly during the soldering process. Shifts can result in open joints, shorts, and crossed signal lines. Shifts can occur due to a variety of reasons, including movement or vibration during the manufacturing process, the solder being at an incorrect temperature, varying humidity levels, an unlevel surface, design error, heat sinks, or a manufacturing error that results in misplacement of the solder.
Short circuits, often referred to simply as “shorts,” most often occur due to a soldering error called solder bridging. Bridging is when two joints on the printed circuit board are soldered together, sometimes connecting components that cause short circuits. Bridging can be caused by an excessive amount of solder being used, design error, an incorrectly applied mask layer, or even a faulty seal in the printing process. Since shorts can be extremely difficult to see and don’t always cause a circuit to fail, they may not be easy to detect. Less often, shorts are caused by contaminated solder that may contain too much moisture.
Shorts tend to cause more physical damage to the board than other types of defects, and upon inspection you may notice blown or burnt components caused by an unnoticed short circuit.
Defects Caused by Manufacturing or Storage Conditions
Printed circuit boards, like any other electrical component, are sensitive to environmental factors, such as temperature and humidity. Many printed circuit board defects are caused by manufacturing or storage conditions. Common causes of defects include:
Printed circuit boards are affected by temperature, both in storage, and when they are installed in components. Extreme temperatures or large temperature fluctuations may cause components or joints to break or fail. Many people take the maximum or minimum safe temperature into consideration, without thinking about the fluctuations in temperature that may occur either during operation or in storage. Temperature fluctuations can cause expansion and contraction to take place too quickly, causing premature failure of the printed circuit board.
Exposure to moisture, both during the manufacturing process and in storage, can cause shorts to occur and may lead to defects in components. Humidity in the air, as well as the moisture content in the solder can wreak havoc on printed circuit boards, causing corrosion. If you are storing your printed circuit boards for an extended period of time, make sure that it is in an area where both temperature and humidity are controlled.
Contaminants can create defects both during manufacturing and in areas where printed circuit boards are stored. If your printed circuit boards are exposed to the elements, dust, insects, and other contaminants can create buildup and cause poor connections, weakening the printed circuit board’s performance or causing it to fail altogether.
Impact and vibration, both during the manufacturing process and during transportation and storage, can have a catastrophic effect on your printed circuit boards. Impacts can be caused by human error, such as dropping the printed circuit boards or handling them roughly, or the impact and vibration may happen during manufacturing, like when a conveyor belt causes too much vibration. Printed circuit boards can also be damaged due to bending or warping when they are not designed to be flexible, which can loosen or break components, wires, and joints.
Defects Caused by Electrostatic Discharge
Defects caused by electrostatic discharge can be extremely frustrating, since they are not always easy to detect. Latent failures caused by electrostatic discharge, or ESD, can cause significant cost increases due to the return or repair of the damaged unit. Electrostatic discharge can even cause shorts to occur by creating enough heat to soften solder.
Electrostatic discharge is caused by both human and machines, and can happen during nearly every point in the manufacturing and assembly processes. Designing printed circuit boards in ways that prevent damage from electrostatic discharge has become standard, with safeguards including adding extra ground planes to the design, adding more space between traces, minimizing line length, and building safer input and output ports.
Printed circuit board manufacturers also go to great lengths during the manufacturing process to reduce losses due to damage caused by electrostatic discharge. Workers typically wear special clothing, shoes, and grounded wrist bands. Grounded anti-static mats are also often used, and the humidity in the air must be controlled so that there is enough moisture to reduce static electricity, but not so much that it could damage the printed circuit boards.
Some of the most costly defects to printed circuit boards are caused by damaged paths, which may continue to work even with a significant defect. These latent defects cause premature failure in the printed circuit boards. Latent defects are also one of the reasons why factories without precautions in place to prevent damage caused by electrostatic discharge tend to have unreliable products with a higher rate of failure. Such failures may not always be able to be definitively traced back to electrostatic discharge, especially if the cost of failure analysis is prohibitive.
Electrostatic discharge is already one of the largest contributors to printed circuit board failure, and there will be an increase in defects caused by ESD as printed circuit boards continue to decrease in size, making the boards and components less resistant to short bursts of high voltages. Since the level of voltage required to damage or destroy a printed circuit board is so low that humans can’t feel it, it is not something that can be easily detected in the design process.
MOS components are particularly sensitive to electrostatic discharge, and extra precautions need to be put in place when components may be damaged by a particularly low amount of static electricity. CMOS chips can usually be damaged by just 250 volts; to put that into perspective, it takes approximately 3,500 volts for a human to feel a static shock.
How to Avoid Printed Circuit Board Defects
Your first defense against printed circuit board defects is going to be your design. Many of the soldering issues that occur, and even many of the problems caused by electrostatic discharge can be mitigated by preventative design elements. Your designers and manufacturing engineers should be able to clearly communicate possible problems so that costly mistakes can be avoided. Something as innocuous as the placement of the power supply, or an incorrect trace width can be extremely costly to fix if it creates defects and failures down the line. An experienced designer will be able to avoid mistakes that may otherwise go unnoticed.
When you buy circuit boards, the easiest way to avoid the majority of printed circuit board defects is to choose a reputable printed circuit board manufacturer. A printed circuit board company should be able to determine if there are issues with your design that may create problems later on. They should also have a variety of precautions in place to reduce electrostatic discharge, as well as systems for testing your printed circuit boards for defects prior to use. A printed circuit board company that is significantly cheaper than the competition should raise red flags; this usually means they are cutting corners in order to cut costs.
You will also want to take care to make sure you are transporting and storing your printed circuit boards safely to help maintain PCB cost down. Prior to receiving your order, you should inspect the location where you will be storing your printed circuit boards or finished products in order to make sure that the temperature and humidity are controlled, and that workers are properly trained on how to handle printed circuit boards in order to avoid creating static electricity, impact, and vibration.