Although PCBs are the basic foundational block for all electronic circuits in today’s generation, it is essential to follow several rules and guidelines while designing the circuits. These rules are not only applicable to the design but to the manufacturing and assembly of the PCBs to improve the overall performance of the board. Designers must make sure that every component and part on the PCB are evenly spaced, ensuring a smooth transfer of data to all ends of the circuit.
The Institute for Printed Circuits (IPC) is an organization that has a set of rules and regulations when it comes to the design, assembly, and quality standards of PCBs. These rules also define the reliability and robustness of the working principles of the PCBs during different operational conditions. This is not just for design; there is also an emphasis on the level of soldering of electrical and electronic components on PCBs for material specifications, process requirements, and acceptability criteria.
Overview of IPC rules
IPC has developed a common language for the global electronics industry that is being used as a guideline for designing, fabricating, and assembling the PCB. These standards are crucial and are designed to guarantee an overall better performance, superior quality, and more reliability of a product. Therefore, a designer needs to be familiar with the assembly and fabricating standards, as working within these standards may help in preventing losses. IPC standards offer some advantages to the designer in the following ways:
- Enhanced quality and reliability of product. Complying with IPC standards can help the manufacturing companies to maintain the quality and reliability of the product. Developing products that work and last a long time may help in keeping the market competitive. Keeping up with these standards improves the process and enhances the consistency of products.
- Improved communication. IPC has developed a globally accepted industrial language that makes communication between the designer and the consumer convenient. This common terminology helps to clearly analyze the established standards and prevents miscommunication throughout the process.
- Smooth workflow and lower cost. When everyone involved in the manufacturing process follow the same standards, it automatically reduces the probability of faulty products and delays in production. Also, following the same criteria can improve the effectiveness of the supply chain and eventually result in lower production costs.
Using IPC component placement rules for designing PCBs
The IPC-2220 family is to be considered solely for designing purposes when it comes to design. Some of the rules that are set by the IPC with respect to the placement of components on PCBs are:
- IPC– This standard defines how electrical parameters such as bus layouts, part clearances, and impedance are supposed to be considered on PCBs. Here, there is also an emphasis on methods to dissipate heat and how to implement thermal management in PCB designs.
- IPC– This standard defines the requirements for the design of PCBs that are physically rigid and whose structure is made of the solid substrate material. This standard is applicable to single-sided PCBs, double-sided PCBs, and multi-layered PCBs.
- IPC-2223. This standard deals with only flexible PCB structures and their design. When it comes to flexible PCB design, their pad/via placement, structural specifications, and bend radius are mentioned in their standard.
Designing components with appropriate spacing on PCBs
Improper component placement can result in a potential malfunctioning of the circuit and increases the possibility of causing harm to the user. In order to get optimized results in the performance of PCBs, there are several rules that designers can follow:
- Mechanical constraints. During the design process, it is very important to take into account the area under which the circuit or a part of the circuit needs to fit on the board. This makes it easier to know where mounting holes and edge connectors need to be drilled for easy assembly of components. Therefore, designers must first create an outline indicating the height limits, trace regions, etc.
- Component selection. Designers must select the components precisely by ensuring accurate properties and electrical parameters to increase conductivity within the circuit. It must also be made sure that there are no spacing constraints in the design of the components selected, which, if not done appropriately, may have an adverse impact on the circuit. Hence, component sizes must be examined from the very start of the design phase to ensure the right spacing is maintained between each component. This creates a hassle-free assembly process and the positioning of the components goes on smoothly.
- Separation of high-voltage components. Wherever possible, designers must always make it a practice to maintain an appropriate distance away from components that consume high power, such as MOSFETs, ICs, etc. It is ideal to leave an approximate spacing of .035 to 0.5 inches between each IC to ensure proper transfer of data, without any shortcomings. Also, if components like ICs are placed too close to each other, it gets difficult to route connecting pins and may cause connection issues.
- Trace width sizes. Usually, the thickness of a coat of copper on a printed circuit board is fixed to ensure that communication between the components takes place in one direction. Designers usually keep a minimum trace width of 6 mm or 0.152 mm due to the etching process. Some of the important factors for designing trace width are:
- Current-carrying capacity of the trace
- Space availability
- Manufacturing limitations
- Layering components on the PCB. For best results, most designers make use of multi-layer PCBs due to their weight-carrying capacity and low space restrictions. In spite of this, if components are placed on multiple layers, there may be difficulties during the assembly process that could result in unnecessarily expensive manufacturing costs. It must also be made sure that overlapping of components must not take place, and a minimum of 40-mm distance must be spaced between all parts.
IPC Classes and their impact on manufacturing
In PCB designing, the standards are characterized by three classes. These class definitions and their terminologies can be summarized as the number and severity of allowable defects in a PCB. These classes define the level of quality of each circuit board, from Class 1 (lowest quality) to Class 3 (highest or superior quality). A designer must be familiar with these classes, as they are the performance and safety specifications that should be met to maintain the quality standards of the PCB. Factors such as customer demands and cost may weigh heavily in the selection of the class to be followed by the designer. The following are the IPC class definitions:
Class 1 (general PCBs). Class 1 defines the specifications of the PCBs with short life and basic functions. The quality of the boards in this class is low, which makes them comparatively cheap. This class includes PCBs meant for everyday use, such as toys, TV remotes, etc.
Class 2 (dedicated service PCBs). The boards in Class 2 exhibit higher characteristics compared with Class 1 and have high reliability and extended life. They follow more strict standards than Class 1, as these boards perform more complicated functions and are often a part of a bigger system, such as laptops, TVs, or air conditioners.
Class 3 (high-performance PCBs). Class 3 comprises all circuit boards that require continuous or on-demand performance and a prolonged life cycle. The major difference between Class 2 and Class 3 boards can be seen while placing the SMT components. Class 3 products have been subjected to more strict guidelines, as they have a huge importance in the industry. Therefore, PCBs under the category of Class 3 must never experience any defects. Class 3 products are always inspected with high precision, which results in rigid and highly reliable boards. PCBs in this class are often used in military, aerospace, and many more vital fields with heavy operations.
To achieve the optimized performance of a circuit, designing a PCB in the right way is the first step that must be taken into account by designers at all times. There are several rules that have been set by the IPC when it comes to designing a circuit in the right manner with the right spacing between each component and part of a circuit board.
Designers can make use of the IPC-2220 family of standards for designing that consist of IPC-2221, IPC-2222, and IPC-2223. These standards are used in defining various techniques and methods that designers can use to lay out their PCB designs. Furthermore, when designing PCBs, there are several factors that designers must consider and carefully control before the assembly process. All mechanical constraints should be inspected to know the area under which the circuits can be embedded. The selection of components must be done in a phased manner for every part of the circuit. The height and width of all components must be evaluated correctly to be aware of the right spacing between the components. High-voltage components must be spaced at a good distance away from other components to avoid data loss during operations.