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Julian Brooks
Julian Brooks

IPC 2221: The Generic Standard that Covers All Aspects of Printed Board Design


IPC 2221: A Guide to Printed Board Design




Printed boards are essential components of electronic products that provide the structure for mounting and interconnecting electronic, electromechanical, and mechanical components. Printed board design is a complex and challenging process that requires careful consideration of various factors such as materials, dimensions, tolerances, electrical properties, mechanical properties, environmental conditions, and reliability. To help printed board designers achieve high-quality and cost-effective designs, the Association Connecting Electronics Industries (IPC) has developed a series of standards and guidelines that cover the generic and specific aspects of printed board design. One of these standards is IPC 2221, which is the generic standard on printed board design. In this article, we will explain what IPC 2221 is, why it is important, and how to use it.




IPC 2221 Generic Standard on Printed Board Design.pdf



What is IPC 2221?




IPC 2221 is a standard that provides information on the generic requirements for organic printed board design. It applies to all types of printed boards that use organic materials or organic materials in combination with inorganic materials (metal, glass, ceramic, etc.) to provide the structure for mounting and interconnecting electronic components. It addresses all aspects and details of the design requirements to the extent that they can be applied to the broad spectrum of those designs. It also serves as the basis for other sectional standards that focus on specific technologies or applications of printed boards.


The purpose and scope of IPC 2221




The purpose of IPC 2221 is to provide guidance and recommendations for printed board designers to achieve high-performance, reliable, and manufacturable designs that meet the functional and environmental requirements of the intended product. It also aims to facilitate communication and understanding between designers, manufacturers, and users of printed boards by establishing common terminology, definitions, symbols, and conventions.


The scope of IPC 2221 covers the general design principles and considerations for printed boards, such as materials selection, dimensional units, interpretation, definition of terms, documentation hierarchy, presentation style, reference documents, etc. It does not cover the specific design rules or criteria for particular technologies or applications of printed boards, such as rigid boards, flexible boards, high-density interconnects (HDI), multichip modules (MCM), etc. These are covered by other sectional standards that supplement IPC 2221.


The hierarchy of IPC design specifications




IPC has developed a documentation strategy that provides distinct documents that focus on specific aspects of electronic packaging issues. A document set is identified by a four-digit number that ends in zero (0). Included in the set is the generic information which is contained in the first document of the set and identified by the four-digit set number. The generic standard is supplemented by one or many sectional documents each of which provide specific focus on one aspect of the topic or the technology selected.


For example, the document set for printed board design is IPC-2220 series. The first document in this set is IPC-2221, which is the generic standard on printed board design. The other documents in this set are:


  • IPC-2222: Sectional Design Standard for Rigid Organic Printed Boards



  • IPC-2223: Sectional Design Standard for Flexible Printed Boards



  • IPC-2224: Sectional Design Standard for PCMCIA Card Standard



  • IPC-2225: Sectional Design Standard for Organic Multichip Modules (MCM-L) and MCM-L Assemblies



  • IPC-2226: Sectional Design Standard for High Density Interconnect (HDI) Boards



The user needs, as a minimum, the generic design document, the sectional of the chosen technology, and the engineering description of the final product. As technology changes, specific focus standards will be updated, or new focus standards added to the document set.


The main sections of IPC 2221




IPC 2221 consists of six main sections that cover the following topics:


  • Section 1: Scope - This section defines the purpose, scope, presentation, interpretation, definition of terms, and documentation hierarchy of IPC 2221.



  • Section 2: General Requirements - This section covers the general design requirements for printed boards, such as design data requirements, design data format, design data presentation, design data transfer, etc.



  • Section 3: Dimensional and Tolerance Requirements - This section covers the dimensional and tolerance requirements for printed boards, such as dimensional units, dimensional stability, dimensional tolerances, hole sizes and tolerances, etc.



  • Section 4: Materials - This section covers the material selection criteria for printed boards, such as material selection for structural strength, electrical properties, environmental properties, etc.



  • Section 5: Electrical Design Considerations - This section covers the electrical design considerations for printed boards, such as electrical clearance and creepage distances, conductor width and spacing, conductor thickness and current carrying capacity, impedance control, signal integrity, etc.



  • Section 6: Mechanical Design Considerations - This section covers the mechanical design considerations for printed boards, such as board shape and size, board edge clearance and spacing, board mounting and support, board warpage and bowing, board stress relief features, etc.



Why is IPC 2221 important?




IPC 2221 is important because it provides a comprehensive and consistent framework for printed board design that ensures quality, reliability, and manufacturability. By following IPC 2221, printed board designers can:


The benefits of following IPC 2221




  • Achieve optimal performance and functionality of the printed board and the electronic product.



  • Reduce design errors and rework costs.



  • Improve communication and collaboration with manufacturers and users of printed boards.



  • Enhance customer satisfaction and trust.



  • Comply with industry standards and regulations.



The challenges of printed board design




Printed board design is a complex and challenging process that involves many trade-offs and constraints. Some of the challenges that printed board designers face are:


  • Selecting the appropriate materials and technologies for the intended application and environment.



  • Balancing the electrical, mechanical, thermal, and environmental requirements of the printed board and the electronic product.



  • Optimizing the layout and routing of conductors and components to minimize noise, crosstalk, interference, signal degradation, etc.



  • Ensuring adequate clearance and spacing between conductors and components to prevent short circuits, arcing, corrosion, etc.



  • Ensuring adequate dimensional stability and tolerance of the printed board to prevent misalignment, deformation, cracking, etc.



  • Ensuring adequate mechanical strength and support of the printed board to withstand mechanical stresses, vibrations, shocks, etc.



  • Ensuring adequate thermal management of the printed board to prevent overheating, thermal expansion/contraction, thermal cycling fatigue, etc.



  • Ensuring adequate reliability and durability of the printed board to withstand environmental conditions such as humidity, temperature changes, contamination, etc.



The best practices for printed board design




  • To overcome these challenges and achieve high-quality printed board designs that meet IPC 2221 requirements, printed board designers should follow some best practices such as:Analyzing the functional and environmental requirements of the printed board and the electronic product.

  • Selecting the most suitable materials and technologies for the printed board based on IPC 2221 criteria.

Using appropriate design tools and software that support IPC 2221 standards How to use IPC 2221?




IPC 2221 is a useful reference and guide for printed board designers who want to create high-quality and cost-effective designs that meet the generic requirements for organic printed board design. However, IPC 2221 is not a substitute for engineering judgment, experience, and creativity. Printed board designers should use IPC 2221 as a starting point and adapt it to their specific needs and situations. They should also consult other sectional standards that provide more detailed and specific information on the chosen technology or application of printed boards. In this section, we will briefly summarize the main topics and recommendations of IPC 2221 for each of the five main sections.


The general design requirements of IPC 2221




The general design requirements of IPC 2221 cover the following topics:


  • Design data requirements: Printed board designers should provide complete and accurate design data to the manufacturers and users of printed boards. The design data should include all the necessary information for fabrication, assembly, inspection, testing, and repair of printed boards. The design data should also include any special requirements or deviations from IPC 2221 or other sectional standards.



  • Design data format: Printed board designers should use a standard format for presenting and transferring design data. The preferred format is electronic data interchange (EDI), which allows for faster and more accurate communication and exchange of design data. The EDI format should conform to IPC-2581 or other recognized standards.



  • Design data presentation: Printed board designers should use a clear and consistent presentation style for design data. The presentation style should include symbols, conventions, abbreviations, units, dimensions, tolerances, etc. that are commonly used and understood in the printed board industry. The presentation style should also follow the guidelines and examples provided in IPC-2221 or other sectional standards.



  • Design data transfer: Printed board designers should use a reliable and secure method for transferring design data to the manufacturers and users of printed boards. The method should ensure the integrity, confidentiality, and authenticity of the design data. The method should also allow for verification and validation of the design data by the recipients.



The material selection criteria of IPC 2221




The material selection criteria of IPC 2221 cover the following topics:


  • Material selection for structural strength: Printed board designers should select materials that have adequate structural strength to withstand the mechanical stresses and strains imposed by fabrication, assembly, handling, mounting, operation, and environmental conditions. The structural strength of materials depends on factors such as modulus of elasticity, tensile strength, flexural strength, shear strength, etc.



  • Material selection for electrical properties: Printed board designers should select materials that have adequate electrical properties to ensure the proper functioning and performance of the printed board and the electronic product. The electrical properties of materials depend on factors such as dielectric constant, dielectric loss tangent, volume resistivity, surface resistivity, etc.



  • Material selection for environmental properties: Printed board designers should select materials that have adequate environmental properties to resist degradation and deterioration caused by environmental conditions such as humidity, temperature changes, contamination, corrosion, etc. The environmental properties of materials depend on factors such as moisture absorption, thermal expansion, thermal conductivity, flammability, etc.



The dimensional and tolerance requirements of IPC 2221




  • The dimensional and tolerance requirements of IPC 2221 cover the following topics:Dimensional units: Printed board designers should use metric units (millimeters) as the primary dimensional units for printed boards. Imperial units (inches) may be used as secondary or supplementary units if necessary. However, printed board designers should avoid mixing metric and imperial units in the same design data.

  • Dimensional stability: Printed board designers should ensure that the printed board has adequate dimensional stability to maintain its shape and size during fabrication, assembly, and operation. The dimensional stability of printed boards depends on factors such as material selection, fabrication process, thermal expansion, moisture absorption, etc.

  • Dimensional tolerances: Printed board designers should specify dimensional tolerances for printed boards that are realistic and achievable by the manufacturers. The dimensional tolerances should account for variations in materials, processes, equipment, measurement methods, etc. The dimensional tolerances should also be compatible with the functional and environmental requirements of the printed board and the electronic product.

  • Hole sizes and tolerances: Printed board designers should specify hole sizes and tolerances for printed boards that are suitable for the intended purpose and function of the holes. The hole sizes and tolerances should account for factors such as drilling method, plating thickness, hole registration, hole quality, etc. The hole sizes and tolerances should also be compatible with the components and interconnections that use the holes.



The electrical design requirements of IPC 2221




  • The electrical design requirements of IPC 2221 cover the following topics:Electrical clearance and creepage distances: Printed board designers should ensure that the printed board has adequate electrical clearance and creepage distances between conductors and components to prevent electrical breakdown, short circuits, arcing, corona discharge, etc. The electrical clearance and creepage distances depend on factors such as voltage level, insulation type, contamination level, humidity level, etc.

  • Conductor width and spacing: Printed board designers should ensure that the printed board has adequate conductor width and spacing to ensure the proper electrical performance and reliability of the printed board and the electronic product. The conductor width and spacing depend on factors such as current carrying capacity, signal integrity, crosstalk, impedance control, etc.

  • Conductor thickness and current carrying capacity: Printed board designers should ensure that the printed board has adequate conductor thickness and current carrying capacity to handle the expected current load without overheating or damaging the conductors. The conductor thickness and current carrying capacity depend on factors such as conductor material, conductor shape, conductor length, ambient temperature, cooling method, etc.

  • Impedance control: Printed board designers should ensure that the printed board has adequate impedance control to match the impedance of the signal sources, loads, and transmission lines. Impedance control is important for high-speed, high-frequency, or sensitive signals that require minimal signal distortion, reflection, or attenuation. The impedance of printed board conductors depends on factors such as conductor width, spacing, thickness, dielectric constant, dielectric thickness, etc.

  • Signal integrity: Printed board designers should ensure that the printed board has adequate signal integrity to preserve the quality, accuracy, and timing of the signals transmitted through the printed board. Signal integrity is affected by factors such as noise, crosstalk, interference, signal degradation, etc. Printed board designers should use appropriate design techniques to minimize these factors, such as shielding, filtering, grounding, termination, etc.



The mechanical design requirements of IPC 2221




  • The mechanical design requirements of IPC 2221 cover the following topics:Board shape and size: Printed board designers should ensure that the printed board has a suitable shape and size for the intended application and environment. The shape and size of the printed board should account for factors such as component placement, interconnection layout, mounting method, enclosure fit, etc.

  • Board edge clearance and spacing: Printed board designers should ensure that the printed board has adequate edge clearance and spacing to prevent damage or interference with adjacent boards, components, connectors, enclosures, etc. The edge clearance and spacing of the printed board should account for factors such as fabrication tolerances, assembly tolerances, thermal expansion, vibration, etc.

  • Board mounting and support: Printed board designers should ensure that the printed board has adequate mounting and support to secure it in place and prevent excessive mechanical stress or deformation. The mounting and support of the printed board should account for factors such as mounting method, mounting hardware, mounting location, mounting orientation, etc.

  • Board warpage and bowing: Printed board designers should ensure that the printed board has minimal warpage and bowing to maintain its flatness and planarity. Warpage and bowing are deviations from a flat plane caused by uneven thermal expansion or contraction of materials. Warpage and bowing can affect the electrical performance, mechanical strength, assembly accuracy, etc. of the printed board. Printed board designers should use appropriate design techniques to minimize warpage and bowing, such as material selection, symmetrical layout, balanced construction, etc.

  • Board stress relief features: Printed board designers should ensure that the printed board has adequate stress relief features to reduce or eliminate mechanical stress concentrations that can cause cracking or failure of materials. Stress relief features are design elements that modify or interrupt sharp corners or edges where stress is concentrated. Examples of stress relief features are fillets, chamfers, notches, slots, holes, etc.



Conclusion




IPC 2221 is a generic standard on printed board design that provides information on the generic requirements for organic printed board design. It is a useful reference and guide for printed board designers who want to create high-quality and cost-effective designs that meet the functional requirements of the intended product. However, IPC 2221 is not a substitute for engineering judgment, experience, and creativity. Printed board designers should use IPC 2221 as a starting point and adapt it to their specific needs and situations. They should also consult other sectional standards that provide more detailed and specific information on the chosen technology or application of printed boards. By following IPC 2221 and its sectional standards, printed board designers can achieve optimal performance and functionality of the printed board and the electronic product, reduce design errors and rework costs, improve communication and collaboration with manufacturers and users of printed boards, enhance customer satisfaction and trust, and comply with industry standards and regulations. FAQs




Here are some frequently asked questions about IPC 2221:


  • What is the difference between IPC 2221 and IPC 2221A?



IPC 2221A is the latest revision of IPC 2221, which was published in May 2003. It supersedes IPC 2221, which was published in February 1998. IPC 2221A incorporates several changes and updates to refl


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