IPC Standards Overview

For PCB Designers

It All Starts With Standards

IPC standards play an important role in ensuring overall system performance by emphasizing the importance of quality and reliability in PCB production. These standards are published by the Association Connecting Electronics Industries, formerly known as 'The Institute of Printed Circuits (IPC)'. Despite the change in name, the acronym IPC is still used in the industry and in this article, we will focus on the IPC standards and their importance in PCB manufacturing.

IPC standards are intended to establish a set of guidelines and best practices that guarantee the quality, dependability, and manufacturability of electronic products. By adhering to IPC standards, companies can achieve consistent and dependable results, reduce manufacturing errors and defects, and increase their overall efficiency and output. Before we begin here is a brief summary of what standards are touched upon in this article. Some standards may be explained more than others but overall, here is an outline of what's to come:

IPC-2220 Series

IPC standards play an important role in ensuring overall system performance by emphasizing the importance of quality and reliability in PCB production. These standards are published by the Association Connecting Electronics Industries, formerly known as'The Institute of Printed Circuits (IPC)'. Despite the change in name, the acronym IPC is still used in the industry and in this article, we will focus on the IPC standards and their importance in PCB manufacturing.

Note that IPC-2222-26 standards are meant to be used in conjunction with IPC-2221. These Standards are briefly explained below:

• IPC-2221 - It is a generic IPC standard that provides guidelines for nearly all aspects of PCB design. This document provides general guidelines for the design of single- and double-sided PCBs, including information on layout, conductor spacing, thermal dissipation, land patterns, hole sizes, and signal integrity.
• IPC-2222 - This standard functions as a guide for rigid PCB cross-sectional design. It provides recommendations for structural elements such as board thickness, hole aspect ratio, and dielectric clearance. This standard is meant to be used in combination with IPC-2221.
• IPC-2223 - This standard specifically caters to a reliable design of Flex-PCBs. It outlines guidelines for key considerations in Flex-PCBs including material selection, impedance control, pad placement, unsupported edge conductor design, bending radius, and shield patterns.
• IPC-2224 - This standard specifies the design requirements for PC card forms of PCBs. The organic materials can be homogeneous, reinforced, or combined with inorganic materials, and the interconnections can be single, double, or multilayered. This standard classifies boards into six types as shown in the table below.

• IPC-2225 - This standard specifies thermal, electrical, electromechanical, and mechanical requirements for the design of an organic mounting structure used to interconnect semiconductor components. Together, these components make up a fully operational SCM-L, MCM, or MCM-L assembly.
• IPC-2226 - The standard gives guidance on how to design signal, power, ground, and mixed distribution layers, as well as dielectric separation, via formation, coating requirements and other important design specifications for organic and inorganic HDI boards. This standard acknowledges six types of industry-approved HDI boards. The quantity and position of HDI layers that may or may not be integrated with a substrate ([C] refers to 'core' substrate and [P] refers to a passive substrate that has no electrical connections) determine the HDI design type.

IPC-7351 Land Patterns

Land patterns are the areas of copper or other conductive substance on a PCB where the leads or pads of SMD electronic components are soldered. These land patterns are crucial for the proper assembly of electronic components onto the PCB, and they must be designed to ensure that the components are mounted in the correct orientation and that the solder connections are robust and reliable.

The IPC-7351 standard specifies the dimensions and tolerances for the land patterns. IPC-7351 also includes recommendations for land pattern shapes based on the type and size of the component being used. This standard ensures that land patterns on a PCB are optimised for manufacturability, reliability, and performance. Following IPC-7351 requirements for designing SMD pads in PCB footprints can reduce design time and avoid common SMD solder defects like bridging.

In short, the purpose of the IPC-7351 standard is to provide an outline of SMD land patterns. Nonetheless, there are additional IPC-735x series PCB footprint standards with more specific requirements for various components.

Base Materials

Selecting the PCB base material is not as simple as one might think. The inventory of available PCB laminate materials may vary from fabricator to fabricator. While specifying the laminate material, it is worthwhile to keep in mind that some materials are compatible with each other in different stackups. IPC standards provide a variety of specifications for PCB laminate materials, which aid in ensuring interchangeability and compatibility in a PCB stackup.

Various IPC standards that provide specifications of base materials for a PCB are summarized in the table below:

Slash Sheets

Before going into detail about various standards, it's important to get familiar with the term 'slash sheets'. Slash sheets are addenda to the IPC standards that outline criteria for several classes of laminates for PCB stackups. Each slash sheet contains information about the properties of the primary material and the results of various tests performed on it as per IPC standards. Information related to the primary material includes:

• Type of reinforcement
• Type of/content of resin
• Fillers and flame retardants
• Glass transition temperature

Additionally, information on various characteristics under IPC-TM-650 Tests is included:

• Peel strength: the amount of force needed to separate two bonded layers
• Thermodynamic properties, including moisture uptake rate and thermal resistance
• Dielectric properties like surface resistivity, loss tangent, and breakdown field strength.
• Prepreg and base material specifications

If you see something like IPC-4101/99 or 4101/24 in the catalog provided by your laminate manufacturer, the numbers '99' and '24' refer to slash sheets of that IPC-4101 standard. In other words, when you see IPC-xxxx/yy, xxxx is the IPC standard for base material and yy is the slash sheet. For each material, the above-mentioned properties, among others are specified in their respective slash sheets.

IPC 4101 and 4103

IPC-4101 was issued as the new standard to supersede MIL-S-13949. Originally, 41 slash sheets were included in this standard but RoHS rules and the emphasis on lead-free products have increased the number of slash sheets from 41 to over 65. The IPC-4101 standard covers conventional laminates and prepreg materials, including fibreglass-epoxy resin composites. Slash sheets included in IPC-4103 extend to bondply materials and copper-clad/unclad plastic laminate materials used in high-speed/high-frequency PCBs.

IPC-SM-840 For Solder Mask and Silkscreen

This standard specifies the criteria for evaluating liquid and dry film solder mask materials and determining their suitability for a standard printed board system. Properties like solvent resistance, adhesion, material qualification, dielectric flexibility, and electrical requirements are covered in this standard. All the requirements are provided for two classes (T and H) based on end-use and application.

• Class T - Practically speaking, this class of PCBs is equivalent to Class 2 PCBs defined in various IPC documents. The end-use in this case comes under the umbrella of 'Telecommunication' and includes applications like computers, telecommunications equipment, complex commercial machines, instruments, and non-critical military applications etc. Solder mask on these PCBs is appropriate for high-performance commercial and industrial items that require extended performance life but are not life-threatening if they suddenly stop working.
• Class H - This class can be considered equivalent to Class 3 PCBs. These PCBs are targeted for 'High Reliability/Military' equipment where downtime can prove to be catastrophic and continued operation is crucial.

PCB Performance Classes

A PCB's performance class is determined by its intended application and corresponding electrical, mechanical, thermal, and environmental performance requirements. IPC has established three performance classifications for PCBs: Class 1, Class 2, and Class 3. Each class denotes a distinct level of reliability and quality required for the PCB's intended purpose.

IPC-6010 Series

The IPC-6010 series covers the PCB qualification and performance specifications. The figure below summarizes various IPC standards covering PCB performance requirements and parameters:

Electronic Assemblies

IPC J-STD standards are a series of guidelines for electronic assemblies. These standards are designed to ensure quality and reliability in the manufacture of electronic assemblies and cover various aspects of the assembly process, including materials, components, and soldering. The IPC J-STD standards are widely recognized in the electronics industry and provide a common framework for manufacturers to produce high-quality electronic assemblies that meet the expectations of customers and end-users. The figure below summarizes a few import IPC J-STD standards:

IPC-A-610

IPC-A-610 is widely used throughout the electronics industry as a standard for the acceptance of electronic assemblies. The standard includes detailed criteria for the visual inspection of electronic assemblies. For instance, it lays out acceptance criteria for terminals, connectors, wiring, insulation, and other parts of the soldering process for both through hole components and SMDs among other things. The criteria are defined for the three PCB classed explained above.

IPC J-STD-001

This standard specifies the materials, processes, and acceptance requirements for soldered electrical and electronic assemblies. This document's goal is to depend on process control technology to achieve constant quality levels during product manufacturing. This standard is often used in combination with IPC-HDBK-001 and IPC-A-610.

IPC-CC-830 For Conformal Coatings

PCBs are frequently coated with a conformal coating to protect them from the rough degradation caused by their operational environments. It is a thin non-conductive dielectric film that can be deposited by brushing, spraying, or automated processes such as spraying or dipping. The primary standard that provides guidelines pertaining to conformal coatings is IPC-CC-830.

This standard sets requirements for conformal coatings in terms of qualification and conformity. It was planned and built with the goal of achieving maximum credibility for the materials while minimizing test redundancy. Materials, viscosity, shelf life, curing, and visual requirements are all covered in this standard. It also includes fungal, moisture, and flammability resistance characteristics, as well as other electrical standards like dielectric withstanding voltage etc.