What are IPC standards for PCB Design, PCB Assembly and PCB Fabrication?

IPC standards are electronic design, manufacturing and inspection standards published by IPC, a global trade and standards setting association focused on the electronics industry.  IPC’s standards are used worldwide and have been essential to the globalization of the electronics industry. Anyone who designs or manufactures PCB assemblies needs to be familiar with the standards.

Most engineers and designers first encounter the IPCstandards in the fabrication notes on PCB drawings or because they have been trained on ubiquitous IPC-A-610 “Acceptability of Electronic Assemblies” which illustrates quality standards for PCB soldering and cleaning.

The IPC publishes standards for every aspect of PCB design, manufacturing, and inspection

The major categories of the standards are:

• General documents
• Design specifications
• Material specifications
• Performance and inspection standards
• Flex assembly and materials standards

The General Documents cover terms and definitions, PCB tolerances, PCB documentation, and bare PCB testing standards.

The Design Specification Section focuses on guidelines for the electrical engineer and PCB layout designer.Perhaps the two best known design standards are IPC-2221 “Generic Standard on Printed Board Design” and IPC-7351B Generic Requirements for Surface Mount Design and Land Pattern Standards.  Fortunately for the PCB designer, these generic standards are encoded in the PC Board layoutsoftware’s internal design rules, so it is not necessary to have them memorized when laying out a PCB.

The Material Specificationsdefine the specifications for everything in the electronics supply chain from the pre-preg to the silkscreen. These specifications are often referenced in the notes on a PCB drawing.  One typical example is IPC-4552“Performance Specification for Electroless Nickel/Immersion Gold (ENIG) Plating for Printed Boards” which sets requirements for the gold plating of PCBs.

The Performance and Inspection Documents contains one of the most important standards, IPC-6011 “Generic Performance Specification for Printed Boards.”   IPC 6011 establishes the requirements for PCBs and defines the level of quality ultimately reliability for PCBS the IPC-6011 standards cover the following topics:

• PCB design
• PCB assembly
• PCB testing
• PCB inspection
• PCB documentation

Flex assembly and materials standardscovers both the materials and the assembly standards for flexible printed circuits

IPC Electronic Product Classes

The most important part of IPC-6011 is the definition of classes of electronic products.  The definition of classes is then used to determine the PCB design, manufacturing, and inspection rules.

IPC 6011 defines three classes of electronic products and one subclass.

• Class 1 – general electronic products: Class 1 products are for applications in which the functionality and low cost primary drivers, and reliability is secondary. This class includes most low-cost electronic products. PNC and most U.S suppliers do not manufacture class 1 PCBs.

• Class 2 – dedicated service electronic products: Class 2 products put more emphasis on high reliability and extended life. Uninterrupted service is preferable, but not mission critical. The use environment of the class 2 product is not extreme enough to cause Printed Circuit Board This is typically the default standard for layout application design rules and for U.S. manufacturers.

• Class 3 – high-performance electronic products: Class 3 products must provide continuous performance or performance on demand with no downtime or performance degradation. The end-use environment may include temperature extremes, vibration, and high altitudes. This category includes critical systems such as medical life support systems.

• Class 3/A -space and avionics: Class 3/A is a new subclass of class 3 specifically for military and aerospace electronics. They are considered mission critical and failure could result in the loss of the spacecraft or aircraft. It is the highest class for PCBs, and class 3/A PCBs have very stringent (and expensive) manufacturing and inspection criteria.  When selecting a manufacturer for class 3/A PCBs it is essential to choose a company like PNC with extensive military and aerospace experience.

Differences Between Class 2 and Class 3 PCBs

 From an engineer’s standpoint, the selection of product class affects the design rules used by the layout software, the PCB construction and most importantly from a cost standpoint, the level of inspection and reject criteria at the bare PCB and finished assembly level.  Oneof the most consequential decisions for the final unit cost of the PCB assembly will be the decision to go with either an IPC class 2 or class 3 quality level.

At the PCB design stage, there are different design rules for class 2 and class 3.The design rule that has the most effect on the layout is that the difference in the size of via pads and drill holes specified for plated through holes.

Larger pad and drill sizes are required on IPC class 3 PCBs to ensure the a 360 deg connection between the pad and the hole plating, and to minimize the potential for drill breakouts from the annular ring on the far side of the hole due to drill drift.   Besides taking up more PCB real estate, the larger via pad specification for IPC class 3 PCBs limit the fan out of BGAs to 0.8 mm pitch and larger. Smaller pitch BGAs cannot be accommodated by class 3 design rules, because traces cannot be routed between the larger pads.

In manufacturing, there are tighter inspection criteria for defects to the bare PCB that increases inspection time and decreases bare PCB yield. Both increase costs.  Similar inspections and occur after soldering and cleaning, and again, the tighter inspection criteria decrease PCB yield.

PNC can help you keep IPC class 3 costs in control

 The best way to keep IPC class 3 PCB costs under control is to work with a manufacturer who has the expertise and equipment to keep yields high.   PNC has deep experience in fabricating space and avionics rated PC Board assembly. Ask the experts at PNC to work with you on your next mission critical design.

Written by Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.