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:
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:
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.
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.