Editor's Note: This article originally appeared in the June 2012 issue of The PCB Magazine.
Requirements for PCB design can vary considerably from one design to the next. I specialize in high-speed design (HSD) but I am often asked to do a board that incorporates a switch-mode power supply. Or, there may be an analog section that needs to be laid out, so the design rules I use vary depending on the application.
Where to Start?
IPC was founded in 1957. The association has provided the worldwide electronics industry with guidelines for design and manufacture of PCBs, compiled over the years, with the support of both committee and industry members.
IPC-2221A is the foundational design standard for all documents in the IPC-2220 series. The series is built around the IPC-2221, Generic Standard on Printed Board Design, the base document that covers all generic requirements for printed board design, regardless of materials. From here, the designer chooses the appropriate sectional standard for a specific technology.
All five sectional standards are included with the series:
- IPC-2222: Sectional Design Standard for Rigid Organic Printed Boards
- IPC-2223: Sectional Design Standard for Flexible Printed Boards
- IPC-2224: Sectional Standard for Design of PWBs for PC Cards
- 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) Printed Boards
This series provides coverage on material and final finish selection, current-carrying capacity and minimum electrical clearances, test-specimen design, guidelines for V-groove scoring, dimensioning requirements and conductor thickness requirements. Some of these standards are now published in Chinese and German.
Several documents apply to HSD and land-pattern design:
- IPC-2251: Design Guide for Electronic Packaging Utilizing High-Speed Techniques
- IPC-2141A: Design Guide for High-Speed Controlled Impedance Circuit Boards
- IPC-7351B: Generic Requirements for Surface Mount Design and Land Pattern Standard
These standards (and their predecessors) have been part of a well-used section of my technical library since 1987. They provide excellent reading and reference material for all PCB designers. These documents are available for purchase from www.ipc.org.
Design rules must keep up with the latest devices and fabrication processes, without losing sight of DFM, which is the practice of designing board products that can be produced in a cost-effective manner using existing manufacturing processes and equipment. If you follow the above IPC guidelines, you will be designing for both manufacturability and mass production.