As chip sizes shrink and system features and functions expand, board designers are increasingly challenged with recalling all the parameters and guidelines they need for every aspect of board layout. The newly revised, 170-page, IPC-2221B, Generic Standard on Printed Board Design, provides a basis for the design of all types of printed boards and addresses areas as diverse as testing, via protection, test coupon designs and surface finishes.
“We provided a lot of information that can help designers make decisions between surface finish alternatives,” said John Perry, IPC technical project manager. Perry added that descriptive data within the standard is augmented by a table that makes it easier to quickly compare the traits of various surface finishes.
Industry’s focus on quality and reliability is addressed with an upgraded section on electrical requirement testing. “There are several pages of new material on electrical testing that explain the various types of tests available, including continuity, Hi-Pot and impedance,” Perry said. “Ultimately, the message is that no one test meets all requirements. Designers are encouraged to use two or three to ensure that they are meeting user requirements.”
IPC-2221B also provides details on via protection, which is becoming more important as the number of via holes on a typical board increases. Another significant addition to the revised standard is the new Appendix A that details a new set of test coupon designs that are utilised for lot acceptance and periodic conformance testing in accordance with performance specifications including IPC-6012C, Qualification and Performance Specification for Rigid Printed Boards, and IPC-6013B, Qualification and Performance Specification for Flexible Printed Boards.
For example, the new AB/R coupon used for plated hole/via evaluation and thermal stress testing has been designed to accommodate blind, buried and mircovia structures used in today’s printed boards. The AB/R coupon and the other eight designs within Appendix A represent a significant improvement over the legacy IPC-2221 coupon designs that date back more than 23 years and which are now contained in Appendix B for existing designs.
For more information contact Nkoka Training, +27 (0)12 653 2629, [email protected], www.nkoka.co.za
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