One of the biggest changes to the document is the addition of a listing of the positives and negatives of popular materials along with some of their performance characteristics. “Having the advantages and disadvantages of common laminates spelled out will help printed board designers select a suitable laminate material,” explains John Perry, IPC technical project manager. This information is provided in the form of a comparison table that also includes CTE (coefficient of thermal expansion) data, dielectric constant, and Tg.
Data on the relative cost of materials as well as their capabilities in terms of dimensional stability, material consistency and other special processing has also been added to this table. “We wanted to provide designers with guidance on laminate materials availability, relative cost, reworkability, moisture stability and suitability for lead-free applications,” says Perry.
Another new facet is the inclusion of data that provides guidance for the tolerances of printed board thickness, an area that hasn’t been addressed by the IPC document in many years. Helping designers address concerns about dimensional stability, the measurements are based on laminate to laminate thickness. The tolerances provided do not include any finishes or coatings and can help users avoid problems such as bowing or twisting.
Guidance on nonfunctioning lands, which can pose problems in multilayer boards, is now a part of IPC-2222A. “We provide a table that explains why you may want to keep or remove nonfunctioning lands,” Perry says. “For example, if a number of nonfunctioning lands are removed from a board with many layers, inner layers may separate during z-axis expansion, causing reliability concerns.”
The standard also examines supported and unsupported holes. Tolerances are provided for diameters of unsupported holes, such as those used to provide clearance for mounting hardware. There’s also a guide for the aspect ratio of holes. This latter section provides guidance on the ability to produce holes of specific diameters in relation to the thickness of the printed board. “Aspect ratio plays a key part in the ability of the printed board fabricator to provide sufficient plating along the barrel of a plated hole,” Perry said.
Designers who use IPC-2222A can help ensure that the boards they design will meet requirements when the boards are manufactured. “End boards usually have to meet the requirements of IPC-6012, Qualification and Performance Specification for Rigid Printed Boards. If a board is designed according to IPC-2222A specifications, the designer should have confidence that the board will meet IPC-6012 requirements,” Perry says.
IPC members may request a free single-user download of IPC-2222 by sending an e-mail to MemberTechRequests@ipc.org within 90 days of the document’s publication date. After that date, IPC members may purchase the standard for $36. The nonmember price is $72. For more information or to purchase IPC-2222A, visit http://www.ipc.org/2222.
IPC (www.IPC.org) is a global trade association based in Bannockburn, Ill., dedicated to the competitive excellence and financial success of its 2,700 member companies which represent all facets of the electronics industry, including design, printed board manufacturing, electronics assembly and test. As a member-driven organization and leading source for industry standards, training, market research and public policy advocacy, IPC supports programs to meet the needs of an estimated $1.7 trillion global electronics industry. IPC maintains additional offices in Taos, N.M.; Arlington, Va.; Garden Grove, Calif.; Stockholm, Sweden; Moscow, Russia; Bangalore, India; and Shanghai, Shenzhen and Beijing, China.