BANNOCKBURN, IL – IPC has released the B revision of IPC-7351, Generic Requirements for Surface Mount Design and Land Pattern Standard.

The revision provides industry consensus guidance on requirements of land pattern geometries, as well as surface mount design recommendations for achieving the best solder joints.

A major addition to IPC-7351B, the new padstack naming convention, consists of combinations of letters and numbers that represent the shape or dimensions of lands on different layers of printed boards or documentation. The padstack naming convention enables a designer to convey all variations and dimensions of a padstack, employing it in combination with intelligent land pattern conventions also defined within the standard, according to design rules established in the IPC-2220 design series. 

The standard directs users on an appropriate land pattern based on desired component density through the provision of three separate land pattern geometries for each component. The revision introduces land pattern design guidance and rules for new surface mount component families such as electrolytic aluminum capacitors; small outline diode, flat lead; small outline transistor, flat lead, and dual flat no-lead devices.

Several device families, including DPAK, QFP and QFN, often feature thermal pads on the bottom of the packages that expose the die to the printed board surface. IPC-7351B now provides a default paste mask for those pads to permit the package body to settle.

The revision also expands its Pb-free coverage with the addition of new solder alloys, and presents discussion on etch-factor compensations at the design and printed board fabrication levels.

“IPC-7351B introduces several new component families and lead forms that include micro-miniature flat-lead and no-lead components, and a new padstack standard naming convention," says committee member Tom Hausherr, EDA library product manager, Mentor Graphics. "Overall, the IPC-7351B standard is a key publication in the electronics industry for accurate CAD library generation."

IPC-7351B includes both the standard and an IPC-7351B Land Pattern Calculator on CD-ROM for accessing component and land pattern dimensional data. The calculator includes the document’s mathematical algorithms. The tool also permits modification of dimensional attributes of IPC-approved land patterns.

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