2.4 International Electrotechnical Commission4IEC-61188 Printed Boards and Printed Board Assemblies -Design and Use2.5 Joint Electron Device Engineering Council (JEDEC)5Publication 95 JEDEC Registered and Standard Outlinesfor Solid State Products3 DESIGN REQUIREMENTS3.1 Dimensioning Systems This section describes a setof dimensional criteria for components, land patterns, positionalaccuracy of the component placement capability andthe opportunity to create a certain size solder joint commensuratewith reliability or product performance analysis.Profile tolerances are used in the dimensioning system todefine the size range between maximum and minimumcomponent/lead dimensions without ambiguity. The profiletolerance is intended to control both size and position ofthe land. Figure 3-1 shows the profile tolerancing method.The use of the profile dimensioning system requires anunderstanding of the concepts. The use of a set of requirementsare adopted and invoke the following rules, unlessotherwise modified.a. All dimensions are basic (nominal).b. Limits of size control form as well as size.c. Perfect form is required at maximum dimensions.d. Datum references and position tolerances apply at maximumdimensions, and are dependent on feature size.e. Position dimensions originate from maximum dimensions.f. Tolerances and their datum references other than sizeand position apply regardless of feature size (RFS).The dimensioning concepts used for this system of analysisconsider the assembly/attachment requirements as theirmajor goal. Specification (data) sheets for components ordimensions for land patterns on boards may use differentdimensioning concepts, however, the goal is to combine allconcepts into a single system. Users are encouraged toestablish the appropriate relationship between their dimensioningsystem(s) and the profile dimensioning system andanalysis concepts described herein to allow for ease of tailoringthese concepts for robust process performance. Asan example, if the tolerance used for positioning is largerthan the machine tolerance used in production, a singledimensional change could modify the land pattern.3.1.1 Component Tolerancing The component manufacturersand industry standards organizations are responsiblefor the dimensioning and tolerancing of electroniccomponents (see 3.1.5.2). The basic dimensions and tolerancelimits published in the specifications have been convertedto a functional equivalent using the profile tolerancingmethod with all components shown with their basicdimensions as limit dimensions (maximum or minimumsize). Profile tolerances are unilateral, and are described toreflect the best condition for solder joint formation.