1

Extensions to the recommended practices

for GD&T in STEP-AP210 in the context 

of packaged electronic components

Jamie Stori

SFM Technology, Inc. 

Urbana, Illinois 

Kevin Brady 

National Institute of Standards and Technology

Electronics and Electrical Engineering Laboratory

Thomas Thurman

Rockwell Collins, 

Cedar Rapids, Iowa 

NISTIR 7634
2

NISTIR 7634

Extensions to the recommended

practices for GD&T in STEP-AP210 in 

the context of packaged electronic 

components

Jamie Stori

SFM Technology, Inc. 

Urbana, Illinois 

Kevin Brady 

National Institute of Standards and Technology

Electronics and Electrical Engineering Laboratory

Thomas Thurman

Rockwell Collins, 

Cedar Rapids, Iowa 

October 2009

U.S. Department of Commerce

Gary Locke, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Director
- 1 - October 20, 2009

Extensions to the recommended practices for GD&T in STEP-AP210 in the 

context of packaged electronic components

October 20, 2009

Introduction

The purpose of this document is to extend the recommended practices for the 

representation of GD&T in STEP (ISO-10303) within the context of packaged electronic 

component models represented in AP210 (ISO-10303:210). The recommendations in this 

document are intended to be consistent with the current GD&T accepted practice in 

STEP. Please refer to the document entitled “Recommended Practices for Dimensions, 

Dimensional and Geometric Tolerances” dated December 6, 2006 by David Briggs, Tom 

Hendrix, and Steve Yates for current practice recommendations for GD&T in STEP. 

This document is available on the website of the CAx Implementor Forum 

(http://www.cax-if.org/) under the Recommended Practices link. The ARM application 

objects, relationships, attributes, and mapping to the corresponding MIM entities, 

relationships, and attributes have been updated to the IS version of the 2nd Edition of AP210.

The largest family of standards for packaged electronic components are those published 

by JEDEC. The JEDEC standards are freely and publicly available, and contain detailed 

dimensioned and toleranced specifications for physical package configurations. JEDEC 

Publication 95 is a series of documents containing specifications for many common 

physical package configurations. The JEDEC Publication 95 documents can be accessed 

on-line at: http://www.jedec.org/DOWNLOAD/pub95/default.cfm. In this document, in 

addition to general guidelines for the representation of tolerances in a packaged electronic 

component, a set of STEP mappings for a typical toleranced JEDEC package model will 

be discussed. These examples are intended to be representative of many of the common 

tolerances encountered in the JEDEC standards.

The GD&T standard referenced by both JEDEC and the 2006 STEP recommended 

practice is ASME Y14.5 (1994). The recommendations in this document are intended to 

be consistent with both the 1994 as well as recent 2009 publication of Y14.5.

Notation

ARM AOs will be denoted with a leading uppercase letter in Courier font (i.e. Datum) 

while a MIM entity will be displayed in all lowercase notation (i.e. datum).

Assembly vs. Single-Solid representation of a packaged component model

There are two primary alternatives for the representation of the three-dimensional 

geometric representation of a packaged component model. The preferred representation is 

one in which each of the physical package features (body, mounting features, terminals, 

etc.) have an explicit three-dimensional geometric model. In the case of a replicated 
- 2 - October 20, 2009

feature, such as a terminal, many terminal instances will share a common template

(package_terminal_template_definition). Figure 1 through Figure 3 illustrate 

the preferred representation of the geometric model for a package_terminal, 

package_body, and seating_plane, respectively. As may be seen in the figures, each 

of the package features has a distinct shape_representation, typically an 

Figure 1. Defining a shape_aspect based on a surface of a terminal in a package model.

package_terminal

package of_shape 

package_terminal_t

emplate_definition

product_definition

_shape

definition 

shape_definition_representation

definition 

used_representation 

usage_concept_usage_

relationship

definition 

used_representation 

mapped_representation 

representation_map

Axis2_placement

_3d mapping_source 

mapping_target 

packaged_part

packaged_part_terminal

relating_product_definition 

related_product_definition 

property_definition

_relationship

{.name = ‘definition’}

property_definition

definition 

property_definition

definition 

product_definition_relationship

related_product_definition 

relating_product_definition 

.name = ‘used package’

{.description = ‘join terminal’}

shape_aspect_relationship

relating_shape_aspect 

related_shape_aspect 

{.name = ‘terminal of package’}

of_shape 

shape_definition

_representation

definition 

shape_representation

used_representation 

description_attribute

described_item 

{.attribute_value = 'part feature template shape model’}

axis2_placement_3d

mapping_origin 

{.name = ‘3d bound volume shape’}

shape_aspect

definition 

nodes [2]

identified_item 

nodes [1]

advanced_brep_shape_

representation

manifold_solid_brep

items [1:?]

closed_shell

outer 

advanced_face

cfs_faces [1:?]

chain_based_item_identified_

representation_usage

undirected_link [1]

{.name = ‘3d bound volume shape’}
- 3 - October 20, 2009

advanced_brep_shape_representation. The package features are 

shape_aspects of the package, and the shape_representation of the feature is 

placed with respect to the shape_representation of the package with a 

usage_concept_usage_relationship. Explicit representation of the geometric 

models for distinct package features significantly enhances the ability to perform detailed 

domain-specific reasoning and functional analysis in contexts such as manufacturability, 

ECAD-MCAD integration, etc. This preferred representation is analogous to that a 

mechanical assembly, and the expression of tolerances and dimensions requires 

representation mechanisms similar to that of mechanical assemblies.

package of_shape package_body

shape_representation

usage_concept_usage_

relationship

definition 

used_representation 

mapped_representation 

representation

_map

Axis2_placement

_3d

mapping_source mapping_target 

shape_definition

_representation

shape_representation

used_representation 

Axis2_placement

_3d

mapping_origin 

definition 

shape_definition

_representation

used_representation 

definition 

property_definition

definition 

Figure 2. Relationship of the shape model of a package_body to that of the package. 
- 4 - October 20, 2009

The alternative is to have a single shape_representation that contains the detailed 

geometric model for the package. In this case, dimensioning and tolerancing can be 

achieved through mechanisms applicable to a single-solid part. 

Shape_elements

Features of the model relevant for GD&T are represented by the Shape_element AO. 

Figure 4 shows several of the important subtypes of Shape_element. A surface of a 

part can be modeled directly as a Shape_element. In the MIM mapping, the feature 

will most likely be associated with an advanced_face. When it is desired to treat 

multiple disjoint regions as a single feature, a Composite_shape_element may be 

employed. A Composite_shape_element has two important subtypes – the 

Figure 3. Representation of the seating_plane in a package model.

package seating_plane of_shape 

shape_representation

usage_concept_usage_

relationship

definition 

used_representation 

mapped_representation 

representation

_map

Axis2_placement

_3d

mapping_source mapping_target 

shape_definition

_representation

shape_representation

used_representation 

Axis2_placement

_3d

mapping_origin 

definition 

shape_definition

_representation

used_representation 

definition 

property_definition

definition 

plane

items [1:?]

axis2_placement_3d

position 
- 5 - October 20, 2009

Composite_group_shape_element and the Composite_unit_shape_element. A 

Composite_unit_shape_element is used to aggregate multiple Shape_elements

that are to be treated as a unit. For example, multiple surfaces of a single feature-of-size. 

A Composite_group_shape_element is used when it is desired to apply a property 

to each of the constituent elements individually. Figure 5 contains the MIM mapping of 

the Composite_shape_element (either composite_group_shape_aspect or 

composite_unit_shape_aspect) and the relationships to its constitutive elements. 

Shape_element

Centre_of_symmetry

Derived_non_feature_

shape_element

Centre_plane

Non_feature_shape

_element Derived_shape_element

Datum_shape_element

Datum

Composite_shape

_element

Composite_group_

shape_element

Composite_unit_

shape_element

Shape_element_composing

_relationship

composing_relationships INV [2:?]

Shape_element

derived_from [1:?]

Shape_element_deriving

_relationship

deriving_relationships INV [1:?]

Shape_element

related 

Shape_element

related 

relating relating 

Figure 4. Several relevant subtypes of the Shape_element AO
- 6 - October 20, 2009

It is often common to require a reference to derived geometry, such as a center plane of a 

feature. Such a feature would be modeled through the appropriate subtype of 

Derived_non_feature_shape_element (a Shape_element that is not on the 

physical boundary of the part). Figure 6 contains the MIM mapping of the 

Centre_plane AO for the common case in which the derived center-plane is defined by 

two faces of the model.

In the context of GD&T for AP210 package models, it is often necessary to reference 

surfaces of individual terminals as well as groups of terminals for the purposes of 

Figure 6. MIM representation of a Centre_plane (a Derived_non_feature_shape_element).

shape_aspect_deriving_r

elationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

shape_aspect_deriving_r

elationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

centre_of_symmetry

{shape_aspect.description = 'plane'}

property_definition

advanced_face

shape_definition_representation

shape_representation

definition 

definition used_representation 

items [1:?]

property_definition

advanced_face

shape_definition_representation

shape_representation

definition 

definition used_representation 

items [1:?]

derived_shape_aspect

shape_aspect

composite_shape_aspect

shape_aspect_relationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

{shape_aspect_relationship.name = 'composing'}

shape_aspect_relationship

shape_aspect

related_shape_aspect 

{shape_aspect_relationship.name = 'composing'}

relating_shape_aspect 

.......

.......

composite_unit_shape_

aspect

composite_group_shape

_aspect

Figure 5. MIM representation of a Composite_shape_element
- 7 - October 20, 2009

defining datum and geometric tolerances. As discussed previously, in an AP210 package 

model, it will often be necessary to individually reference instances of faces used in a 

common template (for example, assigning a dimension between the outer-faces of two 

specific terminals instances). Individual instances of the terminal will typically be placed 

with respect to the shape model of the package using a 

usage_concept_usage_relationship. This case is analogous to a common issue in 

assembly-level tolerance representation. A mechanism for specifying the required 

association between a shape_aspect and a specific face of an individual terminal 

instance has recently been established through the MIM entity 

chain_based_item_identified_reprsentation_usage, a subtype of 

item_identified_representation_usage, defined in Technical corrigendum 2 to 

International Standard ISO 10303-41:2005. As the name implies, the new subtype 

supports a hierarchically linked chain of representations so as to allow unambiguous 

reference to a representation_item in a lower level of the hierarchy. The MIM 

mapping for a Shape_element needed to identify an individual face on a individual 

terminal using the chain_based_item_identified_reprsentation_usage is 

detailed in Figure 1, where the associated entities, attributes, and relationships are 

highlighted in red. 

Representation of dimensional tolerances
- 8 - October 20, 2009

The JEDEC Publication 95 standards employ a combination of dimensional 

tolerances and geometric tolerances. Figure 7 and Figure 8 contains a 

representative dimensioned and toleranced drawing of a typical JEDEC 

component package. As may be seen in the figure, there are a number of 

basic dimensions (D, D1, e, etc.) as well as a number of dimensional 

tolerances (A, A1, A2), and 5 geometric tolerances specified in control 

frames.

The toleranced dimensions are all undirected, and are both dimensional and size 

tolerances. Dimensions A2 and b are size dimensions (height of the body of the package, 

Figure 7. JEDEC Pub. 95 toleranced specification of the QFP package family (MS-029, Figure 1).
- 9 - October 20, 2009

width of a terminal, respectively). 

In each case, the size dimension 

applies to a regular feature of size 

(two opposed parallel surfaces). In 

the case of dimension A2, there is 

a single package body, whereas 

dimension b must apply to each of 

the terminals in the package.

The top-level ARM application 

objects and attributes used in the 

representation of a dimensional 

tolerance are contained in Figure 9

and Figure 10. Dimensions A2 and 

b would be represented as the 

Height_size_dimension and 

Width_size_dimension

subtypes of Size_dimension. 

Each would refer to a single 

Shape_element. In the event that 

the geometric model of the 

terminal was contained within the 

package_terminal_template

_definition, a single dimension 

would intrinsically apply to all 

terminals in the package. In the 

event that a single solid was used 

to represent the complete package 

model, it would be necessary to use a Composite_group_shape_element which 

would explicitly contain a shape element for each of the terminal instances in the 

package. Each of these shape elements would need to reference the two opposing faces 

(advanced_face) of the terminal within the 

advanced_brep_shape_representation. For the majority of the JEDEC 

dimensions, either a minimum / maximum range, or minimum / nominal / maximum 

values are provided explicitly. The dimensional_value attribute would therefore 

reference either a Tolerance_range or a Dimension_value_with_limitation. In 

certain cases, only a minimum or maximum value is provided. In this case, a 

Value_limit would be used for the representation. The MIM mapping for these ARM 

concepts for dimensional tolerances are contained in Figure 11 and Figure 12. 

Dimensions A and A1 would be represented as instances of the 

Linear_distance_dimension, subtype of Location_dimension. Neither of these 

dimensions relates to a feature of size, and would require two distinct Shape_element, 

each of which would be associated with a particular surface, or group of surfaces in the 

model. In both cases, the dimension relates the bottom surfaces of the terminals to a face 

on the body (either top or bottom surface). The bottom surfaces of the terminals could be 

referenced through a single Shape_element in the case where all terminals are 

Figure 8. A dimension and datum specified by a feature 

of size (from JEDEC Pub. 95, MS-029 Figure 4).
- 10 - October 20, 2009

instances of the same package_terminal_template_definition. In the event that 

a single solid was used to represent the entire package, all bottom terminal surfaces 

should be aggregated together as a Composite_unit_shape_element. 

Representation of datum

In this document, we consider three common means of defining a datum plane in the 

JEDEC Publication 95 specification. Per ASME Y14.5 (1994), a datum is a theoretically 

exact point, line or plane derived from geometric counterpart(s) on the physical model. 

The geometric counterpart is known as a datum feature. The AP210 ARM supports a 

family of application objects (AOs) that are subtypes of Datum. Several of the commonly 

used subtypes that are most relevant for the domain of packaged electronic components 

are documented in Figure 13. 

Figure 9. The top-level subtypes and key entities of the Geometric_dimension AO.

Geometric_dimension

is_applied_to element_with_dimension_select

Shape_element

dimension_value_select

dimension_value 

Numerical_item_with_unit

Dimension_value_with_limitation

Tolerance_range

Value_limit

Size_dimension

Angular_size_dimension Curved_size_dimension Diameter_size_dimension

Radial_size_dimension

Thickness_size_dimension

Externally_defined_size_di

mension Height_size_dimension Length_size_dimension

Dimensional_size_based_

on_opposing_boundaries

Width_size_dimension

Location_dimension

Angular_location_dimension Curved_distance_dimension Linear_distance_dimension

placed_element_select

Shape_element

placed_element_select

Shape_element

origin 

target 

directed (OPT) BOOLEAN
- 11 - October 20, 2009

In many cases, a datum feature will correspond to either a surface feature of a part or a 

“feature of size” of a part. When it is required that a specific region of a surface be used 

to determine the datum, a datum target may be used. A “feature of size” must contain 

opposed points, and have a reproducible derived median point, axis, or center plane. An 

example of an internal feature of size would be a slot. A pin or a shaft would be an 

example of an external feature of size. Many times, a feature of size is used as a datum 

feature in defining a datum. 

A common example in the context of JEDEC Publication 95 would be the use of a 

package terminal as a feature of size to define a datum plane. Figure 8 outlines how either 

an internal or an external feature of size would be called out as a datum feature, 

depending on whether a particular package had an even or odd number of leads on a 

particular side. In the case of an odd number of leads per side, an external feature of size 

may be associated with the opposing sides of the lead exiting the body of the component

at its center plane. In the case of an even number of leads per side, an internal feature of 

size may be associated with the opposing (inner) sides of the two center-most leads. 

The boxed x, in conjunction with the filled triangle constitutes the datum feature symbol 

[Y14.5-1994 3.3.2]. In the example of Figure 8, datum features A, B, and D are all 

defined equivalently.

Dimension_value_with_limitation

Tolerance_range

qualifiers [1] Pre_defined_type_qualifier

{.name = minimum}

{.name = maximum}

Numerical_item_with_unit

Measure_item Value_with_unit

Value_limit

Numerical_item_with_unit

limited_value 

Plus_minus_bounds

Value_with_unit

Value_with_unit

lower_bound 

upper_bound 

limitation_definition_select

defined_by 

Numerical_item_with_unit lower_range 

upper_range Numerical_item_with_unit

dimension_value_select

Figure 10. ARM AOs for expressing a value of a Geometric_dimension.
- 12 - October 20, 2009

Datum features A, B, and D represent a derived datum center plane. 

applies_to 

shape_aspect

dimensional_size

dimensional_location

shape_aspect

related_shape_aspect 

{dimensional_size.name = 'thickness size'}

{dimensional_size.name = 'width'}

{dimensional_size.name = 'length'}

{dimensional_size.name = 'height'}

plus_minus_tolerance

toleranced_dimension 

shape_dimension_representation

items [1] measure_representation_item

dimensional_characteristic_representation

dimension 

representation 

measure_representation_item+

qualified_representation_item

shape_dimension_representation

shape_dimension_representation

measure_representation_item

measure_representation_item

{.name = 'lower range’}

{.name = 'upper range’}

items [1]

items [2]

directed_dimensional_location

shape_aspect

angular_location dimensional_location_with_path

derived_shape_aspect

derived_shape_aspect

relating_shape_aspect 

items [1]

dimensional_size

dimensional_location

dimensional_characteristic

dimensional_characteristic

dimension 

dimensional_characteristic

dimensional_characteristic_representation

representation 

dimension 

dimensional_characteristic

dimensional_characteristic_representation

representation 

For a linear distance dimension,

{shape_aspect_relationship.name

 = 'linear distance'}

dimensional_size

dimensional_location

dimensional_size

dimensional_location

dimensional_size

dimensional_location

Figure 11. MIM mappings of the Geometric_dimension AO.
- 13 - October 20, 2009

Figure 12. MIM mappings of the alternate representations for a dimension value.

measure_representation_item

measure_value

unit

unit_component 

conversion_based_unit

dimensional_exponents dimensions 

measure_with_unit conversion_factor 

unit unit_component 

measure_value value_component 

si_unit

value_component 

length_measure_with_unit

MIM mapping of Numerical_item_with_unit

qualifiers type_qualifier [1]

{.name = 'minimum’}

{.name = 'maximum’}

measure_representation_item+

qualified_representation_item

measure_value

unit_component 

value_component 

unit

MIM mapping of Value_limit

plus_minus_tolerance

range tolerance_value

lower_bound measure_with_unit

upper_bound measure_with_unit

dimensional_size

dimensional_location

toleranced_dimension 

shape_dimension_representation

items [1] measure_representation_item

dimensional_characteristic_representation

dimension 

representation 

dimensional_characteristic

shape_dimension_representation

measure_representation_item

measure_representation_item

{.name = 'lower range’}

{.name = 'upper range’}

items [1]

items [2]

MIM mapping of Dimension_value_with_limitation

MIM mapping of Tolerance_range
- 14 - October 20, 2009

The suggested recommended practice is to use the ARM application object 

Datum_defined_by_derived_shape where the derived shape is a Centre_plane. 

The center plane must reference the two surfaces of the internal or external datum 

feature. These two surfaces are a Shape_element of the model. The relationships 

between these AOs are depicted in Figure 14 below. The use of the complex entity 

Datum_defined_by_derived_shape+Datum_plane conveys the information that 

this is a datum plane as well as a datum defined by derived geometry (i.e. a center plane). 

The MIM mapping of the AOs in Figure 14 is contained in Figure 15. The 

Datum_defined_by_derived_shape maps to the datum entity, and the 

Centre_plane maps to the centre_of_symmetry entity, both subtypes of 

shape_aspect. In both cases, the inherited attribute shape_aspect.description

is set to the value ’plane’ in 

order to appropriately 

specialize the two entities. As 

may be seen in Figure 15, the 

centre_of_symmetry is 

defined by two entities of type 

shape_aspect, each of which 

has an advanced_face as its 

shape_representation. 

There are four datum planes 

defined in the JEDEC Pub. 95 

specification of the QFP 

package family (see Figure 7). 

Datum features A, B, C, and D 

are used to define four datum 

planes, A-B, C, and D which 

Figure 13. Selected subtypes of the Datum application object

Datum

Single_datum

Datum_defined_by_

derived_shape

Derived_geometry

Datum_plane Datum_defined_by

_feature

Datum_defined_by

_targets

Shape_element

Datum_feature

defined_by [1:?] defined_by 

Datum_target

Shape_element

derived_from [1:?]

constructive_element_select geometry 

Common_datum

Datum_defined_by_derived

_shape+Datum_plane

Centre_plane

derived_from 

Shape_element_deriving

_relationship

relating 

Shape_element

related 

Shape_element_deriving

_relationship

relating 

Shape_element

related 

Figure 14. A datum defined by a derived center plane.
- 15 - October 20, 2009

together constitute a datum reference frame. 

Datum features A, B, and D would be modeled as discussed previously (see Figure 14

and Figure 15). Datum A-B would be modeled as a common datum (composed of datums

A and B). 

The ARM AO Common_datum is composed of a minimum of two Single_datum AOs. 

Both Datum_plane and Datum_defined_by_derived_shape are subtypes of 

Single_datum (see Figure 13). The MIM mapping for the A-B Common_datum AO 

and its relationship with the two individual datum planes is detailed in Figure 16.

datum

derived_from 

shape_aspect_deriving_r

elationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

shape_aspect_deriving_r

elationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

{shape_aspect.description = 'plane'}

centre_of_symmetry

{shape_aspect.description = 'plane'}

property_definition

advanced_face

shape_definition_representation

shape_representation

definition 

definition used_representation 

items [1:?]

property_definition

advanced_face

shape_definition_representation

shape_representation

definition 

definition used_representation 

items [1:?]

Figure 15. MIM mapping of a derived center plane (and a datum defined by derived center

plane).
- 16 - October 20, 2009

Datum C represents the seating plane. As specified in Design Guide 4.4a of JEDEC Pub. 

95, the seating plane is the “plane established by three or more leads that support the 

device when it is placed on top of a horizontal planar surface.... The feet of the leads are 

datum features that ... establish the datum plane.”

In order to associate a single datum plane with the feet of the leads as datum features, a 

complex instance of the ARM AOs Composite_unit_shape_element and 

Datum_feature may be employed, as it is intended that the collection of all of the lead 

feet be treated as a single unit, as opposed to a group (see also 

Composite_group_shape_element). If choosing to model the collection of datum 

features through a Composite_unit_shape_element, the datum itself can be 

modeled as a Datum_defined_by_feature+Datum_plane. The top-level ARM AOs 

and corresponding MIM mapping for the seating plane datum are detailed in Figure 17.

Single_datum

Common_datum

made_up_by [2:?]

Datum_defined_by_derived

_shape+Datum_plane

Figure 16. The ARM Common_datum AO and MIM mapping of the A-B 

datum plane.

common_datum

composite_shape_aspect

datum

{shape_aspect.description = 'plane'}

shape_aspect_relationship

relating_shape_aspect 

related_shape_aspect 

datum

{shape_aspect.description = 'plane'}

shape_aspect_relationship

related_shape_aspect 

relating_shape_aspect 

datum
- 17 - October 20, 2009

Representation of Geometric Tolerances

In addition to several dimensional tolerances, a number of geometric tolerances are 

contained in Figure 7. The top-level ARM application objects used to represent geometric 

tolerances are contained in Figure 18. Figure 19 contains the MIM mapping for the 

geometric_tolerance hierarchy, as well as a number of the key attributes. Tolerances 

aaa, bbb, and ccc all represent surface profile tolerances. All three have datum references 

(optional for a surface profile tolerance), and none contain a material condition modifier. 

For this reason, each would be represented as a complex instance of 

geometric_tolerance_with_datum_reference+surface_profile_toleranc

Figure 17. The top-level ARM AOs to be used in the representation of the seating plane (datum 

C) and their corresponding MIM mappings.

Datum_defined_by_feature+

Datum_plane

Composite_unit_shape_

element+Datum_feature

defined_by 

Shape_element_composing

_relationship

composing_relationships INV [2:?]

relating 

Shape_element

related 

datum

composite_unit_shape_

aspect+datum_feature

defined_by 

shape_aspect_relationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

{shape_aspect_relationship.name = 'composing'}

{shape_aspect.description = 'plane'}

shape_aspect_relationship

shape_aspect

related_shape_aspect 

{shape_aspect_relationship.name = 'composing'}

relating_shape_aspect 

.......

.......
- 18 - October 20, 2009

e (see Figure 20). The magnitude of the tolerance would be represented as a 

length_measure_with_unit. In order to communicate the datum references, and 

their sequence within the datum reference frame, the 

geometric_tolerance_with_datum_reference.datum_system attribute will 

contain an aggregate of datum_reference. As shown in Figure 20, each of the 

datum_reference entities contains an integral precedence value, as well as a 

reference to an individual datum. Finally, the tolerance must reference a 

shape_aspect. In the case of surface profile tolerance bbb, there are four instances of 

the package body side surface that are controlled by the tolerance. These four surfaces 

(each represented with a shape_aspect associated with an advanced_face) would be 

grouped together through a composite_group_shape_element. In the case of 

tolerance aaa, either a single shape_aspect, or an aggregation of shape_aspect will 

be used, depending on the representation of the underlying package model. 

Positional tolerance ddd is the only positional tolerance called out in Figure 7. This 

tolerance has a maximum material condition (MMC) modifier, in addition to the datum 

references. A positional tolerance only controls position of features of size. In this case, 

tolerance ddd controls the positional accuracy of the center plane of the package 

terminals. When the MMC condition is applied to modify the location tolerance of a size 

feature, the tolerance applies at the maximum material condition of the feature. If a 

material condition modifier is not present, RFS (regardless of feature size) applies 

automatically. 

Tolerance_condition

Geometric_tolerance

Angularity_tolerance Circular_runout_tolerance Coaxiality_tolerance Concentricity_tolerance

Parallelism_tolerance

Perpendicularity_tolerance

Symmetry_tolerance Total_runout_tolerance

tolerance_value Value_with_unit

Shape_element

applied_to 

(OPT) modification 

Cylindricity_tolerance Flatness_tolerance

Position_tolerance Roundness_tolerance

Line_profile_tolerance

Straightness_tolerance

Surface_profile_tolerance

Figure 18. The top-level subtypes of the Geometric_tolerance AO.
- 19 - October 20, 2009

The two opposing parallel side faces of the terminal constitute an external feature of size. 

This shape_aspect will always be shared between the positional tolerance and a size 

dimension (the terminal width b). To represent tolerance ddd, we require a complex of 

position_tolerance+modified_geometric_tolerance+geometric_toleran

ce_with_datum_reference as detailed in Figure 21.

Figure 19. The geometric_tolerance entity hierarchy and certain key attributes.

geometric_tolerance_with_datum_reference

modified_geometric_tolerance

geometric_tolerance

angularity_tolerance

circular_runout_tolerance

coaxiality_tolerance

concentricity_tolerance

parallelism_tolerance

perpendicularity_tolerance

symmetry_tolerance

total_runout_tolerance

datum_reference

datum_system [1:?]

magnitude measure_with_unit

shape_aspect

toleranced_shape_aspect 

geometric_tolerance_with_defined_unit

measure_with_unit

unit_size 

modifier TYPE limit_condition =

ENUMERATION OF

(maximum_material_condition,

least_material_condition,

regardless_of_feature_size);

END_TYPE;

limit_condition

Any tolerance that needs to apply a limit_condition must do so through a 

complex entity that is of type modified_geometric_tolerance.

physical_unit_geometric_tolerance

property_definition

definition 

characterized_definition

cylindricity_tolerance

flatness_tolerance

position_tolerance

roundness_tolerance

line_profile_tolerance

straightness_tolerance

surface_profile_tolerance

For integral features, shape_aspects.product_definitional=”.TRUE.”

For derived elements shape_aspects.product_definitional=”.FALSE.”
- 20 - October 20, 2009

geometric_tolerance_with_datum_r

eference+surface_profile_tolerance

magnitude length_measure_with_unit

toleranced_shape_aspect 

datum_reference

datum_system [1] datum_system [2]

datum_reference datum_reference

datum_system [3]

{.precedence = 1} {.precedence = 2}

datum common_datum datum

referenced_datum referenced_datum referenced_datum 

{.identification = “C”} {.identification = “A-B”} {.identification = “D”}

{.name = “aaa”}

{.precedence = 3}

composite_group_shape_aspect

shape_aspect_relationship

relating_shape_aspect 

shape_aspect

related_shape_aspect 

{shape_aspect_relationship.name = 'composing'}

shape_aspect_relationship

shape_aspect

related_shape_aspect 

relating_shape_aspect 

.......

.......

{shape_aspect_relationship.name = 'composing'}

Figure 20. MIM mappings of surface profile tolerance aaa (bbb and ccc similar).
- 21 - October 20, 2009

position_tolerance+modified_geometric_tolerance+

geometric_tolerance_with_datum_reference

datum_reference

datum_system [1]

geometric_tolerance

modifier limit_condition

{.modifier = maximum_material_condition}

magnitude length_measure_with_unit

toleranced_shape_aspect 

datum_system [2]

datum_reference datum_reference

datum_system [3]

{.precedence = 1} {.precedence = 2}

datum common_datum datum

referenced_datum referenced_datum referenced_datum 

{.identification = “C”} {.identification = “A-B”} {.identification = “D”}

{.name = “ddd”}

centre_of_symmetry

{shape_aspect.description = 'plane'}

shape_aspect

{.precedence = 3}

Figure 21. MIM mapping of tolerance ddd.