IEC 60191-1:2018

IEC 60191-1 ®
Edition 3.0 2018-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Mechanical standardization of semiconductor devices –
Part 1: General rules for the preparation of outline drawings of discrete devices

Normalisation mécanique des dispositifs à semiconducteurs –
Partie 1: Règles générales pour la préparation des dessins d’encombrement
des dispositifs discrets
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IEC 60191-1 ®
Edition 3.0 2018-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Mechanical standardization of semiconductor devices –

Part 1: General rules for the preparation of outline drawings of discrete devices

Normalisation mécanique des dispositifs à semiconducteurs –

Partie 1: Règles générales pour la préparation des dessins d’encombrement

des dispositifs discrets
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.080.01 ISBN 978-2-8322-1092-4

– 2 – IEC 60191-1:2018  IEC 2018
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 General rules for all drawings . 8
4.1 Drawing layout . 8
4.2 Dimensions and tolerances . 9
4.3 Methods for locating the datum . 10
4.4 Numbering of terminals . 11
4.4.1 General . 11
4.4.2 Single-ended devices with terminals in a linear array . 11
4.4.3 Single-ended devices with terminals in a circular array . 11
4.4.4 Double-ended devices . 11
4.4.5 Devices with terminals disposed in a square or rectangular periphery . 11
4.4.6 Particular case of lozenge – shaped bases . 11
4.4.7 Other devices . 12
5 Additional rules . 12
5.1 Rules for device and case outline drawings . 12
5.2 Rules to specify the dimensions and positions of terminals . 13
5.2.1 General rules . 13
5.2.2 Rules to specify the dimensions and the positions of the terminals on a
base drawing . 13
5.3 Rules for gauge drawings . 13
6 Inter-conversion of inch and millimetre dimensions and rules for rounding off . 14
7 Rules for coding . 14
Annex A (informative) Reference letter symbols . 15
Annex B (informative) Rules to specify the dimensions and positions of terminals on a
base drawing . 18
B.1 Example of dimensioning for a circular base outline with no tab and having
four terminals located symmetrically on a pitch circle . 18
B.1.1 Interpretation of the principle of dimensioning . 18
B.1.2 Checking . 19
B.2 Example of dimensioning for a circular base outline with a tab and having
four terminals located symmetrically on a pitch circle . 19
B.2.1 Interpretation of the principle of dimensioning . 19
B.2.2 Checking . 20
Annex C (normative) General philosophy of flat base devices . 24
Annex D (normative) Special rules for SMD-packages . 26
D.1 General reference . 26
D.2 Lead terminals . 26
D.3 Measuring methods . 26
Annex E (informative) Examples of semiconductor device drawings . 27
Annex F (informative) Former rules for rounding off . 33
F.1 Toleranced dimensions . 33
F.1.1 Maximum and minimum values of toleranced dimensions . 33
F.1.2 Nominal value of toleranced dimensions . 33

F.2 Untoleranced dimensions (maximum only or minimum only) . 33
F.3 Untoleranced nominal dimensions given for general information . 33
F.4 Untoleranced nominal dimensions given to specify true geometrical positions . 34
Annex G (informative) Former rules for coding . 35
G.1 General . 35
G.2 Device outlines . 35
G.3 Bases . 35
G.4 Case outlines . 35
G.5 Type variants and provisional drawings . 35
Bibliography . 36

Figure 1 – Numbering of terminals for the particular case of lozenge – shaped bases . 12
Figure 2 – System to indicate the dimensions of the terminals . 13
Figure B.1 – Circular base outline with no tab . 21
Figure B.2 – Tolerances of terminals. 21
Figure B.3 – Gauge for a circular base outline with no tab . 22
Figure B.4 – Circular base outline with tab . 22
Figure B.5 – Gauge for a circular base outline with tab . 23
Figure C.1 − Example of flat base outline . 25
Figure E.1 – Long form package . 27
Figure E.2 – Post/stud mount package . 27
Figure E.3 – Cylindric package . 28
Figure E.4 – Cylindric in-line package . 29
Figure E.5 – Flange-mounted in-line package . 29
Figure E.6 – Press package . 30
Figure E.7 – SMD-package with flat leads . 30
Figure E.8 – SMD-Package with gull-wing leads . 31
Figure E.9 – SMD-package with no leads . 32

Table A.1 – Dimensions of reference letter symbols . 15

– 4 – IEC 60191-1:2018  IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MECHANICAL STANDARDIZATION OF SEMICONDUCTOR DEVICES –

Part 1: General rules for the preparation of outline drawings
of discrete devices
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC
Publication(s)"). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60191-1 has been prepared by subcommittee 47D: Semiconductor
devices packaging, of IEC technical committee 47: Semiconductor devices.
This third edition cancels and replaces the second edition published in 2007. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the Scope has been extended to include surface-mounted semiconductor devices with a
lead count less than 8;
b) a definition of the term "stand-off" has been added;
c) the methods for locating the datum have been extended to be suitable for SMD-packages;
d) the visual identification of terminal position one for automatic handling has been clarified;
e) the rules for the drawing of terminals have been clarified;

f) Table A.1 has been completed with symbols specifically for SMD-packages;
g) Annex B "Standardization philosophy" has been deleted;
h) a normative Annex with special rules for SMD-packages has been added;
i) the examples of semiconductor device drawings have been aligned to state-of-the-art
packages including SMD-packages.
The text of this standard is based on the following documents:
CDV Report on voting
47D/886/CDV 47D/896/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60191 series, published under the general title Mechanical
standardization of semiconductor devices, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60191-1:2018  IEC 2018
MECHANICAL STANDARDIZATION OF SEMICONDUCTOR DEVICES –

Part 1: General rules for the preparation of outline drawings
of discrete devices
1 Scope
This part of IEC 60191 gives guidelines on the preparation of outline drawings of discrete
devices, including discrete surface-mounted semiconductor devices with lead count less than
8.
For the preparation of outline drawings of surface-mounted discrete devices with a lead count
higher or equal to 8, IEC 60191-6 should be referred to as well.
The primary object of these drawings is to indicate the space to be allowed for devices in
equipment, together with other dimensional characteristics required to ensure mechanical
interchangeability.
Complete interchangeability involves other considerations such as the electrical and thermal
characteristics of the semiconductor devices concerned.
The international standardization represented by these drawings therefore encourages the
manufacturers of devices to comply with the tolerances shown on the drawings in order to
extend their range of customers internationally. It also gives equipment designers an
assurance of mechanical interchangeability between the devices obtained from suppliers in
different countries, provided they allow the space in their equipment that is indicated by the
drawings and take note of the more precise information on bases, studs, etc.
NOTE Additional details of reference letter symbols used in this document are given in Annex A.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60191-2, Mechanical standardization of semiconductor devices – Part 2: Dimensions
IEC 60191-4, Mechanical standardization of semiconductor devices – Part 4: Coding system
and classification into forms of package outlines for semiconductor device packages
IEC 60191-6-1, Mechanical standardization of semiconductor devices – Part 6-1: General
rules for the preparation of outline drawings of surface mounted semiconductor device
packages – Design guide for gull-wing lead terminals
IEC 60191-6-3, Mechanical standardization of semiconductor devices – Part 6-3: General
rules for the preparation of outline drawings of surface mounted semiconductor device
packages – Measuring methods for package dimensions of quad flat packs (QFP)
IEC 60191-6-20, Mechanical standardization of semiconductor devices – Part 6-20: General
rules for the preparation of outline drawings of surface mounted semiconductor device
packages – Measuring methods for package dimensions of small outline J-lead packages
(SOJ)
IEC 60191-6-21, Mechanical standardization of semiconductor devices – Part 6-21: General
rules for the preparation of outline drawings of surface mounted semiconductor device
packages – Measuring methods for package dimensions of small outline packages (SOP)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
device outline drawing
drawing that includes all dimensional characteristics required for the mechanical
interchangeability of the complete device
Note 1 to entry: The device outline drawing includes the case or body, all terminals and the locating tab if present.
3.2
terminal
part of the semiconductor device primarily used in making an electrical, mechanical or thermal
connection
EXAMPLE Flexible leads, rigid leads, pins, studs, etc.
3.3
case outline drawing
drawing that includes all dimensional characteristics required for the mechanical
interchangeability of the case or body
Note 1 to entry: The case outline drawing does not include the dimensions of the terminals or the locating tab if
present, but their positions are shown by dotted lines.
3.4
base drawing
drawing that includes all dimensional characteristics required for the mechanical
interchangeability of the terminals and mechanical index
Note 1 to entry: Examples of these characteristics are: lead length, lead diameters with controlled zones, lead
spacing, pitch circle diameter, thickness, width and length of a tab, etc.
Note 2 to entry: The diameter or major axis of the case outline should not be given on the base drawing.
Note 3 to entry: Many semiconductor devices have identical cases, but differ in the number or the length of
terminals. It is also possible to have the same type of base associated with cases that are not identical.
Consequently, there are advantages in having:
a) a single drawing including only the dimensional characteristics of the case outline and separate drawings for
the various bases which can be associated with this case outline,
or
b) a single drawing including only the dimensional characteristics of the base and separate drawings for the
various case outlines which can be associated with this base.
3.5
mechanical index
locating feature, or that portion of the device specifically designed to provide orientation
Note 1 to entry: Examples of a mechanical index are: key, keyway, locating tab, etc.

– 8 – IEC 60191-1:2018  IEC 2018
3.6
visual index
any single terminal (or omission of) readily distinguished by the eye from others or any
distinctive boss, stippled pattern or colour mark adjacent to a terminal
3.7
datum
theoretically exact geometric reference (such as axes, planes, straight lines etc.) to which
toleranced features are related
Note 1 to entry: Datums may be based on one or more datum features of a part.
[SOURCE: ISO 5459:2011, 3.4]
3.8
seating plane
seating base
reference plane from which, in general, outline and base dimensions are given
3.9
seated height
mounted height
distance from the seating plane to the top of any exposed tip or rigid terminal present,
otherwise to the top of the outline
Note 1 to entry: Flexible terminals should not be included as part of the seated height, but the mounted height
should include a minimum allowance necessary for an axially mounted flexible lead to be bent at right angles.
3.10
controlled cylindrical zone
zone that defines a portion of the body of minimum length over which the diameter is
controlled to closer tolerances than is allowed over the full length of the body
3.11
stand-off
distance from the seating plane to the lowest point of a package
4 General rules for all drawings
4.1 Drawing layout
General rules for the drawing layout are as follows.
a) A drawing should show all dimensions required to ensure mechanical interchangeability.
b) The drawing using third angle projection, should include:
– a suitable side-view;
– suitable end-views, where appropriate;
– such additional views and details as are required to show any special configuration or
features.
c) The following information should be put in the title block, at the bottom of the page:
– the projection method where there is more than one view, as indicated below:

– date of publication of the drawing;
– IEC code number;
– country of origin and code of that country indicated by sign ∆;
NOTE This is no longer in practice.
– other countries involved and codes of those countries.
d) When a drawing is re-issued because of modifications, the changes made should be
indicated by arrows in the margin. The date of publication of the revised issue and of the
superseded issue should be stated.
e) While drawings need not to be drawn to scale, they should be roughly in proportion and,
where necessary for clarity, enlarged detail drawing(s) should be used.
4.2 Dimensions and tolerances
Application of dimensions and tolerances are as follows.
a) Dimensions of bases, outlines, etc. quoted shall apply to the finished product. They should,
therefore, not quote manufacturing tolerances, but give customers acceptance limits.
b) The following types of dimension may be used on the drawings as appropriate:
i) Toleranced dimensions
A toleranced dimension can be expressed:
– preferably by both minimum and maximum limits (example: L = 5,77 mm, L =
min max
5,82 mm); or
– by a nominal value and maximum and minimum limits. Such a nominal value need
+0,4
not necessarily be the average of two limits (example: L = 6 mm ).
−0,2
ii) Untoleranced dimensions
– Untoleranced limiting dimensions i.e.: minimum only or maximum only (example:
L = 5,85 mm) .
max
– Untoleranced nominal dimensions. These dimensions may be used:
• either for general information as an actual nominal figure;
• or to specify true geometrical position (by means of linear or angular
dimensions). Such dimensions shall be indicated by an asterisk (*) after the
numerical value, the asterisk in this sense meaning "true geometrical position"
(example: L = 5,85 (*) mm).
nom
c) Single minimum, single maximum or single nominal (where not given for general
information) dimensions should be stated in decimals to such a number of places as is
considered adequate to express the degree of accuracy appropriate for that dimension;
e.g. if measurement to the nearest 0,001 mm is considered appropriate, the dimension
should be expressed to the third decimal place (for example 0,500 mm), but if the
measurement to the nearest 0,01 mm is sufficient, the dimension should be expressed to
the second decimal place (for example 0,50 mm), and so on. Similar consideration should
be given to the number of decimal places necessary when an original dimension is
expressed in millimetres.
d) Limiting values or nominal value and limits of a toleranced dimension should be stated
with the same number of decimal places (e.g. 0,016 mm min. – 0,017 mm nom. –
0,019 mm max.).
e) The use of fractional mm dimensions is permitted to describe nominal hexagon sizes.
f) Numerical dimensions should not be shown directly on the figure(s). They should be
shown in tabular form under the figure(s) and correspond to the reference letter symbols
on the figure(s). The letter symbols on the figure(s) should be upright. Uppercase letters
should be used for device outline and case outline dimensions and lowercase letters for
base dimensions. If confusion could arise, upper case letters should preferably be used
throughout.
– 10 – IEC 60191-1:2018  IEC 2018
g) In the case of a diameter, the symbol "Ø" should appear in front of the reference letter
concerned both on the figure(s) and in the table. In cases where the cross-section is
uncontrolled (not necessarily round), the "Ø" symbol should not be used.
h) The table shall give dimensions in millimetres. The basic dimensions and system
(millimetres or inches) shall be indicated immediately above the table.
NOTE Some outline drawings published in IEC 60191-2 before this document came into effect give
dimensions in inches.
i) The dimensions and limits, which should normally be given, and their corresponding
reference letter symbols, are contained in Annex A. Some examples of drawings prepared
in accordance with these rules are given in Annex E, in Figures E.1 to E.9.
Where a particular reference letter is to be used for more than one dimension on the same
drawing, use should be made of a suffix to identify the dimensions.
Annex A cannot be expected to include all dimensions likely to be necessary for
mechanical standardization, more particularly in the future. A distinction has been made
between primary and secondary reference letter symbols, primary reference letter symbols
being those which are used most frequently, secondary reference letter symbols being
those which are used less frequently and which can, if necessary, be associated with
dimensions other than those given in the table.
j) Where it is self-evident that several angles are equal, it is not necessary to show more
than one angle on the figure(s).
k) Notes will be numbered and placed under the table of dimensions, which will have a
"notes" column on the right-hand side. The note reference will be placed opposite the
dimension to which the note refers in the table or, when this dimension does not appear in
the table, on the figure(s). The numerical sequence of the notes should follow the
alphabetical sequence of the dimensional reference letters to which the notes refer. Notes
referring to the figure(s) should follow notes referring to dimensions given in the table.
4.3 Methods for locating the datum
These methods are listed below in order of preference. When more than one of these
methods is possible for a given device, the method appearing earliest in the list should be
used. When none of the following methods is possible, the method best suited to the device
should be used.
The datum is:
a) the radial line through the centre of the mechanical or visual index;
b) the radial line midway between the two terminals which obviously comprise a gap in an
otherwise equally spaced circular terminal array;
c) the radial line 180° from the locating radius of the most isolated terminal;
d) the radial line 180° from the mid-point of, in order of preference:
– the two most widely spaced terminals;
– the two most closely spaced terminals;
e) the radial line through the centre of the index terminal. In order of preference, the index
terminal is defined as that having:
– the smallest cross-sectional area at the point of emergence from the case;
– the greatest axial length, when one terminal is noticeably longer than the others;
– the smallest axial length, when one terminal is noticeably shorter than the others;
f) datum C is the plane formed by at least three apexes at the bottom of the SMD package
body that exhibit the greatest perpendicular distance from the package bottom;
g) datum A is the plane perpendicular to Datum C and wraps one edge of the package body;
h) datum A is the plane perpendicular to Datum C and crosses the centre line of the package
body;
i) datum B is the plane perpendicular to datum C and A and wraps one edge of the package
body;
j) datum B is the plane perpendicular to datum C and A and crosses the centre line of the
package body.
4.4 Numbering of terminals
4.4.1 General
Where possible, device terminals should be identified by numbers according to the system
outlined in 4.4.2 to 4.4.7. In all instances, terminals are considered as being viewed from their
free ends.
4.4.2 Single-ended devices with terminals in a linear array
4.4.2.1 Symmetrical linear array
The terminal nearest the reference mark should be numbered as No.1, the other terminals
should be numbered progressively from terminal No.1.
4.4.2.2 Asymmetrical linear array
The terminals should be numbered progressively from the end having the most terminals.
4.4.3 Single-ended devices with terminals in a circular array
– The terminal, the centre of which is past the datum, should be numbered as No.1, the
other terminals should be numbered progressively and in a clockwise sequence from No.1.
– Where a terminal is situated in the centre of the base, this should be known as the centre
terminal and shall not be given a number.
– Where omission of one terminal in an otherwise equally spaced array identifies the datum,
the position of the omitted terminal should not be numbered; but, in a fixed modular
circular array, any location of an omitted terminal that does not define a datum should be
numbered.
4.4.4 Double-ended devices
Terminals on both end views should be numbered without duplication of numbers.
4.4.5 Devices with terminals disposed in a square or rectangular periphery
Visual identification on the top of the device should be provided. The means of identification
of terminal position number one should also be provided. These identifications may be
combined. For automatic handling of SMD devices, it is essential to have an additional
significant optical identification of terminal position one on the bottom side of the device.
The terminal positions should be numbered progressively in an anti-clockwise direction
around the periphery of the device as viewed from the top. The number one terminal position
shall be the first position anti-clockwise from the means of identification.
Each terminal shall be identified by the number of its position. Terminals may not necessarily
be present in all the numbered positions but those present shall have the number of the
position.
4.4.6 Particular case of lozenge – shaped bases
Given two orthogonal axes, X'X and Y'Y, the device is oriented so that:
a) the greatest diagonal of the base coincides with the Y'Y axis, whereas the smallest
diagonal coincides with the X'X axis;

– 12 – IEC 60191-1:2018  IEC 2018
b) the greatest number of terminals is in the upper half (Figure 1 a, b, c) or in the right-hand
half (Figure 1 d).
The numeration is clockwise, starting from the quadrant in the upper left-hand side.
If the terminals are disposed in a cross on the axis (Figure 1 e), it is necessary to mark on the
body with a visual index the terminal that shall be considered as the first in the clockwise
numeration.
IEC IEC IEC IEC IEC
a) b) c) d) e)
Figure 1 – Numbering of terminals for the particular case of lozenge – shaped bases
4.4.7 Other devices
For devices having terminals, mounting studs or holes, in more than one plane, the following
rules should apply.
The numbering should start at the end:
– opposite to the end containing a threaded stud or hole;
– opposite to the end with the smallest number of terminals;
– opposite to the end identified by a hand, dot or other applied visual identification;
– opposite to the end with the larger ferrule, flange, insert, etc.
5 Additional rules
5.1 Rules for device and case outline drawings
Rules for device and case outline drawings are as follows.
a) The device outline drawings that appear in Chapter I of IEC 60191-2 should include all
dimensional characteristics required for interchangeability in accordance with general
rules.
b) Where the requirements for mechanical interchangeability will permit, the minimum and
maximum dimensions should be chosen so that the creation of unnecessary drawings of
variants is avoided.
c) The case outline drawings which appear in Chapter III of IEC 60191-2 should include all
dimensional characteristics required for interchangeability in accordance with general
rules, omitting the terminal dimensioning which will be given on the associated base
drawings appearing in Chapter II of IEC 60191-2.
NOTE Terminals given by dotted lines, mostly to be found on older outline drawings, are terminals that could be
shortened according to the application of the device. Leads of SMD-packages are not given with dotted lines.

5.2 Rules to specify the dimensions and positions of terminals
5.2.1 General rules
General rules for specifying the dimensions and positions of terminals are as follows.
a) The terminals should be numbered in accordance with 4.4.
b) The following system should be used to locate the terminals on the bases.
The true geometrical position of the terminals (or of the holes in gauges) is defined by
angular spacing on a pitch circle (polar co-ordinates) or by rectangular co-ordinates in
relation to certain fixed references. Such dimensions are not toleranced.
c) The positional tolerance is indicated by stating that the cross-section of each terminal at
its point of origin or at a specified distance from the seating plane lies in a circle (of stated
diameter) centred at the true geometrical point defining the terminal axis.
d) The system as shown in Figure 2 below should be used either in total or in part to indicate
the dimensions of the terminals.
Seating plane
l
l
l
l
IEC
Ø b1 applies over the length l1
Ø b applies over the length l – l
2 2 1
Ø b3 applies over the length l3 – l2 or where appropriate l – l2
Figure 2 – System to indicate the dimensions of the terminals
e) The base drawings that appear in Chapter II of IEC 60191-2 should include the
dimensional characteristics required for interchangeability of the base and, in certain
instances, for compatibility between the base and a socket.
5.2.2 Rules to specify the dimensions and the positions of the terminals on a base
drawing
See Annex B.
5.3 Rules for gauge drawings
Where possible, the same reference letter symbols should be used as on the associated case
outline or base drawing.
øb
øb
øb
– 14 – IEC 60191-1:2018  IEC 2018
6 Inter-conversion of inch and millimetre dimensions and rules
for rounding off
Conversion of toleranced dimensions from inches into millimetres or vice-versa should be
made according to ISO 370.
Tables I and II of ISO 370:1975 may be extended as necessary.
Warning When converting inch dimensions to millimetre dimensions and vice-versa,
attention is drawn to the fact that the first column of Tables I and II are headed
"equal to at least".
ISO 370 was withdrawn in May 2000. The rules, which were applied before the year 2000, are
given now in Annex F.
7 Rules for coding
The classification of forms of package outline for semiconductor devices is specified in
IEC 60191-4.
NOTE Drawings in IEC 60191-2, published before IEC 60191-4 came into effect, are classified according to the
coding system in Annex G.
Annex A
(informative)
Reference letter symbols
NOTE Some of these symbols such as B or C were used in the past. Nowadays, use of dimensions A, D and E is
preferred.
Where appropriate to the particular drawing being prepared, the dimensions listed in
Table A.1 should be given with the associated reference letter symbols.
Table A.1 – Dimensions of reference letter symbols
Reference Description of the dimension Type of limits Notes
letter symbol
A Height from seating plane to top of case min. - max. P
a)
a Pitch circle diameter of terminals - nom. - P
A Stand-off min. - max.
B, b Diameter of a terminal, or of the larger terminal min. - max. 1, 2, 3, P
if the cross-section is circular. If the cross-
section is not circular, width or major axis of
the cross-section of a terminal.
B , b Other diameter of terminal as shown in Figure 2 - - max. P
1 1
B , b Other diameter of terminal as shown in Figure 2 min. - max. P
2 2
B , b Other diameter of terminal as shown in Figure 2 min. - max. P
3 3
b Terminal width of soldered part, terminal width min. - max.
p
in the projected zone of the terminal
C, c Diameter of smaller terminal, if the cross- min. - max. 1, 2, 3, 4, S
section is circular. If the cross-section is not
circular, thickness or minor axis of the cross-
section of a terminal.
D Diameter or major axis of case min. - max. 1, P
D Smallest diameter of case min. - max. 1, P
D , D , etc. Other diameters of case min. - max. 1, P
2 3
a)
d Distance from an axial reference line to a - nom. - S
terminal centre
E Minor axis of case min. - max. 1, S
E Or across flats dimension of a hexagon min. nom. max. 1, 2, S
a)
e Distance between two terminal centres - nom. - S
(distance between the centres of the nearest
terminal when there are more than two
terminals)
e Or clearance between two terminals min. - - S
a)
e , e , etc. Other distances between terminal centres - nom. - S
1 2
e , e , etc. Or c
...