BS-6943-1988.pdf

BRITISH STANDARD BS 6943:1988 Classification of shapes of electronic components for placement on printed wiring boards UDC 621.3.049.73/.75:621.3 11 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 This British Standard, having been prepared under the direction of the Electronic Components Standards Committee, was published under the authority of the Board of BSI and comes into effect on 30 September 1988 © BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference ECL/- Draft for comment 85/32981 DC ISBN 0 580 16516 7 Committees responsible for this British Standard This British Standard was prepared by the Electronic Components Standards Committee (ECL/-) upon which the following bodies were represented: Electronic Components Industry Federation Electronic Engineering Association National Supervising Inspectorate Society of British Aerospace Companies Ltd. Surface Mount and Related Technologies Institution of Electronic and Radio Engineers Telecommunication Engineering and Manufacturing Association (TEMA) Ministry of Defence Department of Trade and Industry (Electronics Applications Division) British Telecommunications plc British Electrical and Allied Manufacturers Association (BEAMA) Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 © BSI 08-1999i Contents Page Committees responsibleInside front cover Forewordii Section 1. General 1.1Scope1 1.2Definitions1 1.3Related documents1 1.4General principles2 1.5Identification of drawings and dimensions2 1.6Interpretation of reference drawings2 1.7Identification of terminals2 1.8Sockets, heat sinks and stand-offs2 1.9Fixing holes and studs3 1.10 Adjustable components3 1.11 Units of measurement3 1.12 Tolerances3 Section 2. Reference drawings 2.1Reference letter symbols4 2.2Drawing codes: alphabetic index7 2.3Drawings9 Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 ii © BSI 08-1999 Foreword This British Standard has been prepared under the direction of the Electronic Components Standards Committee. It gives a standardized approach to the description of component geometry. The drawings given in this standard are compatible with those given in BS 3934 and the relevant detail specifications in the BS 9000, CECC and IECQ systems. Since much of the work of laying-out electronic components on printed wiring boards is now performed by computer programs, the procedures in this standard have been designed to be compatible with input to and processing by computer systems. It is therefore intended that the classification described in this standard is used as the basis of a system for the description of electronic component geometry on a computer database, which has a direct interface to design programs. All the information is presented in a standard character set using the 7-bit codes described in BS 4730. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 85 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 © BSI 08-19991 Section 1. General 1.1 Scope This British Standard classifies the shapes of the most commonly used electronic components to assist in the design procedures involved in locating and connecting components on printed wiring boards. It gives details, through a set of reference drawings (in section 2), for defining shape and size of the component body, and the positions and sizes of its connecting leads. NOTEThis standard is not concerned with the electrical function of any of the connections. 1.2 Definitions For the purposes of this British Standard the following definitions apply. 1.2.1 seating plane (reference plane) the surface plane of the circuit on which the component is mounted 1.2.2 mounted height (seated height) the furthest distance from the seating plane measured in a direction perpendicular to that plane of any point on the component body or of any rigid terminal 1.2.3 visual index a reference feature, e.g. mark, chamfer, notch, tab etc. which identifies the position of terminal number 1 in a multi-lead component 1.2.4 mechanical index a reference feature, e.g. tab, notch, flat, groove, etc. which provides orientation during automatic handling 1.2.5 origin of coordinates for identification of terminal positions, the origin of coordinates is a point in the seating plane at the geometric centre either, where the leads are not disposed in a regular array, of the orthogonal projection of the outline of the main body of the component on to that plane or, where the leads are disposed in a regular circular or rectangular array, of the true centres of the leads at that plane 1.2.6 horizontal refers to a direction parallel to the reference plane 1.2.7 vertical refers to a direction at right angles to the reference plane 1.2.8 shape the shape of a component is defined when all its external boundary surfaces have been defined 1.3 Related documents This British Standard makes reference to the following publications: BS 308, Engineering drawing practice Part 3: Geometrical tolerancing. BS 3934 (with Addenda), Specification for dimensions of semiconductor devices and integrated electronic circuits. BS 4730, Specification for UK 7-bit coded character set. BS 9000, General requirements for a system for electronic components of assessed quality (together with detail specifications in the BS 9000 series). IEC 191, Mechanical standardization of semiconductor devices. CECC and IECQ systems Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 2 © BSI 08-1999 1.4 General principles The information given for the shapes allows the following to be obtained: a) the maximum area occupied on the seating plane by the component as defined by its orthogonal projection from its mounted position; b) the maximum height of the component above the seating plane which may determine, or be determined by, the minimum spacing between adjacent circuits; c) the positions of leads which may or may not pass through the seating plane; d) the maximum cross section of the leads which determines the minimum diameter of the hole through which the leads should pass; e) the minimum lead length which is related to the thickness of the circuit substrate. In most cases the shape of a component is specified as it is mounted. The main exception to this is where component leads need to be preformed before mounting, e.g. for components with axial leads. In such cases, the shape is specified before the forming operation. 1.5 Identification of drawings and dimensions The complete code for the dimensions list for a component consists of three parts: a) a two-letter drawing code (for a list of codes, see the alphabetic index in section 2), followed by; b) a numeric code giving a salient property of the component, which may be either a major dimension or the number of leads, followed by: c) a hyphen and a serial number to distinguish components with the same drawing and numeric codes. As a guide to the storage required in computer systems, the numeric codes under b) and c) are not expected to exceed three digits each. Under no circumstances will the complete code exceed eight characters. Examples. a) 14-pin dual-in-line packages are coded DL 14-1, DL 14-2, etc. b) Tubular axial-lead components with body lengths between 8.50 mm and 9.49 mm are coded TA9-1 TA9-2, etc. 1.6 Interpretation of reference drawings All drawings are given in third angle projection. Plan views of components are given as viewed from above the component. 1.7 Identification of terminals Where terminals are not in a regular array, all terminal positions are numbered on the drawing and the coordinates of the terminal position are suffixed by the corresponding number. Where terminals are in a regular array, they are numbered sequentially in an anti-clockwise direction as viewed from above the component, i.e. as on the plan view given in the drawing. The position of terminal number one is the first position anti-clockwise from the index mark as viewed from above, and is indicated on the drawing. Each terminal is identified by the number of its positions. Terminals may not necessarily be present in all the numbered positions as provided for on the drawing, but those that are present will have the number of the position they occupy. 1.8 Sockets, heat sinks and stand-offs Component drawings are all given on the assumption that components are mounted directly into the circuit. Where components are plugged into sockets, mounted on heat sinks or mounted on stand-offs such use will generally increase the total effective space occupied by the component, both the seated height and the area of the projection on the seating plane. In the case of drawings of sockets intended for plug-in components, such as integrated circuits, the height shown is the additional seated height of the component resulting from the use of the socket. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 © BSI 08-19993 1.9 Fixing holes and studs Where components are attached to a circuit by studs or bolts through fixing holes, the positions and dimensions of these are shown on the drawings. 1.10 Adjustable components Where components have a facility for mechanical adjustment, e.g. potentiometers, switches, the position of the adjuster or the space within which the adjusters lie is shown on the drawings. 1.11 Units of measurement All linear dimensions are in millimetres and all angular dimensions are in degrees. 1.12 Tolerances Generally, component body dimensions are maximum values taken from the original drawings. No minima are quoted and the values are thus not subject to any tolerance. Likewise, where minimum dimensions are quoted no maxima are given. Where nominal dimensions are given for terminal, lead or mounting hole positions the actual position is within ± 0.2 mm of the nominal position in either coordinate direction. Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 4 © BSI 08-1999 Section 2. Reference drawings 2.1 Reference letter symbols The table below lists the letter symbols used for the various dimensions on the drawings in this standard, together with their descriptions and whether they represent maximum, minimum or nominal values. Also included are numeric codes which may be used in an information retrieval system to distinguish among cases where the same letter symbol is used for a different dimension. All such codes are integers except where they represent subscripted symbols: in such cases the subscript is given by the digit following a decimal point. Reference letter symbol Description on drawing Numeric code Full descriptionLimits ASeated height51The distance of the furthest part of the component above the reference plane measured in a direction perpendicular to that plane max. aIndex angle31The angle subtended by the arc joining the index mark and lead 1 at the centre of the circle on which leads are disposed in a regular array nom. BBody diameter33Maximum overall diameter of a component with axial symmetry max. B1, B2, etc.33.1, 33.2, etc. Other diameters of a component with axial symmetry max. bAngular lead pitch32The angle subtended by the arc joining adjacent leads at the centre of the circle on which the leads are disposed in a regular array nom. CTermination circle38The diameter of the circle on which leads are disposed in a regular array nom. CTermination circle19The diameter of the circle within which all terminations lie max. cTermination angle18Angular limitation of the sector within which all terminations lie max. DDiameter3Maximum overall diameter of a component with circular cross section, measured in a direction parallel to the reference plane max. DLength1Maximum overall length or major axis of a component, measured in a direction parallel to the reference plane max. DBody diameter16Maximum diameter of the body of a componentmax. dLead diameter6The maximum diameter of a lead or termination with circular cross section measured below the reference plane max. dLead diagonal46The maximum diagonal dimension of a lead or termination of rectangular cross section measured below the reference plane max. dTermination diameter 22The maximum diameter of a terminationmax. EWidth2Maximum overall width, thickness or minor axis of the component, measured in a direction parallel to the reference plane max. FFlange thickness43Thickness of flange by which the component is mounted max. GLength47Overall length of the component body, excluding leads max. GBody length23The depth of the body of a component below the mounting plane Licensed Copy: sheffieldun sheffieldun, na, Tue Dec 05 07:54:29 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6943:1988 © BSI 08-19995 Reference letter symbol Description on drawing Numeric code Full descriptionLimits HOverall length20Overall length of the component, including terminations max. KClearance21Clearance between a termination and the mounting plane min. LLead length5Length of a termination or connecting leadmin. LTermination length17Length of a terminationmin. L/1Termination length17/1 L/2Termination length17/2 MStud diameter34Diameter of a threaded stud by which the component is to be attached to the circuit max. NStud length35Length of a fully or partially threaded stud by which the component is to be attached to the circuit min. nNumber of leads58Number of leads or terminations PDimension40Non-specific dimensionmin. 41nom. 42max. pHole diameter30Diameter or minor axis of mounting hole by which the component is to be attached to the circuit min. QDimension60Non-specific dimensionmin. 61nom. 62max. qHole separation29Distance between the centres of two mounting holes, where the line joining them is parallel to a coordinate axis nom. RTag spacing65Tag spacingmax. sHole position59The position of a mounting hole with reference to a nominated point or line nom. tLead thickness37Smaller dimension of a lead or termination with non-circular cross section max. tLead thickness44Smaller dimension of a lead or termination with non-circular cross section max. tTag