IEC 61 747 40 3 Edition 1 0 201 5 01 INTERNATIONAL STANDARD Liquid crystal display devices – Part 40 3 Mechanical testing of display cover glass for mobile devices – Biaxial flexural energy to failure[.]
I E C 61 47 -40 -3 ® Edition 201 5-01 I N TE RN ATI ON AL S TAN D ARD Li q u i d crys tal d i s pl a y d e vi ces – P art 40 -3 : M ech an i cal te s ti n g of d i s pl ay co ve r g l as s for m obi l e d e vi ces – B i axi al IEC 61 747-40-3:201 5-01 (en) fl exu ral en erg y to fai l u re (bal l d rop) T H I S P U B L I C AT I O N I S C O P YRI G H T P RO T E C T E D C o p yri g h t © I E C , G e n e v a , S wi tz e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about I EC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local I EC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab ou t th e I E C The I nternational Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes I nternational Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca ti o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal og u e - webstore i ec ch /catal og u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s s earch - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing more than 30 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l os sary - s td i ec ch /g l oss ary More than 60 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i s h ed - webstore i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C C u stom er S ervi ce C en tre - webstore i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C 61 47 -40 -3 ® Edition 201 5-01 I N TE RN ATI ON AL S TAN D ARD Li q u i d crys tal d i s pl a y d evi ce s – P art 40 -3 : M ech an i cal te s ti n g of d i s pl ay co ver g l as s for m obi l e d evi ce s – B i axi al fl e xu ral e n e rg y to fai l u re (bal l d rop) INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 31 20 ISBN 978-2-8322-221 -9 Warn i n g ! M ake su re th a t you obtai n ed th i s pu bl i cati on from an au th ori zed d i s tri bu tor ® Registered trademark of the International Electrotechnical Commission –2– I EC 61 747-40-3:201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Norm ative references Terms and definitions General Apparatus Testing environment and pre-conditioning Apparatus overview Height adjustment beam Specimen holder 5 Arm ature Ball release mechanism Height adjustment clamp Ball release controller Ball Base Procedure Safety Hazard – Broken glass Hazard – Com pression due to moving ball Sam ple I ndividual specim en 1 Complete the report 1 Calculations Breaking energ y Statistical calculations Reporting I nform ation to be reported for each test I nform ation to be made available upon request Specifications Figure Figure Figure Figure – Apparatus overview – Specim en holder (top view) – Specim en holder (side view, cross-section) – Exam ple Weibull plot I EC 61 747-40-3:201 © I EC 201 –3– INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON L I Q U I D C R YS T AL D I S P L AY D E VI C E S – P a rt -3 : M e c h a n i c a l te s ti n g o f d i s p l a y c o ve r g l a s s fo r m o b i l e d e vi c e s – B i a x i a l fl e x u l e n e rg y t o fa i l u re ( b a l l d ro p ) FOREWORD ) The I nternati on al Electrotechni cal Comm ission (I EC) is a worl d wid e organization for stan dardization com prisin g all n ation al el ectrotechnical comm ittees (I EC National Comm ittees) The object of I EC is to prom ote internati onal co-operation on all questions concerni ng stand ardi zati on in the el ectrical an d electronic fields To this end and in additi on to other acti vities, I EC publish es I nternational Stan dards, Techn ical Specifications, Technical Reports, Publicl y Avail abl e Specificati ons (PAS) an d Gu ides (h ereafter referred to as “I EC Publication(s)”) Thei r preparation is entrusted to technical comm ittees; any I EC National Comm ittee interested in the subj ect dealt with m ay partici pate in this preparatory work I nternational, governm ental an d n on governm ental organ izations l iaising with th e I EC also participate i n this preparation I EC collaborates closel y with the I ntern ational Organi zation for Stand ardization (I SO) in accordance with ditions determ ined by agreem ent between th e two organi zati ons 2) The form al decisions or ag reem ents of I EC on tech nical m atters express, as n early as possible, an i nternati onal consensus of opi nion on the rel evant subjects since each technical com m ittee has representati on from all interested I EC N ational Com m ittees 3) I EC Publications have the form of recomm endations for intern ational use an d are accepted by I EC National Com m ittees in that sense While all reasonable efforts are m ade to ensure that th e technical content of I EC Publications is accu rate, I EC cann ot be h eld responsi ble for th e way in which th ey are used or for an y m isinterpretation by an y en d u ser 4) I n order to prom ote intern ational u niform ity, I EC National Com m ittees und ertake to apply I EC Publications transparentl y to the m axim um extent possible i n their national an d regi on al publicati ons Any d ivergence between an y I EC Publication and the correspondi ng national or regi on al publicati on sh all be clearl y in dicated in the latter 5) I EC itself d oes n ot provi de an y attestation of conform ity I n depend ent certificati on bodies provi de conform ity assessm ent services and, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for any services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that th ey have the l atest editi on of thi s publicati on 7) No liability shall attach to I EC or its directors, em ployees, servants or ag ents inclu din g in divi dual experts an d m em bers of its technical com m ittees and I EC Nati on al Com m ittees for any person al i njury, property d am age or other dam age of any nature whatsoever, wheth er di rect or indirect, or for costs (includ i ng leg al fees) and expenses arisi ng out of the publ ication, use of, or relian ce upon, this I EC Publicati on or any other I EC Publications 8) Attention is drawn to th e N orm ative references cited in th is publ ication Use of the referenced publ ications is indispensable for the correct applicati on of this publication 9) Attention is drawn to the possibility that som e of the elem ents of this I EC Publication m ay be the su bject of patent rig hts I EC shall not be held responsibl e for identifyi ng any or all such patent ri ghts I nternational Standard I EC 61 747-40-3 has been prepared by technical committee 1 0: Electronic display devices The text of this standard is based on the following docum ents: CDV Report on votin g 1 0/569/CDV 1 0/609A/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 I SO/I EC Directives, Part –4– I EC 61 747-40-3:201 © I EC 201 A list of all parts in the I EC 61 747 series, published under the general title Liquid crystal display devices , can be found on the I EC website The committee has decided that the contents of this publication will rem ain unchanged until the stability date indicated on the I EC web site 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 A bilingual version of this publication may be issued at a later date I EC 61 747-40-3:201 © I EC 201 –5– INTRODUCTION Mobile electronic devices have becom e increasingl y sophisticated and often include displays for the purposes of user interface and viewing Such displays commonl y incorporate a transparent cover glass which aids in protecting the display against the introduction of damage through routine device transport and use, as well as occasional or accidental m isuse The purpose of this standard is to provide m echanical testing procedures for cover glasses utilized in such applications Such glasses can be strengthened, for example via an ionexchange process, which acts to increase m echanical strength through the introduction of a surface com pressive layer –6– I EC 61 747-40-3:201 © I EC 201 L I Q U I D C R YS T AL D I S P L AY D E VI C E S – P a rt -3 : M e c h a n i c a l te s ti n g o f d i s p l a y c o ve r g l a s s fo r m o b i l e d e vi c e s – B i a x i a l fl e x u l e n e rg y t o fa i l u re ( b a l l d ro p ) S cop e This part of I EC 61 747-40 is a m echanical perform ance testing procedure for cover glass used in electronic flat panel displays in m obile devices This standard is focused on the measurement of surface impact resistance via biaxial flexure generated by a ball drop N o rm a t i ve re fe re n c e s The following docum ents, in whole or in part, are normativel y referenced in this docum ent and are indispensable for its application For dated references, onl y the edition cited applies For undated references, the latest edition of the referenced docum ent (including an y amendments) applies I EC 61 747-40-1 , Liquid crystal display devices – Part 40-1 : Mechanical testing of display cover glass for mobile devices – Guidelines IEC 61 649: 2008, Weibull analysis T e rm s a n d d e fi n i t i o n s For the purposes of this docum ent, the following term s and definitions apply sp eci m en individual piece of glass to be tested to failure sam pl e group of specimens sharing a comm on pedigree (such as m anufacturing process and period of production), for which failure statistics can be generated and reported 3 sam pl e si ze num ber of specim ens in a sam ple n om i n al val u e value about which a tolerance range is specified G e n e l This test is statistical in nature A ball is dropped onto each of a number of specim ens in a sam ple The energ y required to break each specimen is recorded Statistics that might be specified are calculated and reported The energy required to break a given specim en is determ ined by starting with a m inimum drop height and then increasing the drop height by a fixed increm ent for drops that not result in breakage I EC 61 747-40-3:201 © I EC 201 –7– The typical energy required to break specimens will depend on the specim en nominal dim ensions, length and width, as well as thickness Sam ple breakage values should onl y be compared when the nominal dimensions of the sam ples are the sam e The combination of ball mass and dropping height yield the breakage energy The apparatus allows for a m axim um drop height of at least 80 cm A ball m ass of 28 g m ay be adequate for 50 mm × 50 mm ( ± 0, mm ) specimens with thickness ranging from 0, 55 m m to 2, mm Thicker, stronger or larger specim ens m ay require a larger ball for a 00 % breakage by a drop height of 80 cm Clause describes the apparatus Clause describes the procedures for both the sam ple as a whole as well as for an individual specimen Clause describes the calculations To com plete the test, some m eans of catching the ball when the ball drop does not break the specimen should be provided This could be done by providing the tester with an assistant or by som e apparatus Possible apparatus options are not documented in this standard When the ball drop does not break the specimen and bounces, the rebou nd height m ay be up to approxim atel y 80 % of the original drop height and is parallel to the height adjustment beam When the drop results in breakage, the bounce direction is random but the rebound height is substantiall y reduced When breakage occurs due to a failure to catch the rebounding ball and a double impact results in breakage, the height is recorded, but the specimen is treated as a late suspension (see 2) I t is assumed that all measurements are perform ed by personnel skilled in the general art of mechanical property measurem ents Furthermore, it should be assured that all equipm ent is suitabl y calibrated as is known to skilled personnel and that records of the calibration data and traceability are kept 5 Apparatu s Tes ti n g en vi ron m en t an d p re -co n d i ti o n i n g The standard testing environm ent is specified in 61 747-40-1 Specim ens shall be stored in such an environment for at least four hours before testing App aratu s ove rvi ew Figure shows the overview of the apparatus –8– I EC 61 747-40-3:201 © I EC 201 C D E A G B H F IEC Ke y A Heig ht adjustm ent beam B Specim en hold er C Arm ature D Ball rel ease m echan ism E Heig ht ad justm ent clam p F Ball rel ease controller G Ball (whil e dropping) H Base F i g u re – Ap p aratu s o vervi ew H e i g h t a d j u s tm e n t b e am This beam shall be long enough to allow drops of at least 80 cm in maximum height I t is perpendicular to the testing surface I t shall be marked with distances from the test surface in increments of cm The test surface is the top surface of the specim en when it is inserted into the specim en holder Drop distance is the distance from the test surface to the bottom of the ball when it is attached to the ball release m echanism To accommodate the possibility of different specim en thicknesses or specim en holder dim ensions, a correction factor can be used to convert the height m arkings on the height adjustm ent beam to the actual dropping distances to within ± mm before the energ y calculation is com pleted S p e ci m en h o l d e r This is m ade of a rigidized pol ym er (such as pol yoxymeth ylene (POM), high density pol yeth ylene (H DPE), pol y(m eth yl methacrylate) (PMM A), pol y(meth yl acrylate) (PMA) or pol ycarbonate (PC)) to minim ize damage to specimens as they are mounted into it I t is a square or rectangular fram e that supports a specimen on a ledge of m m to m m , with the ledge surrounded by a specimen containm ent barrier The barrier dim ension shall be large enough to accomm odate all specimens without binding The specim en shall be elevated from I EC 61 747-40-3:201 © I EC 201 –9– the table by a distance that is large enough that no specimen touches the table due to deflection during a test Figure shows a top view and Figure shows a side view cross-section A C B IEC NOTE The key to the l etters i s provid ed in Fi gure F i g u re – S p e ci m e n h o l d e r ( to p vi e w) B C A IEC Ke y A Base surface B Specim en containm ent barrier C Led ge F i g u re – S p e ci m e n h o l d e r ( s i d e vi e w, c ro s s -s e cti o n ) The specimen holder, base and/or height adj ustment beam design shall provide a m eans of repeatability by placing the specimen holder so the ball drops onto the centre of the specimens Displacem ent error from the intended drop location shall not be greater than mm when perform ing drops ≤ m in height and not greater than m m when performing drops > m in height Displacem ent errors can be assessed via the use of a plum b line, a plumb bob and pressure-indicating films, or via other m eans which enable the accurate quantification of intended versus actual drop positions 5 Arm a tu re This connects the ball release m echanism to the height adj ustm ent beam I t shall be perpendicular to the height adj ustm ent beam – 10 – 5.6 I EC 61 747-40-3:201 © I EC 201 Ball release mechanism The ball holding and release mechanism shall either be electromagnetic or vacuum -assisted This ensures free gravitational acceleration of the ball upon release Tethering or the use of a guide tube is not an acceptable m eans of ball release and/or guidance 5.7 Height adjustment clamp This holds the armature at a height that is indicated by the height adjustment beam while a ball is set and dropped from that height The clam p is released following the ball drop to allow movement to a different height 5.8 Ball release controller The controller is an electronic switch with two states: ) load and hold the ball, 2) release the ball 5.9 Ball The ball used for testing shall be produced from a steel alloy with Rockwell hardness of C60 to C67, and shall possess a reflective surface finish The diameter tolerance shall be no greater than ± 0, 05 mm from nominal, and the deviation from sphericity shall be no greater than 0, 025 mm Ball m ass shall be within ± 2, % of the specified value, and the actual (m easured) m ass shall be used for all energ y calculations 5.1 Base The base shall be rigid and fully supported to ensure minimal energ y absorption by the structure Absorption of energ y by the base can lead to variation in the energy applied to the specimen Procedure 6.1 6.1 Safety Hazard – Broken glass Wear safety glasses with side panels at all times Wear gloves when handling broken glass 6.1 Hazard – Compression due to moving ball As previousl y noted, ball drop and rebound energies m ay be substantial and ball travel m ay be erratic Care should be taken to ensure that all operators, assistants and persons in the area are alert and wearing appropriate personal protective equipment 6.2 Sample The sample size is 30, excluding an y specim ens rejected for pre-existing dam age Failures associated with breakage upon double bounce are included in the sam ple, but the valu es are treated as late suspensions (see 2) Specim ens that fail from their edge, and those that not fail at the m aximum dropping height are also treated as late suspensions I f there are more than suspensions, the testing fails and a new sample should be selected I f this occurs due to a high proportion of edge failures, actions m ay be taken to increase specimen I EC 61 747-40-3:201 © I EC 201 – 11 – edge strength or to perform an alternate surface strength test such as a biaxial flexural strength via ring-on-ring Upon receipt of a new sam ple, the following steps shall be taken: a) Determine and record the following information: • sample identification, • sample specimen nominal dimensions: length, width, thickness, • requesting person, • determ ine whether existing test fixtures are compatible I f not, change them b) Record the fixture dim ensions or identification number c) Determine whether a height adjustm ent factor is needed This could be due to testing specim ens with a different thickness than the thickness used to design the height adj ustm ent beam or due to a different specim en holder than that used in the design d) Thoroughl y clean the testing area I n d i vi d u al s peci m en Complete the following steps on each specim en of the sam ple The working surfaces should be clean and free of an ything that can induce dam age Application of the pol ym eric adhesive tape is intended to preserve the fracture surface and to reduce the scattering of glass fragm ents upon breakage a) Determine and record the specim en identification number b) I nspect for an y damage I f dam aged, report this, but not include in the testing c) Cut a section of pol ym eric adhesive tape that can cover the specim en and place it sticky side up on the working surface d) Gentl y attach one edge of the specim en to one end of the tape e) Gentl y lower the rest of the specimen onto the rest of the tape f) Carefull y trim the excess tape away from the specim en g) Place the specim en in the test holder with the pol ym eric adhesive tape side facing downward h) Set the arm ature for a cm ball drop i) Repeat the following for each drop: ) Load the ball 2) Drop the ball 3) I f no breakage, catch the ball I f there is no initial breakage but the ball is not caught and the second impact results in breakage, the height is reported, but the specimen is m arked as suspended 4) I f no breakage, check that the sample rem ains correctl y positioned within the fixture and m ove the arm ature up cm and repeat ) to 4) j) At this point, breakage occurred or the maximum height has been reached without breakage Record the height and note whether the specimen should be suspended due to edge failure I f the height is m axim um without breakage, also note the specim en as a suspension k) Regain possession of the ball and thoroughly clean the area C o m p l e t e t h e re p o rt The calculations will normall y be done by computer: a) Enter the sample identification and dimensions – 12 – I EC 61 747-40-3:201 © I EC 201 b) Com plete the breakage energy calculations of c) Com plete the Weibull anal ysis of d) Print the report Calculations 7.1 Breaking energy The breaking energ y, E, in units of J oules, is given as equation (1 ) E= (h + c ) m g 000 00 (1 ) where m h c g 7.2 is is is is the ball mass (g) the arm ature height (cm ) a correction factor for specimen nominal thickness variation (cm ) the gravitational acceleration factor = 9, 81 m/s Statistical calculations The Weibull anal ysis standard, I EC 61 649, shall be used to calculate the following param eters: • • • Weibull scale param eter, η (J) Weibull shape param eter, β the th percentile fracture energ y, B (J) The maximum likelihood estim ate (MLE) method of calculation shall be used for the Weibull param eters See of I EC 61 649: 2008 The following equations are adapted from equations (1 7) and (1 8) of I EC 61 649: 2008 in order to accomm odate suspensions as variable censoring Following the notation of I EC 61 649, let ti represent the valid fracture energy values, with i =1 to r, and let Tj represent the suspended values, wi th j =1 to s The shape parameter is the value of β that satisfies equation (2) r s i =1 j =1 s β β ∑ ti ln ti + ∑ T j ln T j r ∑ ti i =1 β + − ∑ Tj β − β r ln ti r∑ i =1 = (2) j =1 Given this value for the shape param eter, the scale parameter is given as equation (3) η = r r tiβ + i =1 ∑ s ∑ Tj j =1 β 1/β (3) The point estim ate of the th percentile, B , is calculated using of I EC 61 649: 2008 and equation (20) of I EC 61 649: 2008 Equation (20) is repeated here as equation (4) for I EC 61 747-40-3:201 © I EC 201 – 13 – convenience I n Clause 9, this param eter is recomm ended to be specified for performance standards I t combines the scale and shape parameters to single, m eaningful, metric 1/β (4) B1 = η [− ln (0,9 )] I n addition to the calculation of statistical param eters, a Weibull plot is required (see 8.2) See of I EC 61 649: 2008 for instructions on how to produce such a plot An exam ple Weibull plot is shown in Figure Probability pl ot of ball d rop perform ance Failu re probability (%) 99 90 80 70 60 50 40 30 20 10 IEC Failu re energ y (J ) F i g u re – E x a m p l e W e i b u l l 8 Re p o rt i n g I n fo rm a t i o n t o b e re p o rt e d fo r e a c h test Report the following for each test: • • • • • Sample identification and nominal dim ensions Ball m ass (g) Weibull scale param eter, η (J) Weibull shape param eter, β Fracture energy th percentile, B (J) I n fo rm a t i o n to b e m ad e ava i l abl e u p o n The following inform ation shall be available: • All breakage energy values: re q u e s t IEC pl ot – 14 – • I EC 61 747-40-3:201 © I EC 201 – Note suspensions and causes Weibull plot Specifications The following testing aspects require specification to obtain com parable results: • • • Ball mass (g) Specim en nom inal dimensions Fixture dim ensions The following param eter is recommended for specification in performance standards • The fracture energy th percentile, B (MPa) I N TE RN ATI O N AL E LE CTRO TE CH N I CAL CO M M I S S I O N 3, ru e d e Va re m bé P O B ox CH -1 1 G e n e va S wi tze rl a n d Te l : + 41 F a x: + 22 91 02 1 22 91 03 00 i n fo @i e c ch www i e c ch