IEC TR 6301 8 Edition 1 0 201 5 1 2 TECHNICAL REPORT Flexible printed circuit boards (FPCBs) – Method to decrease signal loss by using noise suppression materials IE C T R 6 3 0 1 8 2 0 1 5 1 2 (e n )[.]
I E C TR 63 ® Edition 201 5-1 TE C H N I C AL RE P ORT colour in sid e F l exi bl e pri n ted ci rcu i t board s (F PC B s ) – M eth od to d ecreas e s i g n al l oss b y IEC TR 6301 8:201 5-1 2(en) u s i n g n oi s e s u ppres s i on m ateri al s TH I S P U B L I C ATI O N I S C O P YRI G H T P RO TE C T E D C o p yri g h t © I E C , G e n e va , S w i tze 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 IEC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local IEC 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 Abou t th e I E C The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes International Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i c a 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 C atal og u e - webs tore i ec ch /catal og u e E l ectroped i a - www el ectroped i a org 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 The world's leading online dictionary of electronic and electrical terms containing 20 000 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 pu bl i cati on s s earch - www i ec ch /s earch pu b I E C G l os s ary - s td i ec ch /g l os s ary 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 65 000 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 P u bl i s h ed - webs tore i ec ch /j u s u bl i s h 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 s to m er S ervi ce C en tre - webs tore i ec ch /cs c 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 TR 63 ® Edition 201 5-1 TE C H N I C AL RE P ORT colour in sid e F l exi bl e pri n ted ci rcu i t board s (F P C B s ) – M eth od to d ecreas e s i g n al l oss b y u s i n g n oi s e s u ppres s i on m ateri al s INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 31 80 ISBN 978-2-8322-3082-4 Warn i n g ! M ake s u re th at 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 TR 6301 8: 201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Norm ative references Test guideline Apparatus Network anal yzer Block diagram for signal loss m easuring Test specim en Structure 2 Preparation 3 Test m ethod Calculation Test result Anal ysis 3 I m provem ent m ethod of signal loss for a shield FPCB Annex A (normative) Block diagram of signal loss test system Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure – Bare/shield FPCB – I ncrem ent of signal loss using N SMs – Signal loss test system – Schematic diagram for two type of test specim en – Cross-section of shield FPCB – Difference of signal loss between bare and shield FPCBs – Signal loss value of the bare and shield FPCB – Signal loss variation according to the Cu conductive layer thickness 1 – Signal loss variation according to the Cu signal line width 1 – Two types of structure for FPCB 1 – Electric field diagram for two types of shield FPCB A – Block diagram of signal loss test system A – Signal loss test system according to the Agilent network anal yzer N5230A Table – Com parison of cut-off frequency with bare/shild FPCB I EC TR 6301 8:201 © I EC 201 –3– INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON F L E XI B L E P RI N T E D C I R C U I T B O AR D S ( F P C B s ) – M E T H O D T O D E C RE AS E S I G N AL L O S S B Y U S I N G N O I S E S U P P RE S S I O N M AT E RI AL S 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 the tech nical 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 n ature 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 The m ain task of I EC technical comm ittees is to prepare I nternational Standards H owever, a technical committee m ay propose the publication of a technical report when it has collected data of a different kind from that which is normally published as an I nternational Standard, for exam ple "state of the art" I EC TR 6301 8, which is a technical report, has been prepared by I EC technical committee 91 : Electronics assem bl y technolog y The text of this technical report is based on the following docum ents: Enqui ry draft Report on votin g 91 /1 284/DTR 91 /1 309/RVC Full information on the voting for the approval of this technical report can be found in th e 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 TR 6301 8: 201 © I EC 201 The committee has decided that the contents of this publication will rem ain unchanged until the stability date indicated on the I EC 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 A bilingual version of this publication may be issued at a later date I M P O RT AN T – T h e ' c o l o u r i n s i d e ' th at it tai n s u n d e rs t a n d i n g c o l o u r p ri n t e r of c o l o u rs i ts wh i c h c o n te n ts l og o a re U s e rs on th e co ve r p ag e o f th i s c o n s i d e re d s h ou l d to t h e re fo re be p u b l i c ati o n u s e fu l p ri n t th i s fo r i n d i c ate s th e d o cu m en t c o rre c t u sin g a I EC TR 6301 8:201 © I EC 201 –5– INTRODUCTION I n recent years, since the use of smart phones, and other m obile and display devices has increased significantl y, the suppl y of FPCBs has also been largel y extended Specificall y, since the FPCB devices seek high speed performance, the requirements with respect to electrom agnetic interference (EMI ) suppression in the devices has also grown in im portance Therefore, FPCBs used inside sm art phones em ploy noise suppression m aterials (N SMs) to solve EMI problem s, as shown in Figure IEC F i g u re – B a re /s h i e l d F PC B Transmission l oss (dB) However, an application of noise suppression m aterials (N SMs) for FPCBs reaches the limit concerning the problem of increm entation of signal loss Therefore, FPCB and N SMs manufacturers need to anal yse signal loss variations of FPCBs shielded by N SMs, as shown in Figure Bare FPCB Shield FPCB Freq uency (GH z) IEC F i g u re – I n c re m e n t o f s i g n a l loss u si n g N SM s As FPCBs are used with high frequency, the problem of signal loss becom es m ore significant As the user of FPCBs has a demand for the lowest value of signal loss by using N SMs, suppliers of FPCBs have to anticipate an appropriate design in order to achieve an adequate signal loss value –6– I EC TR 6301 8: 201 © I EC 201 F L E XI B L E P RI N T E D C I RC U I T B O ARD S ( F P C B s ) – M E T H O D T O D E C RE AS E S I G N AL L O S S B Y U S I N G N O I S E S U P P RE S S I O N M AT E RI AL S S cop e This Technical Report specifies a guideline for im provem ent of signal loss by using noise suppression materials (hereafter referred to as N SMs) for FPCBs This Technical Report also indicates a m easuring m ethod of signal loss variations of FPCBs using N SMs using network anal yzer equipment I n addition, this m ethod only measures the value of the signal loss variation by using N SMs for FPCBs This report, however, neither determines nor indicates the structure or m aterial of FPCBs 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 62333-1 : 2006, Noise sup pression sh e et for digita l de vices a n d equip m en t – Pa rt : De fin ition s a n d ge n era l p rop e rties Te s t g u i d e l i n e 3 Ap p a t u s N e t w o rk a n a l y z e r A network anal yzer is utilized to identify signal loss data at a specific frequency range of FPCBs B l o c k d i a g m fo r s i g n a l l o s s m e a s u ri n g Figure indicates one of the exam ples of the network analyzer setup Network anal yzer I ncident Reflection S1 Transm ission S21 IEC F i g u re – S i g n a l l o s s te s t s ys te m I EC TR 6301 8:201 © I EC 201 3.2 Test specimen 3.2.1 Structure –7– Test specimens shall be designed by two structures, i e with and without NSMs in one FPCB board The part without using N SMs is called bare FPCB The part using N SMs is called shield FPCB, as shown in Figure This test coupon shall also be designed as two types in order to have an object of com parison The first design shall be composed of one bare FPCB with one shield FPCB A design of this structure allows to com pare the bare FPCB with the shield FPCB, as shown in Figure a The second design shall be com posed of one bare FPCB with two over shield FPCBs This structure allows to com pare the bare FPCB with the two over shield FPCBs, as shown in Figure b Via hol e LW1 Bare FPCB LW1 ’ Shield FPCB >5 ㎝ IEC Figure a – Test specimen for comparing one bare FPCB with another shi eld FPCB Via hol e LW1 Bare FPCB LW1 ’ Shield FPCB LW1 ’’ Shield FPCB LW1 ’’’ • • >5 Shield FPCB Shield n FPCB ㎝ IEC Figure b – Test specimen for comparing one bare FPCB with two over shield FPCBs Figure – Schematic diagram for two type of test specimen The test specimen shall be divided into two halves with one board (bare FPCB and shield FPCB) for equitable estim ation with the sam e Cu line (LW1 , LW1 ’… ) This structure has the m erit of uniforml y measuring at once a bare and a shield FPCB under the sam e conditions –8– I EC TR 6301 8: 201 © I EC 201 The Cu line is formed with a linear distance of direction, because the variation of shield effect is very weak for the curved line The width of Cu line shall be chosen freely in the allowance range of a manufacturing process The size and spacing of via holes shall not be limited Especially, via holes offer an im portant role to contact the N SMs with the ground plan of shield FPCB, as shown in Figure However, the size, spacing and amount of via holes shall be as agreed between user and supplier (AABU S) The length of test specimens shall be over cm in order to obtain stable values from measuring equipment The width and thickness of test specim ens shall be in accordance with the needs of the end user Figure indicates one of the examples of a cross-section of a shield FPCB, where the shield region shall be form ed just above the bare FPCB The shield region contains the shield insulation layer, the shield conductive layer and the shield conductive adhesive layer Where the shield conductive layer plays a role in an EM I absorber, the shield conductive adhesive layer plays a role for electric interconnection between the shield conductive layer with the ground layer, and the shield insulation layer plays a role to protect the shield conductive layer from direct contact with the external device Shield i nsulati on l ayer – µm Shield cond uctive l ayer – 0, /2 µm Shield cond uctive adh esive layer – µm C/L PI – µm Shield region C/L ad hesi ve – 25 µm Cu Cu – 23 µ m Cu Bare FPCB PI – 50 µ m Cu – 23 µ m IEC Figure – Cross-section of shield FPCB However, generall y the structure of a test coupon shall also be as agreed upon between user and supplier (hereafter referred to as AABU S) The structure and materials of the test specim ens is required depending on the user’s sam ple specifications But the variation of these test specim ens is not important, because the user for FPCBs shall check onl y the signal loss variation effect by using N SMs 3.2.2 Preparation The following steps are needed to prepare the test a) First, prepare a cm over length for a bare FPCB Then, appl y N SMs lam ination to half of the FPCB b) Each end of the test specimen shall consist of SMA (subm iniature A) connectors c) To designate the Cu line width, write the num ber (or sym bol) to the bare side end (or shield side end) of test specim en near the SMA connector 3.2.3 Test method In order to measure the proper signal loss value, the following procedures shall be respected a) The signal loss values of the test specim en shall be m easured by com position of a network anal yzer, a test specimen and a coaxial cable b) The measurem ent conditions shall be set in the network analyzer, such as the frequency range, dielectric constant, measurem ent point, etc I EC TR 6301 8:201 © I EC 201 c) d) e) f) –9– Coaxial connectors (SMA) of test specimens shall be connected with coaxial cables Measure the signal loss value of the test specimen for bare FPCBs Repeat a measurem ent of above for shield FPCBs I n order to obtain the correct data, a direct hand contact to the specim en should be avoided as the electrostatic capacity varies 3.2.4 Calculation The following applies to the calculation of the loss values ∆ TL (dB) Transmission l oss (dB) a) Calculate the difference of the signal loss value between bare FPCBs and shield FPCBs according to an S-param eter anal ysis, as shown in Figure b) Estim ate the shield effect of N SMs according to frequency The signal loss (transm ission loss, S21 ) shall be increased by the shield effect of N SMs The difference ( ∆ TL ) of the signal loss value between bare FPCBs and shield FPCBs shall be gradually increased by a higher frequency c) Re-design a signal loss m argin of the bare FPCB to predict an application of shield m aterials (N SMs) Bare FPCB Shield FPCB Freq uency (GH z) IEC Figure – Difference of signal loss between bare and shield FPCBs 3.2.5 3.2.5.1 Test result Comparison of signal loss between bare and shield FPCBs Figure indicates an exam ple of the signal loss value of a bare FPCB and a shield FPCB Signal loss (S21 ) of a shield FPCB (at Cu signal line width 40 µm ) has been additionally increased by dB ~ dB as compared with a bare FPCB at GH z frequency I n addition, a signal loss of a shield FPCB with a thin Cu/Ag conductive layer (0, µm ) has been increased to dB as compared to a shield FPCB with a thick Cu conductive layer (2 µm) – 10 – I EC TR 6301 8:201 © I EC 201 Bare Shield (Cu µm ) S21 (dB) Shield (Cu/Ag 0, µm ) 40 µm Cu signal l i ne width Freq uency (GH z) IEC Figu re – Signal loss valu e of the bare and shield FPCB 3.2.5.2 Comparison of cut-off frequency between bare and shield FPCB Table presents a com parison of cut-off frequency between a bare FPCB and a shield FPC, whose shield FPCB has been divided into two types of shield film The dB cut-off frequency in Figure is 5, GH z in the case of a bare FPCB, 2, 71 GH z in the case of a shield FPCB and 0,87 GH z in the case of a shield FPCB Therefore, a bare FPCB can be applicable for a GH z frequency range, but a shield FPCB cannot be applicable for an over GH z frequency range Especially, a shield FPCB cannot be applicable for an over GH z frequency range Table – Comparison of cut-off frequency with bare/shild FPCB Structure Classification Cut-off freq uency (at dB) 3.2.5.3 Bare Shield (Cu µ m ) Shield (Cu/Ag 0, µm ) 5, GHz 2, 71 GHz 0, 87 GHz Effect of the Cu condu ctive layer thickness The shield region shall be included in the Cu conductive layer, as shown in Figure Figure presents a com parison of signal loss variation (S1 , S21 ) according to the thickness of the Cu conductive layer Variation of signal loss according to the Cu conductive layer thickness (2 µm µm, µm ) of a shield FPCB (at Cu signal line width 40 µm ) is within the small range of dB – 11 – d B (S21 , S1 ) I EC TR 6301 8:201 © I EC 201 dB (Cu µm S(2,1 )) dB (Cu µm S(2,1 )) dB(Cu µm S(2,1 )) dB (Cu µm S(1 ,1 )) dB (Cu µm S(1 ,1 )) dB (Cu µm S(1 ,1 )) Freq u en cy (G H z) IEC Figure – Signal loss variation according to the Cu conductive layer thickness 3.2.5.4 Effect of the Cu signal line width Figure presents a comparison of signal loss variation according to the width of the Cu signal line Variation of the signal loss according to the width (40 µm, 60 µm , 80 µm) of a Cu signal line (at Cu conductive layer thickness of µm) is within the sm all range of dB Bare (40 µ m ) Bare (60 µ m ) S21 (dB) Bare (80 µ m ) Shield (40 µ m ) Shield (60 µ m ) Shield (80 µ m ) Shield (40 µ m ) Shield (60 µ m ) Shield (80 µ m ) Freq uency (GH z) µm Cu conducti ve layer IEC Figure – Signal loss variation according to the Cu signal line width – 12 – 3.2.6 3.2.6.1 I EC TR 6301 8:201 © I EC 201 Analysis A cause of the signal loss difference between bare and shield FPCBs Figure presents examples of two types of FPCB structure The major cause of the signal loss increm ent between bare FPCBs and shield FPCBs is the structure variation from the micro-strip line without using N SMs to strip line using N SMs Via hol e NSMs Cover layer PI Cover layer PI G(Cu) Adhesi ve S(Cu ) G(Cu) Adhesi ve S(Cu ) G(Cu) PI GND (Cu) PI GND (Cu) Bare FPCB G(Cu) IEC Figure a – < FPCB of micro strip line stru cture > Shield FPCB IEC Figure b – < FPCB of strip line stru ctu re > Figure – Two types of structure for FPCB Generally, the transmission line of a bare FPCB in its first stage shall be designed by a m icrostrip line structure in order to achieve the lowest signal loss But, after an application of N SMs to a bare FPCB, the transm ission line shall be changed at the strip line structure and then the signal loss increased 3.2.6.2 A cause of the signal loss difference between shield films I n Figure 7, signal loss of a shield FPCB has been increased to compare it with a shield FPCB A signal loss difference between shield FPCB and shield FPCB shall be anal ysed as follows Figure 1 shows the distribution diagram of an electric field of two types of shield FPCBs Shield FPCB is composed of a µm thickness of Cu conductive layer, the electric field around the Cu signal line shall be uniform But, on the other hand, a shield FPCB is com posed of 0, µm thickness of a Cu/Ag conductive layer, therefore the electric field around a Cu signal line shall be non-uniform by the cause of incomplete electric conduction with a too thin film To sim plify the illustration, the ground interconnection line has been omitted in Figure 1 A major cause of the signal loss variation according to the type of shield film s is the formation of an unbalanced electric field by using low conductive N SMs I n the case of the shield FPCB, a possibility of high resistance between a Cu conductive layer and a ground layer shall exist The high resistance shall be caused by a thin Cu conductive layer and/or poor viahole connection I EC TR 6301 8:201 © I EC 201 – 13 – Shield film (Cu µ m , g rou nd ) PI Adhesi ve a) Cu (groun d) Cu Cu (groun d) PI Cu (groun d) Shield film (Cu 0, µ m , g roun d) PI b) Adhesi ve Cu (groun d) Cu Cu (groun d) PI Cu (groun d) IEC Ke y a) Balanced el ectric field distribution at th e shiel d FPCB b) Unbalanced electric fiel d distri bution at the shi eld FPCB F i g u re 1 3 – E l e c t ri c fi e l d d i a g m I m p ro v e m e n t m e t h o d of s i g n al fo r t w o t y p e s o f s h i e l d l o s s fo r a s h i e l d F PC B FPCB To improve the transmission loss for shield FPCBs using commercial shield film , FPCB m anufacturers have to appl y comm ercial shield films of µm over Cu conductive layer thickness Also FPCB m anufacturers need to achieve a minim um loss through a good connection of via holes between bare FPCBs and the shield region – 14 – I EC TR 6301 8:201 © I EC 201 Annex A (normative) Block diagram of signal loss test system Network anal yzer shall be used for signal loss measurem ents according to I EC 62333-1 : 2006 The network anal yzer setup is shown in Figure A Network anal yzer I ncident Reflection S1 Transm ission S21 IEC Figu re A.1 – Bl ock di agram of sign al loss test system Test setup figure by Agilent network anal yzer N5230A is as shown in Figure A IEC IEC Fi gure A a) – Test system Figure A b) – SM A n ector Figu re A.2 – Sign al loss test system according to th e Agi lent network analyzer N 5230A _ _ Agilent n etwork anal yzer N5230A is the trad e n am e of a prod uct supplied by Agil ent Tech nologi es This inform ation is gi ven for the venience of users of th is docum ent an d does n ot constitute an endorsem ent by I EC of th e prod uct nam ed Equivalent prod ucts m ay be used if they can be shown to l ead to the sam e results INTERNATIONAL ELECTROTECHNICAL COMMISSI ON 3, rue de Varembé PO Box 31 CH-1 21 Geneva 20 Switzerland Tel: + 41 22 91 02 1 Fax: + 41 22 91 03 00 info@iec.ch www.iec.ch