IEC TR 63091 Edition 1 0 201 7 05 TECHNICAL REPORT Study for the derating curve of surface mount fixed resistors – Derating curves based on terminal part temperature IE C T R 6 3 0 9 1 2 0 1 7 0 5 (e[.]
I E C TR 63 ® Edition 201 7-05 TE C H N I C AL RE P ORT S tu d y for th e d erati n g cu rve of s u rface m ou n t fi xe d res i s tors – D e rati n g cu rves IEC TR 63091 :201 7-05(en) bas ed on term i n al part tem pe ratu re 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variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing 20 000 terms and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 G l os sary - s td i ec ch /g l oss ary 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 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 TR 63 ® Edition 201 7-05 TE C H N I C AL RE P ORT S tu d y for th e d erati n g cu rve of s u rface m ou n t fi xed re s i s tors – D erati n g cu rve s bas ed on te rm i n al part tem pe ratu re INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 31 040.1 ISBN 978-2-8322-4368-8 Warn i n g ! M ake s u re th a t you ob tai n ed th i s p u b l i cati on from an au th ori zed d i stri b u tor ® Registered trademark of the International Electrotechnical Commission –2– I EC TR 63091 : 201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Norm ative references Terms and definitions Stud y for the derating curve of surface mount fixed resistors 1 General 1 Using the derating curve based on the terminal part tem perature Measuring method of the term inal part temperature of the SMD resistor 4 Measuring m ethod of the thermal resistance R th shs-t from the terminal part to the surface hotspot Conclusions 21 Annex A (informative) Background of the establishm ent of the derating curve based on ambient tem perature 22 A Tracing the history of the mounting and heat dissipation figuration of resistors 22 A How to establish the high tem perature slope part of the derating curve 24 A 2.1 General 24 A 2.2 Derating curve for th e semiconductors 26 A 2.3 Derating curve for resistors 29 Annex B (informative) The temperature rise of SMD resistors and the influence of the printed circuit board 40 B Temperature rise of SMD resistors 40 B The influence of the printed circuit boards 45 Annex C (inform ative) The influence of the number of resistors mounted on the test board 49 C General 49 C The influence of the number of resistors m ounted on the test board 49 C The delay of correspondence for current products with nonstandard dim ensions 51 Annex D (inform ative) I nfluence of the air flow in the test chamber 52 D General 52 D I nfluence of the wind speed 52 Annex E (informative) Validity of the new derating curve 60 E Suggestion for establishing the derating curve based on the terminal part temperature 60 E Conclusion 65 Annex F (inform ative) The therm al resistance of SMD resistors 67 Annex G (inform ative) H ow to m easure the surface hotspot tem perature 72 G.1 Target of the measurem ent 72 G.2 Recomm ended m easuring equipm ent 72 G.3 Points to be careful when m easuring the surface hotspot of the resistor with an infrared therm ograph 72 G General 72 G Spatial resolution and accuracy of peak temperature measurem ent 73 G 3 I nfluence of the angle of the measurem ent target normal line and the infrared therm ograph light axis 75 I EC TR 63091 :201 © I EC 201 –3– Annex H (inform ative) H ow the resistor m anufacturers measure the therm al resistance of resistors 79 H The m easuring system 79 H Definition of the two kinds of tem peratures 80 H Errors in the measurement 83 Annex I (inform ative) Measurement m ethod of the terminal part temperature of the SMD resistors 88 I.1 Measuring method using an infrared thermograph 88 I.2 Measuring m ethod using the thermocouple 89 I.3 Estim ating the error range of the tem perature measurem ent using the therm al resistance of the therm ocouple 90 I General 90 I When using the type T thermocouples 97 I.4 Thermal resistance of the board 97 I.5 Conclusion of this annex 00 Annex J (inform ative) The variation of the heat dissipation fraction caused by the difference between the resistor and its mounting configuration 01 J Heat dissipation ratio of cylindrical resistors wired in the air 01 J Heat dissipation ratio of SMD resistors m ounted on the board 02 J Heat dissipation ratio of the cylindrical resistors mounted on the throughhole printed board 04 Annex K (informative) I nfluence of airflow on SMD resistors 05 K General 05 K Measurem ent system 05 K Test results (orthogonal) 06 K Test results (parallel) 1 Annex L (informative) The influence of the spatial resolution of the thermograph 1 L The application for using the therm ograph when measuring the tem perature of the SMD resistor 1 L The relation between the m inim um area that the accurate tem perature could be m easured and the pixel magnification percentage 1 L Example of the RR1 608M SMD resistor hotspot's actual m easurement 20 L Conclusion 21 Annex M (inform ative) Future subj ects 22 Bibliograph y 23 Figure – Existing derating curve based on ambient tem perature Figure – Suggested derating curve based on terminal temperature Figure – Attachm ent position of the therm ocouple when m easuring the tem perature of the terminal part Figure – Attaching type K thermocouples Figure – Wiring routing of the thermocouple Figure – The true value and the actual measured value of the term inal part temperature Figure – Thermal resistance R th eq of the FR4 single side board (thickness , mm ) Figure – Length that cause the heat dissipation and the therm al resistance of the type-K thermocouple (calculated) Figure – Exam ple of calculation of the measurem ent error ∆ T caused by the heat dissipation of the thermocouple –4– I EC TR 63091 : 201 © I EC 201 Figure – Recommended m easurem ent system of Tshs and Tt for calculating R th shs-t 20 Figure A – Wired in the air using the lug terminal 22 Figure A – H eat path when wired in the air using the lug terminal 23 Figure A – Test condition for resistors with category power W 24 Figure A – Test condition for resistors with category power other than W 25 Figure A – Exam ple of reviewing the derating curve 26 Figure A – Tj , Tc and R th j-c of transistors 27 Figure A – Derating curves for transistors 28 Figure A – Traj ectory of Tj when P is reduced according to the derating curve 29 Figure A – Leaded resistors with small tem perature rise 30 Figure A – Leaded resistors with large tem perature rise 31 Figure A 1 – Traj ectory of Ths for the lead wire resistors with small temperature rise 31 Figure A – Traj ectory of Ths for the lead wire resistors with large temperature rise 33 Figure A – Traj ectory of Ths for resistors with category power other than W 34 Figure A – Tsp and M AT for lead wire resistors with large temperature rise 35 Figure A – Tsp and M AT for lead wire resistors with sm all temperature rise 36 Figure A – Resistors for which the hotspot is the therm all y sensitive point 37 Figure A – Resistor that have derating curve sim ilar to the semiconductor 38 Figure B – Temperature distribution of the SMD resistors m ounted on the board 41 Figure B – Temperature rise of the SMD resistors from the ambient tem perature 42 Figure B – Measurem ent system layout and board dim ension 43 Figure B – Tem perature rise of RR201 2M (thickness 35 μm , , 25 W applied) 44 Figure B – Temperature rise of RR201 2M (thickness 70 μ m , , 25 W applied) 45 Figure B – Traj ectory of the terminal part and hotspot tem perature of the SMD resistors 46 Figure B – Operating temperature of the resistor on the board with narrow patterns 47 Figure C.1 – Test board compliant with the I EC standard for RR1 608M 50 Figure C.2 – Relation between the num ber of samples and the surface hotspot tem perature rise 50 Figure C.3 – I nfrared therm ograph im age in the same scale when power is applied to sam ples and 20 samples 51 Figure D.1 – Wind speed and the term inal part tem perature rise of the RR6332M 53 Figure D.2 – Test system for the natural convection flow 53 Figure D.3 – Observing the influence of the agitation wind in the test cham ber 55 Figure D.4 – Wind speed and the term inal part tem perature rise of the RR5025M 56 Figure D.5 – Wind speed and the term inal part tem perature rise of the RR3225M 56 Figure D.6 – Wind speed and the term inal part tem perature rise of the RR321 6M 57 Figure D.7 – Wind speed and the term inal part tem perature rise of the RR201 2M 57 Figure D.8 – Wind speed and the term inal part tem perature rise of th e RR1 608M 58 Figure D.9 – Wind speed and the term inal part tem perature rise of th e RR1 005M 58 Figure E – Derating conditions of SMD resistors on the resistor m anufacturer test board 60 Figure E – N ew derating curve provided by the resistor manufacturer to the electric/electronic designers 63 I EC TR 63091 :201 © I EC 201 –5– Figure E – Derating curve based on the terminal part tem perature 64 Figure E – Derating curve based on the terminal part temperature 65 Figure F – Definition of the therm al resistance in a strict sense 68 Figure F – Therm al resistance of the resistor 69 Figure G – Difference of the measured hotspot tem perature caused by the spatial resolution 74 Figure G – Measuring system for the error caused by the angle 76 Figure G – Error caused by the angle of the optical axis and the target surface (natural convection) 77 Figure G – Error caused by the angle of the optical axis and the target surface (0, m/s air ventilation from the side) 77 Figure H – Measuring system for calculating the thermal resistance between the surface hotspot and the term inal part 80 Figure H – Simulation m odel 81 Figure H – Tem perature distribution of the copper block surface (calculated) 84 Figure H – I sotherm al line of the fillet part (calculated) 86 Figure I – Tem perature drop caused by the attached thermocouple 89 Figure I – Example of the printed board 90 Figure I – Printed board shown with the therm al network 91 Figure I – Equivalent circuit of the printed board shown with the therm al network 92 Figure I – Equivalent circuit when the thermocouple is connected 93 Figure I – Ambient temperature and the space need for the heat dissipation of the thermocouple 94 Figure I – Equivalent circuit when the thermocouple is connected 95 Figure I – Length that causes the heat dissipation and the therm al resistance of the type K therm ocouple (calculated) 96 Figure I – Length that cause the heat dissipation and the thermal resistance of the type T therm ocouple (calculated) 97 Figure I – Thermal resistance R th eq of the FR4 single side board (thickness , m m) 98 Figure I 1 – Calculating the therm al resistance of the board from the fillet side 99 Figure J – Sim ulation model of the lead wire resistors wired in the air 01 Figure J – H eat dissipation ratio of the leaded cylindrical resistors (calculated) 02 Figure J – Measurem ent system of the heat dissipation ratio of SMD resistors mounted on the board 03 Figure K – Measurem ent system 06 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR6332M (orthogonal) 07 Figure K – Relationship between the terminal part tem perature rise and the wind speed for the RR5025M (orthogonal) 07 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR3225M (orthogonal) 08 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR321 6M (orthogonal) 08 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR201 2M (orthogonal) 09 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR1 608M (orthogonal) 09 –6– I EC TR 63091 : 201 © I EC 201 Figure K – Relationship between the term inal part tem perature rise and the wind speed for the RR1 005M (orthogonal) 1 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR6332M (parallel) 1 Figure K – Relationship between the term inal part tem perature rise and the wind speed for the RR5025M (parallel) 1 Figure K 1 – Relationship between the terminal part temperature rise and the wind speed for the RR3225M (parallel) 1 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR321 6M (parallel) 1 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR201 2M (parallel) 1 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR1 608M (parallel) 1 Figure K – Relationship between the terminal part temperature rise and the wind speed for the RR1 005M (parallel) 1 Figure K – Term inal part tem perature rise of RR6332M, difference between the windward and leeward sides when placed parallel 1 Figure L – Step response of the Gaussian filter of the various cut-off spatial frequencies (calculated) 1 Figure L – Tem perature distribution (cross-section) when measuring the obj ect that becomes high tem perature onl y in the range of 0, mm in diameter 1 Figure L – Measuring system of spatial frequency filter of the infrared therm ograph 1 Figure L – Actual m easured value of the step response of various m agnifier lenses 1 Figure L – Comparison of the actual measured value and the calculated value (step response) 20 Figure L – Comparison of the actual measured value and the calculated value (surface hotspot of the resistor) 21 Table D.1 – N umber of sam ples mounted and the applied power 54 Table H – Results of the fillet part tem perature simulation (calculated value) 82 Table H – Sim ulation result of the fillet part's tem perature where it is m easurable (calculated value) 82 Table H – Sim ulation result of the fillet part's tem perature where it is m easurable (calculated value) 83 Table H – Thermal resistance sim ulation results between the surface hotspot and the term inal part based on the copper block temperature (calculated value) 85 Table J – Anal ysis result of the heat dissipation ratio of SMD resistors (calculated value and value actuall y measured) 04 I EC TR 63091 :201 © I EC 201 –7– INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON S T U D Y F O R T H E D E R AT I N G C U RVE O F S U RF AC E M O U N T F I XE D RE S I S T O RS – D e ti n g c u rve s b a s e d o n te rm i n a l p a rt te m p e tu re 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 an y 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 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 norm ally published as an I nternational Standard, for exam ple "state of the art" I EC TR 63091 , which is a technical report, has been prepared by I EC technical committee 40: Capacitors and resistors for electronic equipment The text of this technical report is based on the following documents: Enqui ry draft Report on votin g 40/2502/DTR 40/2532/RVDTR 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 –8– I EC TR 63091 : 201 © I EC 201 This document has been drafted in accordance with the I SO/I EC Directives, Part The com mittee has decided that the contents of this document will remain unchanged until the stability date indicated on the I EC website under "http: //webstore iec ch" in th e data related to the specific document At this date, the document will be • • • • reconfirmed, withdrawn, replaced by a revised edition, or am ended A bilingual version of this publication m ay be issued at a later date – 112 – I EC TR 63091 :201 © I EC 201 +3 σ 20 Maximum 00 Average Minim um Ttr (K) 80 60 -3 σ 40 20 NC S M Wind speed F IEC Key Ttr Term inal part tem peratu re rise NC Norm al vection (fl at) S 0, m /s to 0, m /s M 0, m /s to , m /s F σ Standard deviati on , m /s to 2, m /s Figure K.1 – Relationship between the terminal part temperature rise and the wind speed for the RR3225M (parallel) Ttr (K) +3 σ 80 Maxim um 60 Average Minimum -3 σ 40 20 NC S M Wind speed F Key Ttr Term inal part tem peratu re rise NC Norm al vection (fl at) S 0, m /s to 0, m /s M 0, m /s to , m /s F , m /s to 2, m /s σ Standard deviati on Figure K.1 – Relationship between the terminal part temperature rise and the wind speed for the RR321 6M (parallel) IEC Ttr (K) I EC TR 63091 :201 © I EC 201 – 113 – 60 +3 σ 50 Maximum Average M inim um 40 30 -3 σ 20 10 NC S M Wind speed F IEC Key Ttr Term inal part tem peratu re rise NC Norm al vection (fl at) S 0, m /s to 0, m /s M 0, m /s to , m /s F , m /s to 2, m /s σ Standard deviati on Ttr (K) Figure K.1 – Relationship between the terminal part temperature rise and the wind speed for the RR201 2M (parallel) 70 +3 σ 60 Maximum 50 Average Minim um 40 -3 σ 30 20 10 NC Key Ttr Term inal part tem peratu re rise NC Norm al vection (fl at) S 0, m /s to 0, m /s M 0, m /s to , m /s F σ Standard deviati on S M Wind speed F , m /s to 2, m /s Figure K.1 – Relationship between the terminal part temperature rise and the wind speed for the RR1 608M (parallel) IEC – 114 – I EC TR 63091 :201 © I EC 201 +3 σ 60 Maximum Ttr (K) 50 Average Minim um 40 30 -3 σ 20 10 NC S M Wind speed F IEC Key Ttr NC S M F σ Term inal part tem peratu re rise Norm al vection (fl at) 0, m /s to 0, m /s 0, m /s to , m /s , m /s to 2, m /s Standard deviati on Figu re K – Relationship between the terminal part temperatu re ri se and th e wind speed for the RR1 005M (parallel) By comparing the orthogonal and parallel airflow applied to the resistor set in a line, the resistors with large rated power (RR6332M, RR5025M and RR3225M) had large differences between their m axim ums and minimum s From this, it can be observed that windward resistors have lower temperature than those leeward and their heat dissipation efficiency is degraded because of the development of the thermal boundary layer on the board from the windward to the leeward sides Figure K is the tem perature distribution of the RR6332M and the smaller sam ple numbers are positioned windward 20 Ttr (K) 00 80 60 Wind speed 0, m /s to 0, m /s 0, m/s to , m /s , m /s to 2, m /s 40 20 n 10 IEC Key Ttr N Tem peratu re rise from norm al tem peratu re Sam ple num ber (sm all num bers are wi nd ward ) Figu re K.1 – Term inal part temperatu re ri se of RR6332M , difference between the windward and leeward sid es when placed parall el I EC TR 63091 : 201 © I EC 201 – 115 – Annex L (informative) The influence of the spatial resolution of the thermograph L.1 The application for using the thermograph when measuring the temperature of the SMD resistor There are two purposes for using the infrared thermograph to m easure the resistor's tem perature The first purpose is to observe the board's surface directl y wi th the thermograph and verify that the SMD resistors are used under suitable tem perature at the electric/electronic designing step: without setting the printed board inside the chassis, turn it on and operate I n this case, to observe the entire printed board, the field of view needs to be widened so the area corresponding to one pixel would be lim ited to around a square of 200 × 200 μ m H owever, the aim is to ascertain the rough temperature, so accuracy is not required The second purpose is for the resistor manufacturer to measure the terminal part tem perature and surface hotspot temperature to calculate the thermal resistance R th shs-t from the term inal part to the surface hotspot where the resistor becomes the hottest The main reason for the resistor m anufacturer to m easure R th shs-t and provide it to the electric/electronic device designers is explained in Annex F But, to serve the obj ectives, R th shs-t should be as accurate as possible The terminal part temperature mentioned here is the narrowl y-defined terminal part temperature that was explained in Annex H This means that it is the surface temperature of the copper block and it has a large area So as long as the em issivity is adjusted, almost an y kind of infrared therm ograph can m easure quite accurately The more difficult tem perature m easurement would be that of the surface hotspot The surface hotspot of a sm all si ze SMD resistor that is arou n d 00 μ m i n d i am eter is very common To m easure it, the standard lens of the therm ograph (applicable to large targets such as buildings, but can only m agnify up to a square of 200 × 200 μ m as pixel) should be exchanged into the fixed focus close-up m agnification lens that can m agnify a square of 25 × 25 μ m as pixel and the resolution capability wi ll be enhanced The point to be aware of is when the close-up m agnification lens that magnifies the square of 25 × 25 μ m as pixel is used, a high tem perature part of a square of 25 × 25 μ m cannot be m easured accuratel y This is caused not onl y by the position gap of the pixel and target part, but because of m an y other elem ents such as the M TF (modulation transfer function) of the lens Before m easuring, the m inimum area of the temperature peak that can be observed according to the com bination of the infrared thermograph and the close-up m agnification lens should be verified I n this annex, the method of simpl y estimating how accuratel y the tem perature of the m icroscopic area can be measured by the infrared thermograph will be suggested However, electric/electronic device designers generall y not use a thermograph with a high m agnification close-up lens in their design process This is because therm ographs with high m agnification close-up lenses have very narrow fields of view, such as a few square centimetres and, additionall y, they have a very short focus Therefore, it is im possible to m easure the tem perature of large areas and have uneven surfaces because of the mounted devices on the printed board, and they need to sweep and focus on each and every device L.2 The relation between the minimum area that the accurate temperature could be measured and the pixel magnification percentage The m agnification percentage of the close-up magnification lens is usuall y indicated as how many μ m of the measured surface is shown as one pixel of the infrared light receiving elem ent For exam ple, a 25- μ m lens would have an optical magnification percentage that will – 116 – I EC TR 63091 :201 © I EC 201 make a square of 25 × 25 μ m as pixel The standard lens can also adjust the pixel to a suitable size, so, in this subclause, the lens that can m agnify a square of A × A μ m as pixel will be called the A - μ m lens I n this annex, the m ethod of simpl y estimating how accurate the tem perature of the microscopic area can be measured by using the spatial frequency characteristic of the measurement system as an index will be introduced and suggested [Step ] For the one-dim ensional step tem perature change shown in Figure L , the repl y when it goes through the Gaussian filter with various cut-off spatial frequencies fc (cycles/mm) will be calculated and made into a graph in advance The parameter of the graph of the theoretical value of the step response is the Gaussian filter cut-off frequency fc that is operated on the ideal step wave However, to m ake it com parable with the pixel A (μ m ), it wi l l be d escri bed as X (μ m ) of th e h al f wa velen gth fc and the explanatory note title is fc half length The relationship between the fc (cycles/m m) and X (μ m ) is sh own as th e fol lowi n g : fc = 000 / (2 X) I n Figure L , the characteristic of the Gaussian filter which would be the param eter shown as X ( μ m ) and would be the half wavelength of the cut-off spatial frequency Mag ,0 0, 0 Gaussian filter Mag 2 G( f) G( f) = exp{- f /(2 s )} ,0 fc s= 0, 2ln(2) 0, 0, f (cycles/mm ) 0, fc fc half length -0, Step response theoretical value fc half length 25 μ m 50 μ m 00 μ m 200 μ m 300 μ m 400 μ m 500 μ m 600 μ m 700 μ m 0, Position (m m) IEC Ke y Gaussian fil ter Filter for transfer fu nction G( f) fc Cut-off spatial freq uency Position Distance from the bou ndary of high tem perature an d low tem perature Step response Response wave form throu gh the Gaussian filter of various chang e from the id eal to fc half l ength Gaussian filter cut-off spatial frequ ency i n half wavel en gth fc in the step down tem peratu re X (μ m ) F i g u re L – S tep re s po n s e of th e G au s s i an fi l ter of th e va ri o u s cu t-off s pati al freq u en ci e s ( cal cu l ated ) For the m aterial that has a part with high tem perature onl y inside the diameter D (mm ) defined beforehand, the two-dimensional repl y when it goes through the Gaussian filter with various cut-off spatial frequency fc (cycles/mm) will be calculated and made into a graph Figure L is a calculation exam ple for 0, mm in diameter This processing can be done by an yone who has the basic knowledge of the discrete Fourier transform I EC TR 63091 :201 © I EC 201 – 117 – ,2 Response ,0 fc half length μm 25 μ m 50 μ m 00 μ m 200 μ m 300 μ m 400 μ m 500 μ m 0, 0, 0, 0, -0, -0, -0, 0, Position (mm ) 0, IEC Key Fc h alf length Gaussian filter cut-off spatial frequ ency i n half wavel en gth X (μ m ) Figu re L.2 – Temperatu re d istribution (cross-section) when m easuring the object that becomes hi gh temperature only in the ran ge of 0, mm i n d iam eter [Step 2] As shown in Figure L 3, attach the A (μ m ) l ens to th e th erm ograph an d observe th e tem perature distribution of the boundary of the surface covered with insulators, such as the epoxy resin part and the solder m ask part of the printed board, and the exposed m etal part such as the pads The em issivity of the insulator is over 0,8 and relativel y high, but the m etal part is extremely low Therefore, the step response can be m easured from the temperature distribution im age of the printed board of the sam e tem perature When observing, the physical dimension of the exposed part of m etal and the insulator part should be, when the lens is A (μ m ), over times A in both length and breadth, and additionall y the boundaries should be a clear straight line However, when m easuring the tem perature, it is preferable to set the entire printed board at more than 50 K higher than the room tem perature, such as through heating with a hot plate Even at room temperature, the temperature difference between the solder m ask part and the exposed m etal part can be observed because of the difference in emissivity, but, by raising the temperature, the difference becomes larger and the accuracy of the measurem ent of step response will im prove This step can be easily im plem ented by the resistor m anufacturers and electric/electronic device m anufacturers – 118 – I EC TR 63091 :201 © I EC 201 W Position Position + L Position - IEC Ke y I nfrared therm ograph A (μ m ) lens Printed board Solder resist coating su rface Metal exposed surface Hotpl ate Position Distance from the bou ndary of high and l ow tem peratu re W L Width of the observed surface, recom m ended to be l on ger than tim es of lens m agnification rate Len gth of observed surface, recomm ended to be longer than tim es of lens m agnification rate A A Fi g u re L – M easu rin g system of spatial frequ en cy fi lter of th e in frared th erm og raph [Step 3] Normalize the temperature difference in the vertical axis from to in the tem perature distribution, which is actuall y m easured in Step as seen in Figure L 4, and overlap with Figure L.1 The overlapped image is shown in Figure L By com paring the value actuall y measured and the calculated value, it would be possible to estimate the cut-off spatial frequency of the MTF of an infrared therm ograph with an A- μ m l ens , when the MTF is a Gaussian filter I n this exam ple, the 25- μ m l ens has th e responsi ve eq u i valent to th e pass through of the cut-off spatial frequency converted to half wavelength of a 50- μ m to 00- μ m Gaussian filter, and the 200- μ m l ens h as th e re sponsive equivalent to the pass through of the fc half wavelength 600- μ m Gau ssi an fil ter I t is om itted in th is stu d y, but it is found that the 00- μ m l ens has th e responsi ve eq u i val ent to th e pass throu g h the fc half wavelength 300- μ m Gaussian filter [Step 4] I f the cut-off spatial frequency of the Gaussian filter of the measurement system can be estim ated, it is possible to estimate from Figure L at which m icro area the peak temperature can be m easured accurately I EC TR 63091 :201 © I EC 201 – 119 – ,2 25 μ m l ens ,0 00 μ m l ens Mag 0, 0, 200 μ m l ens 0, 0, -0, -1 , -0, Position (mm ) 0, ,0 IEC Key Position is the boun dary and m inus side is hig h tem perature an d pl us side is low tem perature Mag Norm ali ze th e hig h and low tem perature by to Figure L.4 – Actual measured value of the step response of various magnifier lenses – 20 – I EC TR 63091 : 201 © I EC 201 ,2 fc half length 25 μ m 50 μ m 00 μ m Mag ,0 0, 0, 0, 0, Actual -0, -1 , -0, 0, Position (m m) ,0 ,2 fc half length 500 μ m 600 μ m 700 μ m Mag ,0 0, 0, 0, 0, Actual -0, 25 μ m -1 , -0, 0, Position (mm ) 200 μ m ,0 IEC Key Position Position < is high tem perature Position > is low tem perature Position = is transi tional reg im e Mag Norm ali ze th e hig h and low tem perature by to fc half l ength Gaussian fil ter cut-off spatial frequ ency i n half wavel en gth sh own i n X μ m Actual Actual m easurem ent value wh en m agnification rate A (μ m ) l en s i s u sed Figure L.5 – Comparison of the actual measured valu e and the calculated value (step response) From the result of Step and Figure L 2, even when it is the 25- μ m l ens, and the part of 0,2 mm in diam eter is only the hot or cold part, m easuring the peak temperature is very close to the limit The cut-off spatial frequency half wavelength of the Gaussian filter of the 200- μ m l en s is 600 μ m , so from Figure L 2, the measurem ent by the 200- μ m l ens m ay onl y show % of the actual peak tem perature L.3 Example of the RR1 608M SMD resistor hotspot's actual measurement Appl y 0, 25 W to the RR1 608M thick-film rectangular chip resistor (m etal-glaze resistive elem ent) and let it self-heat Measure the surface hotspot with the 25- μ m lens, the 00- μ m lens and the 200- μ m l en s Su ppose th at the resu lt m easu red by the 25- μ m lens is the true value Then compare this true value (2-dim ensional temperature distribution im age) with the calculated result put through the Gaussian filter with various cut-off spatial frequencies fc I EC TR 63091 :201 © I EC 201 – 21 – Figure L shows the result I t shows that the actual measured value of the 00- μ m lens is equivalent to the fc half wavelength 300 μm , and the 200- μ m lens is equivalent to the fc half wavelength 600 μm of the Gaussian filter This conforms to the results in step 115 110 05 00 95 90 85 80 75 -2, Actual m easurement Lens 25 μm 00 μ m 200 μ m -1 , 0 ,0 Position (m m) 2, Calculated value 115 110 05 00 95 90 85 80 75 -2, fc half length 25 μ m 00 μ m 300 μ m 600 μ m T °C T °C From the results of the m easurem ent system this tim e, the response wh en the A (μ m ) lens is used will be around X = × A (μm ) when indicated in the fc half wavelength X of the Gaussian filter -1 , ,0 Position (m m) 2, IEC Key Resistor Surface h otspot Position Hotspot centre is (mm ) and the distance in length wise direction of the resistor T fc half l ength Tem peratu re Gaussian fil ter cut-off spatial frequ ency i n half wave l en gth X (μ m ) Lens Lens used Figure L.6 – Comparison of the actual measured value and the calculated value (surface hotspot of the resistor) L.4 Conclusion Even when the centre of the pixel of the infrared therm ograph is set on the hotspot of an A μ m in diameter, the temperature cannot be m easured accuratel y by an infrared thermograph with an A - μm lens I n this annex, the m ethod of estimating MTF's approximate value by using the commonl y-available printed boards and hotplates is shown The im portant point for resistor manufacturers is to provide the right information to electric/electronic device designers Therefore, it is necessary for resistor manufacturers to know the surface hotspot size accuratel y and verify that the infrared therm ograph has the sufficient perform ance to measure the surface hotspot temperature of that size when measuring their in-house products However, it is necessary for electric/electronic device designers to understand the spatial resolution and peak tem perature detection capabilities of the infrared therm ograph that is used to m easure the resistor or the board tem perature – 22 – I EC TR 63091 :201 © I EC 201 Annex M (informative) Future subjects SMD resistors are mounted on the printed board when used , but when the temperature of the resistor substrate surface, which faces the printed board (back side) is high, the tem perature of the printed board m ay rise from the radiation and heat conducti on via the atmosphere The limit of this tem perature rise is to the temperature of the resistor substrate surface which faces the printed board (back side), but, usually, the tem perature of this surface cannot be measured When using SMD resistors, electric/electronic device designers need to estim ate the temperature rise of the printed board surface in som e way and verify that the printed board can resist that tem perature The m ethod of estimating the temperature rise of the printed board surface underneath the SMD resistor is a future subj ect for resistor m anufacturers I EC TR 63091 :201 © I EC 201 – 23 – Bibliography I EC 601 5-4, Fixed resistors for use in electronic equipment – Part 4: Sectional specification: Fixed power resistors Aruga, Y., Hirasawa, K., Ohashi, Y., Kunimine, N and Tomimura,T (201 4), 20th Symposium of Micro connection, m ounting technology in Electronics, pp 87-1 92, Suggestions for Improving the Accuracy of the Temperature Measurement of Small Components by Thermocouples on the Mounting Method Considering the Thermal Constriction Resistance and the Errorcompensation by the Thermal Network Hirasawa, K , Aruga, Y , Ohashi, Y., Kunimine, N and Tomimura,T (201 4), 20th Symposium of Micro connection, m ounting technology in Electronics, pp 81 -1 86, Verification of the Temperature Measurement of Small Components by Using the Infrared Thermograph Investigation of the Angle Dependency and the Space Resolution Ishizuka, M (2008), Netsu Sekkei Gijyutu Kaiseki Handobukku ( Thermal design technology handbook), Tokyo: Maruzen _ 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