IEC TR 60068-3-12
Edition 3.0 2022-10
TECHNICAL
REPORT
Environmental testing –
Part 3-12: Supporting documentation and guidance – Method to evaluate a
possible lead-free solder reflow temperature profile
IEC TR 60068-3-12:2022-10(en)
®
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inside
IEC TR 60068-3-12
Edition 3.0 2022-10
TECHNICAL
REPORT
Environmental testing –
Part 3-12: Supporting documentation and guidance – Method to evaluate a
possible lead-free solder reflow temperature profile
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040; 31.190
ISBN 978-2-8322-5818-7
® Registered trademark of the International Electrotechnical Commission
®
Warning! Make sure that you obtained this publication from an authorized distributor.
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inside
– 2 – IEC TR 60068-3-12:2022 © IEC 2022
CONTENTS
FOREWORD ........................................................................................................................... 4
INTRODUCTION ..................................................................................................................... 6
1 Scope .............................................................................................................................. 7
2 Normative references ...................................................................................................... 7
3 Terms and definitions ...................................................................................................... 7
4 Determination of an envelope reflow profile ..................................................................... 7
4.1 Temperature-time-envelope curve ........................................................................... 7
4.2 Diagram of a theoretical envelope reflow profile ...................................................... 8
4.3 Key parameters of the envelope reflow profile ......................................................... 8
5 Temperature profile measurements ............................................................................... 11
5.1 Determining the measurement locations................................................................ 11
5.2 Selection and attachment of thermocouples .......................................................... 12
5.2.1 Types of thermocouples ................................................................................. 12
5.2.2 Preparation of thermocouples ........................................................................ 13
5.2.3 Attachment of thermocouples ........................................................................ 13
5.2.4 Influence of attachment method and operator on measurement results .......... 16
5.3 Temperature gradient............................................................................................ 16
5.3.1 Gradient calculation ....................................................................................... 16
5.3.2 Sampling rate ................................................................................................ 18
5.4 Analysis, comparison and overlay of different reflow profiles and best
practice ................................................................................................................. 18
5.5 Measuring equipment ............................................................................................ 19
6 Tolerance analysis of the measurement chain ............................................................... 19
7 Optimizing a temperature profile .................................................................................... 21
7.1 General procedure ................................................................................................ 21
7.2 Description of a typical test board and the used reflow oven ................................. 21
7.3 Schematic envelope reflow profile for the example board ...................................... 22
7.4 Preparation of test board ...................................................................................... 24
7.5 Possibility of temperature profiling optimization with simulation tools .................... 25
7.6 Iteration steps for finding reflow equipment setup ................................................. 27
8 Examples of envelope reflow profiles ............................................................................. 30
8.1 Key data for two different solders .......................................................................... 30
8.2 Example of a qualification temperature profile for component used in lead-
free reflow soldering (SAC) ................................................................................... 31
Bibliography .......................................................................................................................... 33
Figure 1 – Schematic envelope reflow profile .......................................................................... 8
Figure 2 – Recommended temperature measurement locations on a test board .................... 12
Figure 3 – X-ray of a sheath thermocouple............................................................................ 12
Figure 4 – Example of a) acceptable and b) unacceptable attachment of the
thermocouples ...................................................................................................................... 13
Figure 5 – Examples of good and bad thermocouple attachment ........................................... 15
Figure 6 – Thermocouples (TC) fixed to an LED.................................................................... 16
Figure 7 – Results of the same test board prepared by different methods ............................. 16
Figure 8 – Gradient calculation ............................................................................................. 17
IEC TR 60068-3-12:2022 © IEC 2022 – 3 –
Figure 9 – Example of a gradient calculation on a temperature-time curve ............................ 18
Figure 10 – Overlay of different reflow profiles (origin at oven entry) ..................................... 19
Figure 11 – Overlay of different reflow profiles (overlap at start of peak zone) ...................... 19
Figure 12 – Measurement chain ............................................................................................ 20
Figure 13 – Description of a test board (electronic assembly) ............................................... 22
Figure 14 – Envelope reflow profile for the test board ........................................................... 24
Figure 15 – Thermal images of the test board after cooling down from 150 °C ...................... 24
Figure 16 – Geometric and thermal description of the test board ........................................... 26
Figure 17 – Geometric and thermal description of the reflow soldering equipment................. 26
Figure 18 – Predicted reflow profile with help of simulation (blue band) ................................ 27
Figure 19 – Overlay envelope curves of the temperature-time curves of three profiling
steps, 0201-chip solder joint ................................................................................................. 29
Figure 20 – Overlay envelope curves of the temperature-time curves of three profiling
steps, ERU25 solder joint ..................................................................................................... 30
Figure 21 – Exemplary qualification reflow temperature profile for the qualification of
components intended for use in assemblies with a wide variation of thermal masses ............ 32
Table 1 – Temperature-time curve – Units .............................................................................. 8
Table 2 – Envelope points of a reflow temperature-time-profile ............................................... 9
Table 3 – Thermocouple attachment methods ....................................................................... 14
Table 4 – Tolerances of the temperature measurement chain ............................................... 20
Table 5 – Envelope points at the envelope reflow profile for the test board ........................... 23
Table 6 – Measurement locations on the sample assembly ................................................... 25
Table 7 – Settings according to experience ........................................................................... 28
Table 8 – Measurement results for the settings from Table 7 ................................................ 28
Table 9 – Settings for second run ......................................................................................... 28
Table 10 – Measurement results for the settings from Table 9 .............................................. 28
Table 11 – Settings after adjustment of the heating zone temperatures ................................. 29
Table 12 – Measurement results from Table 11, adaptation of heating zone
temperatures ........................................................................................................................ 29
Table 13 – Examples for envelope reflow profile key data for two different solders ............... 31
Table 14 – Key parameters for a lead-free SAC reflow temperature profile for
component qualification ........................................................................................................ 32
– 4 – IEC TR 60068-3-12:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-12: Supporting documentation and guidance –
Method to evaluate a possible lead-free solder reflow temperature profile
FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC TR 60068-3-12 has been prepared by IEC technical committee 91: Electronics assembly
technology. It is a Technical Report.
This third edition cancels and replaces the second edition published in 2014. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Extended purpose
Guidance is added on how to create a reflow profile considering the tolerances resulting
from the accuracy of the measuring equipment, preparation method and specifications of
the component manufacturers (components, PCB, solder paste, etc.).
