IEC TR 60068-3-12:2022
(Main)Environmental testing - Part 3-12: Supporting documentation and guidance - Method to evaluate a possible lead-free solder reflow temperature profile
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(E) which is a Technical Report, describes the creation of temperature-time profiles (in specific envelope profiles) for reflow soldering of electronic assemblies, considering tolerances resulting from the accuracy of the measuring equipment, preparation method and specifications of the manufacturers of components, circuit boards, solder paste, etc.).
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.). b) Distinction from existing standards The envelope profile given in this document does not represent a temperature-time profile for the qualification of materials but defines the reflow process limits for the soldering of electronic assemblies.
The schematic temperature-time-limit curves of the envelope profile are derived from generally valid findings (literature data). Additionally, tolerance considerations are given for all envelope points of the envelope profile.
In contrast to IEC TR 60068-3-12:2014, the creation of the envelope profile is not primarily linked to a concrete example. c) Subclause 8.2 presents an approach for establishing a possible temperature profile for a lead-free reflow soldering process using SnAgCu solder paste that is taken from IEC TR 60068-3-12:2014. d) Synergies with existing standards Limit values and tolerances from standards and guidelines for the qualification of materials are included in this document and are listed as examples in the references.
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IEC TR 60068-3-12 ®
Edition 3.0 2022-10
TECHNICAL
REPORT
colour
inside
Environmental testing –
Part 3-12: Supporting documentation and guidance – Method to evaluate a
possible lead-free solder reflow temperature profile
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IEC TR 60068-3-12 ®
Edition 3.0 2022-10
TECHNICAL
REPORT
colour
inside
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
– 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
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
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