IEC TR 61760-5-1:2024
(Main)Surface mounting technology - Part 5-1: Surface strain on circuit boards - Strain gauge measurement applied to chip components
Surface mounting technology - Part 5-1: Surface strain on circuit boards - Strain gauge measurement applied to chip components
IEC TR 61760-5-1:2024 describes examples of methods using electrical strain gauges for determination of critical mechanical stresses in assembly processes. These stresses can damage chip type ceramic components, causing so called “bending cracks”. Area-array components are excluded from the scope of this document.
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IEC TR 61760-5-1 ®
Edition 1.0 2024-01
TECHNICAL
REPORT
colour
inside
Surface mounting technology –
Part 5-1: Surface strain on circuit boards – Strain gauge measurement applied to
chip components
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IEC TR 61760-5-1 ®
Edition 1.0 2024-01
TECHNICAL
REPORT
colour
inside
Surface mounting technology –
Part 5-1: Surface strain on circuit boards – Strain gauge measurement applied to
chip components
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.190 ISBN 978-2-8322-8160-4
– 2 – IEC TR 61760-5-1:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Damaging mechanisms of chip type ceramic components . 7
4.1 Surface strain by board bending. 7
4.2 Typical cracking modes . 8
4.3 Measurement of local strain . 9
5 Crack prevention . 9
5.1 Strain control . 9
5.2 Critical board design factors . 9
5.2.1 Distance from circuit board cutting position . 9
5.2.2 Distance from screw clamping position . 9
5.2.3 Mounting direction . 10
5.2.4 Warpage . 10
5.2.5 Orientation of the component related with the loading point . 10
5.3 Critical assembly process factors . 10
5.3.1 General . 10
5.3.2 Circuit board singulation . 10
5.3.3 Circuit board fitting into the housing. 10
5.3.4 Screw clamp . 10
5.3.5 Manual handling . 11
5.3.6 ICT (In-Circuit Test) / FT (Functional Test) / Programming on assembly
level . 11
6 Example of an instruction on board preparation for strain measurement . 11
6.1 General . 11
6.1.1 Introductory statement . 11
6.1.2 Theory of strain gauge measurement . 11
6.1.3 3-axes strain measurement . 12
6.2 Position of strain gauges (example) . 13
6.2.1 General . 13
6.2.2 Determination of critical positions on a circuit board . 13
6.2.3 Rules for determination of sample size for performing the investigations . 13
6.3 Attachment of strain gauges (example) . 13
6.3.1 Step 1 – Remove components . 13
6.3.2 Step 2 – Polish the attachment area . 14
6.3.3 Step 3 – Indication of attachment point . 14
6.3.4 Step 4 – Application of instant glue . 15
6.3.5 Step 5 – Attachment of strain gauge . 16
7 Typical mistakes and faults occurring in practice . 16
7.1 Strain gauge attachment . 16
7.2 Wrong type of strain gauge used . 16
7.3 Circuit board without components is used . 16
7.4 Irregular stress is not considered . 16
7.5 Insufficient measurement settings . 17
8 Evaluation of data and report . 17
9 Assembly process control . 18
9.1 Machine/Process capability . 18
9.2 Machine maintenance . 18
Annex A (informative) Examples and relevant processes . 19
A.1 Typical measurement results – Press-fit operation, Example 1 . 19
A.2 Typical measurement results – Press-fit operation, Example 2 . 20
A.3 Typical measurement results – Housing assembly by screwing . 22
A.4 Typical critical processes . 23
Bibliography . 24
Figure 1 – Mechanical stress by board bending . 8
Figure 2 – Strain simulation . 8
Figure 3 – Typical bending crack at a ceramic capacitor . 8
Figure 4 – Longitudinal stress . 8
Figure 5 – Diagonal stress . 9
Figure 6 – Strain control and bending strength . 9
Figure 7 – Strain during screwing . 11
Figure 8 – Resistor bridge for strain measurement . 12
Figure 9 – 3-axes strain gauge and maximum principle strain . 12
Figure 10 – De-soldering of components . 14
Figure 11 – Polishing the attachment area . 14
Figure 12 – Marking of the attachment point . 14
Figure 13 – Application of glue by transfer from polyethylene sheet . 15
Figure 14 – Direct application of glue . 15
Figure A.1 – Dosing control unit for exhaust treatment system equipped with a
connector using compliant press-fit technology . 19
Figure A.2 – Top and bottom side of circuit assembly of dosing control unit with strain
gauges replacing passive multilayer chip capacitors . 19
Figure A.3 – Strain measurement evolution for the different strain gauges during the
press-in process . 20
Figure A.4 – Press fit – Strain measurements using different strain gauges and
positions . 21
Figure A.5 – Screwing – Strain measurements using different strain gauges and
positions . 22
Table A.1 – Strain measurement results with different gauges and placements . 21
Table A.2 – Strain measurement results with different gauges and placements . 22
– 4 – IEC TR 61760-5-1:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SURFACE MOUNTING TECHNOLOGY –
Part 5-1: Surface strain on circuit boards –
Strain gauge measurement applied to chip components
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