Printed board assemblies - Part 7: Technical cleanliness of components and printed board assemblies

IEC TR 61191-7:2020(E) serves as a Technical Report and provides information, how technical cleanliness can be assessed within the electronics assembly industry. Technical cleanliness concerns sources, analysis, reduction and control as well as associated risks of particulate matter, so-called foreign-object debris, on components and electronic assemblies in the electronics industry.

General Information

Status
Published
Publication Date
10-Mar-2020
Current Stage
PPUB - Publication issued
Completion Date
11-Mar-2020
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IEC TR 61191-7
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Printed board assemblies –
Part 7: Technical cleanliness of components and printed board assemblies
IEC TR 61191-7:2020-03(en)
---------------------- Page: 1 ----------------------
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IEC TR 61191-7
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Printed board assemblies –
Part 7: Technical cleanliness of components and printed board assemblies
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.180; 31.190 ISBN 978-2-8322-7901-4

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 61191-7:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 8

INTRODUCTION ................................................................................................................... 10

1 Scope ............................................................................................................................ 11

2 Normative references .................................................................................................... 11

3 Terms and definitions .................................................................................................... 11

4 Technical cleanliness .................................................................................................... 11

4.1 What is technical cleanliness? .............................................................................. 11

4.2 History – standardisation of technical cleanliness ................................................. 12

4.3 Technical cleanliness in the electronics industry ................................................... 12

4.4 Potential particle-related malfunctions .................................................................. 12

5 Technical cleanliness as a challenge for the supply chain .............................................. 13

5.1 General ................................................................................................................. 13

5.2 Contamination ....................................................................................................... 14

5.2.1 Definition of particles ..................................................................................... 14

5.2.2 Definition of fibres ......................................................................................... 14

5.3 Test procedure to determine technical cleanliness ................................................ 15

5.3.1 Fundamentals ................................................................................................ 15

5.3.2 Clarification form ........................................................................................... 16

5.3.3 System technology ........................................................................................ 18

5.3.4 Process parameters for pressure rinsing extraction ....................................... 19

5.3.5 Pressure rinsing process ............................................................................... 19

5.3.6 Preparing membrane filters for measurement analysis ................................... 20

5.4 Measurement analysis .......................................................................................... 22

5.5 Evaluating the results of cleanliness analyses....................................................... 22

5.5.1 Overview ....................................................................................................... 22

5.5.2 Particle count relative to component surface .................................................. 23

5.5.3 Procedure for violation of action control limits ................................................ 24

5.6 Extended risk assessment .................................................................................... 25

5.6.1 General ......................................................................................................... 25

5.6.2 Example ........................................................................................................ 25

5.7 Component cleanliness – Data management and visualization ............................. 27

5.7.1 Component cleanliness analysis – flow diagram ............................................ 27

5.7.2 Explanation of SCI (Surface Cleanliness Index) ............................................. 28

5.7.3 Creating a database ...................................................................................... 31

5.7.4 Summary ....................................................................................................... 34

6 State of the art – Technical cleanliness in the electronics industry ................................. 35

6.1 Process flow (per cluster) ..................................................................................... 35

6.1.1 General ......................................................................................................... 35

6.1.2 Electronics manufacturing cluster .................................................................. 35

6.1.3 Passive components cluster (e.g. for inductors and aluminium

electrolytic capacitors) ................................................................................... 36

6.1.4 Electromechanical components cluster .......................................................... 37

6.1.5 PCB cluster ................................................................................................... 39

6.2 Technical cleanliness in the electronics industry – current situation ...................... 39

6.2.1 General ......................................................................................................... 39

6.2.2 Electronics manufacturing .............................................................................. 40

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IEC TR 61191-7:2020 © IEC 2020 – 3 –

6.2.3 Electronic components................................................................................... 41

6.2.4 Electromechanical components...................................................................... 44

6.2.5 Metal housings .............................................................................................. 48

6.2.6 Packaging...................................................................................................... 49

6.2.7 Printed circuit boards (PCBs) ......................................................................... 49

6.3 Determining potential particle sources in production areas .................................... 52

6.3.1 General ......................................................................................................... 52

6.3.2 Particle generation ........................................................................................ 52

6.3.3 Electronics manufacturing cluster .................................................................. 52

6.3.4 Passive components cluster .......................................................................... 53

6.3.5 Electromechanical components cluster .......................................................... 59

6.3.6 PCB cluster ................................................................................................... 63

6.4 Cleanliness-controlled design and process selection ............................................. 72

6.4.1 Aspects of cleanliness-controlled design/production with regard to

metallic particles ............................................................................................ 72

6.4.2 Environmental cleanliness and internal production processes ........................ 74

6.5 Environmental cleanliness analysis and visualisation ............................................ 76

6.5.1 General ......................................................................................................... 76

6.5.2 Procedure for environmental analysis ............................................................ 76

6.5.3 Conclusions: .................................................................................................. 80

6.6 Cleaning tips ......................................................................................................... 81

6.6.1 General ......................................................................................................... 81

6.6.2 Washing ........................................................................................................ 81

6.6.3 Brushing ........................................................................................................ 81

6.6.4 Suction-cleaning ............................................................................................ 82

6.6.5 Blowing.......................................................................................................... 83

6.6.6 Reducing carry-over and controlling cleanliness in workplace design ............. 83

6.6.7 Adhesive methods ......................................................................................... 84

6.7 Packaging and logistics requirements ................................................................... 84

7 Why do metallic particles in assemblies so rarely cause short circuits? ......................... 84

7.1 General ................................................................................................................. 84

7.2 Probability of contact ............................................................................................ 85

7.2.1 Introduction and theory .................................................................................. 85

7.2.2 Testing the probability of contact ................................................................... 88

7.2.3 Results .......................................................................................................... 90

7.3 Rinsing extraction versus actual mobility ............................................................... 92

7.4 Particle sinks ........................................................................................................ 92

7.5 Effect of short circuits on ICs ................................................................................ 93

7.6 Tool for estimating the risk of short circuit ............................................................. 93

7.6.1 Overview ....................................................................................................... 93

7.6.2 Model hypotheses .......................................................................................... 94

7.6.3 Calculation methods ...................................................................................... 95

7.6.4 Orientation factor ........................................................................................... 95

7.6.5 Critical area ................................................................................................... 96

7.6.6 Number of particles per size class ................................................................. 97

7.6.7 Weighting factors ........................................................................................... 98

7.7 Example use of the risk assessment tool ............................................................... 99

7.7.1 Example use of the risk assessment tool for calculating failure rate ............... 99

7.7.2 Example use of the risk assessment tool for design changes ....................... 100

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– 4 – IEC TR 61191-7:2020 © IEC 2020

7.7.3 Example use of the risk assessment tool for specification violations ............ 101

8 Summary ..................................................................................................................... 102

9 Outlook ........................................................................................................................ 102

10 Related topics ............................................................................................................. 103

10.1 Filmic contamination ........................................................................................... 103

10.1.1 General ....................................................................................................... 103

10.1.2 Biological films ............................................................................................ 103

10.1.3 Chemical films ............................................................................................. 103

10.2 Whiskers ............................................................................................................. 103

Annex A (informative) Determining the surface area of components and assembled

circuit boards ............................................................................................................... 106

Annex B (informative) Examples of cleanliness clarification forms ...................................... 109

Bibliography ........................................................................................................................ 114

Figure 1 – Test method as per VDA 19 Part 1 ....................................................................... 16

Figure 2 – Examples of extraction systems ........................................................................... 18

Figure 3 – Component holder during manual pressure rinsing ............................................... 20

Figure 4 – Examples of different options for drying membrane filters .................................... 21

Figure 5 – Slide frame with membrane filter .......................................................................... 21

Figure 6 – Example procedure if specifications are exceeded ............................................... 24

Figure 7 – Particle size distribution and corresponding process capability............................. 26

Figure 8 – Flow diagram for component cleanliness analysis ................................................ 27

Figure 9 – Scope of analytical report ..................................................................................... 27

Figure 10 – Derivation of Illig value ....................................................................................... 28

Figure 11 – Derivation of SCI ................................................................................................ 29

Figure 12 – Evaluation of 7-pin HV strip connector................................................................ 30

Figure 13 – Graph showing cleaning effect based on SCIs .................................................... 30

Figure 14 – Comparison of the three largest particles ........................................................... 31

Figure 15 – Structural levels of a database ........................................................................... 32

Figure 16 – Option A – Evaluation of the largest particles by length and width ...................... 32

Figure 17 – Option B – Extension to include the degree of contamination – SCI ................... 33

Figure 18 – Option C – Extension to include a separate data sheet "direct comparison

of test series" ........................................................................................................................ 33

Figure 19 – Option D – Extension of the database "to include 'comparison with

customer standards'" ............................................................................................................ 34

Figure 20 – Flexible circuit board .......................................................................................... 49

Figure 21 – Rigid circuit board .............................................................................................. 50

Figure 22 – Burr formation on copper wire (D = 2,25 mm) after use of wire-cutter ................. 54

Figure 23 – Particles generated by wire cutting D = 1,8 mm (tinned copper) ......................... 54

Figure 24 – Particles generated by wire cutting D = 1,8 mm (tinned copper) ......................... 55

Figure 25 – Particle (tin) adhering to a tinned copper wire D = 2,25 mm................................ 55

Figure 26 – Hair-like particle (tin whiskers) chipped off a tinned wire (655 µm long) .............. 56

Figure 27 – Milled enamel wires ............................................................................................ 56

Figure 28 – Molten solder balls fused to plastic housings ...................................................... 57

Figure 29 – Ferrite particle, identified as metallic (419 µm) ................................................... 58

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IEC TR 61191-7:2020 © IEC 2020 – 5 –

Figure 30 – Ferrite particle, identified as non-metallic (558 µm) ............................................ 58

Figure 31 – Non-metallic particle, probably burr or plastic residue (217 µm) ......................... 59

Figure 32 – Non-metallic particle, probably pink polystyrene packaging material ................... 59

Figure 33 – Shielding plate ................................................................................................... 60

Figure 34 – Stamped contacts .............................................................................................. 61

Figure 35 – Connector pin ..................................................................................................... 61

Figure 36 – Connector housing ............................................................................................. 62

Figure 37 – 58-pin connector housing ................................................................................... 62

Figure 38 – 12-pin connector with bridged contacts .............................................................. 63

Figure 39 – Plastic particles + fibres ..................................................................................... 64

Figure 40 – Plastic particles .................................................................................................. 64

Figure 41 – Metallic particle .................................................................................................. 64

Figure 42 – Milling crosses V-scoring line ............................................................................. 65

Figure 43 – V-scoring line on milling edge ............................................................................ 66

Figure 44 – Chip formation in milled hole .............................................................................. 66

Figure 45 – Edge plating ....................................................................................................... 67

Figure 46 – Connections for electroplated gold areas ........................................................... 67

Figure 47 – Deep milling ....................................................................................................... 68

Figure 48 – Chip formation caused by stamping .................................................................... 68

Figure 49 – Flexible circuit board with undercut .................................................................... 69

Figure 50 – Punching burr in hole ......................................................................................... 69

Figure 51 – Punching burr ..................................................................................................... 70

Figure 52 – Damaged metallic stiffener ................................................................................. 70

Figure 53 – Stamping residue along stamped edge ............................................................... 71

Figure 54 – Stamping residue loosened by pickling bath ....................................................... 71

Figure 55 – Plastic element with burr .................................................................................... 72

Figure 56 – Particles on externally supplied plastic elements ................................................ 72

Figure 57 – Process chain analysis as per VDA 19 Part 2 ..................................................... 75

Figure 58 – Cleanroom production ........................................................................................ 76

Figure 59 – Example particle trap ......................................................................................... 77

Figure 60 – Position of particle trap ...................................................................................... 77

Figure 61 – Database – Visualisation .................................................................................... 78

Figure 62 – Illustration of the Illig value with max. three particles .......................................... 78

Figure 63 – Airborne dispersion diagram ............................................................................... 79

Figure 64 – Analysis results in the cleanroom ....................................................................... 79

Figure 65 – Analysis results in the area not governed by VDA 19.......................................... 80

Figure 66 – Weighting of factors influencing technical cleanliness ........................................ 80

Figure 67 – Manual cleaning with brush and illuminated magnifier ........................................ 82

Figure 68 – ESD brush.......................................................................................................... 82

Figure 69 – Workstations designed for cleanliness control .................................................... 83

Figure 70 – Adhesive roller system for PCB contact cleaning ................................................ 84

Figure 71 – Diagram showing failure risks based on metallic particles on assemblies ........... 85

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– 6 – IEC TR 61191-7:2020 © IEC 2020

Figure 72 – Sketch of electrical arrangement (particle forming "bridge" between two

conductors) ........................................................................................................................... 86

Figure 73 – Diagram showing contact point of a particle on a conductor – nickel-gold

conductor and copper particle ............................................................................................... 87

Figure 74 – SIR test circuit boards (interleaving comb pattern layout) ................................... 89

Figure 75 – Voltage source that measures current with an analogue picoamperemeter ......... 89

Figure 76 – Automated current measurement with software .................................................. 90

Figure 77 – Comparison of CU particles in three conditions on SAC305 PCBs ...................... 91

Figure 78 – Overview of all metals in the voltage classes, rounded ....................................... 91

Figure 79 – Functional structure of risk assessment tool ....................................................... 94

Figure 80 – Geometric constraints at a contact pair .............................................................. 96

Figure 81 – Clearance areas up to 400 µm (in white) ............................................................ 97

Figure 82 – Clearance areas up to 600 µm (in white) ............................................................ 97

Figure 83 – Clearance areas up to 1000 µm (in white) .......................................................... 97

Figure 84 – Example calculation 1 – Calculating an absolute probability of failure ................ 99

Figure 85 – Example calculation 2 – Calculating probabilities of failure for layout

changes e.g. for a new generation component .................................................................... 100

Figure 86 – Example calculation 3 – Optimising the main variables ..................................... 101

Figure 87 – Example calculation 3 – Calculating the changed probability of failure in

the event of specification violation ...................................................................................... 101

Figure 88 – Whiskers growth of > 8 mm over a period of 10 years ...................................... 104

Figure 89 – Whiskers growth of > 2 mm over a period of 6 months ..................................... 105

Figure A.1 – Dimensions of cuboid components .................................................................. 106

Figure A.2 – Dimensions of cylindrical components ............................................................. 107

Figure B.1 – Ambient cleanliness clarification form ............................................................. 109

Figure B.2 – Ambient cleanliness clarification form ............................................................. 110

Figure B.3 – Component cleanliness clarification form ........................................................ 111

Figure B.4 – Component cleanliness clarification form ........................................................ 112

Figure B.5 – Component cleanliness clarification form ........................................................ 113

Table 1 – Influence of the blank value on the measurement results for different

material surfaces (examples for a blank value fraction of 2,2 % and above) .......................... 24

Table 2 – Electronics manufacturing cluster process flow ..................................................... 35

Table 3 – Process flow for inductors ..................................................................................... 36

Table 4 – Aluminium electrolytic capacitors ........................................................................... 37

Table 5 – Stamped contact production/plastic production (housing) process flow .................. 38

Table 6 – Housing assembly process flow ............................................................................. 38

Table 7 – PCB cluster process flow ....................................................................................... 39

Table 8 – Empirical data from electronics manufacturing cluster ........................................... 40

Table 9 – Empirical data from inductors ................................................................................ 41

Table 10 – Empirical data from aluminium electrolytic capacitors .......................................... 41

Table 11 – Empirical data from tantalum capacitors .............................................................. 42

Table 12 – Empirical data from chip components .................................................................. 42

Table 13 – Empirical data from shunts .................................................................................. 43

Table 14 – Empirical data from quartz ...................................................................................

...

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