IPC-D-279 EN.pdf - 第11页

T able A−2 Quality of Solder Joints with Copper and Alloy 42 Resulting from Different Reﬂow T emperatures...................................................... 38 T able B-1 Estimates of T ensile Properties of Copper Dep…

Appendix L Corrision Basics and Checklist

L-1.0 CORROSION BASICS

...................................... 111

L-2.0 CORROSION OF THE PWA............................. 111

L-3.0 CORROSION IN COMPONENTS..................... 111

L-4.0 OTHER EFFECTS OF WATER AND WATER

VAPOR

............................................................... 111

L-5.0 FRETTING ‘‘CORROSION’’.............................. 112

L-6.0 CORROSION DESIGN CHECKLIST................ 112

L-6.1 Galvanic Corrosion.......................................... 114

Appendix M Solder Joint Variability

M-1.0 SOLDER JOINT VARIABIALITY

..................... 116

Appendix N Adhesives, Solder Mask and Conformal/

Other Coatings

N-1.0 ADHESIVES

...................................................... 119

N-1.1 Electrically Conductive Attachment

Materials........................................................... 119

N-1.2 Thermally Conductive Adhesives.................... 119

N-1.3 Mechanical Attachment Adhesives.................. 119

N-2.0 SOLDER MASK................................................ 119

N-2.1 Types of Solder Masks.................................... 120

N-2.1.1 Liquid Screenprinted Solder Mask.................. 120

N-2.1.2 Dry Film........................................................... 120

N-2.1.3 Liquid Photoimageable.................................... 121

N-3.0 TEMPORARY MASKS AND STOPS............... 121

N-4.0 CONFORMAL COATING.................................. 121

N-4.1 Selection of Coating ....................................... 122

N-4.2 Thermal Stress Design Considerations ........... 122

N-4.3 Chemical Stress Design Considerations.......... 122

N-4.4 Space Environment Design Considerations.... 122

N-4.5 Manufacturing Considerations......................... 122

N-4.6 Other Design Considerations........................... 122

N-5.0 COMMON CRITICAL PROPERTIES OF

SOLDER MASK AND CONFORMAL

COATINGS

........................................................ 123

N-6.0 JUNCTION COATINGS, ‘‘GLOB-TOPS’’......... 124

Appendix O Aerospace and High Altitude Concerns

O-1.0 INTRODUCTION

............................................... 125

O-2.0 THERMAL DESIGN.......................................... 125

O-3.0 LARGE THERMAL EXCURSIONS.................. 125

O-4.0 CONTAMINATION ............................................ 125

O-5.0 RADIATION ENVIRONMENT........................... 126

O-6.0 ELECTRICAL PROPERTIES OF GASES....... 126

O-7.0 GRAVITY (OR LACK OF)................................ 126

Appendix P Technical Acronyms and Abbreviations

Figures

Figure 1−1

General Design Steps.......................................... 3

Figure 1−2

Flow Chart for Reliability Assurance Processes.. 4

Figure 3−1

SMT Assembly Response to Thermal Shock ...... 8

Figure 3−2

Thermal Relief in Ground Planes....................... 12

Figure 3−3

Spacing Between Parts...................................... 13

Figure 6−1 Impact of Solder Mask Thickness on

Stenciling............................................................ 25

Figure 7−1

Type 1B Assembly − All SMT Components....... 25

Figure 7−2 Type 1C Assembly − Mixed Technology

Assembly............................................................ 25

Figure 7−3

Type 2B − All SMT Components........................ 25

Figure 7−4

Type 2C − Mixed Technology............................. 26

Figure A−1 Depiction of the Effects of the Accumulating

Fatigue Damage in Solder

Joint Structure.................................................... 35

Figure A−2 Solder Joint Pull Strengths for Gullwing Leads

Consisting of Alloy 42 from Different Vendors

and Copper......................................................... 39

Figure A−3 Effect of Component Offsets on the Fatigue

Reliability of Three Capacitor

Chip (CC) Sizes ................................................. 44

Figure B−1 Cross-Section Schematic of a PTV With a

Barrel Fracture Near the Center of the MLB..... 52

Figure B−1 Cross-Section Schematic of a PTV With a

Barrel Fracture Near the Centerof the MLB ...... 52

Figure B−2 Schematic Cross-Sectional View of a PTV with

a Shoulder Fracture in a printed board.............. 53

Figure B−3 Reduction of Available Copper Ductility Due to

Localized Nicks Reducingthe Width of the

FlexCircuit Conductors [Ref. B-7: 25] and PTV

Stress Concentration Factor, K

......................... 56

Figure D−1

Thermal Vias and Planes................................... 70

Figure D−2

Other Methods of Conductive Heat Transfer..... 70

Figure D−3

Use of Heat Slug................................................ 71

Tables

Table 1−1

The Design Team................................................. 1

Table 3−1 Realistic Representative

(1)

Use Environments,

Service Lives, and Acceptable Failure

Probabilities for Surface Mounted Electronics

Attachments by Use Categories .......................... 6

Table 4−1 Advantages and Disadvantages of Various

Types of Substrates ........................................... 18

Table 6−1

Solder Mask Guidelines..................................... 24

Table A−1 Realistic Representative

(1)

Use Environments,

Service Lives, and Acceptable Failure

Probabilities for Surface Mounted Electronics

Attachments by Use Categories ........................ 35

IPC-D-279 July 1996

viii

Table A−2 Quality of Solder Joints with Copper and Alloy

42 Resulting from Different Reﬂow

Temperatures...................................................... 38

Table B-1 Estimates of Tensile Properties of Copper

Deposit Inside the PTVs .................................... 52

Table B−2 Estimates of the Fatigue Life and Time to

Failure of PTVs in Some Typical Use

Environments from Table A-1............................. 57

Table C−1

SIR Test Parameters for Some Industry Tests... 63

Table G−1 Typical Values for Coefficients of

Thermal Expansion (ppm/°C)............................. 96

Table G−2

Properties of Printed Circuit Laminates............. 98

Table K-1 Checklist for Design for Manufacturability and

Assembly.......................................................... 109

Table L−1

Galvanic Compatibility of Metals...................... 115

July 1996 IPC-D-279

Design Guidelines for Reliable

Surface Mount Technology Printed Board Assemblies

1.0 SCOPE

This document establishes design concepts, guidelines, and

procedures intended to promote appropriate ‘Design for

Reliability (DfR)’ procedures and to ensure reliable printed

wiring assembly (PWA) characteristics. The major focus of

the information presented is directed toward those PWAs

that have surface mount (SM) components, either totally, or

intermixed with through-hole components, mounted on one

or both sides of the mounting structure.

1.1 Purpose The deﬁnition of reliability in this docu-

ment is:

Reliability is the ability of a product to function under

given conditions and for a speciﬁed period of time with-

out exceeding acceptable failure levels.

This document addresses reliability-related aspects of prod-

uct design, process design, as well as material/component

selection and qualiﬁcation. This document identiﬁes appro-

priate existing IPC documents for basic detailed informa-

tion.

The effort of this document is directed at SMT; the inter-

connect structure and the solder joint will receive most of

our attention.

1.2 Design Philosophy Before the product design effort

can begin, the designers of the product and assembly pro-

cess need to know the customer’s reliability requirements

for the product. These requirements should be deﬁned and

ranked by a concurrent engineering or cross-functional

team through a process such as Quality Function Deploy-

ment (QFD), used to capture the voice of the customer.

1.2.1 Establishing the Design Team The design team

can include but is not limited to the members who partici-

pate in at least the design activities identiﬁed in Table 1-1.

In this table, DfA/M stands for Design for Assembly/

Manufacturability, DfT for Design for Testability, DfR for

Design for Reliability.

The design team can consider the general design guidelines

and issues presented in the body of this document as a

methodology for achieving its reliability goals. Figure 1-1

illustrates the general design steps and process ﬂow using

concurrent engineering. Figure 1-2 illustrates the interac-

tive nature of the design for reliability process.

1.2.2 Defining Reliability Requirements The basic reli-

ability requirements to be deﬁned include:

• years of service

• acceptable failure rate(s)/probability(ies) as a function

of time

• repair/replacement/upgrade/service/maintenance/

warranty strategy

• life cycle environment(s)

• deﬁnition of acceptable performance

• criticality of function(s)

• available test equipment

1.2.3 Understanding the Product Life Cycle The life

cycle begins at the component level (including the printed

board) and continues through the assembly level; the life

cycle includes exposure to the following environments:

• assembly/process

• testing

• storage

• transportation

• operating

Table 1−1 The Design Team

Design/Engineering

Function Team Inprovement Area

Product (QFD) (DfA/M) (DfT) (DfR)

Circuit (QFD) (DfA/M) (DfT)

Printed board (DfA/M) (DfT) (DfR)

Thermal (QFD) (DfR)

EMC, EMI, ESD (QFD) (DfT) (DfR)

Mechanical (QFD) (DfA/M) (DfT) (DfR)

Software (QFD) (DfT)

Marketing (QFD)

Process/

manufacturing (QFD)

(DfA/M)

Test (QFD) (DfT) (DfR)

Package/component DfA/M) (DfT)

Field Service (QFD) (DfT)

Purchasing (DfA/M)

Material (QFD) (DfA/M) (DfT) (DfR)

Reliability (QFD) (DfA/M) (DfT) (DfR)

Regulations (QFD) (DfT)

Upper management (QFD) Conceptual Design

and Cultural Change

July 1996 IPC-D-279