IPC-D-279 EN.pdf - 第12页

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 (Df…

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

Test, storage and transportation need to be considered at

both component and assembly levels as well as before,

during, and after the assembly process.

1.2.4 Defining the Product Environment For each envi-

ronment, in 1.2.3, it is critical to identify, characterize and

quantify the parameters listed below:

• Temperature Range

• Time at Temperature

• Temperature Rate of Change

• Kind and number of temperature cycles

• Duty Cycle

• Humidity (moisture) exposure

• Atmospheric pressure conditions (earth, space, both)

• Vibration and shock

• ESD, EOS, EMC, EMI and high voltage exposures

and requirements

• Chemical exposures (ﬂux, solvents, salt spray, NBC,

decontamination, etc.)

• Radiation (Ionizing, light, UV)

• Contamination (dust, oil, paper)

• Pressure conditions

When the life environments have been identiﬁed and

deﬁned, the engineering team is prepared to analyze and

select the materials, components, assembly processes, ther-

mal management and test strategies required.

1.3 Document Organization This document has been

organized to provide the reader with consistent information

on the various aspects of surface mount technology printed

board assemblies and identiﬁes the parameters that need to

be addressed. Each section serves a speciﬁc function in the

SMT design process. The body of this document addresses

general design guidelines speciﬁc to SMT. The appendices

contain detailed information of SMT design or common

design considerations between SMT and through hole pro-

cesses.

1.3.1 Applicable Documents Section 2.0 lists only those

documents related to surface mount technology and reli-

ability which are mentioned in the text. The design engi-

neers need to know about the primary documents which

underlie the text. The bibliography, Section 9, lists docu-

ments by interest area and some entries are duplicated;

there are many more documents of use and available to the

designer. This lists only those documents used day to day.

1.3.2 Design for Reliability of SM Assemblies Section

3.0, together with Sections 4.0 and 5.0, considers the broad

range of environmental stresses to which the printed wiring

assembly (PWA) must be robust during its life cycle (life

cycle environment) and some speciﬁc mitigation tech-

niques that may be used. A separate Appendix D for SM

thermal design augments Appendix A for the DfR of solder

attachments and Appendix B for DfR of plated-through

vias (PTVs). Appendix C provides DfR information for

insulation resistance aspects. Appendix E provides DfR

information for insulation resistance aspects Appendix E

relates environmental stresses and the corresponding PWA

and component responses. Appendix G provides material

CTE data. Appendix I describes solvent related stresses on

plastics and metals. Appendix L deals with corrosion.

Appendix M discusses solder joint variability. Appendix N

deals with adhesives, solder masks and conformal coatings.

Appendix O covers the special requirements for high alti-

tude and aerospace applications.

1.3.3 Substrates Section 4.0 covers rigid and ﬂexible

substrates and their impact on SM assembly reliability.

Data on material parameters and tradeoffs is provided. Sub-

strate related issues such as thermal expansion mismatch,

moisture absorption, and PTH-via thermal stress are cov-

ered. Related materials CTE data is provided in Appendix

G. Appendix N deals with adhesives, solder masks and

conformal coatings. A detailed DfR treatment for PTVs is

provided in Appendix B.

1.3.4 Components Section 5.0 covers components,

component-related design issues, and component-process

interactions of concern to the designer as well as to the

process engineer. Appendix E relates environmental

stresses and the corresponding PWA and component

responses. Appendix F provides a ready reference to sur-

face mount plastic package cracking during SM reﬂow and

to methods for mitigating those effects. Appendix H pro-

vides a ready reference to the electrostatic discharge sus-

ceptibility groupings of various component families.

1.3.5 Attachment Materials and Coatings Section 6.0

addresses attachment materials and polymer coatings. The

attachment materials include solder, electrically conductive

adhesives, thermally conductive adhesives and structural

adhesives. The polymer coatings include solder mask con-

formal coating.

1.3.6 Assembly Processes and DfM Section 7.0 pro-

vides an overview of the assembly processes used in sur-

face mount assemblies and highlights the speciﬁc reliabil-

ity issues associated with each of the individual processes,

including design for manufacturability (DfM) consider-

ations. The surface mount processing conditions may be

the most severe that the assembly ever sees during its life

cycle, not only in terms of temperature but shock and ﬂex-

ure as well. A DfM checklist is provided listed in Appen-

dix K together with pointers to DfM assessment tools in

software. A detailed list of solvent/plastic/metal compat-

ibilities is provided in Appendix I.

IPC-D-279 July 1996