IPC-D-279 EN.pdf - 第14页

1.3.7 Testing Section 8.0 details the various testing strategies, their purposes and their impact on reliability . Also discussed are design for testability considerations. Checklists for DfT from various sources are pro…

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

1.3.7 Testing Section 8.0 details the various testing

strategies, their purposes and their impact on reliability.

Also discussed are design for testability considerations.

Checklists for DfT from various sources are provided in

Appendix J.

1.4 Terms and Definitions Terms and deﬁnitions used

here are in accordance with IPC-T-50, and IPC-SM-785

except as otherwise speciﬁed.

IPC-279-01

Figure 1−1 General Design Steps

▼

1. Years of Service

2. Acceptable Failure Rate Limit

3. Repair/Replacement Strategy

Identify Reliability Reqts.

Levels:

•

Component

•

Assembly

Identify Life Environment

Phases:

•

Storage

•

Transportation

•

Processing

•

Testing

•

Operating

Temp. Range

•

Vibration/Shock

Identify Storage Env.

Transp. Env.

Proc.

ESD

•

Atmosphere

Analyze & Select

•

Components

•

Materials

•

Assembly Processes

•

Test Strategy

•

Thermal Mgt. Strategy

•

Solder Attachments

•

PWB Design

July 1996 IPC-D-279

IPC-279-02

Figure 1−2 Flow Chart for Reliability Assurance Processes

▼

Determine

missing

data.

information

complete enough

for reliability

analysis?

reliability in

Appendices

A, B & C

Estimate product

reliability

Appendices A, B & C

Redesign product.

Redefine

requirements.

estimated

reliability

adequate?

Finish

Solution:

Redesign

Redefine

Reduce

Uncertainties

Solution:

Redesign

Redefine

Review test

program for

correct-

ness

Finish

reliability

adequate

Collection of all

available inform-

ation & requirements

Flow Chart for Reliability Assurance Processes

Define proper

test, conditions,

IPC-SM-785

Accelerated

reliability

test(s)

Evaluate results

Failure Mode

Analysis

Estimate product

reliability from

test results

▼

Yes

Main Focus of Document

IPC-D-279 July 1996