IPC-D-279 EN.pdf - 第45页

Appendix A Design for Reliability (DfR) of Solder Attachments A-1.0 SURFACE MOUNT SOLDER ATTACHMENT RELIABILITY The fatigue behavior of surface mount solder joints has been investigated experimentally in numerous studies…

Cooling Techniques for Electronic Equipment, 2nd Edition,

Dave S. Steinberg; Wiley Interscience, 1991, ISBN 0-471-

52451-4. Chapter 8 addresses combined vibration and ther-

mal stresses.

Shock and Vibration, 3rd Edition, Cyril M. Harris, Editor,

McGraw-Hill, 1987 ISBN 0-070026801-0

Structural Analysis of Printed Circuit Board Systems, Peter

A. Engel, Springer-Verlag, 1993, ISBN 0-387-97939-5 or

3-540-97939-5

9.17 Accelerated Life Testing

Electronic Materials Handbook, Volume 1, Packaging,

ASM International; 1989; ISBN 0-87170-285-1 (V.1)

Applied Life Data Analysis, Nelson, W., John Wiley &

Sons, NY, 1982 ISBN 0-070026801-0

Accelerated Testing: Statistical Models, Test Plans, and

Data Analyses, Wayne Nelson; John Wiley & Sons, 1990;

ISBN 0471-552-775

Accelerated Testing Handbook, Technology Associates,

1987

Applied Reliability, Tobias, P. A., and Trindade, D., Van

Nostrand Reinhold, 1985, ISBN-0-442-28310-5

‘‘How to Plan and Analyze Accelerated Tests’’, 1900.

ASQC Basic References in Quality Control: Statistical

Techniques, Order Entry Dept., American Society for Qual-

ity Control, 310 Wisconsin Avenue, Milwaukee, WI 53203

(800) 952-6587

‘‘How to Analyze Reliability Data’’, Volume 6, 1983,

ASQC as above.

See also IPC publication on Accelerated Reliability Testing

of Surface Mount Solder Attachments

9.18 Solder, Solderability, Soldered Assembly Quality

See ANSI/IPC J-STD publications on various Solder, Sol-

derability, Solder Assembly Quality

9.19 Solder Mask and Conformal Coating

Contamination Effects on Electronic Products, Carl J. Taut-

scher, Marcel Dekker, 1991

Electronic Materials Handbook, Volume 1, Packaging,

Merrill L. Minges, Technical Chairman, ASM Interna-

tional, 1989; see particularly sections 6, 7 and 9.

See also IPC documents on Solder Mask, Conformal Coat-

ing, SIR, IR, Cleaning, Surface Mount Land Patterns/

Conﬁgurations and Design Rules

9.20 General Reliability

AT&T Reliability Manual, Klinger, Nakada and Menendez

Editors, VNR, 1990, ISBN 0-442-31848-0.

Handbook of Reliability Engineering and Management,

2nd Edition Ireson, Coombs and Moss, Editors, McGraw-

Hill, 1996, ISBN 0-07-012750-6

Practical Reliability Engineering, 3rd Edition, Patrick D. T.

O’Connor, John Wiley & Sons, 1995, ISBN 0-471-96025

Handbook of Electromechanical Product Design, P. L. Hur-

ricks, Longman Scientiﬁc & Technical, 1994, ISBN 0-470-

04083-3

July 1996 IPC-D-279

Appendix A

Design for Reliability (DfR) of Solder Attachments

A-1.0 SURFACE MOUNT SOLDER ATTACHMENT

RELIABILITY

The fatigue behavior of surface mount solder joints has

been investigated experimentally in numerous studies. The

results of the studies that were carried out in a manner to

assure the same damage mechanism as the mechanism

operative in typical electronic products have yielded a

mathematical solder fatigue model. This model has been

expanded and augmented to its current form, presented in

this section, as additional test results became available.

The model is for uncoated solder attachments. The com-

plexity and vast differences in conformal coatings make it

impossible to develop a generic model that considers all

the variables. Products with conformal coatings should be

evaluated using test vehicles having the same coating and

test vehicles without the coating in order to assess the

impact of the coating on reliability.

A-2.0 DAMAGE MECHANISMS AND FAILURE

The reliability of electronic assemblies depends on the reli-

ability of their individual elements and the reliability of the

mechanical thermal, and electrical interfaces (or attach-

ments) between these elements. One of these interface

types, surface mount solder attachment, is unique since the

solder joints not only provide the electrical interconnec-

tions, but are also the sole mechanical attachment of the

electronic components to the printed board and often serve

critical heat transfer functions as well.

A solder joint in isolation is neither reliable nor unreliable;

it becomes so only in the context of the electronic compo-

nents that are connected via the solder joints to the printed

board. The characteristics of these three elements - compo-

nent, substrate, and solder joint - together with the use

conditions, the design life, and the acceptable failure prob-

ability for the electronic assembly determine the reliability

of the surface mount solder attachment.

A-2.1 Solder Joints and Attachment Types

Solder joints are anything but a homogeneous structure. A

solder joint consists of a number of quite different materi-

als, many of which are only superﬁcially characterized. A

solder joint consists of:

(1) the base metal at the printed board

(2) one or more intermetallic compounds (IMC)—

solid solutions—of a solder constituent—

typically tin (Sn)—with the printed board base

metal

(3) a layer from which the solder constituent form-

ing the printed board-side IMC(s) has been

depleted

(4) the solder grain structure, consisting of at least

two phases containing different proportions of

the solder constituents as well as any deliberate

or inadvertent contaminations

(5) a layer from which the solder constituent form-

ing the component-side IMC(s) has been

depleted

(6) one or more IMC layers of a solder constituent

with the component base metal, and

(7) the base metal at the component.

The grain structure of solder is inherently unstable. The

grains will grow in size over time as the grain structure

reduces the internal energy of a ﬁne-grained structure. This

grain growth process is enhanced by elevated temperatures

as well as strain energy input during cyclic loading. The

grain growth process is thus an indication of the accumu-

lating fatigue damage. At the grain boundaries contami-

nants like lead oxides are concentrated; as the grains grow

these contaminants are further concentrated at the grain

boundaries, weakening these boundaries. After the con-

sumption of ~25% of the fatigue life micro-voids can be

found at the grain boundary intersections; these micro-

voids grow into micro-cracks after ~40% of the fatigue

life; these micro-cracks grow and coalesce into macro-

cracks leading to total fracture as is schematically shown in

Figure A-1.

Surface mount solder attachments exist in a wide variety of

designs. The major categories are leadless and leaded sol-

der attachments. Among the leadless solder joints a differ-

entiation has to be made between those without ﬁllets, e.g.,

Flip-Chip C4 (Controlled Collapse Chip Connection) sol-

der joints, BGAs with C5 (Controlled Collapse Chip Car-

rier Connection) solder attachments, BGAs with high-

temperature solder (e.g., 10Sn/90Pb) balls, and CGAs with

high-temperature solder columns; and solder joints with

ﬁllets, e.g., chip components, Metal Electrode Face compo-

nents (MELFs), and castellated leadless chip carriers. The

leaded solder attachments differ primarily in terms of their

compliancy and can be roughly categorized into compo-

nents with super-compliant leads {K

<~9 N/mm}, compli-

ant leads (~9 N/mm<K

<~90 N/mm), and non-compliant

leads {(K

>~90 N/mm}.

The different surface mount solder attachment types can

have signiﬁcantly different failure modes. Solder joints

with essentially uniform load distributions, e.g., Flip-Chip,

BGA, CGA, show behavior as illustrated in Figure A-1.

Solder joints with non-uniform load distributions, e.g.,

those on chips components, MELFs, leadless chip carriers,

IPC-D-279 July 1996

and all leaded solder joints, show localized damage con-

centrations with the damage shown in Figure A-1 preced-

ing an advancing macro-crack.

The solder joints frequently connect materials of highly

disparate properties, causing global thermal expansion mis-

matches [Refs. A-9: 1-6], and are made of a material, sol-

der, that itself has often properties signiﬁcantly different

than the bonding structure materials, causing local thermal

expansion mismatches [Refs. A-9: 4,7].

The severity of these thermal expansion mismatches, and

thus the severity of the reliability threat, depends on the

design parameters of the assembly and the operational use

environment. In Table A-1 guidelines as to the possible use

environments for nine of the more common electronic

applications are illustrated [Refs. A-9: 8,9]. However, it

needs to be emphasized, that the information in Table A-1

should serve only as a general guideline; for some use cat-

egories the description of the expected use environment

Figure A−1 Depiction of the Effects of the Accumulating Fatigue Damage in Solder Joint Structure

Table A−1 Realistic Representative

(1)

Use Environments, Service Lives, and Acceptable Failure Probabilities for Surface

Mounted Electronics Attachments by Use Categories [Ref. A-9: 10]

Worst-Case Environment

Use Category

Tmin

°C

Tmax

°C

∆T

(2)

°C

Dwell Time

hrs Cycles/Year

Typical Years

of Service

Accept.

Failure

Risk

(3)

Consumer 0 +60 35 12 365 1-3 ~1

Computers +15 +60 20 2 1460 ~5 ~0.1

Telecom -40 +85 35 12 365 7-20 ~0.01

Commercial Aircraft -55 +95 20 12 365 ~20 ~0.001

Industrial

and Automotive

Passenger

Compartment

−55 +96 20

&40

&60

&80

185

100

~10 ~0.1

Military

Grounds and

Ship

−55 +95 40

&60

100

265

~10 ~0.1

Space leo

geo

−55 +95 3 to 100 1

8760

365

5-30 ~0.001

Military a

Avionics b

Maintenance

−55 +95 40

&20

365

~10 ~0.01

Automotive

under hood

−55 +125 60

&100

&140

1000

300

~5 ~0.1

& = in addition

1 Does not cover all possible use environments, but only most common.

2 ∆T represents the maximum temperature swing, but does not include power dissipation effects for components; for reliability estimations the actual local tem-

perature swings for components and substrate, including power dissipation should be used.

3 The ‘Acceptable Failure Risk’ is the percentage of product in the ﬁeld that has failed, due to wearout mechanisms, at the end of the ‘Typical Years of Service.’

July 1996 IPC-D-279