IPC-SM-782A 表面安装设计和焊盘设计标准(带BGA).pdf - 第10页

6. High performance pr oducts consisting of ground-based and shipbound military products, high speed and high capacity computers, critical process controllers, and life supporting medical systems. Quality , reliability a…

Surface Mount Design and Land Pattern Standard

1.0 SCOPE

This document provides information on land pattern geom-

etries used for the surface attachment of electronic compo-

nents. The intent of the information presented herein is to

provide the appropriate size, shape and tolerance of surface

mount land patterns to insure sufficient area for the appro-

priate solder ﬁllet, and also to allow for inspection and

testing of those solder joints.

1.1 Purpose

Although, in many instances, the land pat-

tern geometries can be slightly different based on the type

of soldering used to attach the electronic part, wherever

possible, land patterns are deﬁned in such a manner that

they are transparent to the attachment process being used.

Designers should be able to use the information contained

herein to establish standard conﬁgurations not only for

manual designs but also for computer aided design sys-

tems. Whether parts are mounted on one or both sides of

the board, subjected to wave, reﬂow, or other type of sol-

dering, the land pattern and part dimensions should be opti-

mized to insure proper solder joint and inspection criteria.

Although patterns are standardized, since they are a part of

the printed board circuitry geometry, they are subject to the

producibility levels and tolerances associated with plating,

etching, or other conditions. The producibility aspects also

pertain to the use of solder mask and the registration

required between the solder mask and the conductor pat-

terns. (See paragraph 1.2.2).

1.2 Performance Classification

Three general end-

product classes have been established in associated IPC

standards and speciﬁcations to reﬂect progressive increases

in sophistication, functional performance requirements and

testing/inspection frequency. It should be recognized that

there may be an overlap of equipment between classes.

Design requirements determine class. Class deﬁnitions are

useful for identifying degrees of precision needed to meet

design/performance requirements of packaging and inter-

connecting structures, and establish communication media

between design and manufacture and disciplines.

The printed board user has the responsibility to determine

the class to which his product belongs. The contract shall

specify the performance class required and indicate any

exceptions to speciﬁc parameters, where appropriate. In the

event of conﬂict between the design requirements and the

classes deﬁned herein, the former shall take precedence

and be reﬂected in the master drawing.

These classes are:

CLASS 1 General Electronic Products

Includes consumer products, some computer and computer

peripherals, as well as general military hardware suitable

for applications where cosmetic imperfections are not

important and the major requirement is function of the

completed printed board or printed board assembly.

CLASS 2 Dedicated Service Electronic Products

Includes communications equipment, sophisticated busi-

ness machines, instruments and military equipment where

high performance and extended life is required, and for

which uninterrupted service is desired but is not critical.

Certain cosmetic imperfections are allowed.

CLASS 3 High Reliability Electronic Products

Includes the equipment for commercial and military prod-

ucts where continued performance or performance on

demand is critical. Equipment downtime cannot be toler-

ated, and functionality is required for such applications as

life support items, or missile systems. Printed boards and

printed board assemblies in this class are suitable for appli-

cations where high levels of assurance are required and

service is essential.

The land patterns in this standard have the capability of

accommodating all three performance classiﬁcations.

1.2.1 End-Use Applications

In addition to the three per-

formance classiﬁcations, the Surface Mount Council has

established end use applications for electronic products.

These are:

1. Consumer products including games, toys, audio and

video electronics. In general, convenient size and

maximum functionality are important but product cost

is extremely important.

2. General purpose computers, as used in businesses and

personal applications. Compared to consumer prod-

ucts, customers expect longer life and more consistent

service.

3. Telecom products including telephone, switching sys-

tems, PBXs, and exchanges. These products are used

in applications expecting long service life and endur-

ing relatively harsh environments.

4. Commercial aircraft requiring small size, light weight

and high reliability.

5. Industrial products and passenger compartment auto-

motive applications. Size and function is a byword of

these products. Cost is very important, provided that

reducing product cost doesn’t forfeit the highest

achievable product quality, performance, and function.

December 1999 IPC-SM-782A

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6. High performance products consisting of ground-based

and shipbound military products, high speed and high

capacity computers, critical process controllers, and

life supporting medical systems. Quality, reliability

and performance are paramount, closely followed by

size and function. Cost is optimized based on these

requirements but is less important.

7. Space products include all of the products above which

are built to meet harsh outer space conditions. This

implies high quality and performance over a wide

range of environmental and physical extremes.

8. Military avionics products built to meet demanding

mechanical and thermal changes. Size, weight, perfor-

mance and reliability are paramount.

9. Under the hood automotive electronics products

endure the harshest of all use environments. These

products face extreme temperatures and mechanical

variations. Adding to this is the pressure of achieving

the lowest cost and optimum manufacturability in high

volumes.

1.2.2 Producibility Levels

When appropriate this stan-

dard will provide three design complexity levels of fea-

tures, tolerances, measurements, assembly, testing of

completion or veriﬁcation of the manufacturing process

that reﬂect progressive increases in sophistication of tool-

ing, materials or processing and, therefore progressive

increases in fabrication cost. These levels are:

Level A General Design Complexity—Preferred

Level B Moderate Design Complexity—Standard

Level C High Design Complexity—Reduced Produc-

ibility

Producibility levels also pertain to the assembly. The three

component mounting complexity levels which reﬂect pro-

gressive increases in sophistication of tooling, assembly

and joining techniques and therefore progressive increases

in cost are:

Level A simple assembly techniques used to describe

through the board component mounting;

Level B moderate assembly techniques used to

describe surface component mounting and

Level C complex assembly techniques used to

describe intermixing of through-the-board

and surface mounting on the same assembly.

Classiﬁcation of complexity should not be confused with

the performance classiﬁcation of end-item use described in

paragraph 1.2.

1.3 Assembly Types A type designation signiﬁes further

sophistication describing whether components are mounted

on one or both sides of the packaging and interconnecting

structure. Type 1 deﬁnes an assembly that has components

mounted on only one side; type 2 is an assembly with

components on both sides. Type 2 is limited to only class

B or C assemblies.

Figure 1–1 shows the relationship of two types of assem-

blies.

The need to apply certain design concepts should depend

on the complexity and precision required to produce a par-

ticular land pattern or P&I structure. Any design class may

be applied to any of the end-product equipment categories;

therefore, a moderate complexity (Type 1B) would deﬁne

components mounted on one side (all surface mounted) and

when used in a Class 2 product (dedicated service electron-

ics) is referred to as Type 1B, Class 2. The product

described as a Type 1B, Class 2 might be used in any of the

end-use applications; the selection of class being dependent

on the requirements of the customers using the application.

1.4 Presentation

Dimensions and tolerances are

expressed in millimeters (mm) or microns (mn) as appro-

priate. When no unit of measurement is shown, the unit

shall be assumed to be ‘‘mm.’’ Reference information for

inch conversion is shown in the appendix.

1.5 Profile Tolerances

Proﬁle tolerances are used in the

dimensioning system for determining the relationship

between component outlines and land pattern geometries.

The details are described in Section 3.3, and follow the

principles set forth in ANSI Y14.5. All dimensions are con-

sidered maximum or minimum material condition (depend-

ing on the features being analyzed), thus the proﬁle toler-

ances are unilateral (one-direction—maximum to

minimum, or minimum to maximum) as opposed to bilat-

eral (plus or minus) from a nominal characteristic.

1.6 Land Pattern Determination

This document dis-

cusses two methods of providing information on land pat-

terns:

(1) exact details based on industry component speciﬁca-

tions, board manufacturing and component placement

accuracy capabilities. These land patterns are regis-

tered to a speciﬁc component, and have a registered

land pattern number, see Table 3.5 and paragraph

3.3.3.4.

(2) equations that can be used to alter the given informa-

tion to achieve a more robust solder connection, when

used in particular situations where the equipment for

placement or attachment are more or less precise than

the assumptions made when determining the exact land

pattern details.

1.6.1 General Usage of SMT In general, a product is a

good candidate for SMT if it needs to be:

IPC-SM-782A December 1999

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IPC-782-1-1

Figure 1–1 Electrical assembly types

PLCC

CHIP COMPONENT

SOIC

DIP

PLCC

CHIP

COMPONENT

SOIC

DIP

PLCC

CHIP COMPONENT

SOIC

PLCC

2-Sided Thru-hole (NOT RECOMMENDED)

CHIP

COMPONENT

PLCC

CHIP

COMPONENT

CHIP

COMPONENT

SOIC

CHIP

COMPONENT

SOIC

DIP

SOLDER

PASTE

SOLDER

PASTE

SOIC

Through-hole

Simple

SMT

Simple

SMT/TH

Complex

Type 1

Type 2

SMT

Complex

TH/SMT

Simple

SMT/TH

FPT/CMT

Complex

SOLDER

PASTE

Adhesive (Optional)

FPT

Simple

Wire bond or

tab IC chip

attachment

FPT PKG.

(selectively attached)

December 1999 IPC-SM-782A

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