IPC-SM-782A 表面安装设计和焊盘设计标准(带BGA).pdf - 第18页

Proﬁle tolerances are unilateral, and are described to reﬂect the best condition for solder joint formation usually at minimum component size. As the proﬁle tolerance moves in this unilateral direction toward maximum com…

IPC-782-3-1

Figure 3–1 Examples of typical package styles and package descriptive designators

Examples

Package

Outline

Style

and Code

Chip Carrier

PQCC PQCC

(PLCC)

PQCC

(CLCC)

PQCC

(CLCC)

Cylinder

Disk Button

MBCY MBCY

CQFP

LRDB GRDB PRDB

PBCY

Press Fit

Post/Stud

Mount

Small

Outline

Special

Shape

MUPF

MUPM MUPM CRPM

PDSS

PDSO PDSO PSSO

Flatpack

PADB

CDFP PQFP

December 1999 IPC-SM-782A

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Proﬁle tolerances are unilateral, and are described to reﬂect

the best condition for solder joint formation usually at

minimum component size. As the proﬁle tolerance moves

in this unilateral direction toward maximum component

size, the opportunity for a robust solder joint decreases.

The concept for component dimension evaluations is based

on evaluating the surfaces of the component termination

and component lead that are involved in the formation of

the acceptable solder joint. Component manufacturers usu-

ally provide dimensions for their parts with a nominal size

and then put a tolerance on that nominal dimension. Inor-

der to facilitate the dimensioning system, these dimensions

and their associated tolerances are converted to minimum

and maximum size.

As an example, capacitor C1206 has a manufactured nomi-

nal dimension for its length (L) of 3.2 mm. The tolerance

described by the manufacturer is

0.2 mm. Thus, the mini-

mum dimension of ‘‘L’’ is 3.0 mm with a unilateral toler-

ance of 0.4 mm, resulting in its maximum dimension being

3.4 mm.

Figure 3–4 shows the characteristics for the C1206. Figure

3–4a shows the component manufacturers dimensions for

IPC-782-3-2

Figure 3–2 Lead-form (or terminal-shape) examples

BUTT "C" BEND

SOLDER LUG FLAT

GULL WING HIGH-CURRENT CABLE

"J" BEND NO LEAD

PIN/PEG WRAPAROUND

"S" BEND THROUGH-HOLE

"J" INVERTED WIRE

BODY OF PACKAGE LAND STRUCTURE

IPC-SM-782A December 1999

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the length of the capacitor. Figure 3–4b shows the compo-

nent length at its minimum size in the converted dimen-

sions of the new system using proﬁle tolerancing. Figure

3–4c shows the land pattern at its maximum size. These

conditions provide for an optimum toe ﬁllet. For optimum

heel ﬁllet the component basic dimensions are at the maxi-

mum and the land pattern is at its minimum.

Similar concepts are applied to leaded surface mount parts.

The critical dimensional characteristics identiﬁed are those

that relate to the formation of the toe and heel solder ﬁllet.

For components with gull wing leads the basic dimensions

apply across the outer extremities of the part for toe solder

ﬁllet formation; and within the inside of the formed radius

of opposing leads for heel solder ﬁllet formation.

The outer dimensions of leaded or even leadless chip car-

riers are usually easy to determine since these are readily

available from the component manufacturer. The inner

(heel-to-heel) dimensions are not provided in industry stan-

dards or manufacturer’s speciﬁcations, and are more diffi-

cult to determine, not only because of the form of the lead,

Table 3–3 Lead-Form (or Terminal-Shape) Suffixes

Code Form/Shape Description (see Figure A2)

B Butt A noncompliant lead intended for attachment perpendicular to the land structure.

C ‘‘C’’ bend A ‘‘C’’ shaped noncompliant lead bent down and under the body of the package.

D Solder lug A lug terminal on the package

F Flat A noncompliant, nonformed ﬂat lead that extends away form the body of the package.

G Gull wing A compliant lead bent down from the body of the package with a foot at the end pointing

away from the package.

H High-current cable A lug terminal at the end of a ﬂexible lead.

J ‘‘J’’ bend A ‘‘J’’ shaped compliant or noncompliant lead bent down and back under the body of the

package.

N No lead Metallized terminal pads located on the body of the package.

P Pin/Peg A tempered lead extending from the body of the package and intended for attachment to a

plated through-hole in the land structure.

R Wraparound A metallized noncompliant terminal wrapped around the package body.

S ‘‘S’’ bend An ‘‘S’’ shaped compliant lead bent under the body of the package.

T Through-hole A terminal with ﬂat or V-shaped cross section intended for attachment to a plated

through-hole in the land structure.

U ‘‘J’’ inverted A ‘‘J’’ shaped compliant or noncompliant lead bent down form the doby of the package with

the curved end pointing away from the package.

W Wire An untempered wire lead extending from the body of the package.

X Other A lead form or terminal shape other than those deﬁned.

IPC-782-3-3

Figure 3–3 Proﬁle tolerancing examples

0.7

1.27

▼

2.5

MMC

▼

0.1

MMC

Places

December 1999 IPC-SM-782A

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