IPC-7351-2005_表面贴装焊盘布局设计和标准通用要求.pdf - 第71页

14.2.4.2 Solder Mask Defined Land Pattern If solder mask deﬁned patterns are used, then adjust land pattern diameter accordingly (see 14.4). 14.2.5 Defining Contact Assignment Array contact identiﬁcation is assigned by t…

14.2.2.3 Thermally Enhanced Matrix A thermally

enhanced matrix is a perimeter matrix with contacts added

back in the center (see Figure 14-6).

14.2.2.4 Staggered Matrix A staggered matrix is deﬁned

by the removal of every other contact in an interstitial pat-

tern. This provides an effective minimum center-to-center

contact spacing of

√

2 x pitch of the full matrix (see Figure

14-7). In order to retain the A1 contact position, the stag-

gered matrix must be developed using a full odd matrix.

14.2.3 Selective Depopulation In addition to depopula-

tion methods which lead to the matrices described above,

contacts may be removed selectively. Selective depopula-

tion can be accomplished in any manner as long as the pat-

tern matrix is not shifted from the center of the package

outline (see Figure 14-8).

14.2.4 Attachment Site Planning The attachment site or

land pattern geometry recommended for BGA devices is

round with the diameter adjusted to meet contact pitch and

size variation. The diameter of the land should be no larger

than the diameter of the land at the package interface and

is typically 20% smaller than the normal diameter speciﬁed

for the ball contact for pitches greater than 1.0 mm and

10% smaller for pitches less than 1.0 mm. Refer to the

manufacturer speciﬁcation before ﬁnalizing land pattern

array and geometry.

14.2.4.1 Copper Defined Land Pattern The land pat-

terns described are deﬁned by the etched copper. Solder

mask clearance should be a minimum of 0.075 mm

[0.00295 in] from the etched copper land. For applications

requiring a clearance that is less than recommended, con-

sult with the printed board supplier.

IPC-7351-14-06

Figure 14-6 Perimeter and Thermally Enhanced Matrices

IPC-7351-14-07

Figure 14-7 Staggered Matrix

IPC-7351-14-08

Figure 14-8 Selective Depopulation

IPC-7351 February 2005

标准分享网 www.bzfxw.com 免费下载

14.2.4.2 Solder Mask Defined Land Pattern If solder

mask deﬁned patterns are used, then adjust land pattern

diameter accordingly (see 14.4).

14.2.5 Defining Contact Assignment Array contact

identiﬁcation is assigned by the column and row location.

For example, A1 contact position is always at an outside

corner position with alpha characters arranged in a vertical

(row) pattern from top to bottom. Numeric characters are

assigned in a horizontal (column) axis (I, O, Q, S, X and Z

are omitted) (see Figure 14-9).

The designer should note that the A1 position is at the

upper left hand corner when the device is viewed from the

top. Contact pattern is deﬁned when viewed from the bot-

tom. The land pattern provided on the host substrate is

opposite of the contact pattern (with A1 contact position

again at the upper left).

14.3 Handling and Shipping For information on trays

and shipping containers refer to ACH:EIA-481-A,

ACH:EIA-481-3, JEDEC CO-028, and JEDEC CO-029.

14.4 Land Pattern Analysis The following provides an

analysis of tolerance assumptions and result in solder joints

based on the land pattern dimensions shown in Figure 14-9.

The variations that exist in determining these land patterns

include the diameter of the individual ball, the positional

accuracy of the ball in relationship to a true position on the

component and the board, and the manufacturing allow-

ance that can be held for the land on the substrate that

mounts the particular ball. The land pattern of the compo-

nent (where the ball is attached) and the land pattern of the

substrate mounting structure (printed board) should be as

similar as possible. Component manufacturers have made

their determinations that the land pattern of pad on the

component should be less than the ball diameter. They base

their conclusions on the resulting nominal ball diameter

with a slight reduction in the land approximation. Pitch

plays a large role in the determination of what ball diam-

eters can be used in various combinations. Table 14-2

shows the characteristics of those balls that are used with

pitches of 1.5 mm through 1.0 mm, as well as future ball

sizes whose pitches fall between 0.40 mm and 0.25 mm.

14.4.1 Land Approximation In each instance, component

manufacturers and board designers are encouraged to

reduce the land size by some percentage of the nominal

ball diameter. The amount of reduction is based on the

original ball size, which is used to determine the average

land. In determining the relationship between nominal

characteristics, a manufacturing allowance for land size has

been determined to be 0.1 mm between the Maximum

Material Condition (MMC) and Least Material Condition

(LMC). Table 14-3 shows the reduction characteristics, the

nominal land size, and the target land dimensions, as well

as future approximations for ball diameters of 0.25 mm and

below.

14.4.2 Total Variation The total variation of the system

considers three major issues: positioning, ball tolerance,

and substrate tolerance. All three attributes added together

IPC-7351-14-09

Figure 14-9 Device Orientation and Contact A1 Position

Table 14-2 Ball Diameter Sizes (mm)

Nominal Ball

Diameter Total Variation Pitch

0.75 0.90 - 0.65 1.5, 1.27

0.60 0.70 - 0.50 1.0

0.50 0.55 - 0.45 1.0, 0.80

0.45 0.50 - 0.40 1.0, 0.80, 0.75

0.40 0.45 - 0.35 0.80, 0.75, 0.65

0.30 0.35 - 0.25 0.80, 0.75, 0.65, 0.50

0.25 0.28 - 0.22 0.40

0.20 0.22 - 0.18 0.30

0.15 0.17 - 0.13 0.25

February 2005 IPC-7351

result in a worst case analysis, however as with other land

patterns in the standard, a statistical average is determined

by using the RMS (root, mean, square) value. Table 14-4

shows the total variation in the system for each of the four

ball sizes identiﬁed in the standard.

It should be noted that the target value for lands on the

substrate of the component or the board should be at Maxi-

mum Material Condition. The variation from the Maximum

Material Condition indicates that ball-to-land misalignment

is achieved by taking the maximum land size and subtract-

ing the variation. The resulting dimension would indicate

the amount of attachment area that would result from a

system where all conditions are at a negative instance. For

lands that are solder mask-deﬁned, the land size should be

increased by the amount of encroachment of the solder

mask. As an example, if the requirement is that solder

mask should be on the land by 0.05 mm, then the maxi-

mum land size should be increased by 0.1 mm. It should be

noted that for solder mask-deﬁned lands, since the land size

increases, the opportunity to route conductors between

lands is impacted by reducing the available area for con-

ductor width and spacing.

14.4.3 Future Ball Conditions Although not required for

the BGAs shown in the present release of IPC-7351, pro-

jected future ball sizes of 0.40 mm pitch and below are

shown in Table 14-2. Their projected land size approxima-

tions for ball diameters of 0.25 mm and below are shown

in Table 14-3.

14.4.4 Land Pattern Calculator The land pattern calcu-

lations for BGAs are based on ball size. As a result of ball

variation and component conditions, Table 14-5 shows the

land pattern calculator headings needed to describe the

variations in the system. This data is usually described at

the Maximum Material Condition for nonsolder mask-

deﬁned lands and is dimension ‘‘X’’ in the IPC-7351

datasheets for BGA land patterns.

15 IPC-7359 NO LEAD COMPONENTS (QFN, SON, LCC)

15.1 LCC

A leadless chip carrier is a ceramic package

with integral surface-metallized terminations. Leadless

Types A, B, and D chip carriers have a chamfered index

corner that is larger than that of Type C. Another difference

between the A, B, and D types and Type C is the feature in

the other three corners. The types A, B, and D, were

designed for socket applications and printed wiring inter-

connections. The Type C is primarily intended for direct

attachment through reﬂow soldering. This application dif-

ference is the main reason for their mechanical differences.

These packages mount in different orientations, depending

on type, mounting structure and preferred thermal orienta-

tion.

Table 14-3 Land Approximation (mm)

Nominal Ball

Diameter Reduction

Nominal

Land

Diameter

Land

Variation

0.75 25% 0.55 0.60 - 0.50

0.60 25% 0.45 0.50 - 0.40

0.50 20% 0.40 0.45 - 0.35

0.45 20% 0.35 0.40 - 0.30

0.40 20% 0.30 0.35 - 0.25

0.30 20% 0.25 0.25 - 0.20

0.25 20% 0.20 0.20 - 0.17

0.20 20% 0.15 0.15 - 0.12

0.15 20% 0.10 0.10 - 0.08

Table 14-4 BGA Variation Attributes (mm)

Nominal

Ball Size

Positional

Allowance

Ball

Tolerance

Substrate

Tolerance

Variation

RMS

Value

0.75 0.1 dia. DTP 0.25 0.10 0.25

0.60 0.1 dia. DTP 0.20 0.10 0.24

0.50 0.1 dia. DTP 0.10 0.10 0.17

0.45 0.1 dia. DTP 0.10 0.10 0.17

Table 14-5 Land-to-Ball Calculations for Current and Future BGA Packages (mm)

Land Size

Location

Allowance

Ball

Variation

PCB

Fabrication

Allowance

Ball Size

Reduction

from

Nominal

Variation

AllowanceMMC LMC Nominal MMC LMC

0.60 0.50 0.10 0.25 0.10 0.75 0.90 0.65 25% 0.25

0.50 0.40 0.10 0.20 0.10 0.60 0.70 0.50 25% 0.20

0.45 0.35 0.10 0.10 0.10 0.50 0.55 0.45 20% 0.17

0.40 0.30 0.10 0.10 0.10 0.45 0.50 0.40 20% 0.17

0.35 0.25 0.10 0.10 0.10 0.40 0.45 0.35 20% 0.17

0.25 0.20 0.05 0.10 0.05 0.30 0.35 0.25 20% 0.15

0.20 0.17 0.05 0.06 0.03 0.25 0.28 0.22 20% 0.08

0.15 0.12 0.05 0.04 0.03 0.20 0.22 0.18 20% 0.07

0.10 0.08 0.05 0.04 0.02 0.17 0.17 0.13 20% 0.07

IPC-7351 February 2005

标准分享网 www.bzfxw.com 免费下载