IPC-7351-2005_表面贴装焊盘布局设计和标准通用要求.pdf - 第69页

electrical performance and will increase the overall pack- age proﬁle. Also the columns are not as rugged as ball contact and are susceptible to handling damage. 14.2 General Configuration Issues 14.2.1 Device Outlines T…

standard reﬂow system operating within a range of 235 °C

to 260 °C [455 °F to 500 °F] depending on the attachment

alloy being used. Each cycle shall consist of 60 to 90 sec-

onds exposure at the particular temperature selected. See

IPC/JEDEC J-STD-020 for appropriate reﬂow cycles and

proﬁles when using lead free solders.

It is important to consider that Plastic BGAs are moisture

sensitive device/components (MSD). Precaution must be

taken during the printed board assembly process in order to

avoid MSD damages (Delamination, Cracks, etc). Trace-

ability for baking PBGA, might be required mainly when

attached in a double sided/reﬂow printed board assembly.

14.1.2 Fine Pitch BGA Package (FBGA) JEDEC Publica-

tion JEP95, Section 4.5, deﬁnes a Fine-pitch Ball Grid

Array (FBGA) package is a reduced-pitch (<1.00 mm) ver-

sion of a Ball-Grid-Array (BGA) package. The carrier body

of the package has a metallized circuit pattern applied to a

dielectric structure. One or more semiconductor devices are

attached to either the top or the bottom surface of this

dielectric carrier. On the underside of the dielectric carrier

is an array pattern of metallized balls, which form the

mechanical and electrical connection from the package

body to a mating feature such as a printed circuit board.

The surface that contains the die may be encapsulated by

various techniques to protect the semiconductor. The

requirements for a square FBGA package family that

allows four optional contact pitch variations; 0.50, 0.65,

0.75 and 0.80 mm and deﬁnes four device proﬁle (height)

variations as well. The 0.75 mm pitch has been added to

the list thus providing four pitch variations for FBGA type

parts.

The total proﬁle height of the FBGA, as measured from the

seating plane to the top of the component, is greater than

1.70 mm. The Low-Proﬁle Fine-Pitch Ball-Grid-Array

(LFBGA) and is a reduced-height version of an FBGA.

The total proﬁle height of the LFBGA as measured from

the seating plane to the top of the component, is no greater

than 1.20 mm. Thin-Proﬁle Fine-Pitch Ball-Grid-Array

(TFBGA) is a reduced-height version of an FBGA with a

total proﬁle height as measured from the seating plane to

the top of the component that does not exceed 1.00 mm

and the Very-Thin-Proﬁle Fine-Pitch Ball-Grid-Array

(VFBGA) is a reduced-height version of an FBGA with a

total proﬁle height as measured from the seating plane to

the top of the component that is at or below 0.80 mm.

The JEDEC design guide for FBGA allows the manufac-

turer the option to increase ball diameter as the spacing or

pitch between ball contact centers increase as compared in

Table 14-1. As of this release JEDEC standards do not

support the 0.75 mm pitch, however the industry has some

parts available in that pitch.

The larger ball diameter option has been allowed to accom-

modate packages using rigid interposer structures. The

larger diameter ball may compensate to a degree, for the

wide mismatch of the coefficient of thermal expansion

(CTE) between the silicon die and the rigid PCB structure.

Fine pitch ball parts may require special processing outside

the normal pick/place and reﬂow manufacturing operations.

This requirement relates to the amount of solder paste, the

precision of the placement machine and the soldering pro-

cess proﬁle, to permit all parts to become attached at the

same time that the FBGA is reﬂowed.

Ball termination and process considerations for FBGA are

the same as that for BGA as described in 14.1.1.1 and

14.1.1.2.

14.1.3 Ceramic Column Grid Arrays (CGA) Solder col-

umn contacts typical of that illustrated in Figure 14-3 are

used for larger ceramic-based packages (32.0 mm to 45.0

mm). The package resembles the earlier pin-grid-array but

with closer contact pitch and more fragile leads (columns).

The column contact diameter is approximately 0.5 mm

with its length varying from 1.25 mm to 2.0 mm. The col-

umns are attached to the package either by eutectic

(Sn63Pb37) solder or they are cast in place using 90% Pb

and 10% Sn.

The longer columns typically increase solder joint reliabil-

ity by absorbing a great deal of the stresses created by the

CTE mismatch between the ceramic package and the

board. Longer columns, on the other-hand, may reduce

Table 14-1 JEDEC Standard JEP95

Allowable Ball Diameter Variations for FBGA (mm)

Ball Pitch

Ball Diameter

Minimum Nominal Maximum

0.80 0.45 0.50 0.55

0.80 0.35 0.40 0.45

0.80 0.25 0.30 0.35

0.65 0.35 0.40 0.45

0.65 0.25 0.30 0.35

0.50 0.25 0.30 0.35

IPC-7351-14-03

Figure 14-3 Ceramic Column Grid Array (CGA) Package

(Cross-Sectional View)

Solder Columns

(Sn10Pb90)

Underfil

Solder Balls

(Sn5Pb95)

Sealing

Adhesive

IPC-7351 February 2005

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electrical performance and will increase the overall pack-

age proﬁle. Also the columns are not as rugged as ball

contact and are susceptible to handling damage.

14.2 General Configuration Issues

14.2.1 Device Outlines

The Grid Array package outlines

detailed in this document are furnished in JEDEC Publica-

tion JEP95. The overall outline speciﬁcation for the array

device allows a great deal of ﬂexibility as far as lead pitch,

contact matrix pattern and construction. The JEDEC stan-

dards allow for die attachment on either side of the inter-

face structure (cavity up or cavity down). Refer to IPC-

7096 for further deﬁnition and interconnect schemes for

BGAs. The example shown in Figure 14-4 illustrates two

225 I/O devices with a common package outline but, with

the variation of contact pitch, a unique matrix format is

provided.

14.2.2 Contact Matrix Options Contacts may be distrib-

uted in a uniform pattern, however the matrix is always

centered about the centerline of the package (see Figure

14-5). Contact depopulation is permitted at the discretion

of the device manufacturer. Contact patterns can usually be

described in the following methods: full even matrix, full

odd matrix, perimeter matrix, or staggered matrix.

14.2.2.1 Full Matrix For a given package size, there are

two full matrix possibilities: even and odd. One of them is

the largest matrix that theoretically could ﬁt on the pack-

age, given the size and pitch of the contacts. The other

matrix is smaller by one row and column (see Figure 14-5).

14.2.2.2 Perimeter Matrix A perimeter matrix is

achieved by removing an array of contacts from the center

of the matrix. Center-depopulation does not affect the cen-

terline of the matrix (see Figure 14-6). In addition, Perim-

eter matrices are usually described by the number of con-

tact perimeters.

IPC-7351-14-04

Figure 14-4 Bottom View of BGA Devices

IPC-7351-14-05

Figure 14-5 One Package Size, Two Full Matrices

February 2005 IPC-7351

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

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