IPC-7351-2005_表面贴装焊盘布局设计和标准通用要求.pdf - 第68页

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 se…

14 IPC-7358 AREA ARRAY COMPONENTS (BGA, FBGA,

CGA)

The area array device family includes square and rectangu-

lar package conﬁgurations and is furnished in a variety of

base materials. This device family includes Ball Grid Array

(BGA) parts (rigid, ﬂexible or ceramic substrate); Fine

Pitch Ball Grid Array (FBGA) parts (rigid or ﬂexible sub-

strate); and Column Grid Array (CGA) parts (ceramic sub-

strates).

The area array device families are generally marked with

the manufacturer’s name or symbol, part number, date code

and orientation mark in the corner near contact location A1.

Area array devices may be furnished in matrix tray or tape

and reel packaging formats. Tape and reel packaging is

generally preferred for high volume assembly. Plastic trays

and reels must be transported and stored in moisture proof

containers. When plastic array devices are exposed to the

environment for an extended period of time, moisture may

absorb into the device. The absorbed moisture, if excessive,

may expand (when exposed to higher temperatures typical

of reﬂow solder process), causing cracking and other

physical damage.

Area array devices are typically attached to the host inter-

face structure using eutectic solder alloy, however, optional

methods of attachment may include electrically conductive

epoxy or polymer. There is also a process difference

between the solder application for those terminations that

collapse slightly during soldering and those terminations

that do not collapse where a signiﬁcant amount of addi-

tional solder paste is required. Array package assembly

should not require specialized equipment or processes

beyond that used for vision assisted SMT pick and place.

In conjunction with the proper land size, the volume of

solder paste application is a fundamental parameter to keep

under control in order to have a good reﬂow quality yield

and a reliable solder joint. Paste volume deposition may be

a matter of SPC adoption at print process step.

14.1 Area Array Configurations For additional detail on

package variations, mechanical feature dimensions and

allowable physical tolerances beyond the following sec-

tional descriptions, refer to the JEDEC Publication JEP95

and IPC-7095.

14.1.1 BGA Packages Figure 14-1 shows the elements

of a BGA. JEDEC Publication JEP95, Section 4.14, deﬁnes

a Ball Grid Array Package family. A Ball Grid Package

(BGA) is a square or rectangular 1.50 mm, 1.27 mm, &

1.00 mm pitch package with an array of metallic balls or

columns on the underside of the package. The main body

of the package has a metallized circuit pattern applied to a

dielectric structure. To this package body, the semiconduc-

tor die(s) is attached to either the top or bottom surface. On

the underside of the dielectric is an array pattern of metal-

lized balls/columns which form the mechanical and electri-

cal connection from the package body to a mating feature

such as a printed circuit board. The array contact material

will allow conventional reﬂow solder or other attachment

processes. The surface that contains the die may be encap-

sulated by various techniques to protect the semiconductor.

Figure 14-2 compares the top surface attached die to the

cavity down conﬁguration.

14.1.1.1 Termination Materials The BGA ball termina-

tion may consist of a variety of metal alloys. Some of these

include balls with some lead content such as 37Pb63Sn,

90Pb10Sn, 95Pb5Sn, while others do not contain lead such

as Sn96.5Ag3.0Cu0.5, Sn96.5Ag3.5, Sn-9Zn-0.003Al. It is

a good recommendation to use the same alloy, in a paste

form, to attach the BGA balls to the mounting substrate;

however some of the balls that do not collapse require a

paste that is more conducive to reﬂow temperatures.

For lead free ﬁnishes a combination of tin, silver and cop-

per is the prevalent replacement for the tin/lead ﬁnish. Sol-

derability testing should be applied per IPC-J-STD-002 to

determine attachment capability of the applicable compo-

nent type.

14.1.1.2 Process Considerations BGAs are usually

processed using standard reﬂow solder processes. Parts

should be capable of withstanding three cycles through a

IPC-7351-14-01

Figure 14-1 Ball Grid Array (BGA) IC Package Example

IPC-7351-14-02

Figure 14-2 Example of Plastic BGA Package

Conﬁgurations

February 2005 IPC-7351

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