IPC-CM-770D-1996 - 第124页

IPC-CM-770 Januaty 1996 - The rectangular TAB lead has a lower lead impedance -Dynamic bum-in of TAB packages is more costly in and inductance than a round wire, thus enhancing high- both hardware tooling and bum-in. spe…

Januaw

1996

IPC-CM-770

Pattern

recognition

CRT

System

Elevators

Microprocessor

Controller

Transfer Module

rt)f:%y

Epoxy

Dispense

Disk Drive

IPC-1-00351

Figure 23-7 COB Chip Handling System Block Diagram

IPC-1-00352

Figure 23-8 Fully-integrated COB Assembly System

24.1 Advantages

For mounting semi-protected inte- -1nnerlead bonding pads can be 0.05mm square on

grated circuit (IC) dice to printed boards, TAB has the fol- O.lmm spacing, or even smaller.

lowing advantages:

The bonding areas on the die can be hermetically sealed

LOW (0.75mm profile chip-on-board (COB) assemblies.

-High inputloutput counts

(300

or more leads).

by a bump or cap on the bonding land.

-Weight reduction.

TAB requires less gold than gold wire bonding.

Automated mass bonding of the leads is possible.

-TAB test leads provide a means for pretesting and -TAB chips require only a fraction of the surface area

“bum-in” of the dice prior to their final mounting. required for packaged IC dice.

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IPC-CM-770

Januaty

1996

The rectangular TAB lead has a lower lead impedance -Dynamic bum-in of TAB packages is more costly in

and inductance than a round wire, thus enhancing high- both hardware tooling and bum-in.

speed applications.

Since leads are excised during the placement operations,

ration

much

the

Same

that

for

wire-bonded

wders.

24.3 Types of TAB

The initial stage of TAB wafer prepa-

pinhole-free silicon nitride passivation layer, or in some

Improved heat transfer relative to wire-bonded attach cases silicon dioxide or polyimide, is deposited at low tem-

lead damage due to shipping and handling is minimized.

due to copper beam leaded techniques.

peratures. The passivation is selectively removed leaving a

IPC-I-

Figure 24-1 Typical TAB Process Flow (bumbed wafer)

24.2 Disadvantages

Disadvantages of the TAB process

are as follows:

-It may require specially designed equipment to match

each application, at both the chip and board interfaces.

-Wafers are presently expensive in small quantities.

-There is presently a lack of commercially available

“bumped” tape, wafers, or dice.

TAB bonding and bumping equipment is more sophisti-

cated than printed board assembly equipment.

Chip-on-tape components (TAB carriers) are presently

expensive in small quantities.

-TAB inner and outer-lead bonding locations have not

yet been fully standardized.

good portion of the aluminum land exposed. The die can

now be either wire bonded or undergo additional TAB fab-

rication.

There are basically two methods for fabricating TAB Chip-

On-Tape Components: Bumped Die (Basic) TAB and

Bumped Tape TAB (BTAB).

24.3.1 Bumped Die (Basic) TAB

In the “basic” bumped-

chip TAB approach, (Figure

24-2),

a barrier metal, such as

titanium-tungsten, is deposited over both the exposed alu-

minum and over the passivation on the periphery of the

land. This, plus the addition of 0.025mm high gold bumps,

helps ensure the reliability of TAB connections to the tape

during the interlead bonding (ILB) process.

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January

1996

IPC-CM-770

The bumping process is typically performed at the water

level. Water bumping may be performed by the semi-

conductor manufacturer, independent bumping facilities, or

by electronic companies producing “in-house” TAB Chip-

On-Tape components.

Since TAB technology is relatively new, bumped wafers

from semi-conductor manufacturers are not readily avail-

able. In addition, bare wafers may be difficult to obtain (for

bumping) because of the manufacturer’s concerns over pro-

cess propriety and subsequent bumping technology. As

TAB technology matures, these problems will probably be

resolved.

Bumps on the die are electroplated onto the barrier metal

at each land position. When the bump barrier metal passi-

vation overlaps the passivation, this completely seals the

die and further enhances TAB’S reliability as an assembly

process. Solder bumps, copper bumps and other metals can

also be used, and both copper and gold can be tin plated.

24.3.2 Bumped Tape TAB (BTAB)

The other TAB pro-

cessing approach (Figure 24-3) puts the bump on the tape

rather than on the die. This approach is known as BTAB.

In either case, the bumps are necessary to elevate the

etched tape conductors above the die to prevent shorting of

the leads.

24.3.3 Area TAB

One of the most recent interconnection

technologies is known as “Area TAB”. In this approach,

circuit patterns are fabricated on the tape. This allows the

die designer to put the I/O lands at any position on the die,

as opposed to being on the periphery of the die.

(

003’

wlndow)

(Slllcon)

IPC-I-

Figure 24-2 Interconnection Geometry of Bumped Die

TAB

24.4 Types of Tape

In general, there are three types of

TAB construction; Single-Layer, Two Layer, and Three-

Layer (Figure 24-4).

24.1.4.1 Single-Layer Tape

Single-layer TAB tape has a

conductive foil without any insulating layer. The foil most

used for single-layer material is 2 ounce, 0.07mm, rolled

Capper lead

Gold plate

Bump

S1O2

Passlvatlon

(005”

Window)

Alumlnum

lermlnal pad

(Slllcon)

IPC-I-

Figure 24-3 Interconnection Geometry of Bumped Tape

TAB (BTAB)

copper. The lead pattern is formed by a photoresist-etch

operation. Single-layer TAB is the lowest cost TAB con-

struction, but is not electrically testable because the con-

ductive foil ties all leads together.

24.4.2 Two-Layer Tape

Two-layer TAB tape is com-

posed of a conductive layer and an insulating layer. It is

made either by depositing copper directly onto a base insu-

lating film, or by casting a film directly onto copper foil.

The insulator is usually polyimide.

Sprocket and window patterns in the insulation are formed

by chemical etching; lead and spocket patterns are formed

in the copper using normal print-and-etch methods. The

insulating film is a carrier,

that copper leads can be

electrically isolated from each other in order to allow func-

tional electrical testing of tape-mounted IC dice.

24.4.3 Three-Layer Tape

Three-layer TAB uses adhe-

sives to hold conductive and insulating layers together. To

form sprockets and windows, adhesive-coated insolated

film is precisely punched, then conductive foil is laminated

to the film. Print-and-etch of the copper side yields the

desired lead configurations and test lands. As with two-

layer material, the insulator acts as a carrier and electrically

isolates the leads to allow functional testing.

24.4.4 Special Configurations

Multimetal TAB tapes

can be formed in a similar manner. Also, special configu-

rations can be achieved by combining portions of the pro-

cesses used to make the three basic types of TAB. Multim-

eta1 TAB enhances performance and contributes to the

feasibility of area TAB.

24.5 Outer-Lead Bonding (OLB)

After the die has been

tested and burned-in, if applicable, the outer-lead bonding

operation (OLB) transfers the die, with its leads, to the

next-level package or printed wiring board. It is a multiple-

step process that is usually done sequentially on a single

piece of equipment.

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