IPC-CM-770D-1996.pdf - 第123页

Januaw 1996 IPC-CM-770 Pattern recognition CRT System Elevators Microprocessor - Controller - Transfer Module - 1 rt)f:%y I 1 Epoxy Dispense 1 I Disk Drive 1 IPC-1-00351 Figure 23-7 COB Chip Handling System Block Diagram…

IPC-CM-770

Januaty

1996

Figure 23-4 Mechanics

Ultrasonic Wire Bonding

IPC-1-00339

Figure 23-5 Thermosonic Wedge Wire Bonding

Such a system would operate in the following manner.

First, bare boards loaded in 50-unit magazines are pre-

sented to the input feed magazine of the silkscreener,

where adhesive is deposited. Then the boards with adhesive

are automatically transferred to the pick-and-place

machine, where the chips are placed on the board over the

adhesive. The populated boards are then put back in the

magazine for further processing.

The magazines are removed from the output of the chip

attachment unit manually and put into an oven to cure the

adhesive. The boards, after curing in the magazines, are put

into the wirelead bonder's magazine feed. The chips are

then bonded to the boards and automatically put back into

IPC-I-

Figure 23-6 Typical Low-volume COB Chip Handling

System

the magazines. These magazines are manually placed into

another wire/lead bonder for inspection and repair.

The inspected magazines are then taken to the chip-sealing

unit. The boards are environmentally sealed and returned

automatically to the magazines. These sealed units are then

taken to another oven for curing of the sealing compound.

more sophistication is desired, a control console can be

added to oversee the operation of the system that consists

of a closed-circuit television monitor, a keyboard and a

tracking assembly which allows an operator to remotely

intervene in the operation of the equipment.

24.0 TAPE AUTOMATED BONDING (TAB)

One promising type of Fine Pitch Technology is Tape

Automated Bonding (TAB). TAB uses photo-imaging/

etching processes to produce conductors on a dielectric/

conductor tape "movie film" format. (See Figure

24-1).

The most visible aspect of the TAB system is the carrier

tape, which is

mm wide and stored on reels. Win-

dows are formed at specific locations in the tape and a thin

conductive layer is applied to the tape; usually 0.035mm

thick copper. A conductive pattern is then created in the

conductive layer to give the desired interconnection cir-

cuitry with "beam type" leads that extend over the win-

dows in the tape. In subsequent processing, the beams are

bonded to an integrated circuit die that is precisely located

under the windows. Sprocket holes or features on the tape

carrier permits automated tape-handling equipment to

accurately position the individual dice for the subsequent

processing operations, such as testing, bum-in, and board

mounting. Fiducials/registration marks on the tape may be

used for alignment with vision systems during bonding/

handling.

-20

Licensed by Information Handling Services

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.

5-21

Licensed by Information Handling Services

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.

-22

Licensed by Information Handling Services