IPC-CM-770D-1996.pdf - 第120页

IPC-CM-770 Januaty 1996 3. Bond Force R I 6. Second Search 9. Ball is Reformed Torch 1. Home Wire of Wire Ball on End n 4. Tip Withdrawn 7. Wedge Bonding Operation o1 ,ce 8. Alt. Tail Pulling !. Search i. Work Moved Towa…

January 1996 IPC-CM-770

Table 23-3 Minimum Bond Strength

Wire Composition rocessing and screening when

AU 0.0007 in

AU 0.0013 in

grams-force

number of bonds (bumps)

Flip-clip

Any

30 grams force in accordance with linear millimeter of Beam Lead

Any

nominal undeformed (before bonding) beam width.3

'For wire diameters not specified, use the curve of figure 2011-1 to determine the bond pull limit.

2For ribbon wire, use the equivalent round wire diameter which gives the same cross-sectional area as the ribbon wire

3For condition

or H, the bond strength shall be determined by dividing the breaking force by the total of the nominal

being tested.

beam widths before bonding.

or tear off. Flame off produces another ball for the next

bond, cut off used cutters, and tear off pulls the wire until

it breaks. See Figure 23-2 for T/C ball bonding and Figure

23-5 for wedge bonding.

23.3.4.2 Ultrasonic

(UIS)

Bonding (Wedge Bonding)

ultrasonic bond is accomplished by pressing and holding

the wire firmly to the metallized pad site. Ultrasonics are

transferred through a wedge tool, creating a scrubbing

action, producing a metallurgical cold weld. The scrubbing

action may remove thin oxide films which form in standard

atmosphere. Use caution with the amount of power sup-

plied to produce the ultrasonics. Using too much power

may damage the chip during bonding. The most common

failure associated with excessive power is cratering. The

majority of U/S bonding applications use aluminum-alloy

wire, although gold, copper, and other metals have been

used. See Figure 23-4. Bonding dissimilar metals at low

temperatures eliminates, or significantly decreases, the for-

mation of intermetallic compounds and allows bonds to be

made in the immediate vicinity of temperature-sensitive

components without adverse effects.

23.3.4.3 Thermosonic (TIS) Bonding (Ball or Wedge

Bonding)

Thermosonic bonding incorporates T/C and U/S

bonding. Using thermal compression in unison with ultra-

sonic to produce a bond, the amount of force, heat, and

ultrasonics are less than for T/C and U/S. The substrate

temperature for T/S is lower than T/C, around 120" to

150°C. Thermosonic bonding can use either ball or wedge

bonding methods with gold wire. See Figure 23-5.

23.4 Assembly

23.4.1 Equipment Assisted Hand Assembly

Systems

are available for limited hands off use. Stations for place-

ment of die on boards under a microscope include a

vacuum tip and a motion reduction system. The system

allows increased precision placement of one of a kind part.

Some systems also integrate adhesive dispensing options

which can easily toggle between dispensing adhesive and

die placement.

23.4.2 Low-Volume Equipment

The low-volume surface

mount assembly equipment shown in Figure 23-6 is a com-

puter controlled pick-and-place machine. The machine can

select surface mount devices from tray carriers, vibratory

feeders and tape input. The system orients and aligns sur-

face mount devices on an automatic centering nest, then

accurately assembles them on the boards at preprogrammed

locations. Such a system can be equipped with provisions

for chip on board (COB). The additional equipment may

include a die attachment epoxy dispensing system, wafer

frame or die tray loader elevators, and pattern recognition

for orienting the die.

The basic system, Figure 23-7, consists of a transfer mod-

ule and a controller. The system controller provides the

interface and control electronics; the transfer module is

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IPC-CM-770

Januaty

1996

Bond

Force

Second Search

Ball is

Reformed

Torch

Home

Wire

Ball on End

Tip Withdrawn

Wedge Bonding

Operation

,ce

Alt. Tail

Pulling

Work Moved Toward

Position

Tip

Withdrawn

Wedge

Diffusion

Bond

Alt. Tail

Pulling

Ball

Retracted

IPC-1-00341

Figure

23-2

Mechanics

Thermocompression

Ball

Wire

Bonding

5-18

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January

1996

IPC-CM-770

0.1

[0.004

inch]

TYP

TYP TYP

,0.025

[0.001

inch]

ball

IPC-1-00340

Figure 23-3 Thermocompression Ball Wire Bonding Parameters

where the assembly actually takes place. Semiconductor now be turned to the proper angular alignment, picked-off

devices can be handled by equipment such as this, with the nest and placed onto the board. The motion is also pro-

chip dimensions ranging from

0.5

7.5

mm.

vacuum grammable to control chip placement pressure.

force is typically used to pick up the chips, thus eliminat-

ing distortions or scratches from mechanical fingers.

vacuum sensing circuit is also often used to detect if a

23.4.3 Fully-Integrated Systems

High-volume fully

device was picked up and transported correctly.

integrated systems are also being developed for multichip

applications.

typical system, Figure

23-8,

processes up to

The more-sophisticated units have a pattern-recognition

inch by

inch boards in

unit magazine-to-magazine

feature that is performed by a camera system that is fed system equipment.

fully-integrated system could be

mounted directly over the centering nest. The orientation is configured to include equipment for adhesive silk screen-

then electronically compared with stored images and the ing, pick-and-place die attachment, wireAead bonding, and

device is turned to the correct orientation. The chip can chip sealing.

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