IPC-CM-770D-1996 - 第119页

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 F 5 grams-force x number of bonds (bumps) Flip-clip Any G or H 30 grams force in accordance…

IPC-CM-770 Januaty 1996

1980

1985

'NON-IBM YEAR

OTHER

GOLD

BALL

BONDING

73%

BAL

3'1"

ALUMINUM

WEbGE

BONDING

22%

IPC-1-00338

Figure 23-1 Chip Termination Techniques

Table 23-1 Bonding Wire for COB Applications

Wire Diameter Substrate

(inch)

Comments

Temperature("C)

Attachment Method

Thermocompression (hot substrate)

>300

Limited repair ability

0.0007-0.001

(Gold)

0.0007-0.002

Thermosonic ball or wedge 125°C Quality of bonds improved if the

substrate is raised to 125°C. Can bond

chips without raising substrate

temperature.

(Aluminum)

Ultrasonic Wedge

0.0007-0.010

25 Low-temperature process, restricted due

to tool size

Table 23-2 Aluminum and Gold Wire Sizes and Ratings

Wire

Minimum

Standard Wires

Aluminum

Si Aluminum

Si Diameter

Resistance(Rm.)

(inch)

Gold

(Annealed) (Hard)

Gold Aluminum

0.0007

I I

36.06-39.86

34.62-38.273

27.71-29.43

0.001

17.67-19.53

16.0-18.75

13.58-14.42

0.002

I I

4.41-4.88

4.23-4.68

3.40-3.61

23.3.4 Wire Bonding Techniques

300"

400"

C. The majority of T/C bonding uses a ball

bond on the first bond site and a wedge bond on the sec-

23.3.4.1 Thermocompression (T/C) Bonding (Ball Bond-

ond bond site.

ing)

Thermocompression bonding utilizes heat and pres- When bonding an open flame (or spark discharge) melts

sure to bond wire to a metallized pad site.

typical system the end of the wire, molten metal wicks up the end of the

uses a capillary tool of refractory material, such as alumina wire forming the ball. Wire termination after the second

or tungsten carbide, gold wire, and a surface temperature of bond is achieved by flame

off

or as in wedge bonding cut

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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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