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WEST BOND GOLD WIRE BONDER

STANDARD OPERATING PROCEDURE

Purpose of this Instrument: This instrument is for wiring (using gold wire) micro or nano circuits to

larger packages for testing.

Location: ESB G73 Cleanroom

Primary Staff Contact: Dr. Kolin Brown Secondary Staff Contact: Dr. Marcela Redigolo (304) 366-6551 (304)293-9973 Office: ESB G75D Office: ESB G75D kolin.brown@mail.wvu.edu marcela.redigolo@mail.wvu.edu NOTE: The West Bond Gold Wire Bonder is convertible and can allow for different bonding techniques:

ball-crescent bonding, wedge-wedge bonding and deep access wedge-wedge bonding. This SOP

assumes that the tool is configured for a basic ball-crescent bonding. Please see an SRF staff member if

an advanced technique is required for your application. A user must master ball-crescent bonding

before learning any other technique.

The Shared Research Facilities are operated for the benefit of all researchers. If you encounter any

problems with this piece of equipment, please contact the staff member listed above immediately. There

is never a penalty for asking questions. If the equipment is not behaving exactly the way it should,

contact a staff member.

START-UP

1. Sign onto the FOM software and into the logbook.

2. Turn on the Wire bonder power switch shown in Figure 1. Do not turn on the hotplate until the sample is mounted.

WARNING: Do not adjust the Ball Size knob! The ball size adjustment is a calculated number based upon the wire gauge and the capillary size. The ball diameter cannot be adjusted without changing one or both. Adjusting the ball size parameter with the current machine configuration can create threading problems and ruin the capillary. Please see a staff member for assistance if the ball needs to be changed for your application.

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Figure 1: Hotplate and wire bonder power switches.

MOUNTING A SAMPLE TO THE HOTPLATE

1. Before mounting a sample on the hotplate, make sure that the chip and package are firmly bonded

together and that all gold contacts are clean. If necessary, use a cleanroom swab wetted with

isopropyl alcohol to clean the surface of the chip. Dirt or contamination on the surface of the gold

contact will interfere with the bonding process.

2. Place the package on the hotplate against the clamp release shown in Figure 2.

3. Loosen the two clamping screws with an Allen wrench.

4. Slide the clamp arm against the package. The front lip of the clamp arm is beveled to assist in

holding the package in place. The clamp arm only needs to touch the package; do not place it on

top of the package or substrate.

5. With the clamp arm in place, tighten the two clamping screws.

6. Once the package is mounted on the hotplate, it can quickly be removed for repositioning by

pressing the white, clamp release button on the front of the hotplate stand, as shown in Figure3.

Pressing the button will cause the clamp release to move away from the package, allowing it to be

removed without readjusting the clamp arm.

Hotplate Power Switch

Wire Bonder Power Switch

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Figure 2: Test sample properly mounted on hotplate.

Figure 3: White, clamp release button on the front of the hotplate (left) and motion of the

clamp release when depressed (right).

Clamp release

Clamp arm

Clamping

screws

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7. Turn on the hotplate switch to allow the hotplate, sample and package to warm up. The default

temperature setting of the hotplate is 115°C. The maximum temperature used should be no more

than 20°C lower than the maximum temperature your sample, package or epoxy can withstand. The

hotplate temperature set point may be increased or decreased by holding down the “” button on

the hotplate controller, while using the up or down arrows to change the set point. The new set

point is saved when the “” button is released.

8. Wait at least 15 minutes for the substrate and package to heat before trying to bond.

NOTE: The sample must be firmly attached to the hotplate to create a wire bond. Free floating or loose

substrates will move during the wire extraction step of the bonding process, which may result in

bonding placement errors, broken bonds or damaged substrates.

NOTE: Heating the substrate simplifies the wire bonding process, therefore it is highly recommended to

use the hotplate. Wire bonding can be performed on cold substrates with great effort.

MAKING A BOND

The bonding process is performed using the wire bonder manipulator arm, shown in Figure 4, while

viewing the chip through the stereo microscope assembly, shown in Figure 5. While it may be beneficial

for the user to zoom in close with the microscope, it is recommended that the user work with the

microscope zoomed out to a wide field of view.

NOTE: When using the wire bonding manipulator arm, use a light finger touch. It is best to keep a

straight, but loose wrist. The motion for the process should be at the elbow.

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Figure 4: The wire bonder manipulator arm.

Figure 5: The stereo microscope assembly.

Manipulator arm

Microscope focus knob

Microscope focus knob

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1. Making the ball bond (bond 1). The machine is set for bond 1 after a torch process. To make the

bond follow the motion of pattern 1, shown in Figure 6, use the manipulator arm to lower the

capillary until it touches the first bonding pad on the sample. The motion should be straight

down. The machine should beep upon contact.

Figure 6: Basic motions for a ball-wedge bond.

2. After contact, follow motion patterns 2, 3 and 4, as shown in Figure 6. Smoothly lift the

manipulator arm one or two millimeters straight up. Then moves the manipulator one or two

millimeters away from the second contact pad (patterns 2 and 3). The process is called “back

bending”, and will keep the wire from lying flat against the substrate when moving to the second

bond site. After back bending, gently lift the manipulator arm straight up until the bonder beeps

(pattern 4). The beep indicates that the bonder has achieved the preset loop height.

3. Following motion patterns 5, 6, and 7, move the manipulator arm horizontally so that is slightly

over -extending the second bonding pad on the package (pattern 5). Gently move the

manipulator straight down. Just before touching the bonding pad, move the manipulator towards

the first bond. This will create a slight arch in the wire (patterns 6 and 7). Once the capillary

touches the bonding pad, the wire bonder will beep upon contact. The wedge bond (bond 2) is

formed upon contact.

4. As shown in Figure 6, the final motion is to lift the manipulator straight up (pattern 8). Once the

capillary reaches the programmed height, the torch will extend and create a new ball.

NOTE: If the torch does not successfully form a ball, it will remain in the extended position and the

ball fault alarm will sound. A ball fault can be caused by several errors: (1) the wire tail extended by

the machine to form the ball is too short, and therefore an arc did not occur between the torch and

gold wire and a ball was not generated; (2) the wire tail extended by the machine is too long, and

Ball bond (bond1) Wedge bond (bond 2)

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2 3

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6 8

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4

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therefore made contact with the torch and shorted it out; (3) the wire has been broken; (4) the wire is

no longer between the wire clamp pincers, which are directly above the capillary; or (5) the capillary

tip is contaminated. A ball fault may also occur when the ball is still on the wire because it did not

bond to the substrate.

Toggling the US/ESC key up will reset the alarm and release the torch mechanism.

Please see a Shared Research Facilities staff member for assistance if the machine goes into a ball fault

mode for assistance in troubleshooting the error and you do not know how to correct the problem.

NOTE: Operating the wire bonder requires smooth, gentle motions. Any sharp or sudden motions

may break the gold wire. The capillary may need to be rethreaded or replaced if the gold wire is

broken during the process.

NOTE: If bond 1 or 2 repeatedly break at any time in the process, then the program parameter

settings may not be correct for your sample or package. Please see a Shared Research Facilities staff

member for assistance in adjusting the program parameters if you are consistently breaking the wire.

PROGRAM PARAMETERS

The following list is a brief description of the wire bonder program parameters. When programming the

machine, a recommended factory parameter is displayed next to the set point. It is okay for the set

point not to match the factory parameter, because the parameters are set based upon the sample. It is

recommended that the user only adjust one parameter at a time. Adjusting multiple parameters

simultaneously will keep the user from determining the critical parameters for their specific bonding

process.

The following guidelines may help when adjusting parameters:

Hard substrate materials, like semiconductors, usually require a low ultrasonic power for a

longer period of time.

Soft substrate materials, like polymers, usually require a high ultrasonic power for a brief period

of time.

III-V materials usually require low force to prevent cavitation or damage to the crystal structure

under the bonding pad.

NOTE: Because the wire bonder is convertible and can perform multiple types of bond configurations,

the parameters are described in terms of bond 1 and 2. For a ball-crescent bond, the ball is bond 1 and

the wedge is bond 2.

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Bonds per wire- Should always be two for ball-crescent bonding setup. This parameter tells the machine

how many bonds are made for one application.

Lift before torch, mils-Should always be set at the factory default for traditional bonds. This parameter

sets the minimum distance in mils between the capillary tip and the substrate required for torching.

NOTE: Setting this parameter too small may result in damage to the substrate, because the torch

may strike the surface of the substrate.

Ultrasonic power, bond 1 of 2- This parameter sets the ultrasonic power intensity applied to bond 1.

Ultrasonic power, bond 2 of 2- This parameter sets the ultrasonic power intensity applied to bond 2.

Ultrasonic time, bond 1 of 2- This parameter sets the time the ultrasonic power is applied to bond 1.

Ultrasonic time, bond 2 of 2- This parameter sets the time the ultrasonic power is applied to bond 2.

Force, bond 1 of 2- This parameter determines which of the two force settings will be applied to bond 1:

high or low.

Force, bond 2 of 2- This parameter determines which of the two force settings will be applied to bond 2:

high or low.

Loop height, mils, before bond 2 of 2- This parameter determines the length in mils of the bond wire.

Wire tail- This parameter determines how much wire (in motor steps) is extended from the capillary

during the torch process.

Machine setup: Dual force- This parameter determines if there should be high and low force settings.

Usually the first and second bonds require separate forces.

Calibration high force- This parameter allows the user to measure the high force applied during bonding.

To measure the high force:

1. The force is measured using a dynamometer, shown in Figure 7. There are two needles on

the dynamometer: the red needle measures the force applied and the black needle, which

remains stationary unless pushed by the red needle, measures the maximum force applied,

in grams. The silver knob in the center of the dial controls the position of the black needle.

Before measuring the force, make sure that the black needle is positioned at zero on the

right of the red needle (or left, if left handed).

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Figure 7: The dynamometer.

2. Manually hold down the manipulator arm with your left hand (or right hand, if left

handed).

3. With the dynamometer gripped in your right hand (or left hand, if left handed), place the

dynamometer tip directly under the capillary holder, as shown in Figure 8 and Figure 9.

Figure 8: Hold the dynamometer with your free hand to measure the force.

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Figure 9: The dynamometer tip placed directly under the capillary holder.

4. Gently lift the wire bonder head assembly with the dynamometer until the wire bonder

beeps.

5. Remove the dynamometer and read the measured force.

6. For a more accurate reading, this process should be repeated four times.

Calibration low force- This parameter allows the user to measure the low force applied during

bonding. The same procedures are followed to calibrate the low force as the high force.

Machine setup: Ball fault- Should always be left ON. This parameter will notify the user if the torch

cannot form a ball.

Machine setup: Beep upon contact- Should always be left ON. This parameter indicates that the

machine should beep when the bond makes contact with the pad. New users must leave this

parameter on.

Machine setup: U/S power during feed- Should be “Yes”. This parameter allows the use of

ultrasonic waves on the capillary to assist with threading.

NOTE: Three wire bonding parameters are adjusted manually: high force, the difference between high

force and low force and the stage height. Please see a Shared Facility staff member if any of these three

parameters need adjusting. Improper setting of any of these three parameters may result in damage to

the sample, the capillary, or the wire bonder head assembly.

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CHANGING THE CAPILLARY

Over time, the capillary may become contaminated with gold, or a piece of gold wire may become stuck

in the capillary. This requires changing the capillary and rethreading the lower portion of the machine.

The following are guidelines on how to change the capillary and thread the machine. Please contact a

Shared Research Facilities staff member if you need assistance.

WARNING: Do not attempt to replace the gold wire spool and rethread the entire machine. Please see

an SRF staff member for assistance. Incorrect installation of the gold wire spool can result in

entanglement of the wire bonder head with gold wire.

1. Before removing the capillary, take note of its position in the capillary holder, seen in Figure 10.

The capillary should barely extend above the holder. To remove the capillary, loosen the capillary

mounting screw located in the capillary holder.

2. With a pair of tweezers gently remove the capillary and place it in the capillary container that is

marked “used.” This container is located to the right of the wire bonder.

WARNING: If the machine has been running for any period of time and the tool heat is on, the heating

coil that surrounds the capillary will be hot. Users who touch the coil may be severely burned.

3. Replace the capillary with a new one, ensuring that the capillary does not extend too far above the

holder. The intent is to insert the capillary at the exact same position as the previous capillary.

Make sure that the capillary is not taken from the used capillary container.

4. Tighten the mounting screw to secure the capillary in place.

5. Before attempting to rethread the capillary check that the wire clamp is open. There will be a

gentle hissing sound when the clamp is open. The clamp may be opened by toggling the THREAD

key on the wire bonder or by raising the manipulator arm until the clamp opens.

WARNING: Attempting to manipulate the wire while the clamp is closed may result in breaking the wire

at the clamp. If this occurs, please see a SRF staff member for assistance.

6. To rethread the machine, gently grab the end of the gold wire with a pair of sharp tweezers and

gently pull out a half inch of wire.

NOTE: Grabbing the wire too tightly with the tweezers may cut the gold wire.

7. Gently reposition the tweezers so that a length of gold wire equivalent to the length of the capillary

is extending beyond the tweezers.

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Figure 10: The wire bonder head assembly.

Wire Clamp

Capillary

Capillary

Mounting Screw

Gold Wire

Heating Coil

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8. Carefully insert the gold wire into the top of the capillary and gently coax the wire into the full

length of the capillary. If the wire becomes bent or damaged during this process, it must be

removed and that length of wire must be discarded. The user must retry to thread the capillary

with undamaged wire. Any bend or damage point will become a weak point in the wire and the

wire will crimp during insertion.

9. Once the thread is inserted into the capillary, gently grab the small length of wire extending out of

the capillary point and delicately pull on the wire an additional centimeter. Use extreme caution or

the wire will break inside the capillary. If the wire is broken inside the capillary, remove the wire by

pulling it out of the top of the capillary and rethread.

10. Before proceeding, ensure that the wire clamp is open and position the wire so that it is between

the two clamp pincers.

11. Do not pull down on the wire to eliminate any slack or wire crimping may occur. If there is excess

wire between the wire clamp and the capillary, gently roll the gold wire spool backwards to take up

any slack. Ensure that the wire does not entangle on any protrusions while winding the spool

backwards.

12. Using the test chip or any scrap chips, bond off the excess gold wire extending from the capillary.

When the bonder is lifted, the torch should attempt to form a ball.

13. If the torch does not successfully form a ball it will remain in the extended position and the ball

fault alarm will sound. A ball fault can be caused by one of two errors: (1) the wire tail extended by

the machine to form the ball is too short, and therefore an arc did not occur between the torch and

gold wire and a ball was not generated; or (2) the wire tail extended by the machine is too long,

and therefore made contact with the torch and shorted it out.

Inspect the torch to see if the gold wire is touching it or not. If the gold wire is touching the torch

then the user must enter the program menu and reduce the wire tail parameter. If the gold wire is

not touching the torch then the user must enter the program menu and increase the wire tail

parameter. Please see a Shared Research Facility staff member if you need assistance. Toggle the

US/ESC key up to reset the alarm and release the torch mechanism.

14. The capillary has been properly replaced and rethreaded if a ball is formed when the machine

attempts to create one using the torch.

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SHUTDOWN

1. Turn off the wire bonder and hotplate.

2. Check that all required parameters are recorded in the log book.

3. Clean up the work area.

4. Sign out of the FOM.

EMERGENCY PROCEDURES

If no one is available and the gold wire bonder is not acting as expected, the user should do the

following:

Turn OFF the hot plate.

Turn OFF the wire bonder. Do not leave the machine running in an abnormal state. If the machine cannot be placed in standby mode, immediately contact: Primary Contact: Dr. Kolin Brown Secondary Contact: Dr. Marcela Redigolo (304) 366-6551 (304)293-9973 Office: ESB G75D Office: ESB G75D kolin.brown@mail.wvu.edu marcela.redigolo@mail.wvu.edu Then, if possible, the user should stay by the tool while trying to contact a Shared Facilities staff member. If it becomes necessary to leave the instrument then the user should leave a large, legible note on the WIRE BONDER stating the tool is DOWN. The user should also add a comment as to tool status when logging out of the FOM software.

If a dangerous situation is evident (smoke, fire, sparks, etc.), the user should turn off the hot plate and

tool, ONLY if it is safe to do so. The user should notify all other clean room persons within the

cleanroom to evacuate and leave the clean room immediately. The user should then contact proper

emergency personnel from a safe place. The contact numbers can be found posted outside the clean

room.