K&S 4524 Wire Bonder (w/ Leica Stereo Zoom 4)

Prepared by:

Matt Beck, Update: Ying Qi

Location:

Dow 2219

Hazards:

The following materials and equipment associated with this procedure present exposure or physical health hazards. Safety precautions are prudent and mandatory.

Wire bonder stage heats up to 150 degrees C. Careless use of wire bonder may lead to serious burns.



Controls:

Prior to performing this procedure, the following safety equipment must be accessible and ready for use: (e.g. chemical fume hood, biological safety cabinet, laminar flow hood, chemical spill kits)

None.



Protective Equipment:

Prior to performing this procedure, the following personal protective equipment must be obtained and ready for use: (e.g. acid resistant gloves, safety eyewear, lab coat, chemical splash apron)

None, though you should wear gloves to prevent contamination of system.



Waste Disposal:

This procedure will result in the follow regulated waste which must be disposed of in compliance with environmental regulations.

None.



Spill:

In the event that a hazardous material spills during this procedure, be prepared to execute the emergency procedure below.

Not Applicable


Instructions:


You MUST be trained to use the wire bonder before you can use it! Do not assume these instructions are enough for you to use this instrument successfully.

  1. A few notes before starting
    1. Read the instructions for the entire step before attempting anything.
    2. Never take the sample stage above 150 degrees C.
    3. Always be aware of the temperature of the sample stage.
    4. Never operate the Wire Bonder with the Search height for either bond below 0.50.
    5. Always wear gloves when handling the wire or any part of the wire bonder.
    6. Use only clean tweezers.
    7. Keep all body parts clear of the NEFO foot when the NEFO switch is in the ON position.
    8. When not in use, turn the vacuum pump off.
    9. Make sure to look over all settings before operating the Wire Bonder.
  2. Turning the bonder and checking alignment of wire, sample holder, and sample stage
    1. Set the following switches: NEFO to OFF Motor to OFF Clamp to "Mode" to SemiAuto.
    2. Power up the Wire Bonder. Both the 1st and 2nd light should come on, the U/S light should flash. When ready only the 1st light will be lit.
    3. Optional: Turn on SAMPLE STAGE light using the switch on the left panel.
    4. Check wire spool and assembly. Remember to replace the Spool cover. Carefully follow wire from the spool through the TENSIONER, over the KICKER, through the white DRAG CLAMP, through the wire GUIDE, through the WIRE CLAMP, and into the CAPILLARY.
    5. If the wire is not threaded through any of the above, if the wire appears caught, or if there is a lot of slack in the wire at any point, see Procedures for Threading the Wire Bonder below, beginning with the appropriate step.
    6. Using the stereoscope, check to see if the wire is protruding from the end of the CAPILLARY. (This is easiest to do with the
      stereoscope magnification on its lowest level.)
      1. If the wire IS protruding from the tip of the CAPILLARY, make sure that the wire has a ball on the end of it. If there is no ball, see Procedure For Threading the Wire Bonder below, starting with Step #12.
      2. If the wire is not protruding from the tip of the CAPILLARY, see the Symptoms/Solutions Table below.
    7. If everything above checks out, set the following switches: NEFO to ON Motor to ON
    8. Position your sample on the sample holder covering the small hole at the center. Move the mouse to the center of the black circular area. Position the SAMPLE HOLDER on the sample holder PLATFORM such that the work area of the sample is approximately beneath the CAPILLARY.
    9. Grasp the bottom and middle of the sample holder. Rotate the bottom and lower the sample stage to its lowest position.
    10. Set the Loop knob on the left hand panel to 1 (one). Press the left mouse button once. If nothing happens, see the
      Symptoms/Solutions Table below. The CAPILLARY should now be at its lowest position. Using the procedure in step #8, raise the sample stage such that the tip of the CAPILLARY is within ~ 1 mm of the sample.
    11. Press the left mouse button once. The CAPILLARY should now have returned to its RESET position. Repeat Step #6 to make sure the wire still has a good ball on it.
  3. Setting Operational Parameters for the Wire Bonder for Semi-Automatic Mode
    1. Consulting the Table of Recommended Parameters below, set all bonding parameters. Make sure that the SEARCH height is set to no less then 0.5 on both knobs.
    2. Optional: Turn on the power to the vacuum pump.
    3. The Wire Bonder is now ready for Semi-Automatic operation.
      1. Recommended Parameters for 25 micron gold
      1. NEFO Ball Size: 2.75 Tail length: 6.5 Loop height: 4.00+
      2. Ball bond power: 1.50 Ball bond time: 5.00 Ball bond force: 2.50
      3. Wedge bond power: 2.50 Wedge bond time: 6.00 Wedge bond force: 4.00
  4. Semi-Automatic Operation of the Wire Bonder
    1. Set up the Wire Bonder using the Procedure for Set-up of the Wire Bonder (part B).
    2. Using the multi-mouse and the stereoscope, position the CAPILLARY over the general location of the ball bond (first bond.)
    3. Press and hold the left mouse button. The CAPILLARY will lower to its preset (first) SEARCH height. Using the mouse, position the CAPILLARY over the precise location desired for the ball bond (first bond). Feel free to adjust the (first) SEARCH height to any desired value. CAUTION: Be careful to keep the CAPILLARY tip high enough above the sample as not to get caught on previous bonds, or other surface features.
    4. Release the left mouse button. The CAPILLARY tip will place the ball bond (first bond) and retract to the preset LOOP height. Nudge the mouse to slightly offset the CAPILLARY from the ball bond position.
    5. Optional: depress the suction lever located at the middle level of the sample holder. (This will hold your sample in position as you position the CAPILLARY for the wedge bond.)
    6. Press and hold the left mouse button. The CAPILLARY will lower to its preset (second) SEARCH height. Again, using the mouse, position the CAPILLARY over the precise location desired for the wedge bond (second bond.) Feel free to adjust the (second) SEARCH height to any desired value, observing the above CAUTION.
    7. Release the left mouse button. The CAPILLARY will again lower, this time placing the wedge bond (second bond). The CAPILLARY will then rise to its RESET height, the preset TAIL will be spooled, and the NEFO will fire, creating the ball for the next bond.
    8. Optional: Release the suction lever.
    9. Repeat this procedure, beginning with Step #2, as desired.
    10. Note: At any time, to break out of this procedure and return to the default (RESET) conditions, simply press the RESET switch.
  5. Procedure for the Threading the Wire Bonder
      1. Note: Wear gloves at all times when handling the wire or wire bonder assembly!
    1. Set the following switches: NEFO to OFF Motor to OFF Clamp to "Mode" to Man Z
    2. Power up the Wire Bonder. Wait until only the 1st light is on, this indicating that the bonder is ready.
    3. Check the wire spool and assembly. If the spool needs to be replaced, or if the wire is not fed through the funnel and into the TENSIONER, please seek assistance.
    4. When completed, the wire will run through the TENSIONER, over the KICKER, through the white DRAG CLAMP, through the wire GUIDE, through the WIRE CLAMP, and into the CAPILLARY. Identify at which stage the wire is not properly threaded.
    5. If the wire is not threaded at all, then use clean tweezers to remove the glass slide from the TENSIONER. You may use your gloved finger to lift the pressure lever if necessary. With the tweezers, lightly grasp the wire and pull it through the two guideposts at the end of the TENSIONER. Holding the wire slightly taut with the tweezers, replace the glass slide rounded side down in its place over the wire.
    6. If the wire is not threaded through the KICKER, then use clean tweezers to lightly grasp the wire and thread it through the guide ring at the end of the kicker.
    7. If the wire is not threaded through the DRAG CLAMP, then set the Clamp switch to the Up position. Using clean tweezers, lightly grasp the wire. Carefully thread the wire first through the upper guide ring, then between the two hands of the DRAG CLAMP, and finally through the lower guide ring. If need be, you may lightly grasp the wire with your gloved hand. Be careful not to bend the wire. Once through the guide rings and the DRAG CLAMP, set the Clamp switch to the Down position.
    8. If the wire is not threaded through the WIRE GUIDE, gently grasp the end of the wire with clean tweezers. Do not pull on the wire.  While holding the end of the wire, set the Clamp switch to the Up position. Carefully adjust the wire so that when fully extended it passes through the DRAG CLAMP assembly, and terminates just above the WIRE GUIDE. Gently feed the wire through the WIRE GUIDE. While gently holding the wire, set the Clamp switch to the Down position.
    9. If the wire is not threaded through the WIRE CLAMP, gently grasp the end of the wire with clean tweezers, being careful not to displace the wire from the WIRE GUIDE. Do not pull on the wire. While holding the end of the wire, set the Clamp switch to the Up position. Carefully pull the wire downward and in front of the WIRE CLAMP until enough wire is exposed such that when fully extended it will protrude ~ 3mm from the bottom of the WIRE CLAMP. Holding the wire slightly taut, place it between the teeth of the WIRE CLAMP. (Note: The wire clamp may not look open, thread the wire through the clamp as you would dental floss between your teeth.) While holding the end of the wire, set the Clamp switch to the Down position.
    10. If the wire is not threaded through the CAPILLARY, gently grasp the end of the wire with clean tweezers, being careful not to displace the wire from the two clamps above the CAPILLARY. Do not pull on the wire. While holding the end of the wire, set the Clamp switch to the Up position. Gently release the wire. Grasp the wire again, this time ABOVE the DRAG CLAMP. Carefully pull the wire upwards until the end of the wire is just above the top of the CAPILLARY. Be careful not to pull the wire up too far, and unthread the WIRE CLAMP or the DRAG CLAMP. Release the wire, and again grasp it gently at its end. Using the stereoscope set to its lowest magnification, gently begin to thread the wire into the top of the CAPILLARY. Be careful. If at any time you bend the wire, it will not longer fit through the CAPILLARY tube, and you will have to begin this step again. Gently thread the wire through the CAPILLARY small bits at a time. The smaller the steps, the easier it is not to bend the wire. Make use of the stereoscope. If till help you to know where to grab the wire, and whether or not you are actually feeding wire through the CAPILLARY or if it is just bending and stuffing into the mouth. Every now and then check to see if the wire is protruding from the end of the CAPILLARY with your naked eye. Once the wire is threaded all the way through the CAPILLARY set the Clamp switch to the Down position.
    11. After any change in the threading, check to see if there is a ball on the end of the wire. If not...
    12. No ball on the wire? Gently grasp the wire with clean tweezers. Do not pull on the wire. Set the Clamp switch to the Up position.  Release the wire, and gently grasp it again, this time above the Drag Clamp. Carefully pull the wire upwards until the end of the wire is at the same height as the NEFO FOOT. Be careful not to unthread the wire from the CAPILLARY, the WIRE CLAMP, or the DRAG CLAMP. Once the wire is at a specified height, set the Clamp switch to the Down position. Set the NEFO switch to the ON position and the "Mode" switch to Man Z. Depress the manual spark switch until you hear/see a spark jump from the NEFO FOOT to the end of the wire. Again, check for a "good" ball on the end of the wire. Repeat this step if necessary.
    13. If the other Set-up task are completed, the Wire Bonder should be ready for Semi-Automatic operation.
  6. Troubleshooting the Wire Bonder
    1. How to I unblock the CAPILLARY mouth?
      1. Gently grasp the wire with clean tweezers just above the CAPILLARY. Do not pull on the wire. Open the clamps by switching the clamp switch to the position. Now, gently and steadily pull upwards on the wire, until the wire breaks free of whatever is blocking the CAPILLARY. Fully remove the wire from the CAPILLARY. Next, begin the bonding cycle by pressing the left mouse button once while over a "dead" area of your sample (or a test plate.) The blockage in the CAPILLARY mouth should now be stuck to the sample. If so, RESET the wire bonder, and rethread the CAPILLARY. If nothing appears to have been stuck to the sample, complete the bonding cycle by pressing the left mouse button once. Attempt to rethread the CAPILLARY. If either rethreading operation fails, the CAPILLARY may need to be replaced. Please do not attempt this without first seeking assistance.
    2. How do I fix an open or closed NEFO circuit?
      1. First, check that the end of the wire is at the same height as the tip of the NEFO foot. (See "How do I manually adjust the tail length" below, as necessary.) If it is already at the proper height, using the tip of clean tweezers, gently bend the wire so that it points towards (for an open circuit) or away from (for a closed circuit) the NEFO foot. CAUTION: If the wire is bent too sharply, the bonding cycle will not proceed successfully. Use the Manual Spark switch to test the NEFO circuit. If this solution does not work, rethread the capillary. If rethreading does not correct the problem, there may be internal circuitry problems. Please seek assistance.
    3. How do I manually adjust the tail length?
      1. The key here is to gently feed more wire into the capillary without unthreading the capillary. This is the most common adjustment that you will have to make. Set the Clamp switch to the position (open). Gently thread ~2-4 mm of wire into the CAPILLARY. If necessary, use techniques described in "How can I help the wire to move smoothly through the CAPILLARY?", found below. Every few moments check to see how much wire is sticking out of the CAPILLARY. Remember, ideally, the end of the wire should be at the same height as the NEFO foot. Once the wire has been readjusted, set the Clamp switch to the (closed) position, and check to see if the wire has a good ball on it. If not, use the Manual Switch to create a new ball.
    4. How can I help the wire to move smoothly through the CAPILLARY?
      1. If you are having difficulty feeding the wire through the CAPILLARY, first check to see that the wire is not bent or kinked at any point. If so see "How do I straighten the bent wire?" below. If the wire is straight, and you are still having difficulty, try depressing the Test switch as you gently push the wire into the CAPILLARY. Remember, it is much easier to thread the CAPILLARY while using the stereoscope. If the wire seems blocked at some point see "How do I unblock the CAPILLARY mouth?".
    5. How do I straighten a bent wire?
      1. Remove the wire completely from the capillary. Set the Clamp switch to the (closed) position. Gently grasp the wire with clean tweezers, and lightly pull it taut between the tweezers and the WIRE CLAMP. Try to have the wire aligned as vertically as possible to avoid bending the wire at the WIRE CLAMP. If the wire is kinked or extremely bent, set the Clamp switch to the (open) position and gently pull down enough wire so that there is a length of unbent wire above the bent section. Using clean tweezers, gently grasp the wire just above the bent/kinked region. Using gloved fingers or another set of clean tweezers, pull off the bent section of the wire. Set the Clamp switch to the (closed) position.
    6. How do/why should I change wire thicknesses?
      1. If you have to ask, please don't attempt to change the wire. Simply seek assistance.
    7. What is a "good" ball?
      1. A "good" ball hangs from a tail ~ 2-4 mm long. It has a diameter at least 3 times the diameter of the wire that you are using. More specifically, a good ball is any that results in a good ball bond. See "How do I improve the quality of my ball bonds?" below.
    8. How do I improve the quality of my ball bonds?
      1. At current writing, few criteria for "great" ball bonds are known to the author. Some general goals can be staged, though. First, the ball bond needs to stick to the sample and be able to take some stress. Specifically, that stress due to pulling wire as the CAPILLARY tip moves to the wedge bond site. Second, the bond needs to result in an ohmic electrical contact. The following list details the effects of the various bonding parameters of the 4524 on ball bonds.
        TIME: Length of time for which the FORCE is applied. Variation of this parameter does not apparently change the bond. Stick with the recommended value found on the Recommended Parameters table. FORCE: Pressure exerted by the CAPILLARY tip at the sample.
      2. Variation of this parameter does not apparently change the ball bonds. Again, stick with recommended value. POWER: Power supplied to vibrate the CAPILLARY while the bond is being made. Higher power forces more of the ball into the CAPILLARY mouth, forming a smaller, weaker interface with the sample. Keep POWER low, but no lower then the minimum recommended value. BALL SIZE: The larger the ball, the more ball foot is present in the ball bonds. It is unknown whether the presence of a large foot improves electrical properties. Bond strength is not noticeably improved. Repeatability falls off rapidly as ball size increases. Remember to keep ball diameter at least 3 times the wire diameter. For best results, stick with recommended value.
      3. Improving ball bonds is a balancing act with regards to the above. Increasing the sample temperature to ~100-120C seems to give the best ball bonds.
    9. How do I improve the quality of my wedge bonds?
      1. As with ball bonds, at current writing, the author has little information on "great" wedge bonds. Clearly, they must stick to the sample surface and provide an ohmic electrical contact. Beyond these two goals, little can presently be stated. The following list details the effects of the various bonding parameters of the 4524 on ball bonds.
        TIME: Length of time for which the FORCE is applied. Long TIMEs generally cause the CAPILLARY to pull the wedge off the sample surface as it rises to the RESET position after completing the bond. Short TIMEs seem to result in weaker, smaller wedge bonds. Use only the recommended value found on the Recommended Parameters table. FORCE: Pressure exerted by the CAPILLARY tip at the sample. Variation in FORCE applied does not significantly alter the wedge bonds. For higher FORCE, the "smoosh" region of the bond is more linear, and the bond footprint seems slightly smaller. Repeatability may also be reduced by increased FORCE. The recommended value is probably the best to use, and a value smaller then the recommended should not be used. POWER: Power supplied to vibrate the CAPILLARY while the bond is being made. Variation in the POWER supplied to the CAPILLARY while bonding varies the width of the "smoosh" region, or the bond footprint. High POWER seems to result in a wide but very shallow bond, and conversely, low POWER results in a thin but deep bond. For best bond strength and electrical properties, use the recommended value. Avoid using a value lower then this.
    10. How do I improve the repeatability of my bonds?
      1. Bond repeatability is one of the most important aspects of the Wire Bonder. Ideally, few or no adjustments should be needed at an operation session. IN reality, frequent adjustments are often necessary. The closer the SAMPLE STAGE is placed to the tip of the CAPILLARY while aligning the SAMPLE STAGE during the Wire bonder set-up, the better. It may be necessary to realign the STAGE by repeating steps #8-10 of the Procedure for Set-Up of the Wire Bonder. In step #9, try to place the sample surface as close to the tip as possible without actually touching. The best way to improve repeatability is to have all settings at their recommended value. Beyond this, be careful to always bond to a prepared bonding surface. Incomplete bonds are a prime cause of repeatability problems. Make absolutely certain that the ball size is within recommended parameters, and that the actual diameter of the ball on the end of the wire is at least three times the diameter of the wire. Take care while bonding. Allow a few moments between each bond. Insure before and during bonding that no kinks or bends are present in the wire being fed into the CAPILLARY. Check that no excess dust or other contamination has stuck to the wire or the CAPILLARY. At times it may be necessary to clean the carbon scoring off of the NEFO foot. Seek assistance if you think that build up on the foot is reducing its effectiveness. Finally, practice. As you gain experience with the wire bonder, techniques may become evident to you that are not discussed in this document. Feel free to vary certain parameters or techniques, but be careful to remain within the limits of the machine.

Equipment:


Last Revision:

Oct 27, 2020