Notes from service/teaching session of the bonder

Doug Oliver, PDP Equipment,
Stella Tagliati and Holger Motzkau, Cond. Mat. Phys., SU.

SET UP: do not use it ever. It applies the same bonding force to the search height. You would impact at full bond force.
The set up force (by the service) for the search height is now 25 g.
If the bond force is chosen equal to 0: it means that the bond force is still 25 g.
If the bond force is chosen equal to 3.0: it means that the bond force is 50 g (only point known).

TEST: push it maximum for 5 seconds. It applies ultrasonic to the wedge, and it is good for cleaning when the wedge is clogged: put the tweezers in the middle of the needle and then press the button. The yellow led is an indication that there is ultrasound present, but no proof.

RESET: the wedge is brought to home position (set by the service) and the program goes back to step 1.

LIGHT: switches on the lamp.

CLAMP OPEN: opens the clamp (used when one needs to rethread the wire). If the clamp is left opened for too long time, the solenoid becomes very hot and for safety it gets disconnected. One has to reset.

HIGH RESET: not useful. It lifts the wedge to a higher level temporarily and releases it back to home position (set by the service) if the button is released. It is connected to the tension on the spring which is set low by the service so it may not work. To lift the wedge one can just manually gently pull the lever up. This may be useful if you have a chip carrier or something similar with a high border and you want to bond inside. (If you are bonding and the first bond is going wrong you may want to take away the sample from the working area, then you can also use the right lever to lift the wedge, then remove the sample and finish the bond in air).

Parameters:

	Panel 1: Common parameters for panel 1 and 2: SEARCH: height above the work area reached when you press the button in automatic mode: 1.0 means touching. Above 1.0 you do not touch. POWER: amplitude of the ultrasound, not related to the frequency of 60 kHz. The default value is 2, note that the difference in power between 2 and 2.5 is a lot. TIME: time during which the full force (you always have 25 g on the needle) and power are applied (3.0 means 50 ms). This parameter usually does not need to be changed. FORCE: downward mechanical force (default 3.0 which corresponds to 50 g, 0 to 25 g). This parameter usually does not need to be changed.
	Panel 2: parameters for this panel only: LOOP height after the 1st bond: related to the length of the wire used to bond. LOOP has to be higher than SEARCH, 1.0 means that the wedge is touching. TAIL: length sticking up at the front of the wedge (default 1.5). This parameter usually does not need to be changed. Sometimes it is preferred to perform a reverse bond so that the tail will be on the PCB and not on the sample. In this case one should be sure that the sample chip is not too high (otherwise it could hit against the arm). TEAR: the way the clamps move back (default 3.0). This parameter usually does not need to be changed.
	There is then a last page (panel 3) that should not be changed because these settings are for 30 degree bonding (as in our case): MODE: standard TIME: short TAIL: short

IMPORTANT: always start bonding from panel 1. If you start from panel 2 you reverse the bonding and mess up the system. Always finish the bond cycle. Notice that in the middle of a bond the clamp is open, so if you don’t finish the bond it will get overheated and disconnected for safety.

The force and power are correct when the width of the squeezed wire is about 1.5 times the diameter of the wire.

LEVERS: Clamp: moves back the clamp, useful to get more space around the wedge, e.g. when re-threading. Tool: moves up the lever arm, useful for lifting up wedge over a high border surrounding bond pad, or to move away if the first bond steps fail.

Right position of the wire through clamp and wedge

Rethread the wire:

• keep the clamp closed and pull up the left bar to move the clamp backwards to make space.
• Grab a straight piece of wire and insert it through the wedge: do not touch the wire with your fingers, otherwise the wedge gets clogged!
• Open the clamp and make the wire passing through the clamp paying attention to the L-shaped metal guide.
• Pull the bar down to move the clamp at the ordinary place.
• Close the clamp.

Note! If the clamp is left opened for too long time, the solenoid becomes very hot and for safety it closes and one has to reset.

Height of the wedge:

Gauge, length in mils inscribed in base	Old screw, red arrows indicate broken parts

It is very important to get a good mechanical contact and be in resonance to get a good ultrasound. When one needs to remove the wedge (because it is broken or for cleaning), then it is very important to place it back in the correct position.

• Move the clamp backward.
• The screw (volcano shaped) should be weakened to take away the wedge.

To put the needle back do the following:

• Put the wedge down from the top hole and let it go almost all the way.
• Lift the inclined arm and use the gauge to push up the wedge to the right position. Look for 750 mil gauge. The number is the length of the wedge in fractions of inches.
• Then screw it tightly.

  This is the only thing one can touch out of all the mechanical assembly, and the form of the screw is very crucial. It has to be replaced after several uses (not more than once a year), an very bad one is shown in the pictures.

Do not touch these screws. The force is calibrated

Set height of the work holder (see also pdf file on lab computer):

• Remove the work holder.
• Make a first bond in air in automatic mode.
• Set LOOP equal to 1.0.
• Put back the work holder and move it upward or downward by rotating its base in order to align the wedge to the lowest bonding surface, i.e. usually the PCB.
• Take again away the work holder and finish the bond in air.

Obs. The wire will for sure get unthreaded in this step, but you can pull it out a bit more before doing the bonds in air.

SEARCH/LOOP heights

You are now ready for bonding but you have to adjust the parameters first. Power, time and force can be left at the default values. The only parameters that should be set are SEARCH height for 1^st and 2^nd bond, and LOOP.

• Press the left mouse button and hold it: change (increase) at the same time the SEARCH for the 1^st bond while you are looking into the microscope. When you are at about 2 to 5 diameters above the 1^st bonding surface, release the button and bond. Be careful: if the initial search height is set to low you may crash into you sample, so either remove the sample or set search height to some high value before starting.

During the ‘’search’’ the wedge goes smoothly downwards applying 25 g force and stops at the 1^st search height. When you release the left mouse button it continues going down. There is a default time after which the bonder bonds. It is very important that the search is not too high: if it is too high the time is not enough to nicely reach the surface. It starts to bond in the air and will crash into the bond area with full force and ultrasound.

• After the first bond increase the LOOP (looking in the microscope).
• Move to the 2^nd bonding spot using the laser mark. The previously set SEARCH of about 1.5 should be fine. Push the left button and hold it. If necessary adjust the 2^nd search height. However, if you are far away from 1.5 you should recheck the height of the work holder.

BONDING

Black mouse button: height in manual mode,
Left mouse button: automatic mode,
Right mouse button: never used.

Automatic mode (first bond: sample chip, second bond: PCB)

• Push the left mouse button and hold (in this way the wedge will be at the search height for the first bond): move the mouse to find the correct bonding spot. The red light dot is focused and aligned on the PCB, so it should not be trusted on the sample area. On the sample area the red dot just gives a rough estimate of the position.
• Let the button go for the first bond. The wedge will then go up to the loop height.
• Move the wedge towards the second bonding spot that must be along the vertical direction of a line which passes through the first bonding spot, north: in practice you should just move the mouse towards yourself to find the position.
• Push the button and hold (the wedge will be at the search height for the second bond): after you pushed the button you shouldn’t move the wedge too much because, differently from the first bond, the clamp is closed and the wire is pulled: any movement could mess it up. On the PCB the red light dot is focused and aligned, so you can trust it more than in the first bond.

Manual mode

The idea is the same as for the automatic mode: the height of the work-holder is set in the same way, and power, time and force have the same meaning in both modes.

The search heights are just for the automatic mode. The manual mode uses the loop height: one could set a quite big loop height and release the button just at the wanted height (decided looking in the microscope).

Somebody may find it easier to work with the work-holder rotated 90 degrees and use the index-finger to command as shown in the picture.