I am attempting to wirebond gold wire to some gold contact pads but have not yet been successful.
The contact pad is as follows:
Si (substrate) SiO2 (45 nm) Ti (10 nm) Au (100 nm)
I have tried to adjust power, time and force settings for the wirebonder (Kulicke & Soffa 4526) but each time the wire fails to bond.
Any suggestions would be welcomed.
Kindest regards,
Jules
Dear Jules,
If I am not wrong it is a gold wedge bonder.
1) Have you tried to heat the work-holder up to 90-100 C? If you don't do it you cannot make the welding,
2) Depending on application and size you can try to use these settings:
- loop height 4.0, search height (first bond) 5.1, search height (second bond) 4.2, tail length 5.0, power (first bond) 5.5, power (second bond) 7.1, time (first bond) 8.0, time (second bond) 8.0, force (first bond) 4.5, force (second bond) 6.5.
3) Some definitions:
The search height is the position at which the bonding head stops above the bond site. The tail is the length of the wire protruding from the capillary after performing the second bond. Wire bonding is a function of three main bonding parameters: power, time, and force. Bonding power is the amount of ultrasonic energy applied to the bond. Bonding time is the amount of time that the ultrasonic power and force are applied. Bonding force is applied to the wire while the ultrasonic energy is being applied.
Actually I have some experience with the K&S 4524 (gold ball bonder), however If you need some references just let me know.
Hope it helps, Enrico
@Di_Xu, yes it is 25 um Au wire. I'm not sure whether it is 'cross-groove'.
@Enrico_Macrelli, Thank you for your suggestions, the work-holder was heated and I have tried a few different power, force and time settings. I may use an IR thermometer to check the sample is reaching sufficient temperature, I may do as @ H._Grothe suggests and increase the temperature even further. I don't expect it does, but will adjusting the search height provide any significant difference in bond? That's one of the settings I haven't adjusted. Also, if you can recommend any references I would be keen to take a look (also for future reference).
Thank you all for the comments,
Jules.
Dear Jules,
you are welcome. I almost wrote a PhD Thesis about bonding wire assembly of micro-magnetic devices.
Actually the search height is one of the parameters that can produce in perspective better bonds. I put here some suggestions in case the bonds do not hold or are not consistent:
- bonding parameters are incorrect--->change the bonding parameters one at a time to obtain proper settings,
- search height is too high--->check if the search height is 0.127 mm above the bonding surface. If not, reset the search height or the work-holder height,
- bonding surface is dirty, the device is not installed correctly, or the wire is faulty--->check if the surface of the device is dirty. If it is, clean the surface. Check if the device lies flat on the work-holder and it is properly clamped.
- wedge/capillary is not set correctly--->check if the wedge has been installed properly. If not, reinstall the wedge using the setup gauge or replace it.
- wire break just above the first bond--->reduce the bonding parameters settings, etc.
All of this information you can find in (listed for importance):
[1] Kulicke & Soffa Ltd. 4500 Series manual wire bonders operation and maintenance manual. 2002. url: http://www.kns.com/en-us/Pages/Home.aspx (I found the suggestions above in Section 13.2 Bonding Process).
[2] G. G. Harman. Wire bonding in microelectronics. New York (NY): McGraw-Hill
Professional, 2010.
[3] C. A. Harper. Electronic packaging and interconnection handbook, 4th edition. New York (NY): McGraw-Hill Professional, 2004.
[4] M. L. Minges. Electronic materials handbook: packaging, volume I. Boca Raton
(Florida): CRC Press, 1989.
In case you need help let me know (or chat privately),
Enrico
Hello, Jules: I found sometime to inspect failure spots might be useful. Have you got chance to take a close look on what the failure spot looks like?
Sincerely,
Ting
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