Heated Stage for Thermosonic Wedge Bonding

First off, I'd like to thank Jeff Keyzer for his donation of a PID controller to this project and his exepriences building his hotplate for surface mount soldering. Take a look at his project in his MightyOhm blog at http://mightyohm.com/blog/2009/01/diy-pid-controlled-soldering-hotplate/

Thermosonic compression bonding is used to make electrical connections between a bare die chip and other components including other chips, printed circuit susbtrates, packaging frames, etc. A combination of heat, ultrasonic vibration, and compression form a metallic bond between a wire and a pad on the die.

I'm interested in making use of MMIC (Monolithic Microwave Integrated Circuits) chips in the > 30 GHz range, parts which for the most part do not come in solderable packages. So I'm left with wirebonding, something usually relegated to industrial and academic institutions.

Piecing together a wirebonding setup can be costly, as most wirebonders new are >$10,000. I found a great deal on a manual WestBond bonder for $50, and a stereo microscope to go with it. Among the things missing though was a heated stage to hold and heat the workpiece.

Commercial heated stages are costly, and for something like $50 I put together my own, one which I believe is as good if not better than commercially available units.

Here are some features that I wanted:

- Heat to 150C and keep it there with reasonable regulation
- Have a smooth plastic base to allow easy maneuvering under the bonder arm
- Adjustable height for use with machined microwave housings, or bare substrates (need about 1/2 inch of adjustment range)

Step 1 Parts List

Here's what I used to make my heated stage:

Stage:

Block of aluminum ~3x2x1 inches
Plate of aluminum (for baseplate) 1/4 inch thick
Standoff holders/adjusters 1/2 inch aluminum rod stock
Standoffs - 1/4 inch diameter FEP plastic (a PTFE-like material)
Cartridge heater (1/2 inch diameter, 400 watts (which is far too much, going to switch to a 150 watt heater)
Thermocouple
Computer power cord (used for supplying power to the heater)
20 gauge Teflon insulated wire (for grounding the heated portion)
Nylon 'expando' sheath to bundle the wires together
Miscellaneous stainless steel screws and set screws (4-40 size)
UHMW plastic (static dissipating type) 1/8 inch thick.


Controller:

Omega CN9000 PID controller (Thanks Jeff!)
Rocker switch
IEC power socket
Aluminum housing
Rubber grommet for wires
hookup wire and shrink tubing for insulation


Most of the parts here can be purchased from McMaster Carr and Digikey. Getting a good deal on a PID controller is key, as they are ~$200 new.

Comments

[exparrot]

I'm interested to know what you're building that utilises MMICs Also, kudos for such a nice build.

[kc6qhp]

Millimeterwave ham radios. I've been building microwave ham radios for years, and now that I'm working at 47 GHz and above, wire bonding bare MMIC dies becomes necessary.