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Wire bonding

Electric Solar Sail

Collaboration with NASA

The electric solar wind sail is a new space propulsion concept which uses the solar wind momentum for producing thrust. The electric sail is somewhat similar to the more well-known solar radiation pressure sail which is often called simply the solar sail.

A prototype of this sail was launched to low Earth orbit (680 km) on-board ESA Vega launcher and the estonian EstCube-1 satellite.

VV02 lct


Our team is responsible for producing the tether structure made of 25µm and 50µm aluminium wires. Below is a video showing a prototype of the tether factory creating the tether.

A 1km long continuous Heytether was produced in December 2012. The result proves the viability of the tether production technique. Manufacturing of a large-scale E-Sail is possible.



Close up of bond and part of the tether, scale bar is 1 cm (top). 1 km of tether on its output spool (bottom).


Failed and fixed bonds from the 1 km production data analysis.

100 m of E-Sail tether will fly on-board Finland’s first satellite Aalto-1 set to launch in 2015.


100 m of 4-wire Heytether on an Aalto-1 flight reel. There are 15 layers of tether on the reel. The tether is uniformly distributed over the available space, 1 cm (top). Post-unreeling pull test data of the tether. For a full-scale E-Sail the mission critical limit for bond strength is 50 mN. The average pull-strength of the produced bonds on the measured tether is 100±7 mN (bottom).

Contact Resistance

Electron microscope image of a wire to wire bond

Electron microscope image of a wire to wire bond

We have developed a nondestructive real-time method to identify the phases of wire bond development. Using 10MHz sampling rate and a custom amplifier we measure the current and potential over the wire – pad interface during the ultrasonic bonding process. From the resulting contact resistance data we are able to identify the four phases of the wire bond development: touch down, surface cleaning, contact development and fully developed bond. This method can be used to optimize the wire bonding process parameters.

Schematic view (left) and a photo (right) of the real-time contact resistance setup [Seppänen, et al., MEE, vol. 104, 2013].


Schematic figure of the non-contact measurement of the tether bonding.