After microstructures have been fabricated on a substrate, additional steps must often be performed to allow those structures to interact with the macroscopic world. This can include cutting wafers with many copies of a pattern into individual dies; attaching macroscopic electrical leads; mounting the devices in protective packages, and so forth.
Electrical connection
Wire bonding
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What it is used to do
Microscopic electronic structures need intermediate-scale electrical connections in order to interact with the human-scale world.
How it works
There are at least two primary types of wire bonding: ball bonding and wedge bonding. Both are available at the NFC.
Ball bonding usually is restricted to gold and copper wire and usually requires heat. For wedge bonding, only gold wire requires heat. Wedge bonding can use large diameter wires or wire ribbons for power electronics application. Ball bonding is limited to small diameter wires, suitable for interconnect application.
In either type of wire bonding, the wire is attached at both ends using a combination of downward pressure, ultrasonic energy, and in some cases heat, to make a weld. Heat is used to make the metal softer. The correct combination of temperature and ultrasonic energy is used in order to maximize the reliability and strength of a wire bond. If heat and ultrasonic energy is used, the process is called thermosonic bonding.
In wedge bonding, the wire must be drawn in a straight line according to the first bond. This slows down the process due to time needed for tool alignment. Ball bonding, however, creates its first bond in a ball shape with the wire sticking out at the top, having no directional preference. Thus, the wire can be drawn in any direction, making it a faster process.
Instrumentation Available
Strengths
Rapid, accurate wiring process that can be performed without bringing samples out of the cleanroom environment
Limitations
The metal surface on the substrate, to which the wire will be bonded, cannot be too thin
Applications
Additional Reading
Assembly
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What it is used to do
Individually fabricated components may need to be aligned and bonded to each other to form a single more complex device.
How it works
Assembly processes can include a wide variety of attachment techniques, including anodic, eutectic, adhesive, and thermocompressive methods.
Instrumentation Available
Strengths
Limitations
Applications
Additional Reading
Separation
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What it is used to do
Most nanofabrication techniques are intended to operate as parallel processes – that is, a large number of identical dies are fabricated at the the same time. Individual dies must be separated for use.
How it works
Instrumentation Available
Strengths
Limitations
Applications
Additional Reading
