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Bonding wire is is what connect the silicon chip to the external cicuitry,
and normally it is made of aluminium, or gold due to its excellent electrical
properties for electronic signal transmission in semiconducter devices.
However, recent developments are also focusing on copper as a low cost alternative material.
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microchip package outlet leads connect to the rest of the electronics circuit board
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bonding wire connects the silicon chip to the package outlet leads |
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The typical size of bonding inside a microchip will have a diameter smaller than a human hair,
typically smaller than 30 microns, depending on the microchip applications.
Bonding machines are use to link a microchip to the lead frame electrodes which connect to the outer
cicuitry of an electronics components, as can be seen on the right.
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Bonding Wire Profile
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The Scanning Electron Microscope high magnification image on the left show how the
bonding wire works. Series of connections that link the semiconductor chip die pad
to the lead frame connection pad that connects the silicon chip
to the rest of the electronic device to receive and transmit electrical signal.
The die pad-wire-lead frame connections are formed by applying pressure, heat and
ultra-sonic forces to the ball-tip bonding wire to form intermetallic weld with
the chip die pad. Then the wire will form an arch to the corresponding lead frame
pad for the second bonding to complete the chip to leadframe connection. |
The diagram above describe the arch profile of a bonding wire that connects the silicon
chip to the external connector frame. This bonding profile is important in determining
the application of the wire in different types of microchip packages. To achieve
the desired profile of loop height and span, it takes expertise in metallurgical
process to manufacture the suitable type of material for bonding wire.
Bonding Wire Manufacturing
The following is a simplified description of bonding wire manufacturing process, which is done in clean room environment
with stringent control.
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Purified metal are processed into cylinderical rod shaped ingots
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Ingots are turned into large diameter wire through a press roll process.
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The large diameter wire is then put through the drawing process, where the wire is drawn
through a series of dies with increasingly smaller diameter to match the final required product diameter.
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The fine drawn wire then goes through the annealing process, where the wire run through an electrical furnace.
This will heat up the wire to remove the stress of previous drawing process, and promote growth of metallic
crystal structure which give the required elongation and tensile strength mechanical properties to the wire.
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This is followed by rewinding process where the wire is wound to the product spools.
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The final product spools are put into plastic casing to prevent contamination after leaving the clean room
manufacturing environment, and ready to be shipped to customers
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