Chip on Board (COB)

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Chip-on-Board assembly is the process whereby a bare semiconductor die is mounted on a printed circuit board or substrate using conductive or non-conductive epoxies.

Customers may have compelling technical reasons such as mounting an ASIC chip onto a board surrounded by other surface mount components, reducing the footprint required for a soldered package, increased circuit density and higher performance with short interconnects. Directly attaching the chip to a thermally conductive substrate can also improve thermal performance for demanding applications.

For applications which require very high thermal and electrical conductivity, we have a number of pressure-less semi-sintering epoxies which lend themselves to chip-on-board assembly.  Die are typically electrically connected using Au ball bonding or Al Wedge Bonding.

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For RF and millimeter wave devices, Ribbon bonding can also be offered which acts as a waveguide to improve signal quality. Our large working area bonders can accommodate volume production for multi-chip modules such as LED chip on board and RF modules.

The die is then protected using a glob-top or dam & fill encapsulation process. For optical sensors, a dam & fill process can be used to cover the sensitive wire bonds, but leave the chip sensor surface exposed.

To reduce the inductance effects of wire bonding, ALTER can also attach a die face-down onto a PCB using flip-chip technology, this can either be using solder balls pre-applied at wafer level, or using our in-house gold stud bumping process. Thermocompression or thermosonic methods are used to reflow the bumps onto the PCB contact pads.  The die is then protected using an underfill material followed by a glob-top encapsulation process. Microfocus X-ray inspection and sample die shear testing is used to verify the integrity and contact of the bumps after assembly.

Most chip-on-board assembly can also be combined with our fast-turn around service for initial prototypes.

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