Thick film surface mount resistors (chip resistors) are used in high quantities in an extensive range of electronic equipment. Applications range from the simplest consumer product to ultra high reliability Space qualified equipment.
The majority of thick film surface mount resistors are manufactured by applying a resistor film to a substrate (usually Alumina). The resistor material is connected to a wrap around lead frames bonded to each end of the substrate then coated with protective material.
A key advantage of chip resistors is their surface mount capability. Their relatively small size and form factor simplifies the manufacturing process and enables very high levels of automation.
Where the demands of the application or the manufacturing process makes the use of standard chip resistors impractical Thick film flip chip surface mount resistors are an alternative solution.
Why Flip Chip
With Flip Chip there is no need for a wraparound lead frame hence it offers a higher density solution. There are no traditional solder joints so the manufacturing costs can be lower than standard chip resistors. The construction and interface to the system board offer a higher level of strain relief should there be any system board movement due to thermal or mechanical stress.
Other advantages of surface mount resistors in flip chip configuration include resistance to contaminants and lower noise. Flip chip lends itself to wire bond application by bonding to appropriate pads on the top side of the substrate.
However, the most common reason for selecting Flip Chip is its higher voltage and/or higher power capability when compared with chip resistors. Flip chip can deliver a surface mount equivalent to standard through hole devices.
Flip Chip Surface Mount Resistor Manufacture
The general thick film manufacturing process discussed in detail elsewhere on this blog applies. With flip chip the resistor pattern is on the underside of the substrate coated with a protective material. The resistor component is mounted to the system board with the resistor element face down.
The resistor connects to pads on the underside of the substrate. These pads match with pads on the system board. A variety of connection methods between pads may be employed ranging from conductive epoxy, to solder or gold bumps or studs. The resistor element is protected with a suitable coating designed for electrical, mechanical, and environmental protection.
While the vast majority of applications will continue to use standard surface mount thick film resistors the use of Flip Chip resistors is expected to increase. A range of standard devices is available from the large resistor manufacturers with custom devices available from specialist manufacturers.