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Additive Trim of Polymer Thick Film Resistors

IP.com Disclosure Number: IPCOM000040016D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Bonn, R: AUTHOR [+4]

Abstract

A method is described to accomplish the trim of polymer thick film resistors while maintaining the characteristics of the polyimide substrate. A packaging technology for power supplies, Dielectric on Thermal Conductor (DOTC), uses copper-metallized polyimide as a substrate. The polyimide is adhesively bonded to an aluminum structure which sinks the heat generated by the power dissipating elements of the supply. A large percentage of the heat is generated by the several power resistors required by supply design. A method of producing these resistors is by screen printing polymer paste in the appropriate aspect ratios and thicknesses to produce the correct value of resistance.

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Additive Trim of Polymer Thick Film Resistors

A method is described to accomplish the trim of polymer thick film resistors while maintaining the characteristics of the polyimide substrate. A packaging technology for power supplies, Dielectric on Thermal Conductor (DOTC), uses copper-metallized polyimide as a substrate. The polyimide is adhesively bonded to an aluminum structure which sinks the heat generated by the power dissipating elements of the supply. A large percentage of the heat is generated by the several power resistors required by supply design. A method of producing these resistors is by screen printing polymer paste in the appropriate aspect ratios and thicknesses to produce the correct value of resistance. The aluminum heat sink mentioned above provides a common heat sink for all the resistors as well as the other power generating elements and eliminates individual heat sinks, thereby reducing system cost. Power resistors used in power supplies are generally required to have tolerances of approximately +/-20%. To achieve the required tolerance, some trimming method must be used. As the DOTC technology finds applications in other than power systems, such as microprocessor/logic systems, which have lower average power per device (but not necessarily lower power density per system), it will become economic to screen resistors of higher precision on their substrates, and trimming will also be necessary. Laser and abrasive trimming are the two prevalent technologies used by the industry, but neither is used on polyimide substrates. Using laser techniques, the value of the resistor under trim is monitored while the laser cuts away the resistor material until the desired value is attained. This technology has been in use for some time and is well known. Abrasive trimming is an even older technique, but is not used extensively due to the ease of automating the laser technique. The above prior-art trimming techniques are not applicable to the resistors discussed above. The laser generates excessive heat when cutting through the resistor material and degrades the characteristics of the material under the resistor. The abrasive technique has the tendency to cut into the polyimide, which is also not desirable. Economic use of DOTC substrates requires use of integral power resistors. Present methods of screening these...