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Figures 2, 3 and 4 show examples of the raw coated material, followed by sintering and the finished circuit, respectively. The samples were pattern plated with copper, then tin etch resist. The photo resist was stripped off; the circuit was etched in industry standard equipment with ammonia based solution. The tin was stripped off after etching resulting in a copper circuit. The coupons were tested for peel strength and showed a 1.2 N/cm average. Note that the coupons used for the test are industry standard patterns as designated by IPC.
The electroplated copper was also subjected to pull testing to verify adhesion to the base coating of copper. The result of this test was that the pull strength exceeded the detection limit of the device.
The sintered nano-copper, thin-film coating will also auto catalyze in standard PCB electro-less copper solutions. This seed layer technology replaces the palladium catalyst currently used to initiate electro-less copper in the PCB industry.
Similar process development is underway for rigid laminates and alumina as well. Initial testing shows comparable pull and peel strength to currently available laminates. This thin film coating also allows lower temperature processing of the ceramic laminates than current firing methods using precious metal pastes.
Conclusion
Nanocopper based copper foil has great promise for high-density microcircuits. Utilizing conventional coating capability, volume production is easily scalable and cost-effective.
David Ciufo is the PCB program manager at Intrinsiq Materials Inc. a recognized leader in nanomaterials development.
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