Companies Collaborate to Create Copper-Free Flexible Circuits

Massachusetts companies DKN Research and Pyramid Technical Consultants Inc., based in Haverhill and Lexington, respectively, have co-developed ultra thin, copper-free flexible circuits for use in scientific and medical devices. The companies collaborated on a series of processing technologies to generate thin nickel traces on both sides of thin polyimide film specifically targeting those scientific and medical applications that require the elimination of copper metals from electronic devices.

The nickel traces can be as thin as 0.2 microns on both sides of the polyimide film, with small via hole connections as down to 80 microns in diameter. Special polyimide etching and laser drilling processes are employed to generate the tiny holes. A new electroless nickel-plating process was developed to make uniform conductive layers on the surface and inside the polyimide film holes. A set of chemical etching process and laser abrasion process were furnished to make fine traces down to 50 microns line and space. The small via holes formed by this new process remained intact during the heat cycle and flexing endurance tests.    

Virtually all printed circuit boards use metal copper for their conductive material because of its high conductivity and reasonable cost. Unfortunately, several electronic devices designed for scientific and medical equipment cannot have metallic copper in the circuit because of its physical properties and chemical instability. There are a few metal foils such as aluminum and stainless steel that can serve as the conductor material, but they cannot be thinner than 10 microns. Another problem with these metals and alloys is the difficulty in via hole formation for double side and multilayer circuits.

DKN Research is an engineering firm specializing in microelectronics and packaging technology, while Pyramid Technocal Consultants Inc. is a specialty electronic module manufacturer.