Electroplating through Fluidic Channels as Production Technology for 3D Interconnect Devices and Sensing Structures
Authors: Rechel Mathias , Bengsch Sebastian , Wurz Marc Christopher 
Published: February 2020

Three dimensional moulded interconnect devices (3D-MID) have been a growing market in the last decades [1]. They combine mechanical and electrical functionality. Besides the established production technologies of 3D-MIDs, as Laser Direct Structuring (LDS), one and two component injection moulding and hot stamping [2], innovative new processes are developed. All of the them are printing technologies for example Flamecon [3] technology, the Plasmadust process [4] or the Aerosol Jet Printing [5].

We present a production technology which employs 3D printing, vacuum casting, physical vapour deposition, electroplating through fluidic channels and ion beam etching to create interconnects and sensitive structures. The technology can be applied to create in plane and three dimensional structures. The deposition of high current electric conductors is possible, as well as deposition of functional sensor elements on different substrate materials. The employed process chain contains additive manufacturing techniques. We used a milled substrate made of Acrylnitril-Butadien-Styrol (ABS) Polymer instead of an injection moulded one as the studying object for the three dimensional deposition, and a Kapton® foil as a planar substrate. Preparation of the substrate is done by depositing a nickel iron (81/19) seed layer of several hundred nanometres thickness by physical vapour deposition. Using conductive sprays as seed layers will be explored in future.

The fluidic channels for the electrolyte are made by vacuum casting a master profile with Polydimethylsiloxane (PDMS). We employed milled and three dimensional printed masters in the casting process. The fluid is guided into the PDMS channels by attaching hose connector to the master shape before the PDMS casting. The anode wire is embedded into the PDMS form after casting.

Electroplating is done by clamping the PDMS shape onto the substrate. The exchange of the electrolyte is realised using a peristaltic pump, which leads the electrolyte through the fluidic channels by creating a vacuum. The anode to cathode spacing is about 1mm. The applied currents vary from 2 mA to 20 mA. The low current is applied to create functional sensor structures of nickel-iron layers of only a few microns thickness. Higher currents are applied to create thick conducting structures out of copper of about 100 µm. The seed layer is removed by ion beam etching. Future work will prove the use of wet chemical etching.

The deposited structures are analysed regarding the thickness homogeneity in reference to the flow direction, the edge angle and the geometric reproduction compared to the master profile. An analysis of thin structures concerning their sensing ability is also done.

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