Andrew J. Mueller

Demonstration of a novel hybrid silicon-resin high density interconnect (HDI) substrate

We examine the thermomechanical tradeoffs in a novel technology for high density interconnect (HDI) substrates. Fabricated from silicon (Si) wafers with planar cavities of highly-filled composite encapsulant, the technology leverages established Si photolithography but offers improved mechanical properties. Modules are subject to thermomechanical stress during encapsulant cure, assembly reflow, module fabrication, and operation. We show that improvements in junction-to-ambient sinking offset the heat density increase in such systems and low expansion encapsulants prevent failure during cure. We employ finite element modeling and materials testing to show the effect of wafer design and material selection on the stresses in the module.

High density penetrating electrode arrays for autonomic nerves

Electrode arrays for recording and stimulation in the central nervous system have enabled numerous advances in basic science and therapeutic strategies. In particular, micro-fabricated arrays with precision size and spacing offer the benefit of accessing single neurons and permit mapping of neuronal function. Similar advances are envisioned toward understanding the autonomic nervous system and developing therapies based on its modulation, but appropriate electrode arrays are lacking. Here, we present for the first time, a multi-channel electrode array suitable for penetration of peripheral nerves having diameters as small as 0.1mm, and demonstrate performance in vivo. These arrays have the potential to access multiple discrete nerve fibers in small nerves. We fabricated and characterized five-channel arrays and obtained preliminary recordings of activity when penetrating rat carotid sinus nerve. The electrodes were constructed using hybrid microfabrication processes. The individual electrode shafts are as small as 0.01mm in diameter and at its tip each has a defined site that is addressable via a standard electronic connector. In addition to acute in vivo results, we evaluate the device by electrochemical impedance spectroscopy. Having established the fabrication method, our next steps are to incorporate the arrays into an implantable configuration for chronic studies, and here we further describe concepts for such a device.

Thermal and Mechanical Considerations for Silicon-Resin High-Density Substrate

We examine the thermomechanical tradeoffs in a novel technology for high-density interconnect substrates. Fabricated from silicon (Si) wafers with planar cavities of highly filled composite encapsulant, the technology leverages established Si photolithography but offers improved mechanical properties. Modules are subject to thermomechanical stress during encapsulant cure, assembly reflow, module fabrication, and operation. We show that improvements in junction-to-ambient sinking offset the heat density increase in such systems and low expansion encapsulants prevent failure during cure and subsequent processing. We employ finite element modeling and materials testing to show the effect of wafer design and material selection on the in-plane and through-plane stresses in the module.