The development of embedded surface mount devices, IC's, interconnects and power source elements offers the ability to achieve levels of miniaturization beyond the capabilities of current manufacturing techniques. By burying or embedding the whole circuit under the surface, significant reduction in weight and volume can be achieved for a given circuit board design. In addition, embedded structures allow for improved electrical performance and enhanced function integration within traditional circuit board substrates. Laser-based direct-write (LDW) techniques offer an alternative for the fabrication of such embedded structures at a fraction of the cost and in less time that it would take to develop system-on-chip designs such as ASIC’s. Laser micromachining has been used in the past to machine vias and trenches on circuit board substrates with great precision, while laser forward transfer has been used to deposit patterns and multilayers of various electronic materials. At NRL, we have been exploring the use of these LDW techniques to both machine and deposit the various materials required to embed and connect individual components inside a given surface. This paper describes the materials and processes being developed for the fabrication of embedded microelectronic circuit structures using direct-write techniques alongside with an example of a totally embedded circuit demonstrated to date.
Significant reduction in weight and volume for a given circuit design can be obtained by embedding the required surface mount devices, bare die and power source elements into the circuit board. In addition, embedded structures allow for improved electrical performance and enhanced function integration within traditional circuit board substrates and non-traditional surfaces such as the external case. Laser-based direct-write techniques can be used for developing such embedded structures at a fraction of the cost and in less time that it would take to develop system-on-chip alternatives such as ASIC's. Laser micromachining has been used in the past to machine vias and trenches on circuit board substrates with great precision, while laser forward transfer has been used to deposit patterns and multilayers of various electronic materials. This paper describes recent work performed at the Naval Research Laboratory using the above laser direct-write techniques to machine the surface and deposit the materials required to embed, connect and encapsulate individual electronic components and microbatteries inside a plastic substrate.
The experimental characterization of fatigue crack initiation and growth of structural materials can be very expensive and time consuming. Fatigue specimens are typically controlled by a single dominant defect and several specimens are needed to examine the fatigue response for each loading condition of interest. Time and expense add up as millions of load cycles are sometimes required to initiate a crack, and replicate tests are necessary to characterize the inherent statistical nature of fatigue. In order to improve the efficiency of experimentation, we are developing laser-based techniques to produce fatigue test samples with arrays of defects. Controlled arrays of oval shaped micro-defects are laser-micromachined in titanium alloy (Ti-6Al-4V). Crack initiation from the individual defects in the arrays is monitored using a DC potential drop technique. Results indicate the utility of this approach in multiplying the amount of fatigue data generated per specimen-test. The new fatigue test approach is applicable to a wide range of material systems and initial defect structures.
The use of direct-write techniques in the design and manufacture of interconnects and antennas offers some unique advantages for the development of next generation commercial and defense microelectronic systems. Using a laser forward transfer technique, we have demonstrated the ability to rapidly prototype interconnects and various antenna designs. This laser direct-write process is compatible with a broad class of materials such as metals and electronic ceramics and its capable of depositing patterns of any of these materials over non-planar surfaces in a conformal manner. The laser direct-write process is computer controlled so as to allow any given design to be easily modified and adapted to a particular application. To illustrate the potential of this technique, examples of metal lines on laser micromachined polyimide substrates for interconnect applications, are discussed and evaluated. In addition, examples of simple planar and conformal antennas are provided to demonstrate how this technique can influence current and future microelectronic device applications.
Direct-Write techniques have the potential to revolutionize the way miniature sensor devices and microbattery systems are designed and fabricated. The Naval Research Laboratory has developed an advanced laser-based forward transfer process for direct writing novel structures and devices comprising of metals, ceramics, polymers and composites under ambient conditions on both ceramic and plastic substrates. Using this forward transfer technique, we have demonstrated the ability to rapidly prototype various types of physical and chemical sensor devices, and microbatteries. The laser forward transfer process is computer controlled which allows the design of the devices to be easily modified and adapted to any specific application. Furthermore, the same process enables the fabrication of complete sensor or power-source systems by incorporating the passive electronic components required for sensor readout or power management. Examples are provided of various types of miniature sensors, and prototype alkaline and Li-ion microbatteries fabricated using this technique.
We are examining surface characteristics of ultraviolet pulsed-laser micromachined structures in polymide as a function of the incident laser energy and the distance between subsequent laser spots in order to prepare surfaces for laser direct-write deposition of metals. Variations in the spot-to-spot translation distance provide an alternative means of average depth and roughness control when compared to fluence changes and focal distance variations. We find that the average depth is proportional to the inverse of the translation distance, while the root mean square surface roughness reaches a minimum when the translation distance is approximately equal to the full width half maximum of a single ablation mark on the surface. Conductive silver metal lines are deposited on the surface machined features demonstrating the ability to produce conductors with good adhesion over stepped structures on polyimide.
We employ a novel laser forward transfer process, Matrix Assisted Pulsed Laser Evaporation Direct Write, in combination with UV laser micromachining, to fabricate mesoscale ultracapacitors and micro batteries under ambient temperature and atmospheric conditions. Our laser engineering approach enables the deposition of hydrous ruthenium oxide films with the desired high surface area morphology, without compromising the electrochemical performance of this high specific capacitance material. We compare three different desorption formulations incorporating ethylene glycol, glycerol, or sulfuric acid. The best electrochemical performance is achieved using a mixture of sulfuric acid with RuO2 0.5 H2O electrode material. Our ultracapacitors exhibit the expected linear discharge behavior under a constant current drain, and the electrochemical properties of these cells scale proportionately when combined in parallel and series.
KEYWORDS: Sensors, Chemical fiber sensors, Polymers, Silver, Temperature sensors, Fabrication, Biosensors, Chemical elements, Manufacturing, Electrodes
The use of direct-write techniques in the design and manufacture of sensor devices provides a flexible approach for next generation commercial and defense sensor applications. Using a laser forward transfer technique, we have demonstrated the ability to rapidly prototype temperature, biological and chemical sensor devices. This process, known as matrix assissted pulsed laser evaporation direct-write or MAPLE-DW is compatible with a broad class of materials ranging form metals and electronic ceramics to chemoselective polymers and biomaterials. Various types of miniature sensor designs have been fabricated incorporating different materials such as metals, polymers, biomaterials or composites as multilayers or discrete structures on a single substrate. The MAPLE-DW process is computer controlled which allows the sensor design to be easily modified and adapted to any specific application. To illustrate the potential of this technique, a functional chemical sensor system is demonstrated by fabricating all the passive and sensor components by MAPLE-DW on a polyimide substrate. Additional devices fabricated by MAPLE DW including biosensors and temperature sensors and their performance are shown to illustrate the breadth of MAPLE DW and how this technique may influence current and future sensor applications.
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