We fabricated an apparatus for manipulation and welding of fine metal objects using a probe. The apparatus is composed of a work probe of a tungsten alloy needle, stages, a DC power supply, and an observation system. The work probe is held vertically above a gold substrate placed on stages to control the relative position against the work probe. The DC power supply is equipped to apply voltage of 0-10kV between the work probe and the substrate. One application of the apparatus is to repair probe cards. Thousands of contact probes (needles) are mounted on the printed circuit board (PCB) in the probe card. The contact probes are mounted one by one by the hands. Recently, an array of the contact probe on the PCB is produced by the LIGA process in response to narrower semiconductor pitch length. The problem is that there are no methods to repair a wrong contact probe. Whole of the contact probes should be a waste owing to one wrong contact probe. We propose to replace a wrong contact probe with a good one using our apparatus. Experiments to remove a contact probe by the apparatus is carried out using the specimen of a mimic probe card, where a cantilever type contact probes are arranged with a pitch of 25 micrometers. Removal of the wrong contact probe is carried out by a non-contact discharge and a contact discharge using the apparatus. High voltage of about 1-2kV is applied after the work probe is moved to above the target contact probe for the non-contact discharge. While high voltage of about10kV is applied after the work probe is positioned in contact with the target contact probe for the contact discharge. The target contact probe is removed by both methods, though the neighboring contact probes are damaged. The latter method is hopeful for removal for repair of the probe card.
Needle-like probe holds fine objects by adhesions without any holding devices. It can not pick up heavy and large objects, because the gravity rivals the adhesions. Referring to electrostatic chucks (ESCs), we fabricated two needle-like probes, of which adhesions are assisted by the electrostatic force, a monopole probe and a dipole probe. The former corresponds to monopolar ESCs and the latter corresponds to dipolar ESCs. By the assistant of an external electric power, both can pick up heavy and large objects. The monopole probe, which is a tungsten needle, can manipulate 40-80μm gold particles on a gold substrate as follows. The probe is lowered until it touches the particle. After 20-50V is applied between the probe and the substrate, the probe is pulled up. Then the particle is picked up with the probe. Once the particle is in the air, it stays at the tip of the probe even if the voltage is reduced to 0. For release of the particle, the probe is lowered until the particle touches the substrate and is pulled up without applying voltage. The dipole probe is made of two electrodes embedded in an epoxy resin. Different from the monopole probe, the dipole probe attract both conductive and dielectric objects over a gap. The probe jumps up a styrene particle of 3mm over the gap of 1mm by applying 2kV, and it jumps up a gold particle of 0.4mm over the gap of 0.5mm by applying 5kV. The release is possible only by turning the applying voltage off. As the gravity is greater than the adhesions, the objects adhered falls. The assistant electrostatic force of the monopole probe is Johnsen-Rahbek force same with the clamping force of monopolar ESCs, and that of the dipole probe is gradient force same with the clamping force of bipolar ESCs.
Particles dispersively coated with other material is a kind of composite particles, i.e., core particles are dotted with other material. Two methods have been developed for such the composite particles. One is a forced electrification method and the other a rotating drum method. The former utilizes the electrostatic force, i.e., positively electrified core particles and negatively electrified child particles are mixed. The latter is a mechanical method as follows. Core particles and child particles are charged into a cylindrical vessel, and mixed by rotating the vessel for several hours. We prepared composite particles of PTCR (Positive Temperature Coefficient of Resistivity) barium titanate and the junction metal such as indium and solder. When the composite particles are filled, the junction metal always exists between the neighboring core particles. The PTCR property of the filling is almost the same with that of the sintered barium titanate. We fabricated a PTCR thin sheet by packing the composite particles between two sheet electrodes. If the composite particles are electrically connected but fixed not firmly, the sheet shows PTCR property and can bend by rearrangement of the particles. Thin ceramics sheet is practically impossible because of the brittleness. However, flexibility can be given to the sheet of the PTCR-junction metal composite particles. The composite particles are fixed by enveloping in an evacuated bag or by embedding in a heat resistant resin. Advantages and disadvantages of the preparation methods and fabrication methods are discussed. Preliminary experiments for a new approach to the PTCR sheet are introduced.
Electroceramic particles with electrodes of solder are prepared y a low cost and high productivity process. The electroceramic particles can be used as single particle devices, and moreover as multi-functional devices by their assembling. PTCR material is one of the electroceramics, having a positive temperature coefficient of resistivity. We prepare the PTCR particles with electrodes of solder as follows. Semiconducting barium titanate (BaTiO3) particles, a typical PTCR material, and solder particles are charged into a cylindrical vessel, and the vessel is rotated for several hours. The product is semiconducting BaTiO3 coated by solder particles. The solder particles are flattened out at the surface of the core particle. The solder forms small dot-like islands, and they are isolated each other. Several applications of such kind of composite particles are described. Single particle device is a PTC thermistor, which consists of one composite particle of semiconducting BaTiO3. Flexible and self-thermostatic sheets can be produced by packing the composite particles between two thin electrodes. Using NTC particles instead of the semiconducting BaTiO3 single particle devices of NTC thermistor and flexible NTC sheets can be produced. Twin particles device is a combination of a single particle PTC thermistor and a single particle NTC thermistor in series, and will be a V-type thermistor, having both PTC and NTC properties. The V-type thermistor can be obtained also by stacking the layer of PTC composite particles and that of NTC composite particles in series. It can be applied to a protective device.
We aim to fabricate microstructure and microdevices by integrating and arranging powder particles, i.e., the particle assemblage. We have developed three assembling techniques of the particles. The details of the assembling techniques and samples of the assembled microstructures are introduced. A manipulator is developed to manipulate and to weld metal particles by using a tungsten probe. Nickel alloy particles of 50 micrometers were piled on a gold substrate by the manipulator, and a leaning tower of the particles is fabricated. The array of the leaning tower is considered to act as an actuator. For the integration of a great number of particles, we developed another method based on the principle with the xerography. An electron beam or an ion beam is irradiated on an insulating substrate. An electrified pattern is formed on the substrate by the doped electron or doped ion. Fine particles are attracted to the pattern by the electrostatic force. Thus, we can arrange particles by immersing the substrate in the suspension of particles. The third is a productive method of ordered mixture by the electrostatic force. A self- thermostatic heater is made from the composite particles of BaTiO3 and In produced by the method.
Probe manipulation of fine particles has been investigated in our laboratory. The feature of our system is that wide range of voltage, 0-10kV, can be applied between the probe and the substrate. In this method, we can pick up a fine particle at the tip of the probe, carry, place and weld the particle at a predetermined point on the substrate by controlling the applied voltage to the probe. When the particle is picked up, 10-50V is applied. And 2-10kV is applied for the welding. Breaking shear stress of welded particles is measured as follows. A sheet spring, where the strain gauges are stuck, is prepared. One end of the sheet spring is held, and moved to push off the welded particle by the free end. The shear stress is calculated from the output of the strain gauges. The breaking shear stress is 44-71MPa for gold particles welded on a gold substrate. Self- sustaining characters, 'NRIM', are formed from gold particles of 40micrometers as an example of microstructure. Preliminary experiments for the application to the ball grid array are carried out. We also fabricated a slant tower of magnetostrictive particles. It will be used as a micro- actuator in the alternative magnetic field.
Five micrometers silica particles can be arranged on CaTiO3 substrates by drawing an electrified pattern on the substrate (drawing step) and then dipping it in a suspension of the particles (arranging step). The fixing treatment of the arranged particles is necessary in order to repeat the above two steps and to fabricate 3D micro-structures. A thin film of the fluoride polymer is formed on the substrate after the particle arrangement to fix the arranged particles. The effect of the coating film on the drawing step and arranging step was studied. It was found that the coating film improved both steps rather than cause interference. The drawing, arranging and fixing are the elemental techniques of the particle arrangement process, and 3D micro-structures can be constructed by repeating these steps in order. Application of the process to a gas sensor was discussed.
A particle assembly using the electron beam was proposed as a process for creation of multi- functional and intelligent materials. Silica (SiO2) particles of 5.1 micrometers in diameter were arranged along the prescribed pattern on calcium titanate (CaTiO3) substrates as the first step on the particle assemblage. Latent electrified images were drawn on CaTiO3 substrates by scanning electron beam. The substrates were dipped in a suspension of SiO2 (dipping method) or the suspension was dripped on the higher end of the inclined substrates (dripping method). The SiO2 particles in the suspension were adhered on the latent image by electrostatic force. And the latent image was visualized as a image of particles arrangement. The images of particles arrangement were processed by an image analysis software. It was shown that the adhered particles can be represented by the normal distribution for the transversal direction to the electrified line, and the uniform distribution for the longitudinal direction. The sharpness of the images by particles was appraised by the above distribution model. It became quantitatively clear that the better images were obtained by the dipping method than by the dripping method.
We proposed a particles assembling method to create intelligent and multi-functional materials. The arrangement of particles on substrates was studied as one of the important techniques for this approach. The arranging process is as follows. Electrified patterns were drawn on dielectric calcium titanate (CaTiO3) substrates with electron beam scanning. The substrates were dipped in a solvent where silica (SiO2) particles of 5.1 micrometers (phi) were dispersed. The particles were attracted to the electrified patterns by the electrostatic force, and were arranged along the electrified patterns. In this paper, undrawn substrates were used to know how many particles adhered on the unelectrified part, and then, arranging experiments using drawn substrates were carried out under various conditions to confirm the above process. We also discussed on the basic aspects of the arrangement, such as attraction force, motion of particles in the solvent, etc.
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