P.L. Cheng

Quantitative Analysis of Resistance Tolerance of Polymer Thick Film Printed Resistors

Low cost methodologies of resistor fabrications are needed for cost effective embedding of resistors into polymeric substrates. Polymer thick film resistors (PTFRs) are low temperature processable, low cost resistors with a wide resistivity range. The electrical resistance variation of these resistors is in the range of around plusmn20% after deposition and trimming procedure is employed to tune the resistances to meet specifications. This adds to the cost and complicates the fabrication process when the resistors are embedded. In this study, the influences of PTFRs geometries on the resistance tolerances were investigated. Results indicated that the resistance accuracy of stencil printed resistors was markedly higher than that of the screen-printed resistors. The screen-printed resistor edge geometries were observed to be rough. Finite element method analyses revealed that the resistance tolerances were associated with edge roughness. Remedies to reduced variations were proposed and the relationship between resistance tolerances and aperture orientations was also outlined

Low temperature processing and electrical properties of embedded ferrite-cored inductor

The inductance of low temperature processable particulate filled polymer matrix composite inductors is constrained by the limited magnetic properties of the polymer matrix. The microstructural and electrical properties of inductors made from amorphous nickel-zinc-iron oxide matrix filled with polycrystalline nickel zinc ferrite (NZF) fillers are investigated in this study. NZF has high resistance, and is essential for high frequency application to reduce eddy current loss. Planar spiral NZF-composite (with 20v% fillers) inductors were fabricated on a glass wafer substrate and heated treated at different temperatures. The electrical properties of the inductors were characterized at frequencies in the MHz range. The inductance is found to increase between 10%-20% for composite inductors after heating at 300/spl deg/C for 1 hour. The increase is comparable to those reported previously for polymer ferrite composite inductors, albeit the polymer version has significantly higher filler content (90wt%) while the current NZF-composite filler content is markedly less (10-20%). This indicates that the increase is associated with improvement of the matrixs properties. The changes in matrix microstructures were characterized by X-ray diffraction. The increase in inductance and associated electrical properties are then explained based on the observed microstructural changes. The increase in matrix inductance indicates that the current approach has strong potential for giving a large enhancement in inductance when high filler content is used.

Experimental investigation and quantitative analysis of resistance variations and control in printed thick film resistors

Polymer Thick Film Resistors (PTFRs) are low cost resistors with a wide resistivity range. Its low processing temperature makes it a potential candidate in the application of embedded resistors in polymer substrates. The electrical resistance variation of these resistors is approximately /spl plusmn/10% after deposition and the resistors require additional trimming procedure to tune the resistances to meet specifications. This adds to the cost and complicates the fabrication process when the resistors are embedded. In this study, the influences of PTFRs geometries on the resistance tolerances were conducted. Results indicated that the accuracy of stencil printed resistors was markedly higher than the screen printed resistors. The screen printed resistor edge geometries were observed to be irregular under the microscope, and FEM analyses revealed that the resistance tolerances were associated with irregular edge geometry. Remedies to the variations were proposed and the relationship between resistance tolerances and aperture orientations was also outlined.

Quantitative analysis of resistance of printed resistors

Surface-mounted resistors on an electronic circuit board are inexpensive and accurate, but resistors embedded in circuit boards can attain the same accuracy only after costly post-deposition trimming. Improved low cost methodologies of resistor fabrication are needed for cost effective embedding of resistors into polymeric substrates. Polymer Thick Film Resistors (PTFRs) are low temperature processable, low cost resistors with a wide resistivity range. The electrical resistance variation of these resistors is approximately /spl plusmn/10% after deposition and additional trimming procedure to tune the resistances to meet specifications. This adds to the cost and complicates the fabrication process when the resistors are embedded. In this study, the influences of PTFRs geometries on the resistance tolerances were investigated. Results indicated that the accuracy of stencil printed resistors was markedly higher than the screen-printed resistors. The screen-printed resistor edge geometries were observed to be rough. FEM analyses revealed that the resistance tolerances were associated with edge roughness. Remedies to the variations were proposed and the relationship between resistance tolerances and aperture orientations was also outlined.

Quantitative analysis of resistance variations in as-deposited nickel-phosphorus (NiP) embedded resistors

Embedded resistors can be fabricated by plating resistive Nickel-Phosphorus (NIP) alloy in a patterned geometry to form resistors on circuit boards. As-deposited NickelPhosphorus (NIP) alloy resistors typically have poor resistance tolerances and require tuning by costly laser trimming to meet specifications. Cost of plated resistors can be reduced if tolerances can be reduced to meet specified tolerance without laser trimming. Resistance tolerance of the resistor is determined by the plated geometry and sheet resistivities of the plated materials. In this study, a group of parameters affecting patterning accuracies, plating and sheet resistivities were vaned to evaluate their effects on the resistance tolerances of electroless-plated NiP resistors. The effect of substrate on sheet resistivity variations was also characterized. Design guidelines lo obtain NiP resistors with low tolerance without laser trimming are discussed.

Development of low temperature processable core material for embedded inductor

The inductance of low temperature processable particulate filled polymer matrix composite inductors is constrained by the limited magnetic properties of the polymer matrix. The microstructural and electrical properties of inductors made from amorphous nickel-zinc-iron oxide matrix filled with polycrystalline nickel zinc ferrite (NZF) fillers are investigated in this study. NZF has high resistance, and is essential for high frequency application to reduce eddy current loss. Planar spiral NZF-composite (with 20/spl nu/% fillers) inductors were fabricated on glass wafer substrate and heated treated at different temperatures. The electrical properties of the inductors were characterized at frequencies in the MHz range. The inductance is found to increase between 10%-20% for composite inductor after heated at 300/spl deg/C for 1 hour. The increase is comparable to those reported previously for polymer ferrite composite inductors, albeit the polymer version has significantly higher filler content (90 wt%) while the current NZF-composite filler content is markedly less (10-20%). This indicates that the increase is associated with improvement of the matrixs properties. The changes in matrix microstructures were characterized by X-ray diffraction. The increase in inductance and associated electrical properties are then explained based on the observed microstructural changes. The increase in matrix inductance indicates that the current approach has strong potential in giving a large enhancement in inductance when high filler content is used.

Inductance tolerance analyses and design-process map of embedded planar spiral inductor

Inductors can be fabricated directly on chip or on ceramic and organic substrates to enhance the performance of mobile and RF devices. Inductors fabricated on chip are more precise with tighter tolerances, but are more costly. Inductors fabricated on organics are lower in cost, but have higher tolerances owing to higher tolerances in fabrication processes. Inductance simulations and experiments were conducted in this investigation to examine the dependences of inductance on geometric factors. Planar spiral inductors with different line width (100-400 /spl mu/m), coil pitch (100-400 /spl mu/m) and number of turns (4-8) were simulated. Selected inductor configurations were fabricated on FR4 substrates using standard patterning and etching processes. Analysis revealed that etching has a pivotal influence on inductance tolerance. On this basis, a new normalizing procedure is developed to relate the inductor structure, inductance and inductance tolerance to fabrication process precision. The methodology is summarized in an inductor design-process map to facilitate the design of inductors on organic substrates and is illustrated in application case study. With the map, inductors can be designed to have specific level of tolerance with less design-prototyping cycles.

Quantitative Analysis of Resistance Variations in Nickel-Phosphorus (NiP) Resistors

Embedded resistors can be fabricated by plating resistive Nickel-Phosphorus (NiP) alloy to form resistors on circuit boards. As-deposited NiP alloy resistors typically have poor resistance tolerances and require tuning by costly laser trimming to meet specifications. The cost of the resistors can be reduced if the tolerances can be reduced without laser trimming. In this study, a group of parameters affecting patterning accuracies, plating and sheet resistivities were varied to evaluate their effects on the resistance tolerances of electroless-plated NiP resistors. The effect of the substrate on sheet resistivity variations was also characterized. Design guidelines to obtain NiP resistors with low tolerance without laser trimming arc discussed.

Novel low temperature BaTiO/sub 3/ film capacitors

For embedded capacitor application, only dielectric materials with low processing temperature can be applied to printed wiring board manufacturing. Low temperature processable polymer/ceramic composites have been investigated to meet this need. The dielectric constant is a function of matrix and filler dielectric behavior, and the dielectric constant of highly filled composites is theoretically limited by the low dielectric value of the polymer matrix. In this investigation, we have developed a new amorphous low temperature processable matrix for use in dielectric composites. The new matrix processed at 300/spl deg/C was characterized to have a dielectric constant of 30. At a deposited thickness of 0.5 /spl mu/m, the capacitance density of the pure matrix film can reach 1500pF/mm/sup 2/ before addition of high dielectric constant filler.