Yung-Cheng Lee

University of Colorado at Boulder , Boulder, CO, United States

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Publications (18)11.29 Total impact

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    ABSTRACT: This paper presents the results of an investigation of the thermal mechanism between lasers and surface-micromachined micromirrors. Finite element models using ABAQUS are established and used to study the temperature distribution on the surface of micromirrors under high-power laser illumination. It is shown that heat conduction through the gas gap between the mirror surface and the substrate is the dominant thermal dissipation mechanism for high surrounding gas pressure, while heat conduction through the flexures is dominant for low surrounding gas pressure. Based on the simulation results, two novel methods are proposed in order to tolerate more power input under low surrounding gas pressure. The results of optical power testing validate these models, and indicate that these two approaches are efficient in improving micromirror performance for high-energy applications.
    IEEE Transactions on Advanced Packaging 09/2003; · 1.12 Impact Factor
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    ABSTRACT: The emerging technology of micro-optical-electro-mechanical systems (MOEMS) offer promise for automating the alignment of free-space optical systems, especially intra-computer optical interconnects. MOEMS-based microlenses and micromirrors have been fabricated for the purpose of providing initial system alignment and dynamic alignment.
    02/2003
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    ABSTRACT: In this paper, a new micro-optical system for VCSEL-to-fiber active alignment is described. An integrated microsystem platform, which has a thermally-actuated micromirror, a silicon etched v-groove and flip-chip function, is successfully fabricated and actuated for beam adjustment from a vertical-cavity surface-emitting laser (VCSEL) to a fiber. The micro-optical system has 4.0° maximum beam steering angle with the resolution of 0.08°/mA. With the steering angle reaching 2.5°, the coupling efficiency from the VCSEL to the fiber improves to more than 80% from 9% initial efficiency of 25 μm misaligned fiber position.
    Sensors and Actuators A Physical 01/2003; · 1.84 Impact Factor
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    ABSTRACT: We report a new micro-optical system for laser-to-fiber active alignment. An integrated microsystem platform, which has a thermally-actuated micromirror, a silicon etched v-groove and flip-chip bonding pads, is successfully fabricated and actuated for beam adjustment from a vertical-cavity surface-emitting laser (VCSEL) to a fiber. The micromirror has 4.0 degree maximum beam steering angle with the resolution of 0.08 degree/mA. With the steering angle reaching 2.5 degrees, the coupling efficiency improves to 80 % from 9% initial efficiency
    Micro Electro Mechanical Systems, 2002. The Fifteenth IEEE International Conference on; 02/2002
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    Qing Tan, B. Schaible, L.J. Bond, Yung-Cheng Lee
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    ABSTRACT: Thermosonic flip-chip bonding is a wire bonding technology modified for flip-chip assembly. Compared with the soldering technology, it is simpler, faster and more cost-effective. Unfortunately, the yield of thermosonic bonding is low and unreliable because it is difficult to control the ultrasonic energy transmission. A small planarity angle between the bonding tool and stage can result in a nonuniform ultrasonic energy distribution. A self-planarization concept was proposed to solve this problem. A layer of polymer was placed between the bonding tool and the chip to smooth the nonplanar contact. Experimental measurements and finite element modeling were used to study the effect of the polymer layer. Results showed that the polymer layer could assure a uniform ultrasonic energy distribution; however, it also reduced the energy transmission efficiency. A case study for optimization was conducted based on finite element modeling. For a 1000-I/O flip chip assembly with a 250 μm pitch using a bonder with a 0.01° planarity angle, polymer thickness of 350 μm and a Young's modulus of 2 GPa were selected
    IEEE Transactions on Advanced Packaging 09/1999; · 1.12 Impact Factor
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    ABSTRACT: A packaging technology has been developed to integrate a lenslet array with surface micromachined segmented deformable micromirrors. 12 X 12 electrostatic micromirror arrays were fabricated through a commercial surface micromachining process and integrated with glass microlenses positioned directly over the micromirror. Control of the spacing and the lateral alignment between the lenslet array and the micromirrors was important for effective fill factor. The spacing control was accomplished using glass spacer, and the lateral alignments were achieved by the use of an interferometric microscope. Measured results of the micromirrors' optical performance demonstrated the success of the packaging technology.
    Proc SPIE 01/1999;
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    ABSTRACT: This paper reviews the assembly and packaging of miniature liquid-crystal-on-silicon (LCOS) displays. Reflective-mode LCOS displays require thin cell gaps with strict tolerances - a difficult optoelectronics assembly problem. Important assembly and packaging considerations include the substrate thermal properties, substrate flatness and packaging chronology. Two approaches are described: spatial light modulator assembly using self-pulling solder reflow and wafer scale display assembly using photo-definable resins. Simulation and experimental results are summarized.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    04/1998;
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    ABSTRACT: Flip-chip assembly is an important technology for first level electronic packaging. Among different assembly approaches, thermosonic bonding is becoming an attractive choice because it is cost-effective. To increase the bonding capability for high input/output (I/O) assembly, a novel longitudinal bonding system was developed in this study. This bonding system has two advantages over the transverse bonding system: it overcomes the planarity problem and simplifies bonding tool configuration. During the development, an end-effector was designed with rigorous considerations of ultrasonic wave propagation, bonding force and co-planarity between the chip holder and hot stage. The bonding system was then characterized to make sure that it is suitable for flip-chip assembly. This bonding technology was proven successful by mechanical bonding tests as well as a functional complementary metal-oxide-semiconductor/static random access memory (CMOS/SRAM) module demonstration. During the bonding process, the chip is under longitudinal ultrasonic “hammering.” However, there is no apparent damage because the impact stress is low due to the low ultrasonic vibration amplitude
    IEEE Transactions on Components Packaging and Manufacturing Technology Part B 03/1998;
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    ABSTRACT: This paper reviews the assembly and packaging of miniature liquid-crystal-on-silicon (LCOS) displays. Reflective-mode LCOS displays require thin cell gaps with strict tolerances - a difficult optoelectronics assembly problem. Important assembly and packaging considerations include the substrate thermal properties, substrate flatness and packaging chronology. Two approaches are described: spatial light modulator assembly using self-pulling solder reflow and wafer scale display assembly using photo-definable resins. Simulation and experimental results are summarized.
    Proc SPIE 01/1998;
  • B. Schaible, Hong Xie, Yung-Cheng Lee
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    ABSTRACT: When modeling and analyzing manufacturing processes, it may be helpful to know the relative importance of the various process parameters and their interactions. This ranking has traditionally been accomplished through regression modeling and analysis of variance (ANOVA). In this paper, we develop a fuzzy logic modeling technique to rank the importance of process effects. Several different cases are presented using functions that allow the determination of the actual importance of effects. The impact of noisy data on the results is considered for each case. It is shown that in many cases the fuzzy logic model (FLM) ranking methodology is capable of ranking process effects in the exact order or in an order reasonably close to the exact order. For complex processes where regression modeling and ANOVA techniques fail or require significant knowledge of the process to succeed, it is shown that the FLM-based ranking can be performed successfully with little or no knowledge of the process
    IEEE Transactions on Fuzzy Systems 12/1997; · 5.48 Impact Factor
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    ABSTRACT: Optoelectronic technologies and devices have developed at a rapid rate, resulting in a large array of materials systems and structures that may be integrated into optoelectronic modules and subsystems. However, because these devices are made of a variety of materials systems, there is a fundamental mismatch between their optical modes. This mismatch affects coupling efficiency and sensitivity to tolerances. The coupling efficiency between laser diode arrays or OEIC components and single-mode fiber ribbons drops rapidly with increasing misalignment tolerance. There are trade-offs between the allowed minimum coupled power and the cost of establishing the required alignment. We are using a polymeric waveguide film that contains optical structures to transform optical mode patterns between components made from dissimilar materials systems. We demonstrate how tapered polymer waveguides may be used to match the laser mode to the fiber mode, resulting in a module with decreased alignment requirements for a given coupling efficiency Waveguides which simultaneously taper the mode both laterally and vertically have been designed. Waveguides with tapered mode profiles have been constructed using photobleaching of a guest/host dye/polymer system. Amoco 4212 polyimide doped with DCM dye was chosen as the waveguide material due to its good thermal stability and its simple processing. We present numerical results showing the variation of coupling efficiency into tapered waveguides with component misalignment. The alignment between components is established by self-aligned flip-chip solder bonding
    Electronic Components and Technology Conference, 1997. Proceedings., 47th; 06/1997
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    ABSTRACT: This paper reports the results of our thermosonic (T/S) flip-chip bonding process development for the assembly of a smart pixel array (SPA) using an 8×8 vertical cavity surface emitting laser (VCSEL) array. The introduction of ultrasonic energy into the flip-chip bonding process increases the speed of the assembly process while at the same time lowering the physical stresses (temperature and assembly force) applied to bond the components. Many empirical studies have shown that T/S flip-chip bonding is feasible, but there is a lack of detailed understanding of the effects of the ultrasonic energy on the bonding results. We are conducting experiments and developing models that will provide a sound understanding and a rational basis for T/S flip-chip bonding. In particular, we have addressed the problems of the impact of joint bump size, control of the assembly force, and the repeatability of the ultrasonic power. This report details our findings concerning the following aspects important to the development of T/S flip-chip bonding technology: (1) Computer modeling to guide the selection of design parameters and provide a basis to study the effects of the interaction of the critical design and process parameters on process yield. (2) Design of a new end effector for accurately applying and monitoring small assembly force. (3) Monitoring and controlling the impedance of the ultrasonic mechanical and electrical system in order to insure repeatable delivery of acoustic energy to the assembly
    IEEE Transactions on Components Packaging and Manufacturing Technology Part B 06/1997;
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    ABSTRACT: The coupling efficiency between laser diode arrays or OEIC components and single-mode fiber ribbons drops rapidly with increasing misalignment tolerance. There are trade-offs between the allowed minimum coupled power and the cost of establishing the required alignment. We demonstrate how tapered polymer waveguides may be used to match the laser mode to the fiber mode, resulting in a module with decreased alignment requirements for a given coupling efficiency. Waveguides with tapered mode profiles have been constructed using photobleaching of a guest/host dye/polymer system. Amoco 4212 polyimide doped with DCM dye was chosen as the waveguide material due to its good thermal stability, and its simple processing which allows multilayer waveguides to be readily fabricated. In particular, waveguides which simultaneously taper the mode both laterally and vertically have been designed. This waveguide system is compatible with assembly of the laser and waveguide components into a module by flip-chip soldering. Our solder self-alignment technique achieves accurate alignment of touching chips through an understanding of the dynamics during bonding.
    Proc SPIE 11/1996;
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    ABSTRACT: A self-pulling soldering technology has been demonstrated for assembling liquid crystal on silicon (LCOS) spatial light modulators (SLMs). One of the major challenges in manufacturing the LCOS modules is to reproducibly control the thickness of the gap between the very large scale integrated circuit (VLSI) chip and the cover glass. The liquid crystal material is sandwiched between the VLSI chop and the cover glass which is coated with a transparent conductor. Solder joints with different profiles and sizes have been designed to provide surface tension forces to control the gap accommodating the ferroelectric liquid crystal layer in the range of a micron level with sub- micron uniformity. The optimum solder joint design is defined as a joint that results in the maximum pulling force. This technology provides an automatic, batch assembly process for a LCOS SLM through one reflow process. Fluxless soldering technology is used to assemble the module. This approach avoids residues from chemical of flux and oxides, and eliminates potential contamination to the device. Two different LCOS SLM designs and the process optimization are described.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    10/1996;
  • Nina D. Morozova, Yung-Cheng Lee
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    ABSTRACT: An integrated tool has been developed to predict how vertical cavity surface emitting laser (VCSEL) light output power is affected by packaging components. The set that has been developed includes modeling tools for devices and packages. The integrated tool can be useful for choosing an optimum specific package design for a VCSEL structure and to predict its characteristics in different packages under a variety of operating conditions. In this paper the integrated tool has been applied to study how VCSEL light output power is affected by different assembly technologies and packaging materials.
    Proc SPIE 03/1996;
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    ABSTRACT: A self-pulling soldering technology has been demonstrated for assembling liquid crystal on silicon (LCOS) spatial light modulators (SLMs). One of the major challenges in manufacturing the LCOS modules is to reproducibly control the thickness of the gap between the very large scale integrated circuit (VLSI) chip and the cover glass. The liquid crystal material is sandwiched between the VLSI chop and the cover glass which is coated with a transparent conductor. Solder joints with different profiles and sizes have been designed to provide surface tension forces to control the gap accommodating the ferroelectric liquid crystal layer in the range of a micron level with sub- micron uniformity. The optimum solder joint design is defined as a joint that results in the maximum pulling force. This technology provides an automatic, batch assembly process for a LCOS SLM through one reflow process. Fluxless soldering technology is used to assemble the module. This approach avoids residues from chemical of flux and oxides, and eliminates potential contamination to the device. Two different LCOS SLM designs and the process optimization are described.
    Proc SPIE 01/1996;
  • Hong Xie, R.L. Mahajan, Yung-Cheng Lee
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    ABSTRACT: This paper presents fuzzy logic models (FLM) to simulate two thermally based microelectronic manufacturing processes: the “pool boiling” in vapor phase soldering and silicon deposition process in a horizontal chemical vapor deposition (CVD) reactor. After a brief discussion of the various input-output models, we present our general approach to the development of FLM's, followed by their application to the two case studies. For the pool boiling, experimental data are used to develop the fuzzy logic model. Results show that the FLM not only simulates the different regions of the pool boiling curve satisfactorily, but also faithfully represents the two transitions. For the CVD process, pseudo-analytical equations from Eversteyn's paper are used to generate data under simulated production conditions. Results show that the model can describe the process very well. The physico-fuzzy model, incorporating the physical understanding of the process, is shown to improve the model's extrapolation capability
    IEEE Transactions on Semiconductor Manufacturing 09/1995; · 0.86 Impact Factor
  • Jian Tan, Hong Xie, Yung-Cheng Lee
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    ABSTRACT: Fuzzy logic modeling using internal and membership functions is a promising technique for the modeling and control of semiconductor manufacturing and packaging processes. To simplify its implementation procedure, a fuzzy logic model needs to be established with the minimum user interference. An algorithm with two major steps has been proposed and demonstrated for the efficient model establishment The first step develops intermediate fuzzy logic models with different numbers of membership functions assigned to each input variable. The number is one for the simplest model, and is increased one by one according to the pre-defined sequence and pathfinding criteria for more complex models, The second step stops the incremental procedure when the stopping criteria are met. The criteria are the multiple correlation factors R <sup>2</sup> based on the training and the testing data. The algorithm's accuracy and efficiency have been demonstrated by testing it with five two-variable, nonlinear functions
    IEEE Transactions on Semiconductor Manufacturing 03/1995; · 0.86 Impact Factor