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Course Recommendations (These materials are for non-commercial educational use only. If copied for that purpose, a courtesy email to [email protected] is requested) The tutorials presented will not, by themselves, constitute courses. That requires additional work depending on the depth of the various topics and the background and experiences of the instructor(s). The tutorials are intended to serve as the skeleton of a syllabus for several courses. Depending on the expertise and background of individual instructors and the level of laboratory facilities, the tutorials are useful for further development into courses in scaling, lithography, micrometrology, and micromechanical machining. Aspects of the tutorials have also been used as supplementary materials for courses in traditional machining analysis, heat transfer and fluid flow, precision engineering, metrology, robotics and automation, and capstone design projects. The following course syllabi have been taught in roughly the manner shown and have proven to be successful from student feedback and recruitment. Introduction to the Microscale (can be a technical elective, general education science elective, or an introductory graduate course depending on the level of materials presented) Learning Objectives - Students will be able to: Estimate the performance or behavior of systems or phenomena when the macroscale dimensions are reduced to the microscale Predict the optimum dimensions of a component which must interact with a phenomena; what is the optimal degree of scaling to maximize performance, sensitivity, influence, etc? Identify and describe the basic fabrication and measurement technologies used at the microscale and how they can interface with the macroscopic world Establish basic design parameters and restrictions for several classes of microcomponents (sensors such as chemical, optical, magnetic, etc; actuators such as piezoelectric, magnetostrictive, thermal bi-morphs, etc) 1. Historical development of the semiconductor industry and a similar development of microsystems. Many materials are available on the decrease in size of integrated circuits and how microprocessors are being integrated into consumer products. 2. Progression in scale of mechanical components from the early Swiss watch industry through precision machining for defense programs. The development of micro-mechatronics and MEMS from the early 80's. Many aspects of 1 and 2 can be found in the popular literature and the web. 2. Consequences of scaling with applications which are student-driven. Typical assignments are for students to take constitutive relationships from their own areas of interest and produce the scaling equations. From this, they estimate the advantage of shrinking the hardware to the microscale. Then, given the same scaling approaches, they describe the advantages and problems associated with their suggested methods for fabricating their proposed components or systems. 2. A general introduction to how things are measured at the microscale. Because this course is intended to be a survey, topics are introduced which inspire interest and imagination. The technique for “measuring” atoms by a scanning tunneling microscope is quite simple, in concept. Most universities have a scanning probe microscope of some sort, or a scanning electron/transmission electron microscope which can be demonstrated to show how measurements are made with instruments operating with other than light and linear scales. 2. A general introduction to machine tool kinematics and how difficult it can be to accomplish micrometer-scale precision. A general discussion of thermal errors also helps provide added insight. Simple lumped mass or finite element models can be incorporated here to model and predict mechanical distortion due to thermal, static, and dynamic influences. The goal here is to instill an appreciation for the headaches of working at the microscale. 2. One particularly useful endeavor, and one which depends on the specific institution, is to have faculty from engineering and the sciences give a one-period guest seminar on how their research utilizes the microscale. If the faculty also have specific laboratories, have them plan a one-period demonstration. There are many overlaps among the life sciences and engineering approaches to working at the microscale. Many engineering and science students have heard of and are surrounded by microtechnologies, but know little of the capabilities, limitations, materials, manufacturing processes, or integration of them. This introductory course is intended to provide an appreciation of those factors. Introduction to Lithography (senior technical elective or graduate course depending on the level of materials presented). This course requires some hardware and supplies, but they can be compromised and still get good results. The purpose is to teach the processes and not develop a particular micro-component or system. The course also introduces the chemicals and handling precautions used in lithographic fabrication. 1. Learning Objectives - Students will be able to: Identify and describe the basic fabrication steps and equipment used for optical and x-ray lithography Develop a process plan for the fabrication of microstructures by lithography and etching Establish basic design parameters and restrictions for several classes of microcomponents (sensors such as chemical, optical, magnetic, etc; actuators such as piezoelectric, magnetostrictive, thermal bi-morphs, etc) based on lithographic fabrication Know the basic hazards of working with process chemicals, how to deal with safety hazards, and proper disposal of spent chemicals Introduction to lithography via a photographic darkroom. Many students are familiar with the concept of black and white photography. The similarity helps introduce lithography and puts many of the specialized terms into a more commonly used context. 1. Introduction to silicon as an engineering material. Kurt Peterson’s paper and the more recent literature, especially on the web, allow students to get a good understanding of the material with which they will be working, how it is made and processed, and how it is integrated with other materials in microsystems and packages. This is not to say silicon is the only material with which to do lithography but access to an x-ray source for DXRL is probably not possible. “Low aspect ratio” optical lithography can be compared with DXRL and the limitations various high and low aspect ratio resists can be compared 1. Lithographic simulation software is also available. A web search will turn up the commercial vendors of such packages. 1. The laboratory component of the course can be as simple or sophisticated as the equipment allows. Small quantities of resist are normally available from suppliers (again a web search will quickly locate the suppliers). A crude resist spinner was made from a surplus variable speed motor with a maximum speed of 2400 rpm. A wafer chuck was a simple aluminum plate attached to the motor shaft. Relatively low resolution masks can be made using a high resolution laser printer and overhead transparency film. A more sophisticated approach may be found at://mems.isi.edu/archives/tools/PSMASKMAKER/ A UV exposure lamp may be made from an old EPROM eraser and this requires some experimentation to get the exposure time correct. Resist bakes can be performed on an ordinary hot plate. Development of the resist can also use a hot plate and glass beakers. Ordinary chemical fume hoods are very useful for these process steps. The labs can be advanced to etching, dicing, packaging, etc depending on equipment availability. Universities with more advanced capabilities typically have students design and fabricate some sort of microsensor or actuator. These lab procedures are admittedly crude, but are useful for students to understand the sophistication required of modern microlithography. Introduction to Micrometrology (undergraduate elective in engineering, science, or technology or a graduate course). The goal of this course is not to train students in the use of micrometrology equipment but rather a knowledge of the equipment available, its basis of operation, physical limitations, and most importantly the analysis, presentation, and skepticism of metrology data. As with a calculator or computer, students are too ready to accept results from any computer-driven instrumentation without interrogating the data or instruments. Learning Objectives - Students will be able to: Describe the operating principles of scanning electron microscopes, scanning probe microscopes, interferometric measurement systems, and the inherent advantages and disadvantages of each Estimate the performance of metrology systems given the principles of operation and the operating environment Perform analyses in the spatial and frequency domains to identify processing characteristics and errors Apply principles of statistics to sets of metrology data to determine instrument biases, repeatability, and significance tests to variations in processes, particularly micromechanical machining 1. Conventional metrology should first be introduced for students to re-acquire the important concepts of significant digits, repeatability, statistical distributions in a series of measurements, and the importance of calibration and standards. This introduction can make use of ordinary scales, machinist’s calipers and micrometers, dial indicators, etc. The important aspect here is to get the students in the habit of first questioning measurement results, and then accepting them after careful scrutiny. 1. Statistical significance testing can be introduced and experiment design used to investigate importance and interactions of variables associated with metrology. For measurements with good micrometers or dial indicators, the variables include temperature, operator bias such as compression of the sample by the micrometer, cleanliness of the micrometer heads, resolution of the readings, and of course whether the operator wears a hat or not. If a statistical approach is taken, the null variable should be included to see if the process is biased or random. 1. Introduction to metrology parameters include part variables such as squareness, flatness, orthogonality, parallelism, perpendicularity, etc. Micrometrology can go well beyond simple surface roughness. 1. Introduction to roughness parameters such as average, root-mean-square, and peak-to-valley. Students typically write a small program to accept an input data set of horizontal and vertical data points. The program will calculate the three roughness variables. This does not require any type of actual metrology instrumentation. If it is available, so much the better. As a follow on, students write small programs to do a fast Fourier transform, to calculate the spectral density, and the autocorrelation function. This demonstrates the importance and advantages of working in the frequency domain over the spatial domain. Because parts made by machines, lithography, etc where the process can have a subtle periodic nature, this helps students identify the source of the periodic errors or variations based on the frequency content and relative amplitude among those frequencies. 1. After the basics are well founded, the course can then introduce the hardware and methods for micrometrology. Most campuses have a scanning electron microscope and this can be demonstrated after the basics of operation have been explained. A good understanding of the theory of scanning electron microscopy will enable students to better understand the images they acquire and the validity of the metrology the instrument gives them. This is one instrument where students must learn to question the results. 1. Additional micrometrology instruments may be available for demonstrations. Many/most campuses have a scanning probe microscope for demonstrations. Many campuses have a laser or white-light interferometric microscope, confocal microscope, stylus instrument, or other specialized metrology tools. These can also include coordinate measuring machines. Here there flexibility in the course is based on the local capabilities. Introduction to Micromechanical Machining (senior technical elective or graduate course, the students should already have had a course in conventional manufacturing processes and/or machining analysis). The purpose here is to compare and contrast true machining at the microscale with that at the macroscale, and to introduce the advantages and limitations of the processes. Learning Objectives - Students will be able to: Describe the advantages and disadvantages of micromechanical machining compared to other microfabrication techniques and when each is the most appropriate fabrication technique Estimate the resulting feature sizes, surface finish, tolerances, and time to machine based on micromechanical machining Predict the machining forces, stresses induced in the cutting tools and work piece, and life of the cutting tool Establish basic design parameters and restrictions for several classes of microcomponents (actuators such as piezoelectric, magnetostrictive, thermal bi-morphs, etc) 1. Most undergraduate mechanical engineering students take a course in conventional manufacturing where metal cutting processes are introduced and analyzed. Depending on the level of analysis performed on the forces encountered in metal cutting, students may need some introductory material on modeling the metal cutting processes (turning, milling, drilling). There are several excellent references including Boothroyd and Knight’s Fundamentals of Machining and Machine Tools, and DeVries’ Analysis of Material Removal Processes, for example. It is important for the students to have a general understanding how the various machining parameters (speed, depth of cut, rake angle, etc) affect the machining forces because at the microscale the parameters are more difficult to identify, visualize, and quantify. 1. Because machining takes place with machine tools, the factors which influence the machining precision and the ability to machine small features are introduced. Machine tool kinematics share most of the basic characteristics of orthogonal robots so homogeneous transformation equations between coordinate systems is a valuable tool to help quantify machine tool work envelopes, coupled errors, and vibration. Associated with this are the many sources of machining errors which are given in the “Overhead Text” section following the syllabi. This portion of the course is probably the most important because it is applicable at all scales. 1. Each micromachining process is introduced and the machining parameters are identified and compared with the macroscale. Diamond machining is introduced first since its geometry is the least complex. The primary differences between diamond machining and conventional turning is the depth of cut, sharpness of the cutting edge, and relatively low material removal rate. Also, at this point the machinability of various materials by diamond is covered. 1. The next more complex geometry is micromilling, but it is still relatively simple because of the use of straight cutting edges. Forces are modeled, stress in the tool is analyzed, and forces on the work piece are also calculated. Methods to fixture the work piece in the presence of the cutting forces are also covered. 1. The final metal cutting process covered is microdrilling. While not as complex as twist drills, micro-spade drills have sufficient geometric complexity to introduce oblique machining. While not covered in depth, oblique machining is compared to orthogonal machining in terms of the additional force component and its affect on the machining process. 1. Given time, other micromechanical processes can be introduced such as microEDM and laser micromachining. This course must have a laboratory component and can be as extensive as facilities allow. Commercial drills and milling tools can be obtained down to a size of 50 micrometers however use of the tools requires a video microscope system to view the process and also requires machine tools with smooth and slow motions. Integration Into Existing Courses It has been found that integrating miniaturization technologies into traditional courses can make traditional engineering subjects more exciting and applicable. It provides students with further examples how the basic principles can be applied and also the limitations of the basic principles because of certain assumptions made in their development. Each of the following examples was tried and found to be beneficial and interesting to the students. Machining Analysis and Introduction to Manufacturing Processes These courses are normally part of the mainstream mechanical engineering curriculum as either required or elective courses. In machining analysis, the integration of micromilling and microdrilling is very beneficial because it shows the strong dependence of local rake angle (at the cutting edge rather than the gross rake angle of the tool rake face) on the machining forces. Using a large negative rake angle as is present in micromachining, the traditional equations for calculating the shear plane angle break down and give a shear plane angle near zero, or even a negative value. At large negative rake angles, the relative velocity between the cutting tool and the chip in the feed direction may change sign one or more times reversing the direction of the friction force on the tool. Investigation of the specific cutting energy approaches show that the machining forces become very large as the tool strength becomes very small. Many introductory manufacturing courses deal with forming and removal processes and may not have time to cover additive processes such as lithography and plating. However, the time required is minimal for the students to understand the basic advantages and limitations of the lithographic approaches. Certainly, engine blocks are not made by this process but many small components such as fuel injector nozzles are routinely made by lithography and plating. Non-traditional processes such as electrical discharge machining and laser machining are finding wider acceptance in conventional manufacturing and can be integrated with microscale applications. Challenges in the design of injection molding dies and cycle parameters abound at the microscale and can be compared with the process at the conventional scales. Metrology Many curricula offer a course in metrology as a technical elective. Normally the course deals with the basic quantifiers of surface roughness and this can be extended to the microscale very easily. If coordinate measuring machines are included in the discussions, measurement errors due to static deflection and joint feedback resolution can be covered using the homogeneous transformations used to describe errors in precision machine tools. If time or resources permits, demonstrations of micrometrology on a scanning electron microscope or probe microscope give added value to students’ awareness of the spectrum of metrology tools available. Heat Transfer and Fluid Flow All undergraduate mechanical engineering students take a course(s) in heat transfer and fluid flow. Size is addressed in terms of fins for convection, wall resistance, friction factor, pressure drop, pumping power, heat exchanger design and performance, etc. These provide many opportunities for discussion and illustration of how the basic equations apply as the size scale shrinks. There is still considerable research being conducted to better understand and predict these microscale phenomena which shows that some of the underlying assumptions used in the derivation of the macroscale correlations may not be applicable at very small scales. Surface effects tend to dominate at the microscale and many interesting scaling analyses can help illustrate this importance. Capstone Design Opportunities abound for design projects based around miniaturization. If infrastructure is in place, realization of the designs may be possible. Where the design is based on micromechanical machining, larger-scale prototypes can be fabricated and perhaps tested. The list below is not intended to be comprehensive but illustrates several of the design projects which have been conducted with success. 1. Design and realization of a custom 5-way high vacuum cross for an x-ray micromachining beamline; design was conducted to predict cost of commercial production, method of actuating internal x-ray mirrors and location of electrical feedthroughs, determine any physical interferences among moving parts and structure, physical and electrical integration into existing x-ray beamline. 1. Design of fixtures to hold parts for micromechanical machining; design was for generic families of fixtures to hold small wires, gears, shafts, tools, etc which will be micromachined, fixtures had to induce minimal strain in the work piece yet provide sufficiently rigid constraint to maintain precision in the presence of machining forces, fabrication methods were investigated and proposed for making and testing the fixtures, costs for special fabrication processes were also estimated. 1. Cross-flow micro heat exchanger design; prediction of thermal performance and pressure drops for a two-fluid heat exchanger with passages on the order of 100 micrometers hydraulic diameter, methods for fabricating and hermetically bonding the heat exchanger plates together, designs for fluid manifolds, and design of a testing apparatus. 1. Counter-flow micro heat exchanger design; prediction of thermal performance and pressure drops for a two-fluid heat exchanger with passages on the order of 100 micrometers hydraulic diameter, methods for fabricating and hermetically bonding the heat exchanger plates together, designs for fluid manifolds, and design of a testing apparatus. 1. Three-fluid micro heat exchanger design; prediction of thermal performance and pressure drops for a heat exchanger with passages on the order of 100 micrometers hydraulic diameter and the fluid passages oriented orthogonal to each other, methods for fabricating and hermetically bonding the heat exchanger plates together, designs for fluid manifolds, and design of a testing apparatus. 1. Inspection and quality control at the microscale; vision systems are used for inspection and part acceptance/rejection in conventional manufacturing and these methods have been adapted for microscale inspection, part and tolerance resolution requirements for a video microscope system, system resolution required for a range of part tolerances, tests to measure geometries such as perpendicularity, parallelism, radius of curvature, etc. 1. Other generic projects include; design of reconfigurable injection molding dies based on computer-controlled micro/milli-actuators, milliscale turbochargers, milliscale superchargers, milliscale cryocoolers, lubrication oil heaters and circulators for cold engine starting, engine waste heat recovery systems, etc.