Additive Manufacturing History

Special Processing and Assembly Technologies

• Rapid Prototyping and Additive Manufacturing emerged in the mid-1980s.
• Processing of Integrated Circuits began in the 1960s.
• Electronics Assembly and Packaging technologies were developed.
• Microfabrication Technologies followed soon after IC processing.
• Nanofabrication Technologies were introduced in 1990.

Rapid Prototyping and Additive Manufacturing History

• Solid Ground Curing (SGC) exposes photopolymers using a physical mask.
• Selective Laser Sintering (SLS) sinters or melts powder layers with lasers.
• Laminated Object Manufacturing (LOM) cuts paper sheets for part construction.
• Fused Deposition Modeling (FDM) was patented in 1989.
• In 1989, MIT researchers patented "3-D Printing," using ink-jets to deposit binder droplets onto powdered material layers.
• In 1994, a similar inkjet technology approach was developed to deposit the material itself to form layers, rather than a binder on powder.

Fundamentals of Rapid Prototyping and Additive Manufacturing

• RP and AM are families of fabrication processes making engineering prototypes or production parts, based on a CAD model of the item in minimum lead time.
• Traditional methods have longer lead times than RP/AM, where RP/AM takes hours or days compared to weeks.
• Rapid Prototyping is a subset of Additive Manufacturing when the purpose is to make a prototype.
• RP is important because the physical model of a part provides more information than a 2D or 3D drawing, while virtual CAD prototypes do not provide adequate visualization, and designers benefit from the tactile feedback to perceive merits/shortcomings.

Available RP Technologies

• Material Removal RP involves small desktop machining using CNC, with wax as the starting material.
• Material Addition RP builds solid parts from bottom to top by adding layers of material at a time.

Advantages of Material Addition RP Technologies

• Material Addition RP Technologies allow for quick part delivery.
• Material Addition RP Technologies eliminate CNC part programming, because the CAD model is the part program.
• Material Addition RP Technologies have no issues with part geometry complexity.

Steps to Prepare Control Instructions (Part Program)

• Geometric modeling involves designing the component on a CAD system to define its enclosed volume.
• Tessellation of the geometric model converts the CAD model into a computerized format approximating its surfaces using facets, such as triangles or polygons.
• Slicing the model into layers involves slicing the computerized model into closely spaced parallel horizontal layers.

Starting Materials in Material Addition RP

• Liquid polymers are cured layer by layer into solid polymers.
• Powders are aggregated and bonded layer by layer.
• Molten materials are solidified layer by layer.
• Solid sheets are laminated to create the solid part.

Layer Forming Processes

• Lasers are used in layer forming.
• Printing heads operating with ink-jet technology are used in layer forming.
• Extruder heads are used in layer forming.
• Other processes such as electron beams, cutting knives, and UV light systems are used.

Three Basic Channel Modes

• Moving point or moving spot mode builds layers by solidifying a point at a time.
• Moving line mode builds layers by solidifying a line across the entire layer in one translational motion.
• Layer mode builds layers by creating the entire layer at same time.

Additive Manufacturing Processes

• Liquid-based AM processes include Stereolithography (SL) and mask projection stereolithography (MPSL).
• Powder-based AM processes include Selective Laser Sintering (SLS) and three-dimensional printing (3DP).
• Molten material AM processes include Fused Deposition Modeling (FDM) and droplet deposition manufacturing (DDM).
• Solid-based AM processes include Laminated object manufacturing (LOM).

Liquid-Based AM System: Stereolithography (SL)

• Stereolithography is an RP process to fabricate a solid plastic part from a photosensitive liquid polymer by using a directed laser beam to solidify the polymer.
• Part fabrication in Stereolithography is accomplished as a series of layers, where each layer is added onto a previous layer to gradually build the 3-D geometry.
• The first addition RP technology was Stereolithography, introduced in 1988 by 3D Systems Inc. based on Charles Hull's work

Stereolithography Facts

• Typical layer thickness in Stereolithography ranges from 0.05 mm to 0.150 mm (0.002 in to 0.006 in).
• Thinner layers provide better resolution and more intricate shapes but increase the processing time.
• Typical liquid photopolymers used in Stereolithography include acrylic and epoxy.
• Polymerization occurs upon exposure to UV light produced by laser scanning beams.
• Scanning speeds are approximately 500 to 2500 mm/s.

Liquid-Based AM System Mask Projection Stereolithography (MPSL)

• Conventional stereolithography uses a single moving laser beam to cure the polymer.
• MPSL exposes an entire layer using a UV light source through a dynamic mask instead of a scanning laser beam.
• A dynamic mask is digitally altered for each layer, using a digital micromirror device with several hundred thousand microscopic mirrors.
• Exposure and curing processes in MPSL are shorter than in conventional SL.

Powder-Based AM System: Selective Laser Sintering (SLS)

• A moving laser beam sinters heat-fusible powders in areas corresponding to CAD geometry models one layer at a time to build the solid part.
• After each layer is completed, a layer of loose powders is spread across the surface.
• Layer by layer, the powders are gradually bonded by the laser beam into a 3-D solid geometry.
• In areas not sintered, powders remain loose and can be poured out of the completed part.
• A new layer of loose powders is spread and leveled using a counter-rotating roller.
• Layer thickness typically ranges from 0.075 to 0.5 mm.
• The SLS process is usually accomplished in an enclosure with nitrogen to minimize powder degradation from oxidation.
• SLS was developed by Carl Dekard at the University of Texas (Austin) in the mid-1980s as an alternative to Stereolithography, and was patented in 1989.
• SLS machines were marketed by DTM, a company formed by Dekard and two partners; DTM merged with 3D Systems Inc in 2001.
• SLS is more versatile than Stereolithography in terms of work materials.
• SLS materials include polymers, metals, and ceramics.
• SLS is a Powder Bed Fusion (PBF) process.
• Other PBF systems differ from SLS in heating/fusion techniques, powder handling methods, and powder bonding mechanisms.
• Line-wise and layer-wise processes are also used in PBF systems, as opposed to point-wise processes in SLS.

Powder - Based AM System: Three Dimensional Printing (3DP)

• Three Dimensional Printing builds parts by using an ink-jet printer to eject adhesive bonding material onto powder layers.
• The binder is deposited in areas corresponding to the cross sections of the part, as determined by slicing the CAD geometric model into layers.
• A binder holds the powder together to form the solid part, while the unbonded powder remains loose for removal later.
• Sintering strengthens the part by bonding the individual powders.
• Powder layer is deposited, followed by ink-jet printing of areas that will become the part, and then the piston is lowered for next layer.
• Materials used in 3DP include powders of ceramic, metal, or cermet, along with polymeric or colloidal silica, or silicon carbide binders.
• Typical layer thickness ranges from 0.1 – 0.2 mm.
• The ink-jet printing head moves across the layer at roughly 1.5 m/s.
• Ejection of liquid binder is determined during the sweep by raster scanning.
• 3DP has a 2 second cycle time per layer.
• 3DP machines can make 2 to 4 layers per minute.

Molten Material AM Systems: Fused Deposition Modeling (FDM)

• Fused Deposition Modeling involves extruding a long filament made of wax and/or thermoplastic polymer onto an existing part surface from a workhead to complete each new layer.
• The workhead is controlled in the x-y plane during each layer and then moves up by a distance equal to one layer in the z-direction.
• The extrudate is solidified and cold welded to the cooler part surface in roughly 0.1 s, and the part is fabricated layer-by-layer, from the base up.
• Typical layer thickness in FDM is 0.25 to 0.33 mm but can be lessened to 0.076 mm.
• Slow speed occurs because deposited material is applied in a moving point channel mode, and sharp corners are difficult to form because of a circular nozzle orifice.
• Stratasys Inc. developed FDM and sold their first machine in 1990.
• There are currentl more FDM machines used across the world than any other AM machine.

Molten Material Systems: Droplet Deposition Manufacturing (DDM)

• Droplet Deposition Manufacturing is also known as Ballistic-Particle Manufacturing.
• The process uses a melted starting material, where small droplets are shot by a nozzle onto a previously formed layer.
• Droplets cold weld to the surface, creating a new layer
• Deposition for each layer is controlled by a moving x-y nozzle whose path is based on a cross section of a CAD geometric model, which is sliced into layers.
• Work materials include wax and thermoplastics.

Solid Sheet-Based AM Systems: Laminated Object Manufacturing (LOM)

• Laminated Object Manufacturing creates a solid physical model by stacking layers of sheet stock, each an outline of the cross-sectional shape from a sliced CAD model.
• Starting sheet stock includes paper, plastic, cellulose, metals, or fiber-reinforced materials.
• Sheet stock is usually supplied with adhesive backing on rolls that are spooled between two reels.
• After cutting, excess material in the layer remains in place to support the part during building.
• LOM part sizes are relatively large among AM processes.
• Common work volumes are 380mm x 250mm x 350mm, while work volumes reach up to 800mm x 500mm x 550mm.
• Helisys, Inc. originally offered LOM systems.
• The Helisys machine processes paper backed with adhesive.
• The sequence is: the most recently added sheet was bonded to the existing structure before cutting the outline in that layer, where a heated roller is used to melt the thermoplastic adhesive in the bonding operation.
• Modifications in LOM introduced by other companies include cutting blades instead of lasers, polymeric sheets instead of paper, and cutting layers before bonding (for objects with internal features).

Cycle Time and Cost Analysis

• RP cycle time analysis has the formula: Tᵢ = Aᵢ/VD + Tᵣ, where Aᵢ is the area of layer I, V is the speed of the moving spot, D is the diameter of the moving spot, and Tᵣ is the repositioning time between layers. This calculates the time Tᵢ to finish one layer in moving-spot channel mode.
• RP cycle time analysis has the formula: Tᵢ = Lₛ/Vₛ + Tᵣ, to calculate the time Tᵢ to complete a layer in the single-line movement channel mode, where Vₛ is the velocity of the moving line and Lₛ is the length of the sweep across a layer.
• Cycle time analysis has the formula Tᵢ = Tex + Tᵣ, where Tex is the exposure time to complete a single layer in processes that use layer channel mode.
• Total cycle time equation to build part is: T𝒸 = Tₛᵤ + ΣTᵢ , where Tₛᵤ is machine set up time and nₗ is the # of layers to approximate the part and nₗ is the part height divided by the layer thickness
• RP Cost Analysis calculates the cost per piece (Cₚ𝒸) using the formula Cₚ𝒸 = Cₘ + (CₗUₗ + Cₑ𝓆)T𝒸 + CₗTₚₚ , where Cₘ is the material cost per piece, Cₗ is the labor cost per hour, Uₗ is the labor utilization factor, Cₑ𝓆 is the equipment cost per hour, T𝒸 is the cycle time per piece, and Tₚₚ is the post-processing time per part.

Additive Manufacturing Applications

• Rapid prototyping applications fall into four categories including Design, Engineering analysis and planning, Tooling and Parts production
• During design, users confirm their design quickly using RP.
• RP's design benefits include reduced lead times for prototypes, better visualization of part geometry, early detection of errors, and increased capabilities to compute mass properties.
• Engineering analysis and planning are facilitated by the physical parts, as engineering analysis/planning operations would be difficult without the physical entity.
• Using physical products for engineering analysis allows comparison to determine aesthetic appeal, analysis of fluid flow in valves, wind tunnels, the stress of the model, fabrication for pre-production, and combining medical images/RP.

Additive Manufacturing applications in Tooling and Parts Production

• Rapid tool making or RTM occurs during RP to fabricate production tooling.
• Indirect RTM creates a tool pattern, used for casting or electrodes for EDM. Direct RTM describes RP making the tool.
• Parts production is useful in small batch sizes, as well as intricate/custom geometries and spares, like bone replacements for medicine.

Problems with RP

• Part accuracy can be an issue using RP, including the staircase effect from layering, and issues of parts shrinking/distortion.
• RP is limited by material variety and mechanical performance.

Overview of IC Processing

• Integrated Circuits (ICs) are collections of electronic devices (transistors, diodes, resistors) that are fabricated and electrically interconnected on a small semiconductor chip.
• Silicon is the most widely used semiconductor material for ICs, less common materials are germanium and gallium arsenide.

Levels of Integration in Microelectronics

• Small Scale Integration (SSI) included 10-50 devices, established 1959
• Medium Scale Integration (MSI) included 50-103 devices, established 1960s
• Large Scale Integration (LSI) included 103-104 devices, established 1970s
• Very Large Scale Integration (VLSI) included 104-106 devices, established in 1980s
• Ultra Large Scale Integration (ULSI) included 106-108 devices, established 1990s
• Giga Scale Integration included 109 - 1010 devices, established 2000s

History and Overview of IC Technology

• Radar development before WWII lead to transistor development, the invention of Ics and their commercial development.
• Integrated circuits consist of millions of microscopic devices on a rectangular plate 0.5mm thick and 5-25mm per side. Regions consist of layers, with electronic properties to facilitate circuitry.

IC Transistor

• Transistors in integrated circuits have feature sizes of less than 40 mm.

Packaging of ICs

• To connect the IC to the outside world and protect it from damage, ICs are attached to a lead frame, encapsulated inside a package or enclosure.
• The package provides mechanical and environmental protection for the IC, and includes leads to connect to external circuits.
• One such package is the Dual In-Line Package (DIP), including a cutaway view showing the chip attached to a lead frame and encapsulated in an enclosure, in addition to view of user package.

Silicon Processing Sequence

• Silicon Processing involves using sand to create pure silicon, and shaping products into wafers.
• IC fabrication involves using steps to add, alter, and remove thin layers in selected regions to form electronic devices. Lithography is used to define the regions, and Ics are tested, cut and packaged.

IC Processing Sequence in Clean Rooms

• Much of ICs must be carried out in a clean room, similar to a hospital operating room.
• Cleanliness is dictated by decreasing feature sizes in circuits with increasing processing.

Silicon Processing

• Microelectronic chips are built on semiconductor material like silicon, accounting for 95% of manufacture today.
• Silicon substrate preparation is threefold: production of electronic grade silicon, crystal growing, and silicon shaping

Electronic Grade Silicon

• One of Earth's most prevalent materials, silicon occurs as silica and silicate, where the principal raw material is quartzite and electronic-grade is polycrystalline. Impurities are measured in parts per billion.

Crystal Growing and the Czochralski Process

• Silicon substrates are single crystal with certain orientations.
• Substrate wafers are directional to enable planar orientation, where single crystal boules are pulled from molten silicon with the Czochralski process.

Shaping of Silicon into Wafers

• Boules are turned into disc shaped wafers by ingot preparation, wafer slicing, and wafer preparation.
• Boulu preparation involves boule cutting to shape cylinders, and grinding flats for identification and orientation for processing.
• Cylindrical grinding controls shape, and thin, diamond grit cutting wheels are used to slice.
• Diamond abrasive cut-off saws have internal diameter (ID) for kerf control, where slicers have 0.33mm thickness.
• Wafers rims are rounded and etched to reduce process damage, and polished as surface treatment readying it for photolithography/processing. Wafers are then cleaned.

Lithography, Technologies & Photoresist

• Ics consist of microscopic regions on wafers for devices/connections
• In planar processes, regions are built in steps that add, change, and remove layers.
• Each layer is determined by geometric patterns. Different technologies exist using different radiation to transfer the mask pattern.
  • UV Photolithography is the most common process
  • Other processes, such as Electron-beam lithography, X-ray lithography, and Ion Lithography also exist.
• UV based materials must be sensitive light within certain frequency ranges as dictated by circuit.
• UV-sensitive photoresists allow low light operation in the plant and are made of organic polymers. Sensitivity either decreases or increases polymer solubility, with several techniques used in conjunction.

Photolithography Exposure Techniques

• Contact printing is a technique on thin material
• Proximity printing is a technique where thin material may be bent
• Projection printing is a lens-based mask method

Photolithography Processing Sequence

• Silicon wafers must be oxidized on the surface to form thin films.
• These films must be removed by mask patterns that are created in stages: surface prep/resist application, soft baking, masking, and resist exposure. Masks are then developed, hard baked, etched and resist stripped

Other Lithography Techniques

• UV Photolithography is inadequate for Integrated circuits, requiring other Lithography for higher resolution
• Extreme ultraviolet (EUV) lithography, electron beam lithography, X-ray lithography, and Ion lithography are used.

Layer Processes in IC Fabrication

• Fabrication processes on a silicon wafer involve a series of chemical/physical reactions to modify it.
• Insulating, semiconducting, and conducting regions from these reactions create an interconnected IC.
• Layers are built requiring separate masks, all which must be present to create the end material.
• Layering processes include thermal oxidation to add Silicon Dioxide, chemical vapor deposition, diffusion/implantation to alter existing layers, all before metallization for electrical conduction and portion etching for details.

Thermal Oxidation to Silicon

• The process exposes silicon wafer surfaces to an oxidizing atmosphere at high temperatures to form Silicon Dioxide layers.
• Thermal Oxidation uses steam or pure/high-pressure oxygen, as well as creates changes in film thickness.

Functions of Silicon Dioxide

• Silicon Dioxide (SiO2) is an insulator relative to Silicon, which is a semi-conductor, that acts as a mask to prevent doping, electrically isolates circuits and provides electrical insulation for metallization.
• There are alternate processes if a silicon dioxide film must be applied to alter silicon surfaces where direct thermal is ineffective; Chemical Vapor Deposition replaces direct thermal methods.

Doping and Thermal Diffusion

• Silicon electrical properties are improved by changing selected region chemistries, by adding impurities as a common method called Doping, where used elements are Arsenic, Boron, Phosphorous or Antimony Thermal Diffusion is a method in which atoms migrate from higher concentration areas to lowered, for doping. Silicon is doped in controlled amounts in stages, requiring a dopant and heat treatment.
• Doping is also achieved by implanting charged lons on silicon at specific voltages in temperature controlled rooms.

Metallization

• This uses thin film layering/photolithography to form lines of conduction
• Conductive substances have different application, allowing device connection to external circuits or creation of Ics internal components with certain functions.

Metallization Materials

• Widely used is Aluminum for interconnections and circuitry, while Silicides, Gold, and Nitrides with polysilicon are also used for applications such as contacts and gates.

Metallization Process

• Can be achieved by Physical (PVD, vapor evaporation and sputtering,) as well as Chemical Methods. CVD uses tungsten molybdenum. thin film thickness is occasionally increased by electroplating.

Etching

• Wafer material requires removal via etching to achieve fabrication through masking, performed with either wet chemistires or dry, gaseous, ionized plasma reactions.
• Etchant is selected to chemically attack material while protecting parts of the underlayer. Immersion time, concentration, temperature variables in simple etching, causing mask patterns resist altering sizing compensations.

Dry Plasma Etching

• Dry Plasma etching uses ionized gas reacting to vaporize target material. Electrical energy is used to ionize gas and remove surface

Fabrication, Processing, and Packaging

• A NMOS Metal semi-conductor device illustrates processes and the base of the N-channel is lightly doped for different methods in NMOS.
• After processing ICs, they are packaged: a final step to create individual chip with circuitry and protection via a clean room. Design factors include electrical connections, heat/shock, cost/reliability and manufacturability.
• After production, circuit testing encapsulates design. Designs include multiple patterns for different connections and styles for the finished PCB.

I/O Terminals and Manufacturing

• I/O Terminals exist as a compromise between circuit access and I/O limitations. Rent's rule dictates how more device complexity require extra devices. Plastic isn't hermetically sealed however the cost is lower.
• Ics can be mounted as Through-hole (leads mounted/soldered), or surface mounted with surface attachments processed on both sides - with surface components attached with but, J or gullwing leads.

IC Package Designs

• Major dual inline, square and Pin Grid arrays can be present with surface or through-hole mounting
• Wafer testing involves needle probe testing to locate bad cells, to mark them for removal. Wafer cells are then separated with dicing saws, picked up by machines for bond and lead formation. Devices are then packaged in epoxy/ceramic and tested.

Fabrication and Yields

• Ic yields are calculated by crystal, grinding, probe and final tests to check device functionality. Probability determines production/testing steps

Success Factors

• High yields are necessary to maintain profitable wafer processing. Utilizing materials wuth control, clean-rooms and testing helps!

Electronics Packaging

• Electronics packaging comprises the components and their connections while interfacing with external machines. Functions include power, structural support, protection, transmission, heat transfer, and Hierarchy Levels dictate packaging styles.

Printed Circuit Boards

• PCBs consist of insulated laminates with conducting pathways for components: PCBs inter-connect, hold, and package components. Materials are polymer sheets (epoxy phenolic) reinforced w/ glass fibres (E-glass) used for circuit patterns.

Types of PCBs and Production

• Types are multilayer/single sided for high or low component connections
• Production involves fabricating supplies/manufacturers into patterns to interconnect. PCB is sheared, drilled, cleaned for component placement.
• Hole types come in two types: tooling and component attachment. Fabrication uses various operations/materials resist, or electroless plates, or electrolytic.

Assembly and Connection

• Assemblies are connected through SMT/ThroughHole parts, which are affixed through reflow or wave soldering, although through hole requires components/inspection.

Assembly and Connection Electrical Connections

• ThroughHole parts are assembled to wave soldering or other techniques. PCB must be clean and attached to other materials (cables!) with connectors/soldering, where crimping and insulation are prevalent types of separable connection types!

Separable Device Connectors

• Multiple pin connectors, terminal strips are used for wire-wire connections!

Microsystems

• MEMS Microsystems are micromachines with electronic parts that need to have special design considerations due to size in MEMS

Microsystems vs Larger Systems

• Micro is better for matieral use, power space These are used in sensors (heat, pressure, etc) and actuators that convert energies. They are often micro or Nano-scopic.

Design

• Design can combine previous components and packaging with micro instruments such as ink jets! That makes parts!

InkJets

• IjkJets apply printing/design and operate through high accuracy thermal expulsion.

Other Applications of Microsystems

• Microfluidic or Nano components.
• Magnetic storage heads (bit high, and manufactured in billions each year).

Micro System CDs

• Compact discs (hard drives and music), and molds use polymers for data storage.

Micros for Medicine

• Medicine is increasingly assisted by minimally invasive surgeries or even micro-access surgeries.

Manufacturing

• Many MST products use silicon as a base and have high performance.
• Micro and IC tech are quite related.

IC Manufacturing - Differences

• In Microfab, high aspect ratios parts and parts aren't supported without design and material change.

Fabrication methods

• Fabrication needs accurate design from crystalline or chemical wet etching to LIGA/STL parts.
• LIGA, litho and electroforming makes high precision, but