MICRO MACHINING

PRESENTED BYV.VASANTH KUMAR

(11781A03B3)

• INTRODUCTION

Micromachining is the basic technology for fabrication of micro-components of size in the range of 1 to 500 µm. Their need arises from miniaturization of various devices in science and engineering, calling for ultra-precision manufacturing and micro-fabrication.

MICRO MACHINING

Figure: Micro Machining Definition

Definition: material removal at

micro/ Nano level with no constraint

on the size of the component being

machined.

MICRO MACHINING

Removal of material in the form of chips having the

size in the range of microns.

Creating micro features or surface characteristics

(especially surface finish) in the micro/ Nano level.

MICRO MACHINING

WHY MICRO MACHINING?

Final finishing operations in manufacturing of precise parts arealways of concern owing to their most critical, labour intensiveand least controllable nature.

In the era of nanotechnology, deterministic high precision finishingmethods are of utmost importance and are the need of presentmanufacturing scenario.

The need for high precision in manufacturing was felt bymanufacturers worldwide to improve interchangeability ofcomponents, improve quality control and longer wear/fatigue life.

WHY MICRO MACHINING?

Present day High-tech Industries, Design requirements are stringent.

• Extraordinary Properties of Materials (High Strength, High heat Resistant,High hardness, Corrosion resistant etc.)

• Complex 3D Components (Turbine Blades)

• Miniature Features (filters for food processing and textile industries havingfew tens of microns as hole diameter and thousands in number)

• Nano level surface finish on Complex geometries (thousands of turbulatedcooling holes in a turbine blade)

• Making and finishing of micro fluidic channels (in electrically conducting &non conducting materials, say glass, quartz, &ceramics)

DIFFERENT MICROMACHINING TECHNIQUES

Photolithography

Etching

Silicon Micromachining

LIGA

Mechanical Micromachining

PHOTOLITHOGRAPHY

• Photolithography, also termed optical lithography or UV lithography, is a process used in micro fabrication to pattern parts of a thin film or the bulk of a substrate.

• It uses light to transfer a geometric pattern from a photo mask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate.

PHOTOLITHOGRAPHY

PHOTOLITHOGRAPHY PROCESS DESCRIPTION

ETCHING

• Etching is used in micro fabrication to chemically remove layers from the surface of a wafer during manufacturing.

• Etching is a critically important process module, and every wafer undergoes many etching steps before it is complete.

• It is characterized by etch rate , etch selectivity and etch uniformity

PROCESS VARIATIONS:

1. Wet etching

Etching processes used liquid-phase ("wet") etchants. The wafer can be immersed in a bath of etchant, which must be agitated to achieve good process control. For instance, buffered hydrofluoric acid (BHF) is used commonly to etch silicon dioxide over a silicon substrate.

2. Dry etching

• Modern VLSI processes avoid wet etching, and use plasma etching instead.

• plasma etching operates between 0.1 and 5 Torr

• The plasma produces energetic free radicals, neutrally charged, that react at the surface of the wafer. Since neutral particles attack the wafer from all angles, this process is isotropic

BULK MICROMACHINING

• Bulk and surface micromachining are processes used to create microstructures on microelectromechanical MEMS devices.

• While both wet and dry etching techniques are available to both bulk and surface micromachining, bulk micromachining typically uses wet etching techniques while surface micromachining primarily uses dry etching techniques.

• Bulk micromachining selectively etches the silicon substrate to create microstructures on MEMS devices.

SURFACE MICROMACHINING

• Unlike Bulk micromachining, where a silicon substrate (wafer) is selectively etched to produce structures, surface micromachining builds microstructures by deposition and etching of different structural layers on top of the substrate

• Generally polysilicon is commonly used as one of the layers and silicon dioxide is used as a sacrificial layer which is removed or etched out to create the necessary void in the thickness direction

• The main advantage of this machining process is the possibility of realizing monolithic microsystems in which the electronic and the mechanical components(functions) are built in on the same substrate.

PROCESS DESCRIPTION

LIGA PROCESS

• An important technology of MST

• Developed in Germany in the early 1980s

• LIGA stands for the German words

• Lithography (in particular X-ray lithography)

• Galvanoforming (translated electro deposition or electroforming)

• Abformtechnik (plastic molding)

• The letters also indicate the LIGA process sequence

PROCESSING STEPS IN LIGA

• Apply resist, X-ray exposure through mask,

• remove exposed portions of resist,

• electrode position to fill openings in resist,

• strip resist for (a) mold or (b) metal part

ADVANTAGES IN LIGA

• LIGA is a versatile process – it can produce parts by several different methods

• High aspect ratios are possible (large height-to-width ratios in the fabricated part)

• Wide range of part sizes is feasible - heights ranging from micrometers to centimeters

• Close tolerances are possible

DISADVANTAGES IN LIGA

• LIGA is a very expensive process

• Large quantities of parts are usually required to justify its application

• LIGA uses X-ray exposure

• Human health hazard

THANK YOU