exam - materials

what is perovskite structure and which most typical material have it?

that's any material with a crystal structure following the formula ABX3; A corners, B in the middle, X on the sides. Example CaTiO3, BaTiO3

Is the relative permittivity of sintered aliminium oxide Al2O3 stable versus frequency and temperature or not? (In the range f = 100Hz to 100MHz; t = 300 K to 600 K)

The relative permittivity of sintered Al2O3 is generally stable versus frequency and temperature

And how it this in Barium Titanate BaTiO3?

Barriumn Titanate is a ferroelectric material, and therefore ir is higly dependent on temperature and fequency

What is the unique combination of properties od mica?

Excellent electrical insulation properties. High heat resistance. Good chemical resistance. High dielectric strength. Good thermal stability. Low thermal expansion.

Could be glass produced in the form of fibres?

Yes, glass can be produced in the form of fibres. Glass fibres are made by melting glass and then drawing.

what is glass transition temperature?

it is the temperature at which glassy material turns from a rigid to more fluid.

Which two ways of maming polymers electrically conductive are the most useful?

1. Doping with conductive materials. 2. Changing the orientation of polymeric chains to make it parallel.

Which effect could have a long-term exposure of polymers to ultraviolet radiation and how are named additives used for minimizing these effects?

Degradation or losong of their strength, flexibility, and color. To prevent this from happening we use UV stabilizers, UV absorbers, quenchers.

What is piezoelectricity? - desvribe the direct and inverse piezoelectric effect.

Its the ability of certain materials to generate AC voltage in response to a mechanical stress or deformation. Piezoelectric effect can be direct (mechanical stress) or inverse (electric field applied to a material deformates it)

What is called “hierarchical structure”? Show some example.

It is a complicated system of elements in which every element of a structure has its own struxture of a lower scale. Example: wood -> cells -> fiber -> cellulose

How is called the physical factor on atomic level responsible for magnetism

Its a spin. It gives rise to magnetic moment.

Which basic types of magnetism can be found in chemical elements

Ferromagnetism, antiferromagnetism, ferrimagnetism, paramagnetism, Diamagnetism

Can be ferrimagnetism found also within pure elements?

No, its typically associated with compounds rather than pure elements. Ferrimagnetic material often consist of two or more sublattices with magnetic moments aligned in opposite directions but with unequal magnitudes

How is xalled the group of materials having saturated hysteresis loop?

Those are hard or permanent magnetic materials. The term hard implies that these materials retain a significant amount of magnetization even after the external magnetic field is removed

Band model of a metal

look at photo

Electron cloud in the metal

electrons spread out among the atoms to form the electron clouds. These free electrons promote thermal and electrical conductivity

Why the resisitivity of the metal increases when the temperature increseas?

it can be explained by considering the behavior of electrons within the metal lattice.

Fermi dirac distribution

photo

Ohms law

Conditions of validity: the number of charge carriers is constant; the mean value of velocity of the electron versus intensity of the electric field is linear.

Matthiessen rule

thermal conductivity =

Copper

Cu - excellent electrical conductivity; used as conductor, wires, rods, sheets, tubes. Alloys as well - Bronze = copper + tin and Brass = copper + zinc

Aluminium

Al - sheets, wires, rods, foils, Al powder. Light nonmagnetic nonsparking, high strength to weight ratio. Alloys - more frequent use than Al itself AlMn1,5 very good chemical endurance

Silver

Ag - highest electrical and thermal conductivity for a metal. Lowest resistivity

Printed circuit boardas PCBs

invented 20th century. double sided boards use copper traces on both sides while multilayer boards stack multiple layers of copper-clad substrates. Requirements vary by application: medical devices = safe reliable; consumer electronics = cost effective.

Making PCBs

design, printing, drilling, plating, solder mask, silkscreen, assembly, testing

Photolitography

key process in making pcbs. Substrate preparation, cleaning, coating with photoresist, soft bake, alignment and mask placement, exposure to Uv light, development, hard bake, etching or deposition, photoresist stripping, post processing

Basic properties of lead free alloys for soldering

Melting point, wetting ability, reliability, thermal fatigue resistance, compatibility, environmental impact, cost

Types if lead free alloys for soldering

1. Tin silver copper - commonly used in electronics 2. Tin-Copper - Used jn wave soldering 3. Tin-Bismuth - lower melting point 4. Tin-Nickel - improved oxidation resistance

Types of soft soldering

Its a process that uses alloys with lower melting points below 450 C usually. Joining electronic components. 1. Lead-Tin - Traditional commonly used electronics 2. Lead-free - in response to rnvironment 3. Sn-Ag - Higher reliability 4. Sn-Ag-In th fat res

laser and ultrasonic soldering

Both highly precise. Laser contactless while sonic involves contact with joint surfaces. Laser required materials with good laser absorption ultrasonic with ultrasonic absorption. Laser used in fine pitch soldering, microelectronis while Sonic in assembly

Faulty soldered joints

1. Cold solder joint - solder doesnt fully melt 2. Insufficient solder - poor wetting incomplete coverage 3. Excess solder - leads to short circuits 4. Solder splatter - may lead to short circuits 5. Lifted pads or traces - thermal mismatch poor adhesion

Electrically conductive adhesives ECAs

composed of insulating matrix tylically a polymer resin and filler particles that provide electrical conductivity.

Types of insulating matrix

1. Epoxy resin - chemical resistance, thermal stability 2. Acrylic resin - offers good adhesion properties and flexibility 3. Polyurethane Resin- known for its durabllity and resistance to environmental factors

Types of filler particles

1. Silver - expensive high conductivity 2. Copper - chepear 3. Nickel - much cheaper moderate conductivity 4. Carbon Nanotubes - enhance mechanical properties 5. Graphene - excellent conductivity and mechanical strength

Adhesives with isotropic electrical conductivity

Means that elec conductivity same in all directions within the adhesive material. Composed of polymer matrix as insulator and filler particles. application: EMI shielding and flexible electronics. Advantages - uniformity, flexibility, low temp processing.

Adhesives with anisotropic electrical conductivity

Elec conductivity varies in differeny directions within material. Applications LCDs and chip on flex bonding. Harder to allign

Electrically conductive adhesives ECA vs lead free solders

composed of polymer matrix and fillers vs from alloys; Forms conductive path thorugh embedded conductive particles vs relies on melting; Low temperature processing vs high. More flexible vs less; no reflow process required vs required; mor environm friend

Types of electronic circuit assembly

1. Surface Mount Technology - mounted directly on PCB 2. Through hole technology - leads pass through holes spldered on other side 3. Mix of previous ones 4. Chip on board - bare chips mounted onto pcb. 5. Flip chip technology - flipped n attachedfacedown

Electronic component leads

Through hole leads, surface mouny leads, axial leads, radial leads, J-leads, Lshaped leads, coiled leads

Assembly methods for type I II and III circuits

Type I - Surface mount, through hole and manual Type II - Automated, selective or wave soldering Type III - robotic, advanced smt and tht

wire bonding

teo methods thermosonic and ultrasonic. Steps; wire preparation, chip allignment, bonding, loop formation, second bond. Wire types: copper aluminium gold

ball and wedge bolding

spherical balls vs wedges at the end of the wire; used for first bond vs used for second bond. wire pulled away vertically vs horizontally from the substrate

thermocompression vs ultrasonic vs thermosonic bonding

heat vs ultrasonic vs both; slow vs fast vs balanced; commonly used for gold aluminium vs suitable vs applicable

Tape automated bonding TAB

A packaging technology used in semiconductor and microelectronics assembly. Process bonding: connection to leads, wire bonding, encapsulation. High integration, automated assembly. LCDs and PCBs, complex tough. cost effective

flip-chip bonding

Advanced semiconductor packaging technique where the active side of the semiconductor chip is directly attached to the substrate or circuit board. Reduced signal path length, higher packaging density, enhanced thermal performance. Used in GPUs ASICs

Basic characterization of superconductivity

zero electrical resistance, perfect diamagnetism, critical temperature, critical magnetic field, meissner effect, isotope effect, cooper pairs. Applications in MRI maglev trains power transimission

Superconductors type I vs II

sharp and complete transition below Tc vs more gradual; expel all magnetic flux below critical field vs allow partial penetration of magnetic flux; lower critical temp vs higher; limited applications vs widely used

low temperature vs high superconductors

Materials lead, mercury, niobium vs iron-based, YBCO, BSCCO; transition temperature below 30 kelvin vs above; lower critical magnetic field vs higher; type I behavior vs type II behavior. application in magnets vs power transimission and magnet levitation

Which parameters limit using of high temperature superconductors

Cost, fabrication complexity, brittle nature of ceramics, sensitivity to extreme temperatures, inhomogeneity, sensitive to environmental factors

Meissner-Ochsenfeld effect

superconductors exhibit this effect when transitioning to superconducting state. Magnetic firlds are completely expelled from the interior of the superconductor. used in maglev trains

Principle of BCS theory

Electrons in a superconductor form pairs called cooper pairs due to electron-photon interactions. zero electrical resistance due to their movement. below Temp critical cooper pairs condense into the ground state causing transition to siperconducting state

Principle of Josephson Effect

formed by two superconductors separated bh a thin jndulating barrier - quantum tunneling. cooper pairs can quantum tunnel from one supercond to another. Used in qubits in quantum computing

Semiconductors

material which confuct electricity only infrt certain conditions (applied voltage) example silicon and germanium. N type with negative charged electrons and P type with positive ones.

PN junction forward and barrier direction

photo

Intrinsic vs doped semiconductors

no intentional impurities vs intentional impurities (dopants) to modify electrical properities; limited applications vs widely used N type (donor-doped) and P type (acceptor-doped)

Diode and its characteristics

Diode is a semiconductor that allows current to flow in one direction while blocking the opposite one. Forward (conducts allowing flow) or reverse (blocks current flow) bias then has breakdown voltage.

Czochralski technology and float zone technology

processing og single silkcon crystal rods

Processing of single sillivon crystal rods

Czochralski method, floating zone method, slicing into wafers, surface preparation, doping, device fabrication, thermal processing, final testing