4.2 Printed Circuit Boards

Question 1

what are PCB’s properties? (4)

Answer 1

1. robust physical strength
2. good electrical properties
3. cheap
4. easy to manufacture

Question 2

what method of wiring components together has PCB’s replaced?

Answer 2

wiring components together using separate wires to connect soldering eyelets

Question 3

what are the most common materials used for PCB’s? (4)

Answer 3

1. copper laminated paper treated with phenolic resin
2. copper laminated paper treated with epoxy resin
3. copper laminated glass silk weave
4. laminated paper for additive processes

Question 4

where would copper laminated paper treated with phenolic resin PCB’s be used?

Answer 4

radio and tv technology

Question 5

why are copper laminated paper treated with epoxy resin PCB’s useful?

Answer 5

for there flame resistant properties

Question 6

what makes copper laminated glass silk weave PCB’s useful?

Answer 6

reinforced with fibre glass materials makes it strong when subjected to mechanical stress

Question 7

why would you use a laminated paper for additives processes PCB?

Answer 7

when it is required for boards to printed on both sides

Question 8

what other materials are used but for specialised applications?

Answer 8

1. polyester
2. teflon
3. ceramics

Question 9

in subtractive process of manufacturing, what boards are used?

Answer 9

boards laminated with copper on one or both sides

Question 10

in the subtractive process of manufacturing, how is the circuit board made?

Answer 10

-conducting paths and eyelets protected by paint in a silk screen printing process
-unprotected areas are etched away

Question 11

in subtractive process of manufacturing, what are the disdvanatges?

Answer 11

only small area protected and waste of copper material

Question 12

in the additive process of manufacturing, what boards are used?

Answer 12

boards that are not laminated with copper

Question 13

in the additive process of manufacturing, how are boards made?

Answer 13

-conducting paths galvanised onto the board

Question 14

what protective measures must be taken after manufacturing?

Answer 14

-prevent it from corroding
covered in soldering paint
-refrain from touching conducting paths
oils from skin can accelerate corrosion process
-avoid mechanical stress
hairline cracks prevent conductivity

Question 15

what thickness are PCB’s made in? (7)

Answer 15

0.5
0.6
0.8
1.0
1.5
2.5
3.0 mm

Question 16

what is the thickness of the copper laminate? (3)

Answer 16

35 micrometre
70
105

Question 17

what does current carrying capacity depend on? (5)

Answer 17

1. board thickness
2. substrate material
3. arrangement (horizontal/vertical)
4. heat dissipation
5. ventilation

Question 18

what size path creates capacitance?

Answer 18

wide conducting paths

Question 19

what size path creates inductance?

Answer 19

narrow conducting paths

Question 20

what affect does material have on dielectric constants?

Answer 20

they can influence the dimensions of conducting paths

Question 21

what is a digital logic gate?

Answer 21

makes logical decisions based on different combinations of digital signals present on its inputs

Question 22

how many input and outputs do digital logic gates generally have?

Answer 22

more than one input
1 output

Question 23

how are integrated circuits categorised?

Answer 23

according to the number of logic gates or the complexity of circuits in a single chip

Question 24

what may a system on chip include? (4)

Answer 24

1. microprocessor
2. memory
3. peripherals
4. i/o logic

Question 25

how many voltage levels/states are allowed in digital logic design?

Answer 25

2.
logic 1/high/true
logic 0/low/false

Question 26

why is switching from 0 to 1 or 1 to 0 made as quickly as possible?

Answer 26

to prevent faulty operation of the logic circuit

Question 27

what may happen if a logic gate is operated in its intermediate region?

Answer 27

may cause it to produce a false output

Question 28

what is noise?

Answer 28

the name given to a random and unwanted voltage

Question 29

where might noise come from?

Answer 29

switches, power supply fluctuations or wiring that pick up electromagnetic radiation

Question 30

what is factored into logic gates regarding noise?

Answer 30

a certain amount of noise margin or noise immunity

Question 31

what is required in the logic gate to prevent the output to be affected by noise?

Answer 31

the supply voltage to stay above the minimum level

Question 32

what happens if noise goes beyond the voltage minimum?

Answer 32

the gate may interpret it as a low input and switch output

Question 33

why is using discrete components such as diodes, resistors and transistors to make digital logic gates not practical?

Answer 33

because these circuits suffer from propagation delay or gate delay and power loss from pull-up resistors

Question 34

what are the draw backs of a resistor-transistor logic (RTL)? (4)

Answer 34

bulkiness
low speed
limited fan-out
poor noise margin

Question 35

what is definition of a Logic AND gate?

Answer 35

if both A and B are true, then Q is true

00=0
01=0
10=0
11=1

Question 36

what is the definition of a Logic NOT Gate?

Answer 36

if A is not true, then Q is true

0=1
1=0

Question 37

what is the definition of a Logic OR gate?

Answer 37

if either A or B is true, then Q is true

00=0
01=1
10=1
11=1

Question 38

in TTL logic gates, how do they operate?

Answer 38

operate either in completely “cut off” region or completely in saturated region “fully on”

as a switch type operation

Question 39

what are the disadvantages of a TTL logic gate?

Answer 39

-as its current operated is consumes high amounts of power
-based on bipolar logic technology
-limited switching speed (propagation delay)

Question 40

what were developed to replace TTL logic gates?

Answer 40

CMOS logic gates and
Field effects transistors

Question 41

what circuits are CMOS logic gates ideal for?

Answer 41

low power battery circuits due to low power consumption
with switching speeds upwards of 100MHz in high frequency timing and computer circuits

Question 42

in a 2 input CMOS NAND gate, what is the definition?

Answer 42

if A and B is not true, then Q is true

00=1
01=0
10=0
11=0

Question 43

what is a disadvantage of a CMOS?

Answer 43

easily damaged by static electricity