4.2 Printed Circuit Boards Flashcards
what are PCB’s properties? (4)
- robust physical strength
- good electrical properties
- cheap
- easy to manufacture
what method of wiring components together has PCB’s replaced?
wiring components together using separate wires to connect soldering eyelets
what are the most common materials used for PCB’s? (4)
- copper laminated paper treated with phenolic resin
- copper laminated paper treated with epoxy resin
- copper laminated glass silk weave
- laminated paper for additive processes
where would copper laminated paper treated with phenolic resin PCB’s be used?
radio and tv technology
why are copper laminated paper treated with epoxy resin PCB’s useful?
for there flame resistant properties
what makes copper laminated glass silk weave PCB’s useful?
reinforced with fibre glass materials makes it strong when subjected to mechanical stress
why would you use a laminated paper for additives processes PCB?
when it is required for boards to printed on both sides
what other materials are used but for specialised applications?
- polyester
- teflon
- ceramics
in subtractive process of manufacturing, what boards are used?
boards laminated with copper on one or both sides
in the subtractive process of manufacturing, how is the circuit board made?
-conducting paths and eyelets protected by paint in a silk screen printing process
-unprotected areas are etched away
in subtractive process of manufacturing, what are the disdvanatges?
only small area protected and waste of copper material
in the additive process of manufacturing, what boards are used?
boards that are not laminated with copper
in the additive process of manufacturing, how are boards made?
-conducting paths galvanised onto the board
what protective measures must be taken after manufacturing?
-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
what thickness are PCB’s made in? (7)
0.5
0.6
0.8
1.0
1.5
2.5
3.0 mm
what is the thickness of the copper laminate? (3)
35 micrometre
70
105
what does current carrying capacity depend on? (5)
- board thickness
- substrate material
- arrangement (horizontal/vertical)
- heat dissipation
- ventilation
what size path creates capacitance?
wide conducting paths
what size path creates inductance?
narrow conducting paths
what affect does material have on dielectric constants?
they can influence the dimensions of conducting paths
what is a digital logic gate?
makes logical decisions based on different combinations of digital signals present on its inputs
how many input and outputs do digital logic gates generally have?
more than one input
1 output
how are integrated circuits categorised?
according to the number of logic gates or the complexity of circuits in a single chip
what may a system on chip include? (4)
- microprocessor
- memory
- peripherals
- i/o logic
how many voltage levels/states are allowed in digital logic design?
2.
logic 1/high/true
logic 0/low/false
why is switching from 0 to 1 or 1 to 0 made as quickly as possible?
to prevent faulty operation of the logic circuit
what may happen if a logic gate is operated in its intermediate region?
may cause it to produce a false output
what is noise?
the name given to a random and unwanted voltage
where might noise come from?
switches, power supply fluctuations or wiring that pick up electromagnetic radiation
what is factored into logic gates regarding noise?
a certain amount of noise margin or noise immunity
what is required in the logic gate to prevent the output to be affected by noise?
the supply voltage to stay above the minimum level
what happens if noise goes beyond the voltage minimum?
the gate may interpret it as a low input and switch output
why is using discrete components such as diodes, resistors and transistors to make digital logic gates not practical?
because these circuits suffer from propagation delay or gate delay and power loss from pull-up resistors
what are the draw backs of a resistor-transistor logic (RTL)? (4)
bulkiness
low speed
limited fan-out
poor noise margin
what is definition of a Logic AND gate?
if both A and B are true, then Q is true
00=0
01=0
10=0
11=1
what is the definition of a Logic NOT Gate?
if A is not true, then Q is true
0=1
1=0
what is the definition of a Logic OR gate?
if either A or B is true, then Q is true
00=0
01=1
10=1
11=1
in TTL logic gates, how do they operate?
operate either in completely “cut off” region or completely in saturated region “fully on”
as a switch type operation
what are the disadvantages of a TTL logic gate?
-as its current operated is consumes high amounts of power
-based on bipolar logic technology
-limited switching speed (propagation delay)
what were developed to replace TTL logic gates?
CMOS logic gates and
Field effects transistors
what circuits are CMOS logic gates ideal for?
low power battery circuits due to low power consumption
with switching speeds upwards of 100MHz in high frequency timing and computer circuits
in a 2 input CMOS NAND gate, what is the definition?
if A and B is not true, then Q is true
00=1
01=0
10=0
11=0
what is a disadvantage of a CMOS?
easily damaged by static electricity
