Printed circuits Flashcards

1
Q

Since when have Printed Circuit Boards (PCBs) been a popular medium for the installation of electronic components?

A

Since the 1970s.

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2
Q

What advantages do PCBs offer over the previous method of wiring components together?

A

PCBs are robust, have good electrical properties, are cheap, and easy to manufacture.

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3
Q

How are circuit connections made on a PCB?

A

Circuit connections consist of flat, metallic tracks printed onto the PCB surface.

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4
Q

Name two materials commonly used for PCBs.

A

Copper laminated paper treated with phenolic resin and copper laminated paper treated with epoxy resin.

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5
Q

What is the first step in producing a PCB?

A

he first step is called ‘patterning,’ which converts a circuit diagram into a pattern of connected conductors and spaces for the components using Computer-Aided Design (CAD) techniques.

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5
Q

What are the two principal methods of PCB production?

A

The etching method and the addition method.

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5
Q

Describe the etching method.

A

The etching method involves cleaning a copper foil, coating it with a photo-sensitive resist, exposing it to UV light through a mask, washing away the soluble resist, and etching away the unprotected copper.

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5
Q

Describe the addition method.

A

The addition method involves coating the board with a photoresist, printing a negative of the master diagram, chemically activating the exposed areas, and immersing the board in a copper plating solution to deposit copper onto the activated areas.

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6
Q

What is the purpose of lamination in PCB construction?

A

Lamination bonds the copper to the board, forming a sandwich of layered sheets that are bonded in a hot press.

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6
Q

What is the specific resistance of copper used in calculating conducting path resistance?

A

The specific resistance of copper is 0.0175 Ωmm².

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7
Q

Name two factors that influence the maximum current carrying capacity of a conducting path

A

Board thickness and substrate material.

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7
Q

How do wide and narrow conducting paths affect electrical properties in the high-frequency range?

A

Wide conducting paths create capacitance, and narrow conducting paths create inductance.

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8
Q

What is the difference between single-sided and double-sided PCBs?

A

Single-sided PCBs have wiring on one side and components on the reverse side, while double-sided PCBs have wiring and components on both sides, allowing more complex circuits.

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9
Q

What is a multi-layer PCB?

A

A multi-layer PCB has additional layers of connections, utilizing one or more internal conductor planes for added complexity.

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10
Q

What are flexible circuits?

A

Flexible circuits have conductors laminated to one or more layers of a flexible insulating base, such as Mylar or Kapton, and are custom-designed for particular applications.

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11
Q

Why are highly specialised NC drilling machines used in PCB manufacturing?

A

They are used to control drill rotation speeds and feed rates, which is necessary for drilling small hole sizes and handling the mechanical properties of glass/epoxy base materials.

11
Q

What is the advantage of Surface Mount Technology (SMT) over Through Hole Technology?

A

SMT allows for smaller parts, denser layouts, cheaper PCBs, improved shock and vibration characteristics, and easier automation.

11
Q

What are solder resists, and why are they used?

A

Solder resists are organic coatings used to mask off areas where soldering is not required, preventing bridging and corrosion, and maintaining circuit pattern flexibility.

12
Q

What are conformal coatings, and what protection do they offer?

A

Conformal coatings are transparent films applied to PCB conductors, protecting against moisture, shock, vibration, and corrosion, and providing electrical isolation.

12
Q

What can cause a dry solder joint, and how is it repaired?

A

A dry joint is caused by movement during solidification or incomplete melting of solder. It can be repaired by re-heating the joint with a hot iron until the solder flows.

13
Q

What is Integrated Modular Avionics (IMA)?

A

IMA is a design methodology for avionics systems that reduces bulk, space, and weight by using multi-system PCBs mounted in computerised rack assemblies.

14
Q

How are PCBs used in aircraft?

A

PCBs in aircraft are used inside boxes or components, in rack assemblies or card files, and in computer rack assemblies, serving as part of the aircraft’s electronic systems.

15
Q

What kind of damage can cause insulation breakdown on a PCB?

A

A crack in the dielectric can cause insulation breakdown, leading to water ingress, delamination, current leakage, local overheating, and component or board burning.

16
Q

which of the following components attachment methods does not use through holes?

Offset pad
SMT
swaged

A

SMT

17
Q

in the high frequency range, how does the physical dimension of a conducting path influence its electrical properties?

A

wide conducting paths create capacitance, narrow conducting paths create inductance.

18
Q

what are the two main factors affecting current carrying capacity that affect a PCB once installed in an LRU

A

Heat dissipation and ventilation