Printed circuits Flashcards
Since when have Printed Circuit Boards (PCBs) been a popular medium for the installation of electronic components?
Since the 1970s.
What advantages do PCBs offer over the previous method of wiring components together?
PCBs are robust, have good electrical properties, are cheap, and easy to manufacture.
How are circuit connections made on a PCB?
Circuit connections consist of flat, metallic tracks printed onto the PCB surface.
Name two materials commonly used for PCBs.
Copper laminated paper treated with phenolic resin and copper laminated paper treated with epoxy resin.
What is the first step in producing a PCB?
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.
What are the two principal methods of PCB production?
The etching method and the addition method.
Describe the etching method.
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.
Describe the addition method.
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.
What is the purpose of lamination in PCB construction?
Lamination bonds the copper to the board, forming a sandwich of layered sheets that are bonded in a hot press.
What is the specific resistance of copper used in calculating conducting path resistance?
The specific resistance of copper is 0.0175 Ωmm².
Name two factors that influence the maximum current carrying capacity of a conducting path
Board thickness and substrate material.
How do wide and narrow conducting paths affect electrical properties in the high-frequency range?
Wide conducting paths create capacitance, and narrow conducting paths create inductance.
What is the difference between single-sided and double-sided PCBs?
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.
What is a multi-layer PCB?
A multi-layer PCB has additional layers of connections, utilizing one or more internal conductor planes for added complexity.
What are flexible circuits?
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.
Why are highly specialised NC drilling machines used in PCB manufacturing?
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.
What is the advantage of Surface Mount Technology (SMT) over Through Hole Technology?
SMT allows for smaller parts, denser layouts, cheaper PCBs, improved shock and vibration characteristics, and easier automation.
What are solder resists, and why are they used?
Solder resists are organic coatings used to mask off areas where soldering is not required, preventing bridging and corrosion, and maintaining circuit pattern flexibility.
What are conformal coatings, and what protection do they offer?
Conformal coatings are transparent films applied to PCB conductors, protecting against moisture, shock, vibration, and corrosion, and providing electrical isolation.
What can cause a dry solder joint, and how is it repaired?
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.
What is Integrated Modular Avionics (IMA)?
IMA is a design methodology for avionics systems that reduces bulk, space, and weight by using multi-system PCBs mounted in computerised rack assemblies.
How are PCBs used in aircraft?
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.
What kind of damage can cause insulation breakdown on a PCB?
A crack in the dielectric can cause insulation breakdown, leading to water ingress, delamination, current leakage, local overheating, and component or board burning.
which of the following components attachment methods does not use through holes?
Offset pad
SMT
swaged
SMT
in the high frequency range, how does the physical dimension of a conducting path influence its electrical properties?
wide conducting paths create capacitance, narrow conducting paths create inductance.
what are the two main factors affecting current carrying capacity that affect a PCB once installed in an LRU
Heat dissipation and ventilation
