Explain, using a 6-layer PCB structure, which types of vias are possible. Name all elements.
Core only in the middle, other layers are prepreg.
In the core, resin is cured (ausgehärtet) and a copper layer is applied on each side.
Prepreg is only impregnated with resin (Harz), not cured.
Blind Via
Always connects an outer layer with an inner layer (visible from the outside).
Buried Via
Connects two inner layers and is not visible from the outside.
Stacked Via
Combination of multiple vias (blind or buried) that connect at least three layers.
Staggered Via
Connect multiple layers but do not come into direct contact (separate drill axes).
Which data exchange formats for production data of PCBs do you know? Choose and describe one in detail.
Extended Gerber (RS274X)
Excellon Drill
ODB++
IPC-2581
Detail on ODB++: ODB++ is a compressed file format; easy to check
includes…
plain text data
PCB structure, including layers,
drill holes
Create a process flow chart for the development of a PCB design from requirement gathering to manufacturing. How do you ensure that the data is correct?
Requirement Definition: Define the main purpose, cost, quantity, and align with test equipment.
Schematic Design: Draw the schematic, select components, and create a block diagram.
Simulation: Run signal, power, and thermal simulations.
PCB Layout Design: Place components and route traces.
Manufacture: Generate manufacturing files (e.g., Gerber, drill files) and verify them. Produce Prototype
Test: Test prototypes and iterate the design.
Release A: Mass manufacture the PCB.
To ensure data correctness:
Double-check the schematic and layout.
Perform design rule checks (DRC) and electrical rule checks (ERC).
Review simulations and prototype tests.
The dissipated heat of an SMT transistor on the top side of the PCB must be transferred to a heatsink mounted on the bottom side. How do you solve this problem?
To transfer heat from an SMT transistor on the top side to a heatsink on the bottom side:
Use Thermal Vias: Place multiple vias under the transistor's thermal pad to conduct heat to the bottom layer.
Thermal Interface Material (TIM): Apply TIM between the transistor and the PCB to improve heat conduction.
Copper Plane: Use a large copper plane connected to the vias on both top and bottom layers to spread the heat.
Mount the Heatsink: Attach the heatsink on the bottom side directly over the area with thermal vias for efficient heat transfer.
What connection options for schematic symbols/schematic pages do you know? Describe when to use each.
Direct Wire Connections: Used for simple, straightforward connections within a single schematic page.
Net Labels: Used to connect wires across different schematic pages by assigning the same net name.
Bus Connections: Used for connecting multiple signals collectively, such as data buses.
Which factors influence the trace width? When do you use areas (polygons) instead of traces?
Current Carrying Capacity: Wider traces are needed for higher currents to avoid overheating.
Voltage Levels: Higher voltage levels require wider spacing and trace width to prevent arcing.
Signal Integrity: High-speed signals may need controlled impedance, which affects trace width.
Manufacturing Capabilities: Minimum trace width is determined by the PCB manufacturer's capabilities.
Use of Polygons: Polygons are used instead of traces when:
Large areas need to be connected, such as ground or power planes.
High current carrying capacity is required, and a wide trace would be impractical.
Better thermal dissipation is needed.
What basic rules should you follow when creating a schematic.
Preferred page size: A3
Keep a clear structure
Check annotation of all components
Devide the schematic into pages and sub-blocks
Signal flow from left to right and top to bottom
Show necessary information but do not overload
Fill in title block information
Run Electrical rule check (ERC)
Verify and document the schematic design
Do a review meeting (specialists double check your schematic)
List typical test structures used to check the electrical functionality of printed circuit boards. Draw sketches and describe!
Daisy Chains: Used for continuity testing. They consist of a series of interconnected components or pads, forming a loop that can be tested for electrical continuity.
(Placeholder for sketch)
Test Points: Designated points on the PCB used for probing during electrical testing.
Etch Indicators: Patterns used to check the quality of the etching process.
Thermal Performance Indicators: Structures that help assess the thermal management capabilities of the PCB.
Drill Matrix Configurations: Ensure correct layer alignment and drill quality.
What does MSL mean? How to determine the level of a component? How does it influence the soldering process?
MSL stands for Moisture Sensitivity Level. It indicates the sensitivity of electronic components to moisture and the potential for damage during soldering if moisture is absorbed.
Determining the Level: The MSL is determined by standardized tests specified by the JEDEC J-STD-020 standard. Components are exposed to controlled moisture and temperature conditions, and their response is measured.
Influence on Soldering Process: Higher MSL levels indicate greater sensitivity to moisture. Components with high MSL levels require more careful handling and storage to avoid moisture absorption, which can cause defects like "popcorning" during the soldering process.
Why do we need thermal interface materials (TIM)? What is the main purpose? List material types used!
Thermal Interface Materials (TIM) are used to enhance the thermal connection between heat-generating components and heat sinks.
Main Purpose: TIMs fill the microscopic air gaps between the surfaces of a component and a heat sink, improving heat transfer and cooling efficiency.
Material Types:
Thermal Grease: Paste-like substance that provides good thermal conductivity. (non-insulating)
Thermal Pads: Solid pads that are easy to apply and handle. (insulating)
Phase Change Materials: Solid at room temperature but become fluid at operating temperatures, improving thermal contact.
Metal Foils: Thin sheets of metal with high thermal conductivity.
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