Exam 1

To optimize the start-up of prototyping boards:

• divide the Schematic into functional blocks and different pages

• use jumpers or 0 Ohm resistors to connect different functional blocks

• determine the placement of Test points to be able to test the most important Nets

• define a consistent signal flow in the Schematic e.g. from left to right and from top to bottom

• plan meetings to review the overall design

• look for avaliable componets to make decisions

EMS (Electronics Manufacturing Services) companies typically apply the following tests:

• AOI – Automated optical inspection: Visual inspection using cameras to detect defects.

• AXI – Automated X-Ray: X-ray inspection to check hidden solder joints and internal structures.

• Rework – Hand soldering: Manual correction of assembly issues.

• Programming/JTAG test: Use JTAG interface for in-circuit programming and testing.

• Trimming: Fine-tuning components to achieve desired performance.

• Full assembly test: Comprehensive testing of the fully assembled board to ensure functionality.

A typical PCB design includes several key elements:

• Components: Packaged silicon devices, resistors, inductors, capacitors, each having specific functionalities.

• Pads: Used for component connections, measurement points, and come in different shapes and sizes depending on the component and soldering process.

• Vias: Allow layer changes, can be mechanically or laser drilled, and may serve as thermal vias for heat dissipation.

• Polygons: Fill up free space, used for shielding and distributing power, and should be assigned to a net.

• Fill: Used to short logical nets, typically rectangular or square, and not dependent on design rules .

• the right pad size provides a reliable solder connection to components

• teardrops enhance the the ability to withstand mechanical stress as it provides a gradual connection between the solder pad and the trace

A JTAG (Joint Test Action Group)

• is a digital test interface

• used to test isolated IC as well as the interconnection of multiple IC on a PCB by using the integrated baundry-scan cells

• can also be used for programming

• no need to physically access the pins with needels (bed of needles)

JEDEC-22 is a standard for testing semiconductor devices and includes various stress tests such as:

• MSL (Moisture Sensitivity Level): Determines how a component absorbs moisture and its effect on reliability.

• (U)HAST (Unbiased Highly Accelerated Stress Test): Tests for humidity and temperature effects without applying electrical bias.

• BHAST (Biased Highly Accelerated Stress Test): Similar to HAST but with an electrical bias applied.

• THB (Temperature Humidity Bias): Tests components under combined temperature, humidity, and electrical bias.

• TCT (Temperature Cycle Test): Assesses the reliability of components under temperature cycling conditions .

When transferring a schematic into a PCB layout, the following considerations should be made:

• Component Placement: Ensure optimal placement for functionality and manufacturability.

• Definition of Designe Rules: Verify that the layout adheres to the design rules.

• Signal Integrity: Consider the routing of high-speed or sensitive signals to prevent interference.

• Thermal Management: Ensure proper heat dissipation for components that generate heat .

The typical test setup for ICs includes:

• Heavy Carrier Boards: Boards with assembled components used for testing.

• Test Equipment: Connected by cables to the carrier boards.

• Needle Test Handler: Micro manipulators or needles are used to make contact with test points on the IC for precise measurement and testing .

For easy visual inspection, consider the following factors:

• Component Spacing: Maintain adequate spacing between components to allow clear visibility.

• Pad and Trace Layout: Ensure pads and traces are clearly visible and accessible for inspection probes.

• Labeling: Clearly label components and test points.

• Solder Mask: Use a solder mask color that provides good contrast with the traces and pads.

• Teardrops and Jumpers: Use teardrops for small pads and place jumpers on prototypes to facilitate inspection.

• Answer: Common PCB layouts include single-sided, double-sided, and multi-layer PCBs. Single-sided PCBs have components and copper traces on one side only. Double-sided PCBs have traces on both sides of the board, allowing for more complex circuits. Multi-layer PCBs consist of several layers of conductive material, providing a higher circuit density and are used in complex applications like computers and medical devices .