EC-25.4 Packaging: Electrical, Thermal and Mechanical
You can compare wire bonding and flip-chip attachment on their electrical and thermal properties, estimate the inductance a package adds to a supply pin, and explain why mismatched expansion coefficients are the main mechanical hazard.
Before:PE1-1. VLSI TechnologyEC-8. Measurements, Instrumentation and Experimental MethodEC-21. Hardware Verification, FPGA and SoC Design
A package is not a lid. It carries every signal and every ampere into and out of the die, removes the heat, and holds together while everything inside expands at different rates. For fast parts the package inductance limits performance more than the transistors do, and for power parts the thermal path decides the rating. This topic treats it as the three-way design problem it is.
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What a package has to do, and the families that do it differently
Connection, heat removal, protection and mechanical support are four requirements that pull in different directions. Each package family is a different compromise between them at a different cost.
NPTEL: Electronic Packaging and Manufacturing (IIT Kharagpur) · CourseWire bonding against flip-chip, and the inductance each leaves in the path
A bond wire is a few nanohenries of series inductance on every connection, while a solder bump is a fraction of that and can be placed anywhere on the die. For a fast supply pin that difference decides the performance.
NPTEL: Electronic Packaging and Manufacturing (IIT Kharagpur) · CourseGround bounce, and why supply pins are duplicated
Current changing quickly through package inductance moves the internal supply relative to the external one, which is what corrupts signals during simultaneous switching. Many parallel pins in parallel reduce it.
The thermal path from junction to ambient, through the package
The package sets the resistance between the die and whatever is cooling it, and the published figure assumes a specific board and airflow. Using it without those assumptions gives an optimistic answer.
NPTEL: Electronic Packaging and Manufacturing (IIT Kharagpur) · CourseMismatched expansion, and the stress it puts on every joint
Silicon, mould compound, solder and the board all expand at different rates, so every temperature change works the joints between them. Most package reliability failures are that stress accumulated over thousands of cycles.
NPTEL: Basic Overview of Semiconductor Device Processing and IC Fabrication (IIT Kanpur) · CourseMoisture, popcorning and why parts arrive in sealed bags
Absorbed moisture turns to steam during soldering and can crack a package from inside. The floor-life rating on the bag is a real constraint on how a factory handles the parts.
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