Semiconductor Package Gap Structure for Stress-Isolated Analog ICs
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Solution Overview
Problem
Plastic molded IC packages inadequately isolate stress-sensitive circuitry from mechanical stresses, leading to performance inaccuracies in analog and mixed-signal circuits due to non-uniform mold compound pressure and electrical leakage from external filter capacitors on PCBs.
Innovation Solution
Integrating a second circuit, such as a filter capacitor, within the plastic package with a gap over the stress-sensitive circuitry to minimize parasitics and prevent electrical leakage, using a leadframe and attachment layer with a hollow center to encapsulate the mold compound and secure the second circuit to the analog IC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plastic molded IC package is used to encapsulate the analog IC, then the IC is protected from environmental factors, but the mold compound impinges on stress sensitive regions causing output voltage variations and performance inaccuracies
Solution Approach 1:
The package structure is segmented into distinct regions: a first region containing the analog IC with stress-sensitive circuitry, and a second region containing the second circuit. This spatial segmentation allows the mold compound to encapsulate both circuits while the gap prevents stress transfer from the second circuit to the stress-sensitive regions of the analog IC, thus maintaining output voltage stability while providing environmental protection.
2Loss of energy
If external filter capacitors are mounted on a PCB, then noise filtering is provided, but electrical leakage occurs from the capacitors causing output voltage shifts
Solution Approach 1:
The second circuit providing noise filtering functionality is merged with the package structure by integrating it onto the same substrate as the analog IC, rather than using separate external capacitors on a PCB. This integration eliminates the leakage paths associated with external components while maintaining the noise filtering function, thus improving output voltage stability without sacrificing energy loss protection.
Solution Approach 2:
A gap is introduced as an intermediary element between the analog IC and the second circuit. This gap acts as a mediator that electrically isolates the stress-sensitive high-impedance nodes from the second circuit, preventing electrical leakage while still allowing the second circuit to provide noise filtering. The gap serves as a protective barrier that maintains voltage stability.
3Strength
If the mold compound is used to encapsulate the IC, then mechanical protection is provided, but non-uniform pressure is applied to stress sensitive regions causing performance variations
Solution Approach 1:
The package is segmented into regions with different mechanical constraints. The gap creates a stress-free zone that segments the mechanical load path, allowing the mold compound to provide uniform encapsulation pressure on the overall package while preventing concentrated non-uniform pressure on the stress-sensitive circuitry of the analog IC, thus maintaining performance consistency.
4Measurement precision
If a gap is introduced between the analog IC and the second circuit, then stress isolation is achieved, but package volume increases
Solution Approach 1:
The gap is implemented as a thin void space rather than a substantial physical barrier. This thin-film approach provides effective stress isolation between the analog IC and the second circuit while occupying minimal volume, thus achieving stress isolation without significantly increasing package volume.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces output voltage shifts and thermal hysteresis, enhances long-term voltage stability, and improves noise performance by isolating stress-sensitive regions from mold compound stress and reducing leakage errors, akin to an open cavity ceramic package.
Implementation Method 1
A gap is provided between the analog IC and the second circuit, and the mold compound is prevented from entering the gap, thereby providing stress relief to the analog IC
Implementation Method 2
Integrating a second circuit, such as a filter capacitor, within the plastic package with a gap over the stress-sensitive circuitry to minimize parasitics and prevent electrical leakage
Implementation Method 3
The solution effectively reduces output voltage shifts and thermal hysteresis, enhances long-term voltage stability, and improves noise performance
Data Source
AI summary
A packaged integrated circuit (IC) includes a leadframe including a die pad and leads around the die pad, an analog IC die having first bond pads on its active top side, and a second circuit including second circuit bond pads attached to the analog IC die by an attachment layer configured as a ring with a hollow center that provides an inner gap. A bottom side of the analog IC or the second circuit is attached to the die pad. Bond wires couple at least some of the first bond pads or some of the second circuit bond pads to the leads, and there is a second coupling between others of the second circuit bond pads and others of the first bond pads. A mold compound is for encapsulating the second circuit and the analog IC.