Semiconductor Package Cavity Structure for Die Stress Relief
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Solution Overview
Problem
Existing semiconductor packages impose mechanical stress on stress-sensitive circuits due to the mismatch in thermal expansion coefficients and filler material distribution, leading to voltage drift and operational issues, with current solutions like gel materials or dummy dies adding contamination or fabrication costs.
Innovation Solution
A cavity is formed in the molding compound above the stress-sensitive circuit with a reduced thickness of molding compound and filled with a gel material, reducing mechanical stress without the drawbacks of gel contamination or additional fabrication costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If gel material is placed directly over the stress sensitive circuit portion of the die to reduce mechanical stress, then mechanical stress on the die is reduced, but contamination or impurities in the gel material could produce unwanted currents affecting circuit operation
Solution Approach 1:
The patent introduces a molding compound layer as an intermediary between the gel material and the die. This molding compound acts as a barrier that prevents direct contact between the gel material and the die surface, thereby blocking the pathway for contamination and impurities to reach the die and cause unwanted currents, while still allowing the gel material to provide stress relief to the stress-sensitive circuit portion
Solution Approach 2:
The patent segments the encapsulation structure into distinct layers: a first molding compound layer directly contacting the die, a gel material layer in the middle, and a second molding compound layer on top. This segmentation isolates the gel material from direct contact with the die, preventing contamination while maintaining the stress-reducing function
2Stress or pressure
If dummy die or spacer is stacked on the die to form an intermediate interface between the die and EMC, then mechanical stress is reduced, but fabrication costs increase
Solution Approach 1:
The patent changes the physical parameters of the molding compound by creating a cavity with reduced thickness above the stress-sensitive circuit portion. This parameter change (reduced molding compound thickness) directly reduces the mechanical stress on the die without requiring additional components like dummy dies or spacers, thereby avoiding increased fabrication costs while achieving the stress reduction goal
3Ease of manufacture
If uniform thickness of molding compound is used over the die, then fabrication is simplified, but mechanical stress is applied on stress sensitive circuits causing voltage drift
Solution Approach 1:
The patent applies local quality by creating a cavity with reduced molding compound thickness specifically above the stress-sensitive circuit portion of the die, while maintaining normal thickness in other areas. This localized modification reduces mechanical stress on the stress-sensitive circuits and prevents voltage drift, while the rest of the package maintains its standard structure for fabrication simplicity
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
This approach effectively reduces mechanical stress on stress-sensitive circuits by minimizing the thickness of the molding compound and filler concentration, enhancing the reliability and operation of semiconductor packages while avoiding contamination and cost increases.
Implementation Method 1
the cavity is filled with a gel material... effectively reduces mechanical stress on stress-sensitive circuits
Data Source
AI summary
A semiconductor package comprises a lead frame, a die pad, bond pads, and leads. A die may be arranged on the die pad, the die comprising an integrated circuit. In an example, the die and at least a portion of the lead frame are encapsulated with a molding compound (MC). A first thickness of the MC over a first portion of the die is less than a second thickness over a second portion of the die to form a cavity in the MC and the MC directly contacts the first portion and the second portion of the die.