Reinforcement Layer Packaging for Die Crack Prevention
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Solution Overview
Problem
The difference in thermal expansion coefficients between the silicon die and trench filler materials in integrated circuit packages leads to cracking in the metal active layer, exacerbated by mechanical stresses during manufacturing, and increasing insulation thickness to mitigate this results in longer fabrication times and increased package thickness.
Innovation Solution
A reinforcement layer, comprising the original wafer carrier, is attached to the active side of the die via a bonding material, providing stiffness to prevent cracks and extending the carrier's functionality beyond fabrication to serve as a cap, while wire bonds connect the die to the leadframe, and a mold compound encapsulates the assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulation thickness is increased to prevent cracks, then the reliability is improved, but the fabrication time increases and the package thickness increases
Solution Approach 1:
A reinforcement layer is introduced as an intermediary component between the trench filler material and the active layer. This reinforcement layer has mechanical properties that bridge the mismatch between the rigid silicon die and the softer trench filler, distributing stresses and preventing crack formation without requiring increased insulation thickness, thereby avoiding extended fabrication time and additional package thickness.
Solution Approach 2:
The patent employs a composite structure consisting of multiple materials with different properties: the reinforcement layer is made of a material that combines the stiffness needed to prevent cracks with compatibility to both the silicon die and the trench filler material. This composite approach allows crack prevention without increasing the overall package dimensions or fabrication complexity.
2Reliability
If the insulation thickness is increased to prevent cracks, then the reliability is improved, but the package thickness increases
Solution Approach 1:
The reinforcement layer serves as a mediator that provides the necessary mechanical support to prevent cracks at the interface between the trench filler and active layer, while maintaining a compact structure that does not increase the overall package thickness. The reinforcement layer is integrated within the existing package structure rather than adding external thickness.
3Adaptability or versatility
If trenches are filled with trench filler material, then the isolation or conduction function is achieved, but the CTE mismatch causes stress and cracks in the active layer
Solution Approach 1:
The reinforcement layer acts as a stress-distributing intermediary between the trench filler material and the active layer. It has a coefficient of thermal expansion that bridges the gap between the trench filler and silicon die, preventing stress concentration and crack formation at their interface while allowing them to maintain their respective isolation or conduction functions.
Solution Approach 2:
The patent changes the mechanical and thermal parameters of the interface region by introducing the reinforcement layer with specific material properties. This layer has a CTE that is intermediate between the trench filler and silicon die, and possesses appropriate mechanical strength to distribute stresses, thereby preventing crack formation while maintaining the functional properties of the trench filler material.
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 reinforcement layer effectively reduces the likelihood of cracks between the trench material and the active layer, maintaining package integrity without increasing fabrication time or thickness, thus addressing the thermal expansion mismatch and mechanical stress issues.
Implementation Method 1
the CTE mismatch causes stress in the package, which can create the cracks
Implementation Method 2
A reinforcement layer is disposed on the active layer
Implementation Method 3
A mold compound encapsulates the die, the reinforcement layer, and the wire bonds
Implementation Method 4
wire bonds are attached from the active layer of the die to the leads
Data Source
AI summary
An electronic device includes a leadframe having a die pad and leads. A die that includes an active layer is attached to the die pad. A reinforcement layer is disposed on the active layer and wire bonds are attached from the active layer of the die to the leads. A mold compound encapsulates the die, the reinforcement layer, and the wire bonds.