Dielectric Package Structure for CTE-Mismatch Crack Prevention
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Solution Overview
Problem
Conventional electronic devices experience cracks in dry films due to mismatched coefficients of thermal expansion (CTE) between the dry film and the silicon oxide layer during manufacturing and reliability tests, leading to structural integrity issues.
Innovation Solution
The electronic device incorporates a dielectric layer with a controlled CTE between 40 ppm/°C or lower, encapsulating the inductor to mitigate cracking by reducing thermal stress and warpage, using materials like epoxy resin-based molding compounds and fillers to enhance modulus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a dry film is formed on the silicon oxide layer to cover the inductor, then the inductor is protected, but cracks are generated in the dry film due to CTE mismatch during thermal operation
Solution Approach 1:
The patent introduces an encapsulant layer as an intermediary between the silicon oxide layer and the dry film. This encapsulant has a CTE that is intermediate between the silicon oxide layer and the dry film, acting as a buffer to reduce thermal stress and prevent crack formation while still providing protection to the inductor
Solution Approach 2:
The patent changes the CTE parameter of the encapsulant layer to be between that of the silicon oxide layer and the dry film. By selecting materials with appropriate CTE values and adjusting composition, the thermal expansion characteristics are optimized to minimize stress during thermal cycling operations
2Reliability
If multiple cycles of thermal operation are performed during manufacturing and reliability tests, then reliability is tested, but CTE mismatch causes cracks in the dry film
Solution Approach 1:
The encapsulant layer is designed beforehand to cushion against thermal stress during subsequent thermal cycling tests. By pre-positioning this stress-absorbing layer with appropriate mechanical and thermal properties, the structure is prepared to withstand reliability testing without developing cracks
3Stress or pressure
If the CTE of the encapsulant is between the CTE of the first dielectric layer and the CTE of the second dielectric layer, then thermal stress is reduced, but material selection becomes more constrained
Solution Approach 1:
The encapsulant is formulated as a composite material system where the base resin provides the matrix and various fillers (such as silica, alumina, or other ceramic particles) are added to adjust the CTE. This composite approach enables precise tuning of the CTE parameter within the required range while maintaining other necessary properties like mechanical strength and processability
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 thermal stress and prevents cracking during manufacturing and reliability tests, ensuring structural integrity and reliability of the electronic device.
Implementation Method 1
The first dielectric layer has a first coefficient of thermal expansion (CTE). The encapsulant encapsulates the electronic element and has a second CTE. The second dielectric layer is disposed over the encapsulant and having a third CTE. The second CTE ranges between the first CTE and the third CTE.
Data Source
AI summary
An electronic device is provided. The electronic device includes a first dielectric layer, an electronic element, an encapsulant, and a second dielectric layer. The first dielectric layer has a first coefficient of thermal expansion (CTE). The electronic element is disposed over the first dielectric layer. The encapsulant encapsulates the electronic element and has a second CTE. The second dielectric layer is disposed over the encapsulant and having a third CTE. The second CTE ranges between the first CTE and the third CTE.