Redistribution Layer Reinforcement at Die-Mold Boundaries
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Solution Overview
Problem
Fan out wafer level packages face disconnection issues due to thermal stress at the boundary between the die and the mold material layer, where the difference in linear expansion coefficients causes bending stress, leading to cracks in the redistribution layer wiring.
Innovation Solution
A semiconductor device with a redistribution layer featuring a thicker reinforcing portion in the thickness direction within the boundary region between the die and the mold material layer, which increases mechanical strength and suppresses disconnection without increasing the wiring width or causing impedance mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wiring width is increased to improve mechanical strength at the boundary region, then the robustness against disconnection is improved, but the wiring area increases and wiring properties deteriorate
Solution Approach 1:
The patent transitions from increasing wiring width (planar dimension) to increasing wiring thickness (vertical dimension) to improve mechanical strength. The reinforcing portion is formed with greater thickness in the thickness direction of the redistribution layer, thereby enhancing robustness against disconnection without increasing the wiring area in the plan view and avoiding wiring property deterioration.
Solution Approach 2:
The patent applies local quality by creating a reinforcing portion only in specific areas where disconnection risk is highest (boundary regions between die and mold material layer, and regions with large bending stress). The wiring structure varies locally with thicker portions at critical locations and normal thickness elsewhere, optimizing both reliability and wiring properties.
2Strength
If the wiring width is increased to suppress cracks, then the mechanical strength is improved, but the impedance matching deteriorates
Solution Approach 1:
The patent resolves the contradiction between mechanical strength and impedance matching by shifting the strengthening mechanism from the planar dimension (width) to the vertical dimension (thickness). This allows the wiring to have adequate mechanical strength through increased thickness while maintaining the original wiring width, thereby preserving proper impedance characteristics for high-speed signal transmission.
3Reliability
If the wiring is bent obliquely to reduce stress, then the mechanical strength is improved, but the wiring area increases and signal quality decreases
Solution Approach 1:
The patent avoids the need for oblique bending by utilizing the thickness dimension to create reinforcing portions. This vertical dimension approach provides mechanical strength and stress relief without requiring the wiring to bend in the planar direction, thereby maintaining straight wiring paths and preserving signal quality for high-speed communications.
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 enhances the robustness of the redistribution layer against disconnection due to thermal stress, maintaining signal quality and reducing the risk of cracks while minimizing the wiring area and maintaining proper wiring properties.
Implementation Method 1
bending stress is generated in a boundary region between the die and the mold material layer due to a difference in a linear expansion coefficient between the die and the mold material layer when the semiconductor package is subjected to a temperature change during use
Data Source
AI summary
A semiconductor device includes: a die; a mold material layer in which the die is embedded in a state where an electrode surface of the die is exposed from the mold material layer; and a redistribution layer provided on a surface of the mold material layer and having an insulating layer and a wiring in a multilayer state, as a fan out wafer level package. The wiring of the redistribution layer has a reinforcing portion that is thicker in a thickness direction within an area corresponding to a boundary region between the die and the mold material layer than the other area.