Semiconductor Package Planarization for Redistribution Layer Flatness
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Solution Overview
Problem
The semiconductor industry faces challenges in achieving a smooth and flat surface during the wafer level packaging process, which can lead to distortion of the redistribution layer and defects such as line-bridging or broken-lines due to uneven surfaces of the molding compound.
Innovation Solution
A planarization process is employed to remove portions of the over-molded molding compound and protection layers, exposing conductive pillars, and forming shallower and smaller recesses/pits, followed by the formation of a redistribution structure with a polymer dielectric layer that fits into these recesses and pits, ensuring a flat and smooth surface for subsequent layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If over-molding is performed to encapsulate the semiconductor die, then the die is protected and encapsulated, but the molding compound surface becomes uneven with deep recesses and pits, causing distortion of the redistribution layer
Solution Approach 1:
A planarization process is performed on the molding compound surface before forming the redistribution structure. This preliminary action removes portions of the molding compound to create a substantially flat surface, preventing subsequent distortion of the redistribution layer and eliminating the need for additional compensation steps
Solution Approach 2:
Portions of the molding compound are selectively removed through the planarization process to extract the uneven surface features (deep recesses and pits). This extraction creates a flat surface while preserving the encapsulated semiconductor die underneath, resolving the surface unevenness problem without compromising die protection
2Reliability
If the redistribution layer is formed over an uneven molding compound surface, then the die is protected, but defects such as line-bridging or broken-lines occur due to surface distortion
Solution Approach 1:
The planarization process is performed as a preliminary step before forming the redistribution layer. By flattening the molding compound surface in advance, the subsequent deposition of the redistribution pattern occurs on a uniform surface, preventing line-bridging and broken-lines defects while maintaining die protection
Solution Approach 2:
The planarization process acts as an intermediary step between die encapsulation and redistribution layer formation. It mediates the transition from an uneven encapsulated surface to a flat surface suitable for precise pattern formation, eliminating defects without compromising the protective encapsulation
3Reliability
If deep recesses and pits are present in the molding compound, then the die is encapsulated, but subsequent layers cannot be formed with fine pitch due to surface irregularities
Solution Approach 1:
The planarization process is performed preliminarily to remove deep recesses and pits from the molding compound surface before forming fine-pitch structures. This creates a substantially flat surface that enables subsequent deposition of thin films and formation of fine-pitch patterns without surface interference, while the encapsulated die remains protected underneath
Data Source
AI summary
A semiconductor package including a semiconductor die, a molding compound and a redistribution structure is provided. The molding compound laterally wraps around the semiconductor die, wherein the molding compound includes a base material and a first filler particle and a second filler particle embedded in the base material. The first filler particle has a first recess located in a top surface of the first filler particle, and the second filler particle has at least one hollow void therein. The redistribution structure is disposed on the semiconductor die and the molding compound, wherein the redistribution structure has a polymer dielectric layer. The polymer dielectric layer includes a body portion and a first protruding portion protruding from the body portion, wherein the body portion is in contact with the base material and the top surface of the first filler particle, and the first protruding portion fits with the first recess of the first filler particle.