Semiconductor Via Hole Metal Layer Structure for Void-Free Soldering
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Solution Overview
Problem
In semiconductor devices, the presence of a Ni film can lead to air voids in the solder due to its repelling properties, which impede heat diffusion and degrade semiconductor element characteristics.
Innovation Solution
A semiconductor device design that includes a semiconductor substrate with a first metal layer, a barrier metal layer (Ni) to prevent solder reaction, and a second metal layer (Au) in close contact with the solder, ensuring complete filling of the Via Hole and preventing void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ni film is provided in the opening to prevent solder reaction with the Au film, then solder reaction is prevented, but air voids are generated due to solder repulsion
Solution Approach 1:
The metal layer is divided into three segments: first metal layer (Au) at the bottom for heat diffusion, barrier metal layer (Ni) in the middle for reaction prevention, and second metal layer (Au) at the top for solder contact. This segmentation allows each layer to perform its specific function without interference.
Solution Approach 2:
The barrier metal layer acts as an intermediary between the first metal layer and the solder, preventing direct contact between solder and the repelling Ni film while still allowing thermal conduction. The second metal layer serves as an intermediary that provides a solder-friendly surface.
2Device complexity
If a single metal layer is used in the opening, then the structure is simple, but solder repulsion causes void formation and poor close contact
Solution Approach 1:
Different regions of the opening are assigned different metal layers with different properties: the bottom region has Au for thermal conductivity, the middle region has Ni for barrier function, and the top region has Au for solder compatibility. Each location has the quality it needs for its specific function.
Solution Approach 2:
The metal layer structure uses a composite of different metals (Au and Ni) with distinct properties. The combination leverages the thermal conductivity of Au, the barrier properties of Ni, and the solder compatibility of Au to achieve overall performance that a single metal cannot provide.
3Reliability
If the barrier metal layer is in direct contact with solder, then solder reaction with the first metal layer is prevented, but heat diffusion is impaired due to air voids
Solution Approach 1:
The thermal path is segmented into three layers, each contributing to heat diffusion. The first metal layer provides the primary thermal path, the barrier metal layer provides secondary thermal conduction, and the second metal layer ensures good thermal contact with the solder, collectively maintaining heat diffusion without voids.
Solution Approach 2:
The second metal layer acts as an intermediary that bridges the barrier metal layer and the solder, ensuring continuous thermal contact. This intermediary layer prevents air voids from forming at the solder interface while maintaining the barrier function of the Ni layer below.
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 design ensures close contact of the solder in the Via Hole, preventing voids and maintaining semiconductor element performance by preventing solder reaction and ensuring effective heat diffusion.
Implementation Method 1
the first metal layer covers the side surface and the bottom surface
Implementation Method 2
The second metal layer is in close contact with the solder higher than the barrier metal layer
Implementation Method 3
the barrier metal layer covers the first metal layer in the opening
Data Source
AI summary
A semiconductor device includes a semiconductor substrate, a first metal layer, a barrier metal layer, and a second metal layer. The semiconductor substrate includes a front surface and a back surface. A semiconductor element and an electrode of the semiconductor element are located on the front surface. An opening in the back surface reaches a lower surface of the electrode, and the opening is defined by a side surface and a bottom surface. The first metal layer covers the side surface and the bottom surface. The barrier metal layer covers the first metal layer in the opening. The second metal layer is in contact with solder in the opening and is closer to the electrode than parts of the barrier metal layer. The second metal layer is laminated on the barrier metal layer and covers at least a part of the barrier metal layer in the opening.