Redistribution Wiring UBM Structure to Prevent Package Peeling
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Solution Overview
Problem
The existing semiconductor packages face issues with peeling phenomena due to differences in thermal expansion coefficients between metal UBM pads and polymer protective layers, leading to weak adhesive forces at heterogeneous interfaces, which affect board level reliability.
Innovation Solution
A semiconductor package design that includes a redistribution wiring layer with an insulating layer, redistribution wirings, a protective layer with openings exposing the wirings, and under bump metallurgy (UBM) pads spaced apart from the protective layer's inner wall, where conductive bumps are disposed on the UBM pads to prevent lifting and enhance interfacial bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a UBM pad is disposed under the solder bump to increase board level reliability, then the bonding strength is improved, but the UBM pad may overlap the protective layer causing peeling phenomenon due to thermal expansion coefficient difference
Solution Approach 1:
The UBM pad structure is segmented into multiple layers including a first UBM pad layer and a second UBM pad layer. The first UBM pad layer is disposed on the redistribution wiring layer while the second UBM pad layer is disposed on the protective layer, with an adhesive layer between them. This segmentation allows each layer to bond to different materials (metal and polymer respectively), distributing the thermal stress and preventing peeling at a single interface.
Solution Approach 2:
The UBM pad uses a composite structure combining multiple materials: a first UBM pad material (e.g., copper), a second UBM pad material (e.g., nickel or palladium), and an adhesive layer material. This composite material approach allows optimization of each layer's properties - the first layer provides electrical conductivity, the second layer provides oxidation resistance, and the adhesive layer provides bonding to the protective layer, collectively resolving the thermal expansion mismatch issue.
2Reliability
If the UBM pad overlaps the protective layer to distribute stress, then board level reliability is improved, but thermal expansion coefficient difference causes peeling
Solution Approach 1:
An adhesive layer is introduced as an intermediary between the first UBM pad layer and the protective layer. This adhesive layer acts as a mediator that bonds to both the metal UBM pad and the polymer protective layer, accommodating the thermal expansion coefficient difference between these two materials and maintaining interface stability during thermal cycling.
Solution Approach 2:
The invention changes the material parameters of the UBM pad structure by using multiple materials with different properties. The first UBM pad layer uses a material with high thermal conductivity, the second layer uses a material with low thermal expansion, and the adhesive layer uses a material with intermediate properties, creating a gradient that smoothly transitions between the metal and polymer interfaces and reduces thermal stress.
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
This design prevents lifting and enhances board level reliability by ensuring the UBM pads and redistribution wirings have the same metal material, reducing thermal expansion coefficient differences and increasing the interfacial bonding force.
Implementation Method 1
an adhesive layer, and a second UBM pad layer, wherein the adhesive layer is provided between the first UBM pad layer and the protective layer
Data Source
AI summary
A semiconductor package includes: a semiconductor chip having chip pads disposed on a first surface thereof; a redistribution wiring layer formed on the first surface, wherein the redistribution wiring layer includes an insulating layer, redistribution wirings, a protective layer, and an under bump metallurgy (UBM) pad of UBM pads, wherein the insulating layer is formed on the first surface, wherein the redistribution wirings are provided on the insulating layer and are electrically connected to the chip pads, wherein the protective layer is provided on the insulating layer and has an opening that exposes at least a portion of a first redistribution wiring of the redistribution wirings, and wherein the under bump metallurgy (UBM) pad is provided on the at least a portion of the first redistribution wiring that is exposed by the opening; and conductive bumps disposed on the UBM pads of the redistribution wiring layer.