Buffer Layer Mitigates Thermal Stress in Semiconductor Package Vias
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Solution Overview
Problem
Conventional semiconductor packages face challenges with thermal stress and reliability due to heat expansion coefficient mismatches between semiconductor chips and substrates, leading to solder bump detachment and reduced yield, especially during the reflow process.
Innovation Solution
A semiconductor package design incorporating a buffer layer on the end surfaces of conductive vias and pads to reduce thermal stress, using materials like silicon oxide, silicon nitride, or PBO, and forming conductive pads to electrically connect with the vias and cover the buffer layer, which mitigates cracking and enhances reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a through silicon interposer is formed between the substrate and semiconductor chip to solve heat expansion coefficient mismatch, then bonding reliability is improved, but thermal stress concentrates at the interface between conductive elements and conductive vias during reflow process, causing cracking and reducing yield
Solution Approach 1:
A buffer layer is introduced as an intermediary between the conductive elements and the conductive vias in the interposer. This buffer layer has intermediate thermal and mechanical properties that gradually transition the stress from the rigid conductive elements to the interposer substrate, preventing stress concentration and cracking at the interface during reflow processing.
Solution Approach 2:
The interposer structure is designed as a composite material system comprising multiple layers with different thermal and mechanical properties: the silicon interposer substrate, the buffer layer with intermediate properties, and the conductive elements. This composite structure distributes thermal stress across layers with graded properties, preventing catastrophic failure at any single interface.
2Device complexity
If the semiconductor chip is directly attached to the substrate, then device complexity is reduced, but heat expansion coefficient mismatch causes solder bump detachment and reduced bonding reliability
Solution Approach 1:
The thermal expansion parameters of the package structure are modified by introducing the silicon interposer with thermal expansion properties matching the semiconductor chip. This parameter matching prevents differential thermal stress during temperature cycling, eliminating solder bump detachment while maintaining bonding reliability.
3Speed
If fine trace lines with small line width are used in the interposer design, then electricity transmission speed is improved, but manufacturing precision requirements increase due to smaller features
Solution Approach 1:
The conductive vias and buffer layers are formed in the interposer substrate before the fine trace lines are patterned. This preliminary structuring establishes precise alignment references and stress-management features that guide subsequent fine-line fabrication, enabling accurate formation of sub-3μm traces while maintaining manufacturing feasibility.
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 buffer layer significantly reduces thermal stress during the reflow process, resulting in a 24% decrease in cracking occurrences and improved reliability and yield of the semiconductor package.
Implementation Method 1
thermal stress to be focused on the interface between the conductive element 14 and conductive vias, as shown as the thermal concentrated area K′ in FIG. 1
Data Source
AI summary
A semiconductor package is provided, including a semiconductor substrate having a plurality of conductive vias, a buffer layer formed on the semiconductor substrate, a plurality of conductive pads formed on end surfaces of the conductive vias and covering the buffer layer. During a reflow process, the buffer layer greatly reduces the thermal stress, thereby eliminating the occurrence of cracking at the interface of conductive pads. A method of fabricating such a semiconductor package is also provided.