Semiconductor Joint Layer Structure for Crack-Resistant Lead-Free Soldering
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Solution Overview
Problem
Conventional lead-free soldering methods in semiconductor devices result in the formation of Ni—Sn intermetallic compounds that lead to crack formation and premature failure under thermal stress, while adding Cu to the solder increases melting point and viscosity, degrading assemblability.
Innovation Solution
A semiconductor device design featuring a copper-based wiring layer with nickel covering layers and a joint layer composed of Sn, Cu, and Ni intermetallic compounds, forming columnar protrusions to prevent crack propagation and ensure corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cu is added to the solder material to form Cu-Sn compound layer, then crack extension is prevented, but melting point increases and assemblability deteriorates
Solution Approach 1:
The joint layer is divided into multiple functional layers: a Ni-Sn intermetallic compound layer formed on the Ni-plated mounting board surface, and a Sn-based solder layer formed on top of it. This segmentation allows the Ni-Sn layer to provide crack resistance while the Sn-based solder layer maintains low melting point and good assemblability, resolving the contradiction between reliability and ease of manufacture.
2Ease of manufacture
If Sn-based solder is used without Cu addition, then assemblability is maintained, but crack extension occurs in the joint layer
Solution Approach 1:
The Ni-Sn intermetallic compound layer acts as an intermediary between the Ni-plated mounting board and the Sn-based solder layer. This intermediate layer prevents direct formation of brittle Ni-Sn compounds in the solder itself, allowing the use of Sn-based solder with good assemblability while the controlled Ni-Sn layer provides crack resistance at the interface.
3Reliability
If joining temperature is increased to form Cu-Sn compound layer, then crack prevention is achieved, but thermal deformation of joining member increases
Solution Approach 1:
The joining process uses parameter changes to form the Ni-Sn intermetallic compound layer at a controlled temperature and time, creating a crack-resistant structure without requiring excessive heat that would cause thermal deformation. The Sn-based solder layer is then applied at appropriate temperatures to maintain assemblability while achieving reliable crack-resistant joints.
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 suppresses crack extension and maintains assemblability by using Sn-based solder without Cu, preventing thermal deformation and ensuring corrosion resistance.
Implementation Method 1
a joint layer which is metallurgically joined to the wiring layer in the opening; a second covering layer which contains nickel, and is metallurgically joined to the joint layer on an upper surface of the joint layer
Data Source
AI summary
A semiconductor device encompasses a mounting member having a copper-based wiring layer; first covering layer which contains nickel, covering the wiring layer so that a part of upper surface of the wiring layer is exposed in opening; joint layer metallurgically joined to the wiring layer in the opening; second covering layer which contains nickel, metallurgically joined to the joint layer on upper surface of the joint layer; semiconductor chip having bottom surface covered with the second covering layer. The joint layer has lower layer in contact with the wiring layer, upper layer in contact with the second covering layer, and intermediate layer between the lower layer and the upper layer, the lower layer and the upper layer have intermetallic compounds as main components which contain tin, copper and nickel, and the intermediate layer is alloy containing tin as the main component and no lead.