Warped Semiconductor Electrodes for Void-Free Soldering
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Solution Overview
Problem
Void formation within the solder during the mounting of semiconductor elements leads to electrical and thermal conduction issues, requiring complex equipment for void removal, which decreases productivity when mounting multiple elements.
Innovation Solution
A semiconductor element with electroless nickel-phosphorus and gold plating layers on both the front and back electrodes, where the front-side electrode is bowed inward by controlling the thickness and surface area ratios, allowing voids to be discharged during soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroless plating is used to form thick nickel films on aluminum electrodes, then soldering becomes feasible, but production costs increase due to material and process complexity
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the nickel-phosphorus plating layer (3-10 μm) and phosphorus content (6-12 mass%) to achieve optimal soldering performance. By adjusting these parameters, the invention enables reliable soldering while controlling production costs through efficient material usage and process optimization.
2Reliability
If vibrations are applied during soldering to remove voids, then electrical and thermal conduction improve, but equipment complexity and processing time increase
Solution Approach 1:
The patent applies preliminary action by pre-forming the nickel-phosphorus plating layer with specific characteristics (thickness 3-10 μm, phosphorus content 6-12 mass%) before soldering. This preliminary preparation ensures that gases are effectively managed during the soldering process itself, eliminating the need for additional vibration equipment or post-processing steps to remove voids.
Solution Approach 2:
The patent converts the potentially harmful effect of gas generation during soldering into a beneficial outcome by designing the plating layer to facilitate gas escape. The specific composition and thickness of the nickel-phosphorus plating create controlled pathways for gas release, transforming what would be void-forming harm into a benefit where gases are safely discharged, improving conduction without requiring complex void removal equipment.
3Reliability
If thicker nickel plating layers are used to prevent reduction during soldering, then soldering reliability improves, but production costs increase
Solution Approach 1:
The patent optimizes the balance between plating layer stability and material consumption by precisely controlling the nickel-phosphorus plating parameters: thickness of 3-10 μm and phosphorus content of 6-12 mass%. This parameter optimization ensures sufficient protection against reduction during soldering while minimizing nickel material usage, achieving cost-effective production.
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
Prevents void formation within the solder, enhancing the reliability and efficiency of the semiconductor element mounting process without the need for complex equipment, thereby improving productivity.
Implementation Method 1
an electroless plating layer is formed by substituting zinc for Al on the surface of an Al electrode, to elicit thereby precipitation of catalyst nuclei
Implementation Method 2
Zincate solutions used in this method are inexpensive, and hence the method is widely used
Implementation Method 3
an electroless plating layer is formed by causing palladium to precipitate, as a catalyst nucleus, on the surface of an Al electrode
Implementation Method 4
an electroless plating layer is formed by causing palladium to precipitate, as a catalyst nucleus, on the surface of an Al electrode
Implementation Method 5
a semiconductor element is deliberately warped so that the front surface of the semiconductor element is bowed inward, as a result of which the voids inside the solder are allowed to be readily discharged out
Data Source
AI summary
In a semiconductor element of the present invention, an electroless nickel-phosphorus plating layer and an electroless gold plating layer are formed on both a front-side electrode and a back-side electrode of a front-back conduction-type substrate. The front-side electrode and the back-side electrode are formed of aluminum or an aluminum alloy. The proportion of the thickness of the electroless nickel-phosphorus plating layer formed on the front-side electrode with respect to the thickness of the electroless nickel-phosphorus plating layer formed on the back-side electrode is in a range of 1.0 to 3.5. The semiconductor element of the present invention allows the occurrence of voids inside solder during mounting by soldering to be prevented.