Power Module Substrate Brazing Burr Control
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Solution Overview
Problem
The existing power-module substrates face issues with braze stains due to melted braze exuding from between the copper or aluminum plates and the ceramic substrate, which deteriorates the appearance and wettability of soldering materials, and attempting to prevent these stains can compromise bondability.
Innovation Solution
The method involves forming metal plates with controlled burrs and fracture surfaces through press blanking, where the burr height is set to 0.021 mm or smaller and the fracture surface thickness is 0.068 mm or larger, ensuring the burrs are pressed against the ceramic substrate to prevent braze exudation during brazing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the metal plate is bonded to the ceramic substrate by brazing with active metal, then the bondability between metal plate and ceramic substrate is improved, but the melted braze may exude and crawl up the metal plate surface causing braze stains that deteriorate appearance and soldering wettability
Solution Approach 1:
The invention applies preliminary action by forming burrs on the metal plate surface before brazing. These burrs are created through controlled blanking with specific clearance (0.03-0.08mm) and may involve multiple blanking passes. The burrs serve as preventive structures that will contain the braze material during subsequent brazing operations, preventing it from crawling up the plate surface and creating stains.
Solution Approach 2:
The invention converts the potentially harmful effect of braze material exudation into a beneficial outcome. By designing controlled burrs on the metal plate surface, the braze material that would normally crawl up and stain the surface is instead directed into the burr structures. This transforms the harmful braze stain problem into a beneficial feature where the braze fills the burrs, preventing surface contamination while maintaining strong bonding.
2Object-generated harmful factors
If the burr height is increased to prevent braze crawling, then the prevention of braze stain is improved, but the bondability of soldering material to the metal plate surface may be deteriorated
Solution Approach 1:
The invention applies local quality by creating non-uniform surface features (burr structures) only at specific locations where braze material tends to crawl. The burrs are formed along the peripheral edges or at specific zones of the metal plate, while the central bonding surfaces remain relatively smooth and clean. This localized modification prevents braze stains without interfering with the overall soldering wettability of the plate surface.
Solution Approach 2:
The invention carefully controls the parameters of the burr structures, specifically limiting the burr height to 0.021mm or smaller and controlling the fracture surface thickness to 0.068mm or larger. These precise parameter specifications ensure that the burrs are sufficient to contain braze material but not so large as to create significant surface irregularities that would hinder soldering wettability. The blanking clearance is controlled within 0.03-0.08mm to achieve the desired burr characteristics.
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 approach effectively prevents braze stains on the metal plates while maintaining bondability between the metal plates and ceramic substrates, improving the soldering of semiconductor chips without compromising the bond between the metal and ceramic substrates.
Implementation Method 1
a metal plate which is formed by blanking of a metal raw-plate by press working is stacked on one surface of a ceramic substrate and bonded by brazing
Implementation Method 2
the active metal braze for bonding the copper plate and the ceramic substrate is provided as paste, and this braze paste and mother material of copper generates Ag-Cu melted braze
Data Source
Figure 1~3
Figure 4
AI summary
To prevent braze stain and improve solder bondability of a semiconductor chip without deteriorating bondability between a metal plate and a ceramic substrate: a producing method of a power-module substrate by braze-bonding a metal plate which is blanked by press working on a metal raw-plate on one surface of a ceramic substrate: in the metal plate, a height of burrs is 0.021 mm or smaller, a thickness of a fracture surface is 0.068 mm or larger; the metal plate is stacked on the ceramic substrate so as to stack a surface thereof on a side at which the burrs are generated is in contact with the one surface of the ceramic substrate and brazed.