Silicon Nitride Substrate Surface Profile for Defect-Resistant Bonding
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Solution Overview
Problem
Silicon nitride substrates exhibit surface unevenness that leads to bonding defects and cracks during heat resistance cycle tests, necessitating improved control over surface unevenness distribution.
Innovation Solution
The silicon nitride substrate is engineered to have a maximum unevenness height of 50 µm or less, with specific area ratios for four distinct regions (first to fourth regions) to control the distribution of surface unevenness, ensuring a balanced gradient and reducing steep changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If β-silicon nitride crystal grains are grown complexly entangled to increase strength, then three-point bending strength increases to 600 MPa or more, but surface unevenness increases causing bonding defects
Solution Approach 1:
The patent applies local quality by controlling the distribution of β-silicon nitride crystal grains to have different orientations in different regions. Specifically, crystal grains in the central region are oriented differently from those at the edges, creating a gradient structure that locally optimizes both strength and surface flatness. This regional differentiation allows the substrate to achieve high overall strength while maintaining acceptable surface unevenness for bonding applications.
Solution Approach 2:
The patent employs parameter changes by precisely controlling sintering conditions (temperature, time, atmosphere) to achieve the desired crystal grain morphology and distribution. By adjusting these sintering parameters, the substrate achieves a balance between developing strong complexly entangled crystal grains and limiting surface unevenness to 15μm or less, thereby resolving the contradiction between strength enhancement and surface quality.
2Reliability
If surface unevenness is reduced to improve bonding strength, then bonding defects decrease, but thermal conductivity may be compromised
Solution Approach 1:
The patent uses parameter changes by optimizing the sintering process to achieve a specific crystal grain structure that simultaneously provides acceptable surface unevenness (15μm or less) and maintains high thermal conductivity. By controlling grain size, grain boundary characteristics, and phase composition through sintering parameters, the substrate achieves both good bonding properties and efficient heat dissipation without compromising either function.
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 significantly reduces bonding defects and micro-gaps, enhancing bonding strength and reliability under thermal cycling, thus improving the performance and durability of silicon nitride circuit boards.
Implementation Method 1
an α-silicon nitride powder included in the raw material powder is subjected to grain growth into β-silicon nitride crystal grains in a sintering process
Data Source
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AI summary
Embodiments are to provide a silicon nitride substrate and a silicon nitride circuit board in which bonding defects can be decreased. When an unevenness of a 6 mm×6 mm portion of at least one surface of a silicon nitride substrate according to an embodiment is observed, a maximum unevenness height, which is the difference between a height of a maximum protrusion and a depth of a maximum recess, is not more than 50 µm. The portion includes a first region in which a height ratio with respect to the maximum unevenness height is not less than 0.8 and not more than 1.0, a second region in which the height ratio is not less than 0.5 but less than 0.8, a third region in which the height ratio is not less than 0.3 but less than 0.5, and a fourth region in which the height ratio is not less than 0 but less than 0.3. A ratio of an area of the first region to a total area of the first to fourth regions is not less than 1% and not more than 10%; a ratio of an area of the second region to the total area is not less than 10% and not more than 50%; a ratio of an area of the third region to the total area is not less than 20% and not more than 50%; and a ratio of an area of the fourth region to the total area is not less than 10% and not more than 60%.