Silicon Nitride Substrate Surface Treatment for Brazing Bond Strength
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Solution Overview
Problem
The silicon nitride substrates used for mounting circuits face issues with bond strength due to mechanical processing methods like sand blasting, which causes silicon nitride grains to detach, leading to poor adhesion of brazing materials and potential detachment of metal circuit boards during heating and cooling cycles.
Innovation Solution
Integrating granular bodies containing silicon onto the silicon nitride substrate surface, with needle or column crystals of silicon nitride extending from these bodies, enhancing the anchor effect when bonded with metal members using a brazing material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical processing such as sand blasting is used to condition the silicon nitride substrate surface, then the surface properties are improved for bonding, but the silicon nitride grains detach and bond strength deteriorates
Solution Approach 1:
The invention changes the surface conditioning approach from mechanical removal of grain boundaries to chemical etching that creates a specific microstructure. By controlling etching parameters (time, temperature, reagent concentration), the surface develops a controlled roughness with embedded silicon-rich granular bodies that enhance bonding without grain detachment.
Solution Approach 2:
The surface treatment creates a composite structure where silicon-rich granular bodies are embedded in the silicon nitride matrix. This composite microstructure provides both the surface roughness needed for mechanical interlocking and maintains grain boundary integrity for strong bonding.
2Shape
If grain boundaries are mechanically removed to condition the surface, then surface texture is improved, but brazing material does not fill voids and reliability deteriorates
Solution Approach 1:
Instead of removing grain boundaries, the invention changes the surface treatment parameter from mechanical abrasion to chemical etching. This creates a surface with controlled porosity and silicon-rich regions that actively attract and retain brazing material, ensuring complete void filling.
Solution Approach 2:
The silicon-rich granular bodies formed by etching act as intermediaries between the silicon nitride substrate and the brazing material. These granular bodies provide nucleation sites for brazing material deposition and ensure complete wetting and void filling.
3Ease of manufacture
If mechanical processing is used to prepare the surface, then surface conditioning is achieved, but the substrate cannot withstand repeated heating and cooling cycles and detachment occurs
Solution Approach 1:
The invention replaces mechanical surface preparation parameters with chemical etching parameters, creating a surface microstructure that is inherently more stable under thermal stress. The etched surface with embedded silicon-rich bodies maintains its integrity during thermal cycling, preventing grain detachment.
Solution Approach 2:
The chemical etching process beforehand creates a cushioning layer of silicon-rich granular bodies that absorb and distribute thermal stresses during subsequent heating and cooling cycles. This prevents stress concentration and grain detachment that would occur with mechanically processed surfaces.
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 results in a strong and durable bond between the silicon nitride substrate and metal members, preventing detachment even under repeated thermal stress, thus enhancing the reliability of electronic devices.
Implementation Method 1
a plurality of needle crystals or column crystals comprising mainly of silicon nitride are extended from a portion of the granular bodies... enhancing the anchor effect when bonded with metal members using a brazing material
Implementation Method 2
bonded through a brazing material to each of principal surfaces on both sides of the support substrate
Data Source
Figure 1(a)~1(c)
Figure 2
Figure 3(a)~3(b)
AI summary
Provided is a silicon nitride substrate capable of enhancing the bond strength when a member made of a metal is bonded to the substrate, and a circuit substrate and an electronic device capable of improving reliability by using the silicon nitride substrate. The silicon nitride substrate 1 comprises a substrate 1a comprising a silicon nitride sintered body, and a plurality of granular bodies 1b containing silicon and integrated to a principal surface of the substrate 1a, wherein a plurality of needle crystals 1c or column crystals 1d comprising mainly silicon nitride are extended from a portion of the granular bodies 1b. A brazing material is applied to a principal surface of the substrate 1a, and a circuit member and a heat radiation member are arranged on the applied brazing material, and bonded by heating. Because of a plurality of granular bodies 1b integrated to the principal surface of the substrate 1a, and a plurality of the needle crystals 1c or the column crystals 1d extended from a portion of the granular bodies 1b, a high anchor effect is produced so that the circuit member and the heat radiation member are firmly bonded to the silicon nitride substrate 1.