Multilayer Substrate Structure for Thermal Stress-Resistant Bonding
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Solution Overview
Problem
Existing multilayer substrates with ceramic and thermoplastic resin layers experience thermal stress, leading to cracking and peeling at the connection portions between electrodes and interlayer connection conductors.
Innovation Solution
A multilayer substrate design that includes a protective layer covering part of the electrode outline, reducing the area where intermetallic compounds form, thereby minimizing thermal stress and preventing cracking and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the electrode outline is fully exposed to allow complete intermetallic compound formation for bonding, then the bonding strength between the electrode and interlayer connection conductor is improved, but the thermal stress concentration increases leading to cracking and peeling
Solution Approach 1:
The patent applies local quality by creating different regions with different properties: the center region of the electrode allows complete intermetallic compound formation for strong bonding, while the peripheral region is covered by a protective layer to prevent intermetallic compound formation and reduce thermal stress concentration. This spatial differentiation of bonding quality resolves the contradiction between bonding strength and thermal stress resistance.
Solution Approach 2:
The electrode outline is segmented into two functional zones: an exposed central region for bonding and a protected peripheral region for stress reduction. The protective layer is selectively positioned to cover only the peripheral portion, creating a segmented structure that simultaneously achieves strong bonding and thermal stress resistance.
2Reliability
If the intermetallic compound layer is formed extensively across the entire electrode surface, then the connection reliability between layers is improved, but the area susceptible to thermal stress-induced cracking increases
Solution Approach 1:
The intermetallic compound formation is made local rather than extensive. The protective layer restricts intermetallic compound formation to specific regions where it is needed for bonding, while preventing it in regions where it would be susceptible to thermal stress. This localized approach maintains connection reliability while reducing thermal stress susceptibility.
3Reliability
If the protective layer covers the entire electrode outline, then thermal stress is minimized, but the bonding area between electrode and interlayer connection conductor is reduced
Solution Approach 1:
The protective layer coverage is optimized to be partial rather than complete. It covers the peripheral region where thermal stress concentration occurs but leaves the central region exposed for bonding. This selective coverage achieves stress minimization without sacrificing bonding area.
Solution Approach 2:
Instead of complete protective layer coverage (excessive action), the patent applies partial coverage only where needed for stress reduction. This partial action approach prevents over-protection that would eliminate bonding areas while still achieving sufficient stress mitigation.
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 effectively reduces the likelihood of cracking and peeling at the connection portions, even under thermal stress, enhancing the reliability and durability of the multilayer substrate.
Implementation Method 1
the first terminal electrode of the ceramic multilayer substrate and an interlayer conductor in the first thermoplastic resin layer are bonded by transient liquid phase diffusion bonding, and the second terminal electrode of the ceramic multilayer substrate and an interlayer conductor in the second thermoplastic resin layer are bonded by transient liquid phase diffusion bonding
Implementation Method 2
a metal such as Sn or an Sn alloy of the interlayer connection conductor melts when heated and reacts with a metal (e.g., Cu) of the conductive wiring layer
Implementation Method 3
reacts with a metal (e.g., Cu) of the conductive wiring layer
Implementation Method 4
The linear thermal expansion coefficient of the ceramic layer is different from the linear thermal expansion coefficient of the thermoplastic resin layer. Thus, when heat is applied to the multilayer substrate, thermal stress occurs between the ceramic layer and the thermoplastic resin layer
Data Source
AI summary
A multilayer substrate that includes: a first thermoplastic resin layer including a first main surface, a second main surface opposite to the first main surface, and a via hole penetrating from the first main surface to the second main surface; a ceramic layer in contact with the first main surface; a second thermoplastic resin layer in contact with the second main surface; a first electrode on a surface of the ceramic layer in contact with the first main surface; a protective layer covering at least part of an outline of the first electrode; a second electrode on a surface of the second thermoplastic resin layer in contact with the second main surface; an interlayer connection conductor in the via hole and connecting the first electrode and the second electrode; and an intermetallic compound between the interlayer connection conductor and the first electrode.