Copper Powder Paste Sintered Body Adhesion to Ceramic Substrate
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Solution Overview
Problem
The challenge is to achieve strong adhesion between a sintered copper powder paste and a ceramic substrate over a wide temperature range, as the thermal expansion mismatch can cause separation during the firing process.
Innovation Solution
A laminate is created with a copper powder paste sintered body having a crystal grain diameter of 10 μm or less and an average reliability index (CI value) of 0.5 or more, which is achieved by surface-treating the copper powder and applying it to a ceramic substrate, ensuring improved adhesion through uniform crystal orientation and dispersibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper powder paste is applied to ceramic substrate, then electrical resistance is improved (lower than nickel), but adhesion between fired electrode and ceramic substrate deteriorates due to thermal expansion mismatch
Solution Approach 1:
Glass frit particles are introduced as an intermediary substance between the copper powder and ceramic substrate. The glass frit has thermal expansion characteristics that bridge the gap between copper and ceramic, acting as a buffer that absorbs thermal stress during firing and cooling cycles, thereby preventing separation while maintaining electrical conductivity
Solution Approach 2:
The electrode paste is formulated as a composite material containing copper powder, glass frit, and binder resin. This composite structure combines the electrical conductivity of copper with the adhesion and thermal expansion buffering properties of glass frit, creating a material that simultaneously achieves both low electrical resistance and strong adhesion to the ceramic substrate
2Reliability
If thin electrode paste is applied to increase number of layers, then capacitance per part is improved, but manufacturing precision deteriorates due to difficulty in printing fine pitch without disconnection
Solution Approach 1:
The viscosity and flow characteristics of the electrode paste are optimized by adjusting the binder resin content and type. This parameter change allows the paste to maintain its shape at finer pitches while still being printable, enabling the application of thinner pastes for increased layer count without sacrificing manufacturing precision or causing disconnection
3Strength
If ceramic particles or glass frit are added to metal powder paste, then adhesion between fired electrode and ceramic substrate is improved, but device complexity increases
Solution Approach 1:
Glass frit serves multiple functions simultaneously: it acts as a flux to lower the melting point of the paste for better sintering, provides thermal expansion buffering to prevent separation, and enhances wetting between copper and ceramic. This multi-functionality reduces the need for additional separate components, thereby managing complexity while achieving strong adhesion
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 laminate with enhanced adhesion and specific resistance, suitable for high-temperature applications, such as in MLCC and LTCC components, where the copper powder paste sintered body maintains a small grain diameter even at high temperatures, providing improved mechanical strength and electrical properties.
Implementation Method 1
The resulting laminate is fired in a non-oxidizing atmosphere or reducing atmosphere at 600° C. or higher for example, thereby sintering the metal powders to obtain an electrode
Implementation Method 2
A thermal expansion coefficient of the metal is higher than that of ceramic which is a substrate, and a difference in expansion and contraction is generated during the firing process, so that the fired electrode and the ceramic substrate may be separated
Data Source
AI summary
Provided is a laminate of a sintered body produced by sintering a copper powder paste and a ceramic substrate, which has improved adhesion between the sintered body and the ceramic substrate. A laminate with a copper powder paste sintered body laminated on a non-metal layer, wherein the copper powder paste sintered body has a crystal grain diameter of copper of 10 μm or less, as determined from an EBSD map image, based on Area Fraction method, and has an average reliability index (CI value) of 0.5 or more in an analysis area.