Ceramic Substrate Warpage Control via Staged Cooling
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Solution Overview
Problem
There is a growing demand for increased flatness in circuit substrates, which requires improved bonding between ceramic and metal sheets, and existing methods do not adequately address this need.
Innovation Solution
A ceramic substrate with a specific three-dimensional shape, featuring convex curvatures in both directions from the center, and a manufacturing method involving rapid cooling and precise cutting of the substrate's edges to achieve a warpage of less than 6 pm/mm, ensuring excellent flatness and adhesion with metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional ceramic substrates are used without specific warpage control, then manufacturing is simpler, but the flatness of the resulting circuit substrate deteriorates
Solution Approach 1:
The patent applies preliminary action by intentionally forming a saddle shape warpage in the ceramic substrate before metal layer bonding. This pre-formed curvature compensates for subsequent warpage that occurs during metal layer attachment, thereby achieving flat final circuit substrates. The warpage is created in advance through controlled cooling rates during sintering, not as a corrective measure after defects occur.
Solution Approach 2:
The patent utilizes parameter changes by controlling the cooling rate during the sintering process to achieve specific warpage characteristics. By adjusting cooling parameters (rapid cooling at certain temperature ranges), the ceramic substrate develops the desired saddle shape. This parameter control allows precise manipulation of the substrate's three-dimensional shape without adding mechanical complexity.
2Stability of the object's composition
If the ceramic substrate is cooled slowly during sintering, then the material structure is more stable, but residual thermal strain increases causing warpage
Solution Approach 1:
The patent applies phase transitions by utilizing controlled cooling through specific temperature ranges during sintering. The cooling process is divided into stages: slow cooling above 900°C to maintain structural stability, and rapid cooling below 900°C to minimize residual thermal strain. This staged cooling exploits the different thermal expansion characteristics at various temperature phases to achieve both structural stability and reduced warpage.
Solution Approach 2:
The patent implements periodic action through staged cooling rates at different temperature intervals. The cooling process alternates between slow cooling (at higher temperatures to preserve structure) and rapid cooling (at lower temperatures to reduce strain). This periodic variation in cooling rate optimizes both structural integrity and warpage control.
3Reliability
If metal layers are bonded to ceramic substrate without pre-formed warpage, then bonding process is simpler, but adhesion and flatness deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-forming the saddle shape warpage in the ceramic substrate before metal layer bonding. This pre-curvature compensates for the natural warpage that occurs during metal attachment, ensuring flat final substrates and improving adhesion. The warpage is created in advance through controlled cooling, eliminating the need for complex post-bonding correction processes.
4Stress or pressure
If rapid cooling is applied throughout the entire sintering process, then residual thermal strain is reduced, but the ceramic structure may become unstable
Solution Approach 1:
The patent applies parameter changes by varying the cooling rate according to temperature intervals. Rapid cooling is applied only in the lower temperature range (below 900°C) to minimize residual thermal strain, while slow cooling is used at higher temperatures (above 900°C) to maintain structural stability. This temperature-dependent parameter adjustment optimizes both strain reduction and structural integrity.
Solution Approach 2:
The patent utilizes phase transitions by exploiting different thermal behaviors at various temperature ranges. The staged cooling approach recognizes that the ceramic structure has different thermal expansion and stress characteristics at high versus low temperatures, adjusting cooling rates accordingly to maintain stability while reducing strain.
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 approach results in circuit substrates with enhanced flatness and improved adhesion to metal layers, reducing residual thermal strain and stress, thereby producing substrates with superior joining properties.
Implementation Method 1
a cooling rate of 100° C./hour or more, a rapid cooling region in which the cooling rate is further increased when a temperature in the firing chamber is equal to or higher than 900° C. and equal to or lower than 1200° C.
Implementation Method 2
reducing residual thermal strain and stress
Implementation Method 3
a sintering step of disposing the individual green sheet in a firing chamber, heating an inside of the firing chamber until a temperature in the firing chamber reaches at least equal to or higher than 1600° C., then, cooling the inside of the firing chamber, and sintering the individual green sheet
Data Source
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AI summary
A ceramic substrate of the present invention is a ceramic substrate having a rectangular shape in a plan view, in which, in a case where an intersection formed by a pair of diagonal lines of the ceramic substrate is regarded as a reference in a sheet thickness direction of the ceramic substrate, out of four regions divided by the pair of diagonal lines, one pair of a pair of first regions facing each other across the intersection and a pair of second regions facing each other across the intersection is located on one side in the sheet thickness direction with respect to the intersection, the other pair is located on the other side in the sheet thickness direction with respect to the intersection, and a value obtained by dividing a maximum projection amount in the sheet thickness direction of the ceramic substrate by a length of the diagonal line of the ceramic substrate is equal to or less than 6 µm/mm.