Metal Ceramic Bonding Substrate Solidification Control
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Solution Overview
Problem
Conventional methods for producing metal/ceramic bonding substrates often result in defects such as shrinkage cavities and voids due to insufficient molten metal and thermal expansion issues, leading to unreliable bonding and reduced heat sink characteristics in power modules.
Innovation Solution
A method involving the solidification of molten aluminum or aluminum alloy within a mold while pressurizing the metal injected from an inlet, creating a temperature gradient and controlled cooling to prevent defects, ensuring a reliable bond between the metal and ceramic substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mold with a cavity corresponding to the shape and size of a metal plate is used for production, then the metal plate can be bonded to a ceramic substrate, but shrinkage cavities and voids are easily caused due to insufficient molten metal supply during solidification
Solution Approach 1:
The mold is divided into multiple cooling zones with different cooling rates. The region corresponding to the metal plate has enhanced cooling capacity compared to other regions, creating localized rapid solidification that prevents shrinkage cavities while maintaining the desired plate shape.
Solution Approach 2:
Different regions of the mold are assigned different thermal properties. The metal plate region has higher thermal conductivity and/or lower heat capacity in the cooling system, creating a local temperature gradient that directs molten metal flow and prevents void formation during solidification.
2Manufacturing precision
If conventional cooling is used after molten metal injection, then the metal member can be solidified, but corner portions become rounder than desired due to shrinkage
Solution Approach 1:
The cooling system is segmented into regions with different cooling intensities. Corner regions receive enhanced cooling to maintain sharp geometries during solidification, preventing the rounding that occurs with uniform cooling while preserving structural integrity through controlled solidification.
3Weight of moving object
If aluminum alloy is used for the metal member, then weight reduction is achieved, but hot cracks are produced during cooling process
Solution Approach 1:
The cooling rate is locally optimized in regions prone to hot cracking. By controlling the temperature gradient and cooling rate in critical areas, the solidification process prevents crack formation in aluminum alloys while maintaining the weight advantage of the material.
Solution Approach 2:
The cooling parameters (rate, temperature distribution) are optimized for aluminum alloy solidification. By adjusting these parameters, the phase transformation process is controlled to prevent hot cracking while maintaining the low-density advantage of aluminum alloys.
4Ease of manufacture
If soldering is used to bond base plate to ceramic substrate, then assembly is achieved, but base plate warps due to thermal expansion difference
Solution Approach 1:
The metal plate is pre-bonded to the ceramic substrate in a planar state using direct bonding before any subsequent assembly steps. This preliminary bonding prevents warpage by establishing a flat configuration before thermal expansion differences can cause deformation during later soldering operations.
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 effectively prevents shrinkage cavities and voids, resulting in a reliable metal/ceramic bonding substrate with improved thermal conductivity and structural integrity, enhancing the heat sink characteristics of power modules.
Implementation Method 1
solidifying the molten metal to bond a metal member of aluminum or the aluminum alloy to the ceramic substrate by cooling the mold
Implementation Method 2
when a molten metal of aluminum or an aluminum alloy is solidified by cooling the mold
Implementation Method 3
by cooling the mold while pressurizing the molten metal injected into the mold
Implementation Method 4
there are some cases where the amount of the supplied molten metal is insufficient for solidification and shrinkage to easily cause the so-called 'shrinkage cavities' and/or 'voids'
Data Source
AI summary
After a molten metal of aluminum or an aluminum alloy having a temperature, which is higher than the liquidus line temperature of aluminum or the aluminum alloy by 5 to 200° C., is injected into a mold, when the mold is cooled to solidify the molten metal, the molten metal injected into the mold is pressurized at a pressure of 1.0 to 100 kPa from a high-temperature side to a low-temperature side, and the mean cooling rate is set to be 5 to 100° C./minute while the mold is cooled from the liquidus line temperature to 450° C., the temperature gradient formed in the mold being set to be in the range of from 1° C./cm to 50° C./cm.