Semiconductor Die Bonding with Segmented Silver Paste
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Solution Overview
Problem
Silver paste used as die bonding material in power semiconductor devices experiences thermal stress due to differences in linear expansion coefficients, leading to destruction and delamination, especially under the corners of semiconductor chips, and thinned die pads deform during curing, affecting warpage and reliability.
Innovation Solution
A manufacturing method involving the use of sintered-silver-use paste applied to corners and silver paste in between, with both materials being bonded under heat and pressure to enhance bonding strength and prevent deformation, improving reliability and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silver paste is used as die bonding material, then ease of manufacture is improved, but reliability deteriorates due to thermal stress concentration under chip corners causing destruction and delamination
Solution Approach 1:
The bonding material is segmented into two distinct types: sintered-silver-use paste applied at corner regions and silver paste applied in intermediate regions. This segmentation allows each material to be optimized for its specific functional requirements - sintered silver for thermal stress resistance at corners and regular silver paste for general bonding in less stressed areas.
Solution Approach 2:
Different bonding materials are applied to different locations on the chip mounting part. Corner regions receive sintered-silver-use paste which has superior thermal stress resistance properties, while intermediate regions receive standard silver paste. This local differentiation of material quality addresses the specific thermal stress concentration problem at corners without compromising overall bonding performance.
2Reliability
If sintered-silver-use paste is used as die bonding material, then reliability is improved by suppressing destruction under corners, but device complexity increases due to multiple paste application steps
Solution Approach 1:
The bonding material application process is segmented into two distinct steps: first applying sintered-silver-use paste to corner regions, then applying silver paste to intermediate regions. This segmented approach maintains reliability benefits while organizing the complexity into manageable, sequential operations.
Solution Approach 2:
Instead of applying sintered-silver-use paste to the entire chip mounting surface, the invention applies it only to corner regions where thermal stress concentration occurs. This partial action approach maintains the reliability benefits of sintered silver while reducing the complexity and cost associated with processing the entire surface with the more complex material.
3Temperature
If die pad thickness is thinned for heat dissipation improvement, then heat dissipation capability is improved, but reliability deteriorates due to deformation during paste curing affecting warpage
Solution Approach 1:
The bonding material composition is locally optimized at corner regions where the thinned die pad creates higher stress during curing. Sintered-silver-use paste with its superior mechanical properties is applied specifically at these vulnerable corner locations to prevent deformation and warpage, while intermediate regions use standard silver paste.
Solution Approach 2:
Sintered-silver-use paste is applied beforehand at corner regions to provide structural support and cushioning during the curing process. This pre-positioned stronger material compensates for the reduced mechanical strength of thinned die pads, preventing deformation and warpage before they can occur during subsequent curing 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
The method effectively suppresses destruction and delamination under corners, enhances bonding strength, and reduces warpage, improving the reliability and heat dissipation capabilities of power semiconductor devices.
Implementation Method 1
a sintered-silver-use paste is applied to each of a plurality of first regions on the second front surface of the chip mounting part
Implementation Method 2
applying heat and pressure to the semiconductor chip and thereby bonding the first rear surface of the semiconductor chip, and the sintered-silver-use paste and the silver paste together
Implementation Method 3
thermal stress occurs in a temperature cycle test and so forth performed after completion of a product due to a difference in linear expansion coefficient between the semiconductor chip and the die pad and the thermal stress is concentrated on the silver paste which is located directly under corners of the semiconductor chip
Implementation Method 4
In the power semiconductor device for which high adaptability to heat dissipation is requested
Data Source
AI summary
A die bonding process for assembling a semiconductor device includes the steps of applying a sintered-silver-use paste to each of a plurality of first regions on an upper surface of a chip mounting part, drying the sintered-silver-use paste and applying a silver paste to a second region located between/among the respective first regions. Further, the process includes the step of mounting a semiconductor chip onto the chip mounting part in such a manner that a rear surface of the semiconductor chip faces an upper surface of the chip mounting part with the sintered-silver-use paste and the silver paste being interposed. After mounting the chip, part of each of first, second, third and fourth corners of a principal surface of the semiconductor chip is located in each of the first regions.