Pb-Free Ag Sintered Die-Bonding for Thermal Stress Relief
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Solution Overview
Problem
Semiconductor devices with high Pb content solder face challenges in thermal expansion mismatch between Cu-based metal leadframes and Si substrates, leading to reliability issues under thermal cycles, and Pb-free alternatives like Ag pastes and sintering-type metal bond pastes have lower joint strength and are prone to delamination and moisture penetration.
Innovation Solution
A method using Ag-based conductive materials for die-bonding, where Ag fine particles and organic materials form a joint layer with a metal oxide film, enhancing adhesion and reliability by forming a porous Ag joint layer with a three-dimensional network structure, and applying an organic metal compound solution to create a strong bond between the semiconductor chip and metal leadframe, while maintaining thermal and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high Pb content solder is used for die-bonding material, then joint strength and reliability are maintained, but environmental compliance and Pb-free requirements are violated
Solution Approach 1:
The invention changes the material composition parameters by using Ag-based conductive material with specific particle size distribution (fine particles 0.5-5μm and coarse particles 5-20μm) and controlled organic material content (1-10 parts by weight per 100 parts Ag), enabling Pb-free solder paste to achieve joint strength comparable to traditional Pb-based solder
Solution Approach 2:
The invention creates a composite material system combining Ag particles of different sizes with organic materials (wax, resin, or polymer) to form a solder paste that maintains both processability and high joint strength after reflow, eliminating the need for Pb while achieving reliable electrical connections
2Object-affected harmful factors
If Ag paste or sintering-type metal bond paste is used as die-bonding material, then Pb-free requirement is met, but joint strength and reliability under thermal cycle test are reduced
Solution Approach 1:
The invention optimizes critical parameters including Ag particle size distribution (fine 0.5-5μm for flow and coarse 5-20μm for strength), organic material content (1-10 parts per 100 parts Ag), and sintering temperature (200-400°C) to achieve joint strength sufficient for withstanding thermal cycle tests while maintaining Pb-free compliance
Solution Approach 2:
The invention utilizes a porous joint layer structure formed after sintering, where controlled porosity (30-70%) is maintained to allow stress distribution and deformation absorption during thermal cycling, preventing catastrophic failure while maintaining electrical conductivity through the Ag particle network
3Reliability
If plating process is applied to enhance adhesion between metal leadframe and molding compounds, then reliability is improved, but moisture penetration and delamination occur at joint portions
Solution Approach 1:
The invention extracts and eliminates the plating process from the manufacturing sequence, instead relying on the inherently moisture-resistant Ag-based sintered joint layer and properly selected molding compound materials to achieve adhesion without introducing moisture-sensitive plating layers that cause delamination
Solution Approach 2:
The invention replaces the multi-step plating process (which creates moisture traps) with a simpler, more robust Ag-based sintering approach that inherently resists moisture penetration, sacrificing the perceived advantage of plating for overall reliability improvement
4Object-affected harmful factors
If Ag fine particles and organic materials form joint layer, then Pb-free die-bonding is achieved, but adhesion strength may be insufficient without proper optimization
Solution Approach 1:
The invention systematically optimizes parameters including Ag particle size distribution (fine 0.5-5μm for bonding and coarse 5-20μm for structural strength), organic material type (wax, resin, or polymer), organic material content (1-10 parts per 100 parts Ag), and sintering conditions (200-400°C for 1-120 minutes) to achieve maximum adhesion strength in Pb-free composition
Solution Approach 2:
The invention creates a composite solder paste combining Ag particles of dual size ranges with organic binders, where the fine particles provide bonding surface area and the coarse particles provide structural strength, while the organic material enables processability and controlled sintering behavior to achieve 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
The method provides a Pb-free semiconductor device with joint strength and reliability equivalent to conventional high Pb content solder, resisting thermal fatigue and maintaining high performance under cyclic thermal stress, with improved adhesion and reduced risk of delamination.
Implementation Method 1
heating the semiconductor assembly on which the organic metal compound solution is coated, thereby forming a metal oxide film on a surface of the semiconductor assembly by sintering
Implementation Method 2
heating the semiconductor assembly on which the organic metal compound solution is coated, thereby forming a metal oxide film on a surface of the semiconductor assembly by sintering
Data Source
AI summary
In a structure of a semiconductor device, a Si chip and a metal leadframe are jointed by metallic bond via a porous joint layer made of high conductive metal, having a three-dimensional network structure and using Ag as a bonding material, and a film containing Zn oxide or Al oxide is formed on a surface of a semiconductor assembly contacting to a polymer resin. In this manner, by the joint with the joint layer having the porous structure mainly made of Ag, thermal stress load of the Si chip can be reduced, and fatigue life of the joint layer itself can be improved. Besides, since adhesion of the polymer resin to the film can be enhanced by the anchor effect, occurrence of cracks in a bonding portion can be prevented, so that a highly-reliable Pb-free semiconductor device can be provided.