Conductive Bonding Composition for Lead-Free Power Semiconductor Die Attach
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Solution Overview
Problem
Existing lead-free solders face challenges in achieving both heat resistance and mounting reliability for semiconductor devices, particularly with wide-gap semiconductors like SiC and GaN, due to issues such as high material costs, poor wettability, and environmental toxicity, along with flux-related moisture absorption and bleed-out problems.
Innovation Solution
An electrically conductive composition comprising a sulfide compound with two or more sulfur atoms and metal particles, including Cu, Sn, or Ni, along with a thermosetting resin, which functions as a flux to remove oxide films and enhance bonding reliability without lead, using a low-temperature sintering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If lead-free solder such as AuGe is used to achieve heat resistance for wide-gap semiconductor devices, then the melting point increases, but the material cost and process cost rise drastically
Solution Approach 1:
The patent uses inexpensive metal particles (Cu, Sn, Ni) as consumable sacrificial materials that form a protective oxide layer and then sinter to create a high-melting-point bonding interface. The low-cost metal particles are consumed during the sintering process to achieve the desired high-temperature performance without requiring expensive AuGe solder throughout the entire structure.
Solution Approach 2:
The patent changes the physical and chemical parameters of the bonding material by controlling the oxidation state and sintering temperature. Metal particles are oxidized to form a protective layer, then sintered at elevated temperatures (800-1500°C) to create a dense, high-melting-point bonding interface. This parameter transformation allows low-cost metals to achieve high-temperature performance.
2Object-affected harmful factors
If lead-free solder is used to eliminate lead toxicity, then environmental safety improves, but wettability deteriorates causing solder to not spread properly on die pad
Solution Approach 1:
The patent applies a preliminary oxidation treatment to the metal particles before sintering, creating a protective oxide layer that improves wettability and bonding characteristics. This preliminary chemical modification of the particle surface ensures proper spreading and adhesion to the die pad before the final sintering process, solving the wettability issue inherent in lead-free solders.
Solution Approach 2:
The patent creates a composite structure consisting of metal particles (Cu, Sn, Ni) combined with oxide layers formed through controlled oxidation. This composite material combines the beneficial properties of both metals (low cost, high melting point after sintering) and oxides (improved wettability, bonding characteristics), achieving both environmental safety and reliable bonding.
3Temperature
If diffusive sintering-type solder such as Cu/Sn is used to achieve low melting point for mounting, then mounting temperature decreases, but the sintered body becomes hard and brittle with low stress relaxation property
Solution Approach 1:
The patent uses a composite of multiple metal particles (Cu, Sn, Ni) rather than a single-metal solder. This multi-metal composite provides a balance between low mounting temperature (due to Sn content) and adequate ductility (due to the composite structure and controlled sintering), preventing the excessive brittleness seen in single-component diffusive sintering solders.
Solution Approach 2:
The patent creates local variations in composition and structure within the bonding material. Different metal particles (Cu, Sn, Ni) are distributed throughout the paste, creating local regions with different properties. The Sn-rich regions provide low melting point for easy mounting, while Cu and Ni regions provide structural integrity and stress relaxation, achieving both low mounting temperature and adequate ductility.
4Manufacturing precision
If flux such as carboxylic acid and alcohol is added to remove metal oxide films, then oxide film removability improves, but moisture absorption and bleed-out increase causing anti-reflow reliability to deteriorate
Solution Approach 1:
The patent extracts and removes the problematic flux components (carboxylic acid, alcohol) from the bonding paste formulation. Instead of using traditional fluxes that cause moisture absorption and bleed-out, the patent relies on the controlled oxidation and sintering of metal particles to remove oxide films, eliminating the source of moisture-related reliability issues while maintaining oxide removal capability.
Solution Approach 2:
The metal particles in the patent perform a self-service function by undergoing controlled oxidation to form protective layers and then self-sintering during the bonding process. This self-organizing behavior of the metal particles eliminates the need for external flux additives, allowing oxide removal and bonding to occur through the intrinsic properties of the metal particles themselves without introducing moisture-absorbing chemicals.
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 composition provides excellent heat resistance, mounting reliability, and moisture absorption resistance, reducing environmental burden and eliminating the need for flux rinsing, while ensuring stable bonding and thermal fatigue resistance.
Implementation Method 1
the sulfide compound...which functions as a flux to remove oxide films
Implementation Method 2
using a low-temperature sintering process
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The purpose of the present invention is to provide a means that exhibits excellent heat resistance and mounting reliability when bonding a semiconductor power element to a metal lead frame, which is also free of lead and thereby places little burden on the environment. Namely, it is an electrically conductive composition, which contains at least a sulfide compound represented by R-S-R' (wherein R is an organic group containing at least carbon; R' is an organic group that is the same as or different from R; and R and R' may be bonded to each other to form a so-called cyclic sulfide) and metal particles containing at least Cu, Sn or Ni as its essential component. Further, a conductive paste and a conductive bonding film, each of which are produced using the electrically conductive composition, as well as a dicing die bonding film, which is obtained by bonding the conductive bonding film with an adhesive tape, are provided.