Low-Temperature Semiconductor Die Bonding Using Ultrafine Metal Paste
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Solution Overview
Problem
High-temperature bonding methods in die bonding of semiconductor chips result in increased thermal stress, affecting electrical properties, necessitating a method for bonding at a temperature not higher than 300°C to minimize this stress.
Innovation Solution
A bonding method using a metal paste composed of high-purity gold, silver, platinum, or palladium powders with an organic solvent, applied to one bonded member, dried, and sintered at 80-300°C to form a compact, followed by pressure bonding while heating, optionally with ultrasonic waves, to achieve a dense and strong bond.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If brazing filler metal is used for bonding semiconductor chip to substrate, then bonding strength is achieved, but bonding temperature becomes high (above 300°C) causing thermal stress
Solution Approach 1:
The invention changes the material parameters by using ultrafine metal powder (0.005-1.0 μm) with high purity (99.9 wt% or more) instead of conventional brazing filler metal. This parameter change enables bonding at lower temperatures (80-300°C) while maintaining sufficient bonding strength, resolving the contradiction between bonding strength and bonding temperature
Solution Approach 2:
The invention creates a composite structure consisting of metal powder sintered compact formed from ultrafine metal particles. This composite material approach allows the bonding interface to achieve adequate strength at reduced temperatures, avoiding the high thermal stress associated with conventional brazing methods
2Strength
If high purity metal powder is used in metal paste, then plastic deformation is facilitated for bonding, but powder hardness increases making deformation difficult
Solution Approach 1:
The invention changes the particle size parameter to ultrafine range (0.005-1.0 μm) which fundamentally alters the mechanical properties of the metal powder. At this scale, the powder exhibits both high purity characteristics and enhanced deformability, resolving the contradiction between purity-related hardness and bonding-required plastic deformation
3Manufacturing precision
If metal powder with small particle diameter is used, then sintering density is improved, but powder aggregation occurs during paste formation
Solution Approach 1:
The invention optimizes the particle diameter parameter to a specific ultrafine range (0.005-1.0 μm) that balances two opposing requirements: small enough to achieve high sintering density but large enough to prevent excessive aggregation during paste preparation and application. This precise parameter control resolves the contradiction between sintering quality and manufacturing ease
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 method enables bonding with sufficient strength at low temperatures, reducing thermal stress and maintaining the integrity of the bonded members, with bonding strengths exceeding 100 MPa, as demonstrated in examples.
Implementation Method 1
A step of drying the metal paste and sintering the dried metal paste at a temperature of 80 to 300° C. to form a metal powder sintered compact
Implementation Method 2
A step of arranging the one bonded member and the other bonded member via the metal powder sintered compact and bonding the bonded members to each other by applying pressure from one direction or both directions while at least the metal powder sintered compact is heated
Data Source
AI summary
The present invention provides a bonding method in which a bonded portion having a sufficient bonding strength can be obtained at a relatively low temperature, for example, in die bonding a semiconductor chip. A metal paste 20 was applied to a semiconductor chip 10, the metal paste 20 consisting of metal powder of one or more kinds selected from gold powder, silver powder, platinum powder, and palladium powder having a purity not lower than 99.9 wt % and an average particle diameter of 0.005 μm to 1.0 μm and an organic solvent. After being applied, the metal paste 20 was dried in a vacuum in a dryer. The chip was heated at 230° C. for 30 minutes to sinter the metal paste, by which a metal powder sintered compact 21 was formed. Next, a nickel plate 30 was placed on the semiconductor chip 10, and bonded to the semiconductor chip 10 by heating and pressurization.