Silver-to-Silver Bonded IC Package with Exposed Ceramic Substrates
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Solution Overview
Problem
Existing integrated circuit packages for power devices rely on soft solder and wire bonds, which can be unreliable and inefficient for mechanical and electrical contact, and do not effectively utilize ceramic substrates for heat dissipation.
Innovation Solution
A packaged power device using direct metal bonded ceramic substrates with sintered silver pads and ultrasonic welding, where silver nanoparticle paste is applied to aluminum bond pads, forming direct silver-to-silver bonds between the die and substrate, eliminating the need for soft solder and wire bonds, and allowing exposed ceramic substrates for improved heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft solder and wire bonds are used in traditional IC packages, then electrical connection is achieved, but reliability and efficiency of mechanical and electrical contact deteriorate
Solution Approach 1:
The patent removes soft solder and wire bonds from the traditional packaging process, extracting the problematic bonding elements and replacing them with direct silver-to-silver bonding between dice and substrate, eliminating the need for intermediate solder joints and wire connections
Solution Approach 2:
The invention changes the bonding material parameters by using sintered silver pads instead of soft solder, and evaporative silver instead of wire bonds, fundamentally altering the physical and chemical properties of the bonding interface to achieve superior electrical and mechanical contact
2Temperature
If ceramic substrates are used for heat dissipation, then thermal management is improved, but the ceramic substrates are not effectively utilized for heat dissipation in traditional packages
Solution Approach 1:
The package structure is segmented to expose ceramic substrates on opposite outer surfaces, creating dedicated thermal pathways that separate heat dissipation functions from electrical connection functions, allowing each ceramic substrate to serve as an independent heat sink
Solution Approach 2:
The patent utilizes the third dimension by exposing ceramic substrates on opposite outer surfaces of the package, creating vertical thermal pathways that extend from the dice through the substrate to the package exterior, maximizing heat dissipation surface area in the vertical dimension
3Reliability
If direct silver-to-silver bonding is implemented, then mechanical and electrical contact is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
Silver nanoparticle paste is applied to aluminum bond pads and sintered to form sintered silver pads before die attachment, preparing the bonding surface in advance to facilitate direct silver-to-silver bonding when the dice are pressed onto the substrate
Solution Approach 2:
Silver nanoparticle paste serves as an intermediary material that bridges the aluminum bond pads and the evaporative silver on the dice, enabling direct silver-to-silver bonding through the sintering process while maintaining manufacturing feasibility
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 solution provides a reliable, solderless, and wire-bond-free integrated circuit package with enhanced mechanical and electrical contact, and improved heat dissipation through exposed ceramic substrates, resulting in a more efficient and durable power device.
Implementation Method 1
Silver nanoparticle paste is applied to aluminum bond pads on the frontside (i.e., device side) of a die and the paste is sintered so that the aluminum bond pads on the front side of the die are covered with sintered silver pads
Implementation Method 2
Silver formed by an evaporative process covers the entire backside of the die
Implementation Method 3
The two DBAs are attached to a leadframe by ultrasonic welding
Implementation Method 4
the pressing causes a direct silver-to-silver bond to be formed between the evaporative silver on the backside of the die and a corresponding sintered silver pad of one of the DBAs
Data Source
AI summary
A packaged power device involves no soft solder and no wire bonds. The direct-bonded metal layers of two direct metal bonded ceramic substrate assemblies, such as Direct Bonded Aluminum (DBA) substrates, are provided with sintered silver pads. Silver nanoparticle paste is applied to pads on the frontside of a die and the paste is sintered to form silver pads. Silver formed by an evaporative process covers the backside of the die. The die is pressed between the two DBAs such that direct silver-to-silver bonds are formed between sintered silver pads on the frontside of the die and corresponding sintered silver pads of one of the DBAs, and such that a direct silver-to-silver bond is formed between the backside silver of the die and a sintered silver pad of the other DBA. After leadforming, leadtrimming and encapsulation, the finished device has exposed ceramic of both DBAs on outside package surfaces.