Fluidic Self-Assembly Solder Stack for High-Temp Interconnects
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Solution Overview
Problem
Existing self-assembly methods face challenges in scaling to large areas and achieving reliable interconnects at elevated temperatures due to limitations in solder melting points and shear forces caused by protruding components, which restrict the use of self-assembled objects in industrial applications.
Innovation Solution
A method using a solder stack with multiple layers of increasing melting points, where the outermost layer forms a selective adhesive at low temperature for self-alignment and attachment, and the inner layer reflows at higher temperature to create a robust interconnect, combined with a fluidic self-assembly apparatus that minimizes shear forces by collecting and reusing excess components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer solder is used for self-assembly, then the assembly process is simple, but the interconnect cannot withstand elevated temperatures
Solution Approach 1:
The solder structure is divided into multiple layers with different melting points. The first solder layer has a lower melting point for self-assembly, while the second solder layer has a higher melting point for high-temperature reliability. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The invention changes the melting point parameter of the solder by using different solder compositions in different layers. The first layer uses solder with melting point T1, and the second layer uses solder with melting point T2 where T2 > T1. This parameter differentiation enables the system to achieve both low-temperature assembly and high-temperature operation.
2Area of stationary object
If components are assembled on large areas, then the application scope increases, but shear forces from protruding components increase
Solution Approach 1:
The substrate is tilted at a specific angle before component deposition. This preliminary action creates a gravitational component that counteracts the shear force generated by protruding components, preventing them from dislodging during the self-assembly process on large substrate areas.
Solution Approach 2:
The invention changes the orientation parameter of the substrate by tilting it at an angle θ. This parameter change modifies the force balance on the assembled components, reducing the effective shear force to below the adhesion strength of the solder interconnect.
3Manufacturing precision
If conventional robotic assembly is used, then precise placement is achieved, but throughput and cost efficiency deteriorate
Solution Approach 1:
The system uses self-assembly where components automatically position themselves on the substrate through controlled deposition and adhesion forces. This eliminates the need for precise robotic manipulation of each component, enabling massively parallel assembly that dramatically increases throughput while maintaining placement precision through the physics of the self-assembly process.
4Strength
If solder temperature is increased for reliable interconnects, then interconnect strength improves, but solder melting and component damage occur
Solution Approach 1:
The solder interconnect is segmented into two layers with different melting points. The first layer melts at a lower temperature to enable self-assembly, while the second layer remains solid during this process and provides structural support. After assembly, both layers are reflowed together to create a strong, reliable interconnect that does not require excessive temperatures that would damage components.
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
Enables reliable self-assembly of components over large areas with interconnects that withstand elevated temperatures, reducing shear forces and increasing the yield of self-assembled objects, thus facilitating their use in industrial processes.
Implementation Method 1
self-alignment of components on a substrate on the basis of surface tension of liquid solder
Implementation Method 2
solder stack with multiple layers of increasing melting points, where the outermost layer forms a selective adhesive at low temperature for self-alignment and attachment, and the inner layer reflows at higher temperature to create a robust interconnect
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method of self-assembly including self-alignment of components (1) on a substrate (2) on the basis of surface tension of liquid solder, involving a solder stack composed of an outermost layer of solder (3) on top and at least another layer of solder (4), the layers of solder having successively increasing melting points from top to bottom. In a first step the solder stack is heated to melt the outermost layer of solder (3), this solder layer is used to form a receptor, which adheres to the components (1), which are self-assembled, self-aligned, and attached in the following. In the next step the solder stack is heated to a temperature further elevated above the melting point of the at least another layer of solder (4). Thereby a reflow soldering-process is initialised and the two layers of solder (3, 4) form a mixed solder layer as an alloy (5). As a consequence, an interconnect between the components (1) and the substrate (2) with a melting point higher than that of the outermost layer of solder (3) is formed. The invention further relates to an apparatus for self-assembly of components (1) onto receptor sites (11) of the surface of a substrate (2) where each receptor site (11) is formed of a selective adhesive element which adheres to at least part of the components (1) resulting in the capture, self-assembly, self-alignment and/or attachment of the components at the receptor sites (11). Such an apparatus comprises a basin (14) containing a fluid (13), first transporting means for transporting the substrate (2) with the receptor sites (11) being in an essentially upright position at a predetermined speed and/or angle of inclination into and out of a delivery zone (16) in the fluid (13), a dispensing unit (17) located above the delivery zone (16) for dispensing components (1), rotating means for rotating the substrate (2) into a position where the receptor sites (11) take an essentially upside-down position, collecting means for collecting excess components (18) not attached to receptor sites (11) at the bottom of the basin (13), and second transporting means for returning excess components (18) to the dispensing unit (17).