Transient Liquid Phase Soldering for High Lateral Accuracy
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Solution Overview
Problem
Current soldering methods for optoelectronic components on substrates face challenges in achieving high positioning accuracy due to large tolerances in PCB industry compared to optoelectronic requirements, as standard reflow processes and self-alignment methods cannot ensure precise placement of components with the necessary 10 μm accuracy required for applications like automotive lighting.
Innovation Solution
The method employs transient liquid phase soldering with a solder paste containing a mixture of metals and metal alloys, where high-temperature melting particles form intermetallic phases creating a solid framework within the solder, allowing precise positioning of electronic components using reference features independent of contact pads, and maintaining accuracy even after placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard reflow soldering process is used, then the soldering process is simple and fast, but the positioning accuracy deteriorates to 50-100 μm due to tolerance accumulation
Solution Approach 1:
The solder paste is pre-heated to its melting point before component placement, creating a liquid solder surface that enables self-alignment. This preliminary heating action prepares the solder in advance to receive the component at the correct position, achieving high accuracy without complex positioning mechanisms during the actual soldering step.
Solution Approach 2:
The liquid solder surface automatically performs the alignment function through self-alignment of the electronic component on the molten solder. The component naturally settles into the correct position on the liquid solder surface, eliminating the need for complex external positioning systems and achieving 10 μm accuracy through the solder's own properties.
2Manufacturing precision
If solder paste with high melting point metal particles is used, then lateral movement is inhibited and positioning accuracy is maintained, but the solder paste composition becomes more complex
Solution Approach 1:
The solder paste is formulated as a composite material containing multiple metal types with different melting points. Low-melting-point metals (Sn, Pb, In, Zn) provide the liquid phase for self-alignment, while high-melting-point metals (Cu, Ag, Au, Al) form a solid framework that inhibits lateral movement. This composite structure combines the benefits of both liquid and solid phases to achieve high positioning accuracy.
Solution Approach 2:
The solder paste exhibits different properties at different stages of the process: initially liquid to enable self-alignment, then transitioning to a semi-solid state with a solid framework to inhibit lateral movement. The high-melting-point metal particles are distributed throughout the paste to provide localized structural support where needed, while allowing fluidity where self-alignment is required.
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 approach enables high positioning accuracy of electronic components, ensuring they remain fixed at the desired position during solder solidification, achieving the required 5-10 μm accuracy and forming reliable solder joints suitable for optoelectronic applications.
Implementation Method 1
The solder paste is melted for transient liquid phase soldering and the melted solder is allowed to solidify
Implementation Method 2
Intermetallic phases form between the remaining solid particles. This results in the formation of a solid framework within the still liquid solder
Data Source
Figure 1~3
AI summary
The present invention relates to a method of soldering an electronic component (3) to a substrate (1) with high accuracy using transient liquid phase soldering. The component (3) is exactly positioned above the substrate (1) with a handling tool, placed in the melted solder (2) and pressed against the substrate (1). The component (3) is then released and the solder (2) allowed solidifying. Due to the use of a solder (2) having a sufficiently high amount of a second metal or metal alloy of a higher melting point which only partly dissolves in the melted first metal or metal alloy of a lower melting point, a solid framework forms during the liquid phase soldering which inhibits a lateral movement of the placed component (3) during soldering. Since the positioning of the component (3) is made using exact reference features on the substrate (1), the whole soldering process results in a highly accurate lateral position of the soldered component.