PCB Brazed Joint Height Control for Thermomechanical Fatigue Resistance
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Solution Overview
Problem
Low-cost electronic components used in consumer applications lack robustness to withstand harsh military environments, particularly due to thermomechanical fatigue issues, and existing methods to increase solder joint height are limited by geometric constraints and integration density.
Innovation Solution
A method involving thermosonic bonding to form stacks of bosses on either the printed circuit or electronic component, increasing the height of solder joints, which enhances thermomechanical fatigue resistance without requiring filler metal, using materials like copper or silver, and allowing precise control of boss height and spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional screen printing processes are used to deposit solder paste, then the manufacturing process is simple and low-cost, but the solder joint height is limited to approximately 50 μm which is insufficient for military-grade robustness
Solution Approach 1:
The solder paste is segmented into discrete spherical beads through a filtering process, separating the paste into retained beads (forming joints) and passed particles (excess material). This segmentation enables precise control of joint height while simplifying the manufacturing process by allowing automatic removal of excess material.
Solution Approach 2:
A filter mesh acts as an intermediary element between the screen printing process and the substrate. The mesh with controlled aperture sizes serves as a mediator that selectively retains solder beads of specific diameters, enabling precise control of joint geometry without complex process adjustments.
2Manufacturing precision
If the screen opening size is increased to deposit more solder paste, then the solder joint height increases, but the integration density is limited by the ratio between height and width of screen printing
Solution Approach 1:
The filter mesh provides locally differentiated aperture sizes that correspond to specific joint height requirements. Different regions of the mesh can have different aperture dimensions, allowing each solder joint to receive the precise amount of paste needed for its specific height requirement, thereby enabling high integration density without compromising joint quality.
3Reliability
If shims are installed to increase solder joint height, then the robustness improves, but manual or semi-automatic transfer processes are required which are difficult to automate
Solution Approach 1:
The solder paste itself performs the function of forming elevated joints through the filtering process, eliminating the need for separate shim components. The excess paste is automatically removed by the filter mesh, and the retained beads self-align to form joints of precise height, enabling full automation without manual intervention.
4Reliability
If the solder joint height is doubled to increase fatigue resistance by a factor of five, then the robustness greatly improves, but the geometric constraints and material consumption increase
Solution Approach 1:
The filter mesh aperture size is precisely controlled to match the desired solder bead diameter, creating a direct relationship between mesh parameters and joint geometry. By changing the aperture size parameter, the system can produce joints of various heights with optimized material consumption, achieving high fatigue resistance without excessive material use.
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 method significantly increases the robustness and thermomechanical fatigue resistance of electronic devices, enabling them to withstand extreme temperature cycles over 25 years, while being adaptable and flexible, and can be integrated into standard assembly processes.
Implementation Method 1
The forming step consists of implementing thermosonic bonding. Such a weld involves combining ultrasound, a force (or contact pressure) and a temperature
Implementation Method 2
an operation of heating a metal wire by means of an electrode
Data Source
Figure 1~3
Figure 4~7
Figure 8A~8E
AI summary
The method for joining at least two elements (E1, E2), corresponding to a printed circuit board (4) and an electronic component (5), comprises a step of forming a plurality of stacks (2) of stud-type bosses (3), the stacks (2) of bosses (3) being formed on one face (10) of a first (E1) of said elements (E1, E2), said stacks (2) of bosses (3) each comprising the same given number of bosses (3), said method also comprising a step of depositing a solder product (7) onto this first element (E1) provided with the stacks (2) of bosses (3), a step of arranging the second (E2) of said elements (E1, E2) onto said first element (E1), and a step of reflow soldering the assembly thus formed to obtain an electronic device (1). This method allows for precise and flexible elevation of surface-mount electronic components.