Stacked Stud Bump Brazed Joints for Thermal Fatigue Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low-cost electronic components used in military applications are prone to thermomechanical fatigue due to inadequate brazed joint height, which limits their durability in severe environments, and existing solutions face challenges in geometry, integration density, and automation.
Innovation Solution
A method involving thermosonic bonding to form stacks of stud bumps on one element, allowing for increased brazed joint height by depositing a brazing alloy and remelting, enhancing the thermomechanical fatigue resistance of electronic devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional screen printing methods are used to create brazed joints, then the manufacturing process is simple and cost-effective, but the brazed joint height is limited to approximately 50 μm which reduces fatigue resistance
Solution Approach 1:
The brazed joint is segmented into multiple layers by stacking multiple bumps (e.g., 2-5 bumps per stack) to achieve the desired total height. Each bump is formed separately and then stacked vertically, allowing precise control of joint height while maintaining manufacturing simplicity through automated bump stacking processes
Solution Approach 2:
The solution transitions from increasing joint height through lateral expansion (wider screen openings) to vertical stacking of multiple bumps. This dimensional change from horizontal to vertical space utilization enables greater joint height without increasing the lateral footprint, thereby maintaining integration density while improving fatigue resistance
2Manufacturing precision
If screen opening size is increased to improve brazed joint height, then more material can be deposited, but integration density is limited due to the ratio between height and width of screen printing
Solution Approach 1:
The invention resolves the integration density limitation by moving from horizontal material distribution (screen printing width) to vertical material accumulation (stacked bumps height). Multiple bumps are stacked vertically at each connection point, achieving greater joint height without increasing the lateral area occupied, thus maintaining high integration density while improving fatigue resistance
Solution Approach 2:
Multiple bumps are nested vertically one on top of another to form stacks, similar to nested dolls. This vertical nesting allows the brazed joint to achieve greater height while occupying the same lateral footprint, effectively decoupling joint height from lateral dimensions and maintaining high integration density
3Manufacturing precision
If manual or semi-automatic wedge transfer methods are used to increase joint height, then brazed joint height can be increased, but automation is difficult and extensive assembly controls and inspections are required
Solution Approach 1:
The bump stacking process is designed to be self-aligning and self-positioning. Each bump is formed with precise dimensional control and automatically stacks vertically on previous bumps through self-alignment mechanisms, eliminating the need for manual positioning or complex alignment procedures. This enables full automation of the high-precision bump stacking process without extensive inspection requirements
Solution Approach 2:
Manual or semi-automatic mechanical wedge transfer methods are replaced with an automated bump formation and stacking process. The bumps are formed through a controlled deposition process and then automatically stacked using automated assembly equipment, replacing manual mechanical operations with automated processes that achieve higher precision and eliminate the need for extensive human intervention and inspection
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 effectively increases the robustness and fatigue life of electronic devices by raising the brazed joints, enabling them to withstand extreme temperature cycles, and is adaptable and automatable, improving integration density and reducing thermal stresses.
Implementation Method 1
a step of forming a plurality of stacks of stud bumps, said stacks of bumps being formed on a face of a first of said elements
Implementation Method 2
thermosonic bonding to form stacks of stud bumps on one element
Implementation Method 3
depositing a brazing alloy and remelting
Implementation Method 4
a step of remelting the assembly thus formed in the arranging step in order to obtain a connected assembly
Implementation Method 5
connection method comprises at least the following sequence of steps: a) a step of forming a plurality of stacks of stud bumps... b) a step of depositing a brazing product... c) a step of arranging the second of said elements on said first element... d) a step of remelting the assembly thus formed
Data Source
AI summary
The connection method between at least two elements (E1, E2) corresponding to a printed circuit (4) and to an electronic component (5), comprises a step of forming a plurality of pad-type stacks (2) of bosses (3), the stacks (2) of bosses (3) being formed on a face (10) of a first (E1) of the elements (E1, E2), the stacks (2) of bosses (3) each comprising the same given number of bosses (3), said method also comprising a step of depositing a brazing product (7) on this first element (E1) provided with stacks (2) of bosses (3), a step of arranging the second (E2) of the elements (E1, E2) on the first element (E1), and a step of remelting the assembly thus formed, in order to obtain an electronic device (1). This method makes it possible to produce a precise and flexible raising of surface mounted electronic components.