Porous-Core Composite Solder Balls for Precise Board Assembly
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Solution Overview
Problem
Current flexible solder balls used in electronic board assembly have a dense polymer core that increases manufacturing costs and is prone to differential thermal expansion issues during brazing, affecting their calibration and final density.
Innovation Solution
The development of composite solder balls with a core of expanded polystyrene (EPS) having intergranular porosity and a metallic shell comprising copper, nickel, and gold layers, which are calibrated through a process involving granulometric sorting, activation, and multiple metallization steps to achieve a specific diameter and thickness, allowing for reduced size through heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dense core polymer material is used in flexible solder balls, then structural integrity is maintained, but manufacturing costs increase and calibration precision deteriorates
Solution Approach 1:
The patent replaces the dense core polymer material with expanded polystyrene beads having intergranular porosity of at least 50%. This porous structure reduces the core volume, allowing for better size calibration and reduced manufacturing costs while maintaining sufficient structural integrity through the metallic shell composition.
Solution Approach 2:
The patent employs a composite structure consisting of an expanded polystyrene core combined with a multi-layer metallic shell (copper, nickel, and gold layers). This composite material approach allows the porous core to provide cost-effectiveness and calibratability while the metallic shell provides the necessary structural strength and mechanical integrity.
2Strength
If dense core polymer material is used in flexible solder balls, then structural integrity is maintained, but production costs increase
Solution Approach 1:
The use of expanded polystyrene beads with high intergranular porosity (≥50%) reduces the amount of material required and simplifies the manufacturing process compared to dense core polymers. The porous structure can be more easily formed and calibrated, leading to reduced production costs while maintaining adequate structural properties through the metallic shell.
Solution Approach 2:
The patent changes the density parameter of the core material from dense to expanded (porous) state. This parameter change reduces material costs and manufacturing complexity while the multi-layer metallic shell composition is optimized to provide the necessary structural integrity at lower overall production cost.
3Strength
If dense core polymer material is used in flexible solder balls, then structural integrity is maintained, but thermal expansion stability deteriorates
Solution Approach 1:
The expanded polystyrene core with high porosity has different thermal expansion characteristics compared to dense polymers. The porous structure allows for better thermal management and reduced differential thermal expansion with the metallic shell during brazing operations, improving thermal expansion stability while the metallic shell maintains structural integrity.
Solution Approach 2:
The composite structure of expanded polystyrene core with multi-layer metallic shell creates a system where the thermal expansion properties can be balanced. The porous core compensates for thermal expansion differences, reducing differential expansion issues during high-temperature brazing while the metallic shell provides the necessary structural strength.
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 solution reduces production costs, enhances the calibration of solder balls, and mitigates thermal expansion issues, providing stable interconnections for miniaturized electronic components while maintaining mechanical integrity.
Implementation Method 1
The balls made of expanded polystyrene (EPS) have the advantage of being able to reduce in size when they are heated, and thus offer the possibility of being calibrated by heat treatment.
Implementation Method 2
a first step of metallization of said activated support particles by means of autocatalytic chemical deposition of one or more layers of copper
Implementation Method 3
a third step of metallization of the support particles coated in chemical nickel (consisting in a step of deposition of gold by means of a method of galvanic displacement implemented by immersion in an aqueous solution containing gold ions)
Data Source
AI summary
The present invention relates to a method for manufacturing composite solder balls that are metallized on the surface and calibrated, these balls comprising a core consisting of a spherical support particle of diameter D0 made of expanded polystyrene and having an intergranular porosity of at least 50%, and a shell covering said support particle and formed by a plurality of metallic surface layers. The present invention also relates to balls that can be obtained by the method according to the invention, as well as to the use thereof for the assembly of electronic boards.