Riveted Copper Pillar Electrode for High Current Semiconductor Packages
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Solution Overview
Problem
Conventional solder joints and wire bonds in semiconductor devices have limited current density and thermal capacity, restricting the safe conduction of high currents due to their limited cross-sectional area and thermal limitations.
Innovation Solution
A copper lead frame or laminate substrate is directly riveted to the semiconductor die electrodes, with spaced copper pillars and a thick lead frame fitted over them, secured using ultrasonic energy and pressure to form a low resistance connection, eliminating the need for inner solder attach and inter-metallic formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder joints or wire bonds are used to connect electrodes to circuit board pads, then the device can be assembled using conventional methods, but the current density and thermal capacity are limited due to the limited cross-sectional area of the connection structure
Solution Approach 1:
The connection structure is segmented into multiple parallel copper pillars instead of using a single solder joint or wire bond. This segmentation increases the total cross-sectional area for current flow while maintaining modular assembly processes. Each pillar acts as an independent current path, collectively providing high current density capacity.
Solution Approach 2:
The invention transitions from planar connections (solder joints on a 2D surface) to three-dimensional vertical pillars. The copper pillars extend vertically from the die surface, utilizing the third dimension to increase effective connection area without expanding the footprint on the circuit board, thereby achieving higher current capacity within the same spatial envelope.
2Reliability
If conventional solder attach methods are used, then assembly is straightforward, but thermal capacity and current conduction are restricted
Solution Approach 1:
The material parameters are changed from solder alloy to pure copper, which has superior electrical and thermal conductivity. The copper pillars are formed with controlled dimensions (diameter, height, spacing) to optimize current density and thermal dissipation. This parameter change enables higher thermal capacity and current conduction while the pillars are integrated into the die assembly process.
3Reliability
If a thick lead frame with copper pillars is used to increase current capacity, then current density capacity improves, but assembly complexity and manufacturing difficulty increase
Solution Approach 1:
The lead frame and copper pillars are merged into a single integrated component. The copper pillars are directly formed on the lead frame substrate, eliminating the need for separate attachment steps. This merging simplifies the overall structure while maintaining the high current capacity benefits of thick copper connections, as the lead frame itself provides the structural support and electrical pathway.
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 enables a higher current density capacity connection with reduced assembly costs and time, providing a faster and more efficient assembly process while avoiding inter-metallic formation.
Implementation Method 1
application of ultrasonic energy along with thermal energy and/or pressure to rivet each lead frame to a respective set of pillars
Implementation Method 2
application of ultrasonic energy along with thermal energy and/or pressure to rivet each lead frame to a respective set of pillars
Data Source
AI summary
A semiconductor package that includes a lead frame riveted to pillars electrically connect to an electrode of a semiconductor die.