Cu Core Bump Electrode Alignment via Controlled Heating Rate
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Solution Overview
Problem
The existing methods for forming bump electrodes on semiconductor packages using Cu-cored solder balls often result in non-joining issues due to eccentricity of the Cu ball, leading to exposure of intermetallic compounds and mal-wettability, which can cause short-circuits and uneven spacing between packages during secondary mounting.
Innovation Solution
A controlled heating process with a rate of 0.01° C./sec to 0.3° C./sec is applied to the substrate during solder plating melting, slowing the creeping and running down rates of the flux and solder, ensuring the Cu ball's center aligns with the solder shell's center on the electrode pad, thereby maintaining even spacing and preventing non-joining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional heating methods are used to melt solder plating on Cu-cored solder balls, then the soldering process can be completed, but the Cu ball becomes eccentric relative to the solder shell center, causing non-joining and mal-wettability
Solution Approach 1:
The patent applies a specific heating rate parameter (0.01°C/sec to 0.3°C/sec) during the soldering process to control the melting behavior of solder plating. This parameter change ensures that the Cu ball remains centered within the solder shell, preventing eccentricity and maintaining alignment precision while achieving reliable joining.
2Productivity
If fast heating is applied to increase productivity, then the soldering process time is reduced, but the flux and solder creep and run down too quickly, causing Cu ball eccentricity and non-joining
Solution Approach 1:
The patent optimizes the heating rate parameter to a specific range (0.01°C/sec to 0.3°C/sec) that balances productivity and reliability. This controlled heating rate prevents the flux and solder from creeping and running down too quickly, maintaining Cu ball centrality and ensuring reliable joining while still achieving efficient production.
3Loss of time
If high heating rate is used to reduce manufacturing time, then production efficiency increases, but the center of Cu ball does not align with solder shell center, leading to short-circuits
Solution Approach 1:
The patent implements a controlled heating rate (0.01°C/sec to 0.3°C/sec) that maintains center alignment precision between the Cu ball and solder shell. This parameter optimization ensures that even though the process takes longer than fast heating, the alignment remains precise, preventing short-circuits and rework.
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 ensures reliable alignment and joining of bump electrodes, reducing the occurrence of non-joining and uneven spacing between semiconductor packages, enhancing the reproducibility and reliability of the bump electrode formation process.
Implementation Method 1
a step of heating and melting the solder plating
Implementation Method 2
slowing the creeping and running down rates of the flux and solder
Data Source
AI summary
A bump electrode is formed on an electrode pad using a Cu core ball in which a core material is covered with solder plating, and a board which has bump electrodes such as semiconductor chip or printed circuit board mounts such a bump electrode. Flux is coated on a substrate and the bump electrodes are then mounted on the electrode pad. In a step of heating the electrode pad and the Cu core ball to melt the solder plating, a heating rate of the substrate is set to have not less than 0.01° C./sec and less than 0.3.