Copper Post Bump Cup Geometry for Solder Bridging Prevention
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Solution Overview
Problem
The challenges in chip packaging include solder bridging, flux residue, and underfill voids due to reduced bump pitch and width, leading to signal errors, shorting, and early bump failure, which are exacerbated by the difficulty in flux removal and the formation of inter-metallic compounds between copper and solder.
Innovation Solution
The use of copper post bumps with specific dimensions and a process flow involving flux application and controlled solder reflow, followed by careful flux removal and underfill formation, to maintain an optimal standoff and α ratio, preventing solder bridging and ensuring complete flux removal and void-free underfills.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bump pitch and width are reduced to increase circuit density, then productivity and integration are improved, but solder bridging and shorting risks increase
Solution Approach 1:
The patent changes the geometric parameters of the bump structure by introducing a cup-shaped configuration with specific depth-to-diameter ratios. This parameter modification allows reduced bump pitch and width while maintaining adequate solder flow control, preventing bridging even at higher densities
Solution Approach 2:
The cup-shaped bump structure utilizes curvature in its geometry, with the凹陷 (depression) forming a concave surface that naturally directs solder flow. This curved geometry prevents solder from spreading laterally between adjacent bumps, reducing bridging risk while allowing closer bump spacing
2Reliability
If flux is used to facilitate solder reflow, then bonding reliability is improved, but flux residue and cleaning difficulty increase
Solution Approach 1:
The cup-shaped bump structure extracts or contains the flux within its凹陷 (depression) during the soldering process. The geometry naturally traps flux in the cup interior, preventing it from spreading across the surface and leaving residue on surrounding areas, thereby reducing cleaning requirements
3Reliability
If copper posts are used to form bumps, then electrical conductivity is improved, but inter-metallic compound formation with solder increases
Solution Approach 1:
The patent employs a composite material structure with the cup-shaped bump consisting of copper post combined with other materials. This composite approach maintains the electrical conductivity benefits of copper while the additional material layers control or reduce unwanted inter-metallic compound formation with the solder
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 reduces the risk of solder shorting and flux residue, enhancing the reliability and yield of chip packages by maintaining an optimal standoff and α ratio, thus preventing early bump failure and ensuring proper underfill protection.
Implementation Method 1
solder reflowing
Data Source
AI summary
A method of forming a chip package includes providing a chip with a plurality of first bumps, wherein the plurality of first bumps has a first height. The method further includes providing a substrate with a plurality of second bumps, wherein the plurality of second bumps has a second height. The method further includes bonding the plurality of first bumps to the plurality of second bumps to form a first bump structure of the chip package, wherein the first bump structure has a standoff, wherein a ratio of a sum of the first height and the second height to the standoff is equal to or greater than about 0.6 and less than 1.