Core Material for Reverse Reflow in Semiconductor Packages
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Solution Overview
Problem
Existing semiconductor packages face challenges in maintaining a constant gap height between stacked semiconductor packages and printed circuit boards (PCBs), leading to issues with bonding strength and reliability, particularly when using copper core solder balls, which require thick solder layers for large bump pads and become economically inefficient with reduced core sizes.
Innovation Solution
A semiconductor package design incorporating a core material for reverse reflow with a core, a nickel or cobalt first metal layer, and a gold or platinum second metal layer, surrounded by a solder member, where the bump pads are larger than the core material, ensuring a consistent gap height and improved bonding strength through a reflow process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If copper core solder balls are used with large bump pads, then bonding strength is improved, but solder layer thickness increases causing economic inefficiency
Solution Approach 1:
The patent uses a composite core material structure consisting of a copper core surrounded by a nickel alloy layer. This composite structure allows the solder to bond effectively to the nickel alloy surface while the copper core provides mechanical strength, enabling thinner solder layers to achieve the same bonding strength as thicker layers on copper alone.
Solution Approach 2:
The patent changes the surface properties of the core material by coating copper with nickel alloy, which has different wetting characteristics and melting point properties. This parameter change allows for reduced solder layer thickness while maintaining bonding strength, as the nickel alloy surface promotes better solder adhesion and requires less solder material to achieve reliable joints.
2Productivity
If core material size is reduced for high-density mounting, then mounting density is improved, but bonding reliability deteriorates
Solution Approach 1:
The nickel alloy coated core material provides enhanced surface properties that maintain bonding reliability even as core size is reduced. The nickel alloy layer has superior wetting characteristics and forms stronger intermetallic compounds with solder, compensating for the reduced core diameter and enabling high-density mounting without sacrificing bonding reliability.
Solution Approach 2:
The patent applies local quality enhancement by coating only the surface of the core material with nickel alloy, while the core itself maintains its mechanical strength properties. This localized modification of surface properties allows smaller core sizes to achieve the same bonding performance as larger cores, enabling higher mounting density while maintaining reliability.
3Strength
If thick solder layers are used to ensure bonding strength, then bonding strength is improved, but manufacturing cost increases
Solution Approach 1:
The nickel alloy coated core material enables thinner solder layers to achieve the same bonding strength as thicker layers on uncoated cores. The nickel alloy surface promotes better solder adhesion and forms stronger intermetallic compounds, reducing the amount of expensive solder material needed while maintaining or improving bonding strength, thereby lowering manufacturing costs.
Solution Approach 2:
The nickel alloy coating acts as a sacrificial layer that improves solder adhesion and allows for reduced solder thickness. By using this intermediate coating layer, the overall material cost is reduced because less expensive solder material is required, even though the nickel alloy itself adds a small cost that is offset by the solder material savings.
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 maintains a constant gap height and enhances bonding strength while reducing the failure rate and economic inefficiencies associated with thick solder layers, offering a more reliable semiconductor interconnection.
Implementation Method 1
A reflow process is performed such that the first solder paste and the second solder paste are bonded to each other to form a solder member
Implementation Method 2
The core material for reverse reflow includes a core, a first metal layer directly coated on the core, and a second metal layer directly coated on the first metal layer. The first metal layer includes nickel (Ni) or cobalt (Co), and the second metal layer includes gold (Au) or platinum (Pt)
Data Source
AI summary
Provided is a semiconductor package including a first bump pad on a first substrate, a second bump pad on a second substrate, a core material for reverse reflow between the first bump pad and the second bump pad, and a solder member forming a solder layer on the core material for reverse reflow. The solder member is in contact with the first bump pad and the second bump pad. Each of a first diameter of the first bump pad and a second diameter of the second bump pad is at least about 1.1 times greater than a third diameter of the core material for reverse reflow. The core material for reverse reflow includes a core, a first metal layer directly coated on the core, and a second metal layer directly coated on the first metal layer.