Low Temperature Solder Coating for Microelectronic Package Warpage Control
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Solution Overview
Problem
Warpage in microelectronic package structures, particularly in thin packages, is a fabrication challenge due to differences in coefficients of thermal expansion between materials, which can lead to reliability issues during temperature cycling.
Innovation Solution
The use of low temperature solder materials with a melting point below 200 degrees Celsius, applied on high temperature solder balls, allows for reliable solder mounting by forming joints between substrates without significant warpage, using a process that includes a nickel layer to prevent solid state diffusion and maintaining a flat profile during reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thin microelectronic packages are used, then device compactness is improved, but warpage increases due to CTE differences between materials
Solution Approach 1:
The patent applies parameter changes by modifying the solder material composition to create a low melting point solder alloy (melting point below 200°C) with specific chemical composition ratios. This parameter change allows the solder to remain pliable during temperature cycling, compensating for CTE differences between substrates and die, thereby reducing warpage in thin packages while maintaining compactness
Solution Approach 2:
The patent uses composite materials by creating a multi-layer structure consisting of low temperature solder material applied over high temperature solder balls, with a nickel diffusion barrier layer in between. This composite approach combines the low-temperature flow characteristics of the first solder layer with the high-temperature strength of the second layer, while the nickel layer prevents unwanted diffusion, achieving both thin profile and warpage control
2Stability of the object's composition
If low temperature solder material is applied, then warpage is reduced, but manufacturing process complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the solder joint structure into distinct functional layers: a first solder layer with low melting point for warpage control, a nickel diffusion barrier layer, and a second solder layer with high melting point for mechanical strength. This segmentation allows each layer to perform its specific function optimally while managing the overall manufacturing process
Solution Approach 2:
The patent introduces a nickel layer as an intermediary element between the low temperature solder material and the high temperature solder balls. This intermediary prevents solid state diffusion between the different solder materials, simplifying the manufacturing process by eliminating the need for complex diffusion control measures while maintaining package flatness
3Strength
If conventional high temperature solder is used, then joint strength is maintained, but warpage occurs during reflow processing
Solution Approach 1:
The patent applies preliminary action by first applying the low temperature solder material and forming it into a flat profile before attaching the die and second substrate. This preliminary formation of the low-temperature solder layer creates a compliant joint that can absorb thermal expansion differences during subsequent reflow processing, preventing warpage while the high-temperature solder layer provides the ultimate joint strength
Solution Approach 2:
The patent changes the temperature parameter of the soldering process by using a two-stage approach: first reflowing the low melting point solder (below 200°C) to establish a flat, compliant joint, then proceeding with high-temperature reflow for the second solder layer. This parameter change allows the joint to maintain flatness during processing while achieving the required 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 approach enhances the reliability of solder joints, reduces warpage, and maintains a flat profile, minimizing contact opens and allowing for thinner, more compact package designs without yield loss, while maintaining the reliability of high temperature solder joints.
Implementation Method 1
The low temperature solder material may be melted at a first temperature, wherein the low temperature solder material wets the surface of the high temperature solder balls
Implementation Method 2
the low temperature solder material wets the surface of the high temperature solder balls
Implementation Method 3
using a process that includes a nickel layer to prevent solid state diffusion
Implementation Method 4
the array of joint structures may comprise a low temperature alloying element concentration below about 5 percent
Data Source
AI summary
Methods/structures of joining package structures are described. Those methods/structures may include a device disposed on first side of substrate and an array of conductive interconnect structures disposed on a second side of the first substrate. The conductive interconnect structures of the array may comprise a solder material, wherein the solder material comprises a low temperature alloying element concentration of less than about 5 percent. A second substrate is coupled to the array of conductive interconnect structures.