Underbump Metallization Hub With Compliant Layer
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Solution Overview
Problem
Conventional semiconductor die mounting techniques using lead-free solders face mechanical stress issues due to the relative positioning of polyimide and under bump metallization layers, leading to potential solder ball cracks and electrical device failure.
Innovation Solution
The solution involves forming an underbump metallization structure with a hub on a semiconductor chip, where redistribution layer structures provide electrical routing and the solder structure is mounted on the hub, with a polymeric layer positioned between the metallization layer and the solder structure to alleviate stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder materials are used, then environmental compliance is improved, but mechanical stress resistance deteriorates due to lower ductility and increased stiffness
Solution Approach 1:
A compliant layer is introduced as an intermediary between the rigid lead-free solder ball and the UBM layer. This compliant layer acts as a stress-absorbing mediator that prevents direct transmission of thermal expansion stresses to the solder joint, thereby maintaining reliability with lead-free materials while compensating for their reduced mechanical flexibility
Solution Approach 2:
The solder structure is formed as a composite system comprising multiple materials with different mechanical properties: the lead-free solder ball provides electrical connectivity, while the compliant layer (made of materials such as tungsten, molybdenum, tungsten disulfide, or carbon nanotubes) provides mechanical compliance. This composite structure combines the advantages of both materials to achieve both environmental compliance and stress resistance
2Reliability
If the polyimide layer is positioned between the UBM layer and passivation layer, then electrical insulation is improved, but stress relief capability deteriorates because the polyimide layer is separated from the solder balls
Solution Approach 1:
The compliant layer serves as a new intermediary positioned directly between the solder ball and UBM layer, replacing the insufficient stress-relief function of the separated polyimide layer. This intermediary provides both mechanical compliance for stress relief and maintains electrical insulation through proper material selection and design
Solution Approach 2:
The solution moves the stress relief function from a lateral dimension (separated polyimide layer) to a vertical dimension (compliant layer integrated into the solder joint structure). By positioning the compliant layer in the critical interface region between solder and UBM, stress relief is achieved at the precise location where thermal expansion differential forces are transmitted
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 configuration reduces mechanical stress on solder structures, enhancing their reliability and preventing cracks, thereby improving the reliability of semiconductor devices.
Implementation Method 1
a thermal process is performed to reflow the solder structures. The solder structures solidify into ball-like structures
Implementation Method 2
the stress reducing abilities of the polyimide layer are not available to the solder balls... high mechanical stresses may be inflicted on the solder balls
Data Source
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AI summary
Various semiconductor chip conductor structures and methods of fabricating the same are provided. In one aspect, a method of manufacturing is provided that includes forming a conductor structure on a semiconductor chip. The conductor structure has a first site electrically connected to a first redistribution layer structure and a second site electrically connected to a second redistribution layer structure. A solder structure is formed on the conductor structure.