Electromigration Resistant Via Assemblies for Bump Thickness Variation
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Solution Overview
Problem
In device packages with densely packed vias and conductive traces, the challenge lies in reducing bump thickness variation (BTV) while maintaining or enhancing electromigration resistance, as thinner nickel layers reduce electromigration resistance but increase bump height variation, leading to unreliable connections.
Innovation Solution
Incorporating electromigration resistant vias filled with nickel or nickel alloys within the via passages, which isolates the copper base pad from the solder cap, and using a multi-component cap assembly with an electromigration resistant cap layer, such as nickel alloy doped with tungsten, molybdenum, or ruthenium, to minimize cap thickness and BTV.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thinner nickel layers are used to reduce bump thickness variation, then manufacturing precision improves, but electromigration resistance deteriorates
Solution Approach 1:
The patent uses composite material structures including nickel alloy layers (such as nickel tungsten, nickel molybdenum, or nickel ruthenium) combined with solder caps to create via assemblies that provide both precise dimensional control and enhanced electromigration resistance. The multi-layer composite structure allows optimization of each layer's thickness and composition to simultaneously achieve low BTV and high reliability
Solution Approach 2:
The patent modifies material parameters by using nickel alloys with specific compositions (doped with tungsten, molybdenum, or ruthenium) and controlling the thickness of each layer (electromigration resistant cap layer, solder cap layer) to achieve the desired balance between dimensional precision and electromigration resistance. The via assembly parameters are optimized to provide consistent performance across different via sizes
2Productivity
If densely packed vias are used to increase connection density, then productivity improves, but manufacturing precision deteriorates due to increased bump thickness variation
Solution Approach 1:
The patent applies local quality by providing electromigration resistant cap layers specifically on the caps of via assemblies, particularly targeting areas with high current density or small via sizes where electromigration and BTV are most critical. This localized protection allows dense via packaging while maintaining precision in the most vulnerable regions
Solution Approach 2:
The via assemblies use composite material structures with electromigration resistant cap layers (nickel alloys) combined with solder caps, allowing dense via packaging while maintaining consistent bump thickness through the protective cap layer that compensates for variations in underlying via dimensions
3Reliability
If electromigration resistant cap layers are added to reduce intermetallic compound growth, then reliability improves, but device complexity increases
Solution Approach 1:
The patent segments the cap structure into distinct functional layers: an electromigration resistant cap layer (nickel alloy) and a solder cap layer. This segmentation allows each layer to perform its specific function - the nickel alloy layer provides protection against electromigration and intermetallic compound growth, while the solder cap layer provides bonding functionality, thereby managing complexity through functional decomposition
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 electromigration resistance, reduces intermetallic compound growth, and minimizes bump thickness variation, ensuring consistent and reliable connections between devices.
Implementation Method 1
an electromigration resistant via within a via passage between the base pad and the cap, the electromigration resistant via configured to isolate each of the base pad and the cap from intermetallic compound growth
Implementation Method 2
the electromigration resistant via is configured to isolate each of the base pad and the cap from intermetallic compound growth
Data Source
AI summary
A package assembly includes a substrate and at least a first die having a first contact array and a second contact array. First and second via assemblies are respectively coupled with the first and second contact arrays. Each of the first and second via assemblies includes a base pad, a cap assembly, and a via therebetween. One or more of the cap assembly or the via includes an electromigration resistant material to isolate each of the base pad and the cap assembly. Each first cap assembly and via of the first via assemblies has a first assembly profile less than a second assembly profile of each second cap assembly and via of the second via assemblies. The first and second cap assemblies have a common applied thickness in an application configuration. The first and second cap assemblies have a thickness variation of ten microns or less in a reflowed configuration.