Stacked CSP Module Wire Bonding Interconnect
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Solution Overview
Problem
Current stacked package assemblies face challenges in design flexibility, cost, and manufacturability due to the need for precise matching of substrate pads for z-interconnect, which limits the ability to mix-and-match packages from different vendors and adapt to changing market demands, and restricts the integration of additional components without redesigning the entire assembly.
Innovation Solution
The solution involves a stacked CSP module with a molded top chip scale package and a bottom package affixed to its substrate, connected via wire bonding, allowing for flexible stacking and interconnection without solder balls, enabling the integration of various components and allowing for second-level interconnections with additional components such as BGA, LGA, or MEMS packages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If substrate pads for z-interconnect are precisely matched, then manufacturing precision is improved, but design flexibility deteriorates
Solution Approach 1:
The patent introduces a compliant interconnect structure that acts as an intermediary between substrate pads, allowing mechanical and electrical connection without requiring precise pad alignment. This compliant structure absorbs misalignment through elastic deformation, enabling mixing packages from different vendors while maintaining reliable z-interconnect.
Solution Approach 2:
The invention changes the physical state of the interconnect from rigid to compliant, allowing the interconnect material to deform elastically under stress. This parameter change enables the system to tolerate variations in pad positioning while maintaining electrical connection, thus resolving the contradiction between precision and flexibility.
2Reliability
If solder balls are used for z-interconnect, then electrical connection reliability is improved, but device complexity deteriorates
Solution Approach 1:
The patent extracts the solder ball interconnection step from the stacking process, replacing it with a compliant wire or tape interconnect that is already attached to the substrate. This eliminates the need for separate solder ball placement and reflow processing, reducing manufacturing complexity while maintaining connection reliability through the compliant structure's ability to accommodate misalignment.
Solution Approach 2:
The invention replaces the mechanical solder ball system with a flexible wire or tape interconnect system that uses elastic deformation instead of rigid mechanical contact. This substitution simplifies the interconnection process by eliminating precise alignment requirements and soldering operations.
3Manufacturing precision
If packages are stacked with precise alignment, then manufacturing precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The compliant interconnect serves as a mediator that decouples the alignment requirements between stacked packages. Each package can be positioned independently on its substrate without requiring precise alignment with packages on other substrates, as the compliant interconnect absorbs the misalignment through elastic deformation.
Solution Approach 2:
The patent segments the stacking process into independent substrate-level operations rather than requiring coordinated multi-package alignment. Each substrate with its attached compliant interconnect can be prepared and positioned separately, then assembled into the final stacked configuration without requiring precise relative alignment between packages.
4Adaptability or versatility
If standard CSPs are selected for integration, then adaptability is improved, but manufacturing precision deteriorates
Solution Approach 1:
The invention changes the compliance parameter of the interconnect from rigid to flexible, allowing it to accommodate variations in package dimensions and pad positions. This enables the use of standard CSPs from different vendors with varying tolerances while maintaining reliable z-interconnect through elastic deformation of the compliant interconnect structure.
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 provides excellent manufacturability, high design flexibility, and low cost, enabling a low-profile, small-footprint stacked package module with the ability to select from standard CSPs for integrating various functions, accommodating size differences and allowing for the addition of components without increasing package size or cost.
Implementation Method 1
wire bonding between the top chip scale package and the bottom package
Implementation Method 2
affixed to the substrate side of the top chip scale package
Data Source
AI summary
Stacked CSP (chip scale package) modules include a molded first (“top”) chip scale package having a molding side and a substrate side, and a second (“bottom”) package affixed to the substrate side of the top chip scale package, the second package being electrically connected to the first package by wire bonding between the first and second package substrates.