Composite Stiffener Resists Warpage in Chip Package Assembly
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Solution Overview
Problem
Conventional chip packaging schemes face issues with out-of-plane deformation, where stiffeners can bend, twist, or delaminate, leading to warpage and solder connection failure, especially in larger assemblies, and heavy-duty stiffeners induce excessive stress on interconnect substrates, particularly with lead-free solder.
Innovation Solution
A composite stiffener is used, comprising a first stiffener member with a higher Young's modulus and a second member with a lower Young's modulus, bonded in a configuration that provides tailored stiffness and stress distribution to resist warpage without damaging electrical connections, allowing for the use of lead-free solder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a heavy duty stiffener is used to stiffen the chip package assembly, then resistance to out of plane deformation is improved, but stress on the interconnect substrate increases excessively
Solution Approach 1:
The patent applies composite materials by combining a first stiffener member (e.g., ceramic material like aluminum oxide or aluminum nitride) with a second stiffener member (e.g., metal material like Kovar or stainless steel). This composite structure provides tailored mechanical properties where the ceramic layer provides high stiffness and strength while the metal layer provides ductility and stress distribution, achieving resistance to out-of-plane deformation without inducing excessive stress on the interconnect substrate
Solution Approach 2:
The patent applies local quality by creating a stiffener with non-uniform material properties through the composite structure. The first stiffener member has different material properties (higher Young's modulus) than the second stiffener member, allowing different regions of the stiffener to perform different functions: the first member provides primary stiffening while the second member provides stress relief and flexibility where needed
2Shape
If a stiffener is used to prevent warpage, then flatness is improved, but the stiffener itself may bend, twist, or delaminate
Solution Approach 1:
The composite stiffener structure combines materials with complementary properties: the ceramic first stiffener member provides high stiffness and dimensional stability to maintain flatness, while the metal second stiffener member provides ductility and toughness to prevent bending, twisting, and delamination. The bonded connection between the two members creates a unified structure that is more reliable than a single-material stiffener
Solution Approach 2:
The patent applies parameter changes by carefully selecting and controlling the Young's modulus of each stiffener member. The first stiffener member has a higher Young's modulus than the second stiffener member, creating a gradient of stiffness that allows the stiffener to maintain flatness while accommodating thermal and mechanical stresses without structural failure
3Reliability
If lead-free solder is used for electrical connections, then environmental compatibility is improved, but connection strength decreases
Solution Approach 1:
The composite stiffener structure serves as a protective measure that cushions and distributes thermal and mechanical stresses before they reach the solder connections. By providing a compliant yet stiffening structure, the patent protects the lead-free solder joints from stress-induced failure, enabling their use in applications where environmental compatibility is required
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
The composite stiffener enhances the resistance to out-of-plane deformation, improves the reliability of solder connections, and maintains the flatness and performance of chip package assemblies, even with lead-free solder, resulting in a more robust and reliable assembly.
Implementation Method 1
The second stiffener member has a Young's modulus less than a Young's modulus of the first stiffener member
Implementation Method 2
The composite stiffener is configured to provide an overall stiffness and stress inducing properties
Data Source
AI summary
A chip package assembly and method for fabricating the same are provided which utilize a composite stiffener selected to provide excellent resistance to warpage without detrimentally imposing excessive stress on a package substrate of the package assembly. In one example, the chip package assembly includes an integrated circuit die stacked on a top surface of a package substrate, and a composite stiffener coupled to a first edge of the package substrate. The composite stiffener includes a first stiffener member and a second stiffener member. The first stiffener member has a bottom surface bonded to the top surface of the package substrate. The second stiffener member is disposed over the first stiffener member. The second stiffener member has a bottom surface bonded to the top surface of the package substrate. The second stiffener member has a Young's modulus that is less than a Young's modulus of the first stiffener member.