High-CTE Alloy Package Stiffeners for IC Warpage Control
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Solution Overview
Problem
Conventional IC die package stiffeners, typically made of Austenitic stainless steel or aluminum alloys, fail to provide sufficient stiffness and counteract the larger temperature coefficients of emerging substrate materials, leading to package warpage and constrained IC die-to-package ratios.
Innovation Solution
A metallic alloy stiffener with a high Young's Modulus and exceptionally high temperature coefficient of linear thermal expansion (CTE), exhibiting the anti-invar effect, is used to counteract bending induced by CTE mismatches between the IC die and package substrate, enhancing the rigidity and thermal expansion properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional stiffener materials (Austenitic stainless steel or aluminum alloys) are used, then manufacturing ease and cost are maintained, but sufficient stiffness and CTE matching for novel substrate materials cannot be achieved
Solution Approach 1:
The patent changes the material parameters by selecting alloys with specific compositional ranges that provide both high stiffness (Young's Modulus ≥120 GPa) and high CTE (≥17 ppm/K). This involves selecting from specific alloy systems (Fe-Ni, Fe-Mn, Fe-Co, etc.) with controlled composition ranges to achieve the desired mechanical and thermal properties simultaneously.
Solution Approach 2:
The patent employs composite alloy formulations combining multiple elements (e.g., Fe-Ni-Mn, Fe-Co-Al) to achieve property combinations that cannot be obtained with conventional single-phase stainless steels or aluminum alloys. These composite materials provide both the required stiffness and elevated CTE for matching novel substrate materials.
2Reliability
If conventional stiffener materials are used, then current package architectures function adequately, but package warpage increases with thinner substrates and novel compositions
Solution Approach 1:
The patent directly applies thermal expansion principles by selecting stiffener materials with high CTE values (≥17 ppm/K) to match and compensate for the thermal expansion characteristics of novel substrate materials. This CTE matching reduces thermal mismatch stresses and prevents package warpage during temperature cycling and processing.
3Strength
If package stiffener size is increased to improve stiffness, then warpage reduction improves, but package substrate footprint area increases
Solution Approach 1:
The patent changes the material parameters (Young's Modulus ≥120 GPa, high CTE) to achieve high stiffness-to-weight and stiffness-to-volume ratios. This allows the use of smaller stiffener dimensions while maintaining the required mechanical support and warpage control, thereby reducing the overall package footprint.
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 high CTE and stiffness of the metallic alloy stiffener significantly reduce package warpage, allowing for increased IC die-to-package ratios and improved package yield by effectively balancing thermal expansion stresses.
Implementation Method 1
a metallic alloy stiffener with a high Young's Modulus and exceptionally high temperature coefficient of linear thermal expansion (CTE), exhibiting the anti-invar effect, is used to counteract bending induced by CTE mismatches
Data Source
AI summary
A stiffener for an integrated circuit (IC) package assembly including an IC die electrically interconnected to a substrate. The stiffener is to be mechanically attached to the substrate adjacent to at least one edge of the IC die and have a coefficient of linear thermal expansion (CTE) exceeding that of the substrate. The stiffener may be an “anti-invar” metallic alloy. Anti-invar alloys display “anti-invar” behavior where thermal expansion of the material is significantly enhanced relative to other compositions of the particular alloy system. A package stiffener may be a high-Mn steel, for example, such as ASTM International A128. In other examples, a package stiffener is a MnCuNi, FeNiMn, or FeNiCr alloy having an average CTE over a range of 25-100° C. of at least 18 ppm, and a room temperature modulus of elasticity of at least 120 GPa.