Exposed-Die Stiffener Ring Package for Thermal Stress and Warpage
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Solution Overview
Problem
Semiconductor packages with exposed dies experience warpage and damage due to thermal stress at the interface between the stiffener ring and the package substrate, leading to die cracks and chip-offs, especially as package sizes increase.
Innovation Solution
A system is introduced where molding material with a specific coefficient of thermal expansion (CTE) is applied to the substrate and die surfaces, ensuring a flush alignment with the die surface, reducing stress and warpage by distributing thermal expansion mismatch between the die, substrate, and stiffener ring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a stiffener ring is attached to the periphery of the package substrate to reduce warpage, then warpage reduction is achieved, but high tensile stresses are generated at the contact interface due to CTE mismatch
Solution Approach 1:
The patent introduces molding material as an intermediary layer between the stiffener ring and the package substrate. This molding material has a CTE value that is greater than the die but less than the substrate, creating a gradual transition that mediates the thermal expansion mismatch. This intermediary layer distributes the thermal stress more evenly across the interface, preventing the concentration of high tensile stresses that would otherwise occur at the direct contact interface between the stiffener ring and substrate.
Solution Approach 2:
The patent changes the physical and thermal parameters of the interface by selecting molding material with specific CTE properties. The molding material's CTE is engineered to fall between that of the die and the substrate, creating a gradient that reduces the abrupt parameter change at the interface. This parameter optimization allows the stiffener ring to effectively reduce warpage while the molding material absorbs and distributes the resulting thermal stresses.
2Area of stationary object
If the package size is increased to accommodate larger dies, then device functionality is improved, but susceptibility to thermal stress and cracking increases
Solution Approach 1:
The molding material serves as a stress-distributing intermediary that becomes increasingly important as package size increases. In larger packages, the total thermal expansion mismatch generates higher cumulative stresses. The molding material's intermediate CTE value allows it to absorb these expanded stresses across the larger area, preventing stress concentration that would lead to cracking in the substrate or die-attach interface.
Solution Approach 2:
The patent employs a composite structure consisting of the substrate, die, stiffener ring, and molding material, each with different CTE properties. This composite arrangement creates a graduated CTE profile from the die through the molding material to the substrate and stiffener ring. This composite material strategy allows the large package to maintain structural integrity by distributing thermal stresses across multiple materials with complementary properties, rather than relying on a single material that would have to compromise between conflicting CTE requirements.
3Stress or pressure
If molding material with CTE greater than die is used, then thermal stress is reduced, but CTE mismatch with substrate remains
Solution Approach 1:
The patent optimizes the CTE parameter of the molding material to fall within a specific range: greater than the die CTE but less than the substrate CTE. This parameter selection creates a CTE gradient that reduces thermal stress at the die-molding material interface while the molding material-substrate interface handles the remaining mismatch. The stiffener ring, with CTE matched to the substrate, then manages the outer boundary conditions. This staged parameter transition distributes thermal stress reduction across multiple interfaces rather than requiring a single material to match all CTE values.
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 solution effectively prevents die cracking and substrate warpage by minimizing thermal stress, enhancing the stability and integrity of larger semiconductor packages.
Implementation Method 1
coefficient of thermal expansion (CTE) value of the molding material is greater than a CTE value of the die
Data Source
AI summary
A package, and method for building the package is disclosed. The package includes a substrate having a first surface. The package further includes a die having opposing first and second surfaces, and a lateral surface, with the second surface of the die coupled to the first surface of the substrate. The package further includes a stiffener element having a first surface and a lateral surface, with the first surface of the stiffener element coupled to the first surface of the substrate. The package further includes molding material disposed on the first surface of the substrate and the lateral surface of the die. The coefficient of thermal expansion (CTE) value of the molding material is greater than a CTE value of the die. The first molding surface of the molding material is coplanar with the first surface of the die.