Carrier Warpage Control for 3DIC Stacking
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Solution Overview
Problem
Conventional Package-on-Package (PoP) device fabrication processes fail to adequately prevent warping, especially when stacking relatively thin integrated circuit dies, due to material coefficient of thermal expansion mismatches.
Innovation Solution
A method involving the use of a carrier with a low coefficient of thermal expansion, such as glass or silicon, to temporarily mount substrates and dies, followed by pressure annealing, underfill material application, and molding to inhibit warping, while allowing for horizontal offset stacking and subsequent removal of the carrier and molding material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication processes are used to stack packages, then the manufacturing process is simple, but the packages warp due to thermal expansion mismatches
Solution Approach 1:
A carrier substrate is introduced as an intermediary component during the stacking process. This carrier has a low coefficient of thermal expansion that acts as a stable reference plane, preventing warping of the stacked packages. The carrier is temporarily used during assembly and then removed, serving as a mediator that enables precise stacking without introducing permanent structural changes to the final product.
Solution Approach 2:
The process utilizes controlled temperature changes during pressure annealing to reduce warpage. By heating the stacked packages on the carrier to elevated temperatures and then cooling them under pressure, the thermal expansion differences between materials are minimized, allowing the packages to conform to the carrier's flat surface and reducing warpage.
2Volume of moving object
If thin dies are stacked to reduce product size, then the electronic product size is reduced, but warping becomes more severe due to thermal expansion mismatches
Solution Approach 1:
The carrier substrate serves as a rigid intermediary that supports thin dies during stacking. Because the carrier has a low coefficient of thermal expansion and high stiffness, it provides a stable reference plane that prevents thin dies from warping, even when multiple layers are stacked. This enables the use of thin dies for miniaturization while maintaining manufacturing precision.
Solution Approach 2:
Pressure annealing is applied in advance to the stacked thin dies on the carrier to counteract thermal expansion mismatches before final assembly. This preliminary treatment pre-compresses and stabilizes the thin die stack, preventing warping from occurring during subsequent handling and operation, thus enabling reliable miniaturized products.
3Productivity
If multiple dies are stacked vertically, then integration density is improved, but warpage control becomes more difficult
Solution Approach 1:
The carrier substrate acts as a common reference plane for stacking multiple dies vertically. Each die is aligned and bonded to the carrier or to previous die layers while the carrier maintains the overall structural integrity and flatness. This intermediary support system enables high integration density through vertical stacking while maintaining warpage control across the entire multi-die structure.
Solution Approach 2:
Pressure annealing is applied to the entire multi-die stack on the carrier, using controlled temperature and pressure parameters to reduce cumulative warpage from thermal expansion mismatches. This parameter control enables the stacking of multiple dies with different material properties while maintaining manufacturing precision.
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 effectively prevents warping during the stacking of thin dies, enabling reliable assembly of multiple dies with or without overhangs, even with thermal expansion mismatches, and facilitates the formation of stable PoP devices.
Implementation Method 1
conventional processes used to fabricate the PoP devices may not be able to sufficiently prevent the packages from warping. This is particularly true when relatively thin dies or integrated circuits are being stacked
Implementation Method 2
followed by pressure annealing, underfill material application, and molding to inhibit warping
Data Source
AI summary
An embodiment method of forming a package-on-package (PoP) device includes temporarily mounting a substrate on a carrier, stacking a first die on the substrate, at least one of the die and the substrate having a coefficient of thermal expansion mismatch relative to the carrier, and stacking a second die on the first die. The substrate may be formed from one of an organic substrate, a ceramic substrate, a silicon substrate, a glass substrate, and a laminate substrate.