Stacked Semiconductor Dies Selective Capillary Underfill Warpage
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Solution Overview
Problem
The curing of capillary underfill (CUF) material in stacked semiconductor devices often leads to wafer warpage, impairing the singulation and subsequent processing of the dies.
Innovation Solution
The use of a two-sealing material approach, where a first sealing material with higher thermal expansion and viscosity is applied to only one side of the stacks and a second sealing material with lower thermal expansion and viscosity covers the remaining sides, reducing the overall amount of CUF material and minimizing wafer warpage during curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capillary underfill (CUF) material is used to fill gaps between stacked dies, then the gaps are properly filled and device reliability is improved, but wafer warpage occurs during curing which impairs singulation and subsequent processing
Solution Approach 1:
The patent divides the sealing material application into two distinct segments: a first sealing material applied to selected sides of the stack, and a second sealing material applied to remaining sides. This segmentation allows different material properties to be used in different locations, specifically using lower viscosity material only where needed for capillary action while using higher viscosity material elsewhere to minimize warpage during curing.
Solution Approach 2:
The patent applies different sealing materials with different properties to different sides of the stack based on local requirements. The first sealing material with lower viscosity is applied only to selected sides where capillary action is needed, while the second sealing material with higher viscosity is applied to remaining sides to minimize warpage. This local differentiation resolves the contradiction between achieving proper gap filling and maintaining wafer flatness.
2Stability of the object's composition
If CUF material is cured before singulation, then gap filling is secured, but wafer warpage impairs singulation and subsequent processing
Solution Approach 1:
The patent segments the sealing material properties so that the first sealing material with lower viscosity provides effective capillary filling, while the second sealing material with higher viscosity provides dimensional stability during curing without causing excessive warpage. This segmentation enables both stable gap filling and ease of singulation.
Solution Approach 2:
The patent applies local quality by using higher viscosity second sealing material on selected sides to provide structural support that maintains wafer flatness during curing, while using lower viscosity first sealing material only where capillary action is needed. This localized approach ensures gap filling stability while preserving singulation ease.
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 configuration reduces the likelihood of wafer warpage during the curing process, enabling more precise singulation and improved processing of stacked semiconductor dies.
Implementation Method 1
The gaps between adjacent stacked dies are often filled using a capillary under fill (CUF) material that is cured before singulating the stacked dies from the wafer
Implementation Method 2
The gaps between adjacent stacked dies are often filled using a capillary under fill (CUF) material that is cured before singulating the stacked dies from the wafer. In many cases, curing the CUF material results in wafer warpage
Data Source
AI summary
Stacked semiconductor dies are provided with selective capillary under fill to avoid wafer warpage during curing. In one embodiment, a method of manufacturing a semiconductor device includes forming at least three stacks of semiconductor dies over a substrate, the stacks spaced apart from one another by gaps. A first sealing material such as a capillary under fill material is deposited into a first subset of the gaps. A second sealing material such as a mold resin is deposited into a second subset of the gaps. The first and second sealing materials are cured, and the die stacks are then singulated.