PoP Package Underfill Structure for Sidewall Protection and Singulation
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Solution Overview
Problem
The semiconductor industry faces challenges in achieving high integration density and reliable packaging techniques for semiconductor dies, particularly in Package-on-Package (PoP) technology, where existing underfill processes are limited by low pressure and slow underfill flow, affecting the protection of sidewalls and the complexity of the package singulation process.
Innovation Solution
A full coverage underfill process is introduced, which involves curing the underfill under higher pressure to accelerate void movement and improve flow speed, and includes a redistribution structure with multiple dielectric and metallization layers to enhance package reliability and simplify singulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional underfill processes are used, then the package structure is simple, but the underfill flow speed is slow and sidewall protection is insufficient
Solution Approach 1:
The patent implements a nested package structure where a first package is stacked on a second package in a Package-on-Package configuration. The underfill material is nested between these packages, filling the gap and surrounding conductive connectors. This nesting approach enables full sidewall coverage while maintaining a compact overall structure, resolving the contradiction between improved sidewall protection and structural simplicity.
Solution Approach 2:
The patent extends the underfill coverage from traditional partial coverage to full sidewall coverage by utilizing the vertical dimension in the PoP structure. The underfill flows up along the sidewalls of conductive connectors and packages, providing protection in the vertical dimension that was not adequately addressed in conventional lateral underfill processes. This dimensional extension achieves comprehensive sidewall protection without significantly increasing horizontal complexity.
2Speed
If conventional underfill processes are used, then the process pressure is low, but the underfill flow speed is slow
Solution Approach 1:
The patent changes the pressure parameter during the underfill curing process. By applying higher pressure during curing, the underfill material achieves faster flow speed and more complete coverage. This parameter change resolves the contradiction by using elevated pressure to simultaneously increase flow speed and ensure proper filling, with the pressure being controlled within safe limits for the package structures.
3Quantity of substance
If Package-on-Package technology is used, then integration density is high, but the singulation process becomes complex
Solution Approach 1:
The patent merges the singulation process with the underfill curing process. The underfill material is applied before singulation and serves dual functions: providing sidewall protection and acting as a cutting guide during the singulation process. The underfill's curved top surface between packages naturally guides the singulation cut, combining two operations into one coordinated process and reducing overall process complexity despite the high integration density of the PoP structure.
4Reliability
If underfill is dispensed in scribe line regions only, then the process is simple, but sidewall coverage is incomplete
Solution Approach 1:
The patent applies underfill material in advance before the singulation process, allowing the underfill to flow and settle into position while the package structures are still aligned. This preliminary application enables the underfill to naturally cover sidewalls and form curved top surfaces that will guide subsequent singulation cuts. By performing the underfill application before singulation, the process achieves complete sidewall coverage without requiring complex dispensing patterns or post-singulation adjustments.
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 enhances the protection of package sidewalls, increases underfill flow speed, and simplifies the package singulation process, leading to improved reliability and yield in semiconductor packaging.
Implementation Method 1
curing the underfill under higher pressure to accelerate void movement and improve flow speed
Data Source
AI summary
An embodiment is a structure including a first package including a first die, and a molding compound at least laterally encapsulating the first die, a second package bonded to the first package with a first set of conductive connectors, the second package comprising a second die, and an underfill between the first package and the second package and surrounding the first set of conductive connectors, the underfill having a first portion extending up along a sidewall of the second package, the first portion having a first sidewall, the first sidewall having a curved portion and a planar portion.