Solder Resist Trenches for Underfill Confinement in PoP
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Solution Overview
Problem
In Package-on-Package (PoP) processes, the integration of underfill material between stacked packages can lead to electrical connectivity issues due to the underfill material spreading onto un-bonded connectors, causing adverse effects on the electrical connection and reducing yield.
Innovation Solution
The formation of trenches in the solder resist, specifically trench rings, confines the underfill material, preventing it from spreading onto un-bonded connectors by creating a barrier that stops its flow, thereby ensuring proper bonding and improving yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If underfill material is applied between stacked packages, then bonding strength and structural stability are improved, but underfill material spreads onto un-bonded connectors causing electrical connectivity issues
Solution Approach 1:
The solder resist is segmented by forming trenches that divide the connector array into bonded and un-bonded regions. These trenches create physical barriers that segment the underfill material's spread path, preventing it from reaching un-bonded connectors while maintaining bonding strength in the bonded regions.
Solution Approach 2:
The solder resist structure is modified locally by adding trenches only in specific regions where un-bonded connectors are located. This creates different properties in different areas: regions with trenches provide underfill confinement, while regions without trenches allow normal bonding, thus maintaining electrical connectivity where needed.
2Reliability
If underfill material is confined to prevent spreading, then electrical connectivity is improved, but additional process steps are required
Solution Approach 1:
The trenches are formed in the solder resist before the underfill material is applied. This preliminary action of creating barriers in advance prevents the need for complex post-application confinement methods, simplifying the overall process while ensuring electrical connectivity is maintained.
Solution Approach 2:
The trenches in the solder resist act as intermediary structures that mediate between the underfill material and the un-bonded connectors. These intermediary barriers allow the underfill to be contained without requiring direct intervention or complex control mechanisms during the bonding process.
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 trench formation in the solder resist effectively confines the underfill material, reducing the risk of electrical connectivity issues and enhancing the reliability and yield of the PoP structure by maintaining the insulation and preventing underfill from reaching un-bonded connectors.
Implementation Method 1
A trench is disposed in the solder resist, wherein a portion of the trench spaces the second plurality of connectors apart from the first plurality of connectors.
Data Source
AI summary
A device includes a first package component and the second package component. The first package component includes a first plurality of connectors at a top surface of the first package component, and a second plurality of connectors at the top surface. The second package component is over and bonded to the first plurality of connectors, wherein the second plurality of connectors is not bonded to the second package component. A solder resist is on the top surface of the first package component. A trench is disposed in the solder resist, wherein a portion of the trench spaces the second plurality of connectors apart from the first plurality of connectors.