InFO Pad Openings for Thermal Stress Relief
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Solution Overview
Problem
In Package-on-Package (PoP) structures, the stress caused by thermal cycles can lead to cracking of dielectric layers due to the large metal pads used in Integrated Fan-Out (InFO) packages, which are not effectively managed by existing bonding methods.
Innovation Solution
The formation of openings in the metal pads allows for reduced stress absorption by segregating the metal pads into smaller portions, thereby minimizing the expansion and cracking risk during thermal cycles, while maintaining effective electrical connectivity through enlarged pad sizes that extend beyond the edges of Under-Bump Metallurgies (UBMs).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large metal pads are used in InFO packages, then electrical connectivity is improved, but thermal stress causes dielectric layer cracking
Solution Approach 1:
The metal pad is divided into multiple segments by forming openings (via holes) through it. This segmentation reduces the continuous metal area, thereby reducing thermal stress accumulation while maintaining electrical connectivity through the segmented paths and underlying via structures.
Solution Approach 2:
The metal pad is transformed into a porous structure by forming openings through it. This porous configuration reduces the thermal mass and stress concentration in the metal pad, allowing thermal expansion and contraction without transmitting excessive stress to the dielectric layer, thus preventing cracking.
2Object-affected harmful factors
If metal pads are segmented into smaller portions, then thermal stress absorption is improved, but electrical connectivity may be compromised
Solution Approach 1:
The segmented metal pad structure is nested with via structures that extend through the openings. The via structures are positioned within and connected to the segmented pad portions, creating a nested configuration that maintains electrical continuity while the segmented outer structure absorbs thermal stress.
Solution Approach 2:
The via structures act as intermediaries that bridge the segmented metal pad portions. These via structures maintain electrical connectivity between the separated pad segments while allowing the segments to move independently for thermal stress absorption, thus mediating between stress relief and electrical continuity requirements.
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 absorption of thermal stress without causing dielectric layer cracking, ensuring reliable bonding and reduced failure rates in InFO packages within PoP structures.
Implementation Method 1
the stress caused by thermal cycles can lead to cracking of dielectric layers due to the large metal pads used in Integrated Fan-Out (InFO) packages
Data Source
AI summary
A package includes a conductive pad, with a plurality of openings penetrating through the conductive pad. A dielectric layer encircles the conductive pad. The dielectric layer has portions filling the plurality of openings. An Under-Bump Metallurgy (UBM) includes a via portion extending into the dielectric layer to contact the conductive pad. A solder region is overlying and contacting the UBM. An integrated passive device is bonded to the UBM through the solder region.