Via-Guided Ball-to-Ball Alignment in High-Density PoP
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Solution Overview
Problem
Package-on-package (PoP) structures face challenges in achieving high-density interconnects due to standoff height issues, where solder balls cannot span the gap between packages, leading to misalignment and increased manufacturing costs in conventional designs, especially with fine-pitch designs.
Innovation Solution
A bare-die first package with a patterned insulating solder resist layer that exposes vias to guide second package balls, eliminating the need for over-molded encapsulation and reducing standoff height, allowing for guided ball-to-ball contact without flattening or coining, and enabling cost-effective manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solder ball size is decreased to accommodate fine-pitch designs, then interconnect pitch is reduced, but solder balls cannot reach the bottom package substrate due to standoff height
Solution Approach 1:
The patent divides the connection path into two segments: first package solder balls on the bottom package substrate and second package solder balls on the top package substrate. The via structures in the insulating layer create guided pathways that connect these segmented solder balls, enabling electrical continuity despite the standoff height barrier that would prevent a single continuous solder ball from spanning the gap.
Solution Approach 2:
The via structures formed in the insulating layer act as intermediary elements between the first package solder balls and second package solder balls. These vias provide guided pathways that mediate the connection, allowing the solder balls to align and connect electrically without requiring the solder balls themselves to physically span the standoff height gap.
2Length of stationary object
If conventional over-molded encapsulation is used, then standoff height is reduced, but manufacturing complexity and cost increase due to laser ablation or mechanical cutting
Solution Approach 1:
The patent extracts the insulating layer with integrated via structures from the over-molded encapsulation approach. Instead of enclosing the entire first package die in mold compound and then laser ablating or mechanically cutting vias through it, the invention uses a standalone insulating layer with pre-formed via structures that expose the first package solder balls, eliminating the need for costly and complex post-encapsulation via formation processes.
Solution Approach 2:
The via structures are formed in the insulating layer before the second package is attached to the first package. This preliminary formation of guided pathways allows for easier alignment and connection of solder balls, avoiding the need for costly and complex laser ablation or mechanical cutting operations that would be required if vias were formed after over-molded encapsulation.
3Manufacturing precision
If first package die is ground down to reduce standoff height, then solder ball alignment is improved, but die becomes fragile and manufacturing cost increases
Solution Approach 1:
The via structures in the insulating layer serve as intermediary guided pathways that enable precise alignment of second package solder balls with first package solder balls. This intermediary guidance mechanism eliminates the need to grind down the first package die to achieve alignment, thereby preserving the die's structural integrity and avoiding the fragility and cost issues associated with grinding operations.
4Ease of manufacture
If unguided ball-to-ball coupling is used, then manufacturing is simpler, but misalignment occurs due to round ball shapes
Solution Approach 1:
The via structures in the insulating layer act as intermediary guided pathways that constrain and guide the round solder balls into proper alignment during assembly. These vias provide physical walls or boundaries that prevent misalignment of the spherical solder balls, enabling precise ball-to-ball coupling without requiring complex alignment mechanisms or modifying the spherical shape of the balls themselves.
Solution Approach 2:
The insulating layer with integrated via structures functions as a thin film structure that provides guidance for solder ball alignment. This thin insulating layer with formed vias creates constrained pathways that guide the spherical solder balls into proper positions, maintaining the simplicity of manufacturing while achieving precise alignment through the geometric constraints provided by the via structures.
Data Source
AI summary
A bare-die first package includes a patterned insulating layer that exposes first package balls in vias. The vias enable a second package to be positioned on the first package in a proper ball-to-ball alignment without the need for flattening or coining.