Stacked Package Structure With Conductive Spacers Against Solder Bridging
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Solution Overview
Problem
Integrated fan-out (InFO) packages experience warpage due to mismatched coefficients of thermal expansion, leading to bowing issues that result in solder bridging when attached to printed circuit boards (PCBs), causing connectivity problems.
Innovation Solution
Incorporating conductive spacers between the InFO package and the PCB, which serve as both spacers and electrical connectors, maintaining a consistent distance during reflow and utilizing a flux with a predetermined pattern to prevent tilting, thereby preventing solder bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If InFO package is attached to PCB without conductive spacers, then manufacturing process is simpler, but solder bridging occurs due to warpage-induced bowing
Solution Approach 1:
The conductive spacer acts as an intermediary element between the InFO package and PCB. It compensates for the bowing caused by CTE mismatch by providing a mechanical buffer that maintains proper spacing, thereby preventing solder bridging while preserving electrical connectivity through its conductive properties
Solution Approach 2:
The conductive spacer changes the physical parameters of the assembly by introducing a controlled height difference and mechanical support. This parameter modification compensates for the warpage-induced dimensional changes, ensuring consistent spacing between the InFO package and PCB during thermal cycling
2Reliability
If conductive spacers are used to prevent solder bridging, then connectivity reliability improves, but device complexity increases
Solution Approach 1:
The conductive spacer performs multiple functions simultaneously: it provides mechanical support to counteract bowing, maintains precise spacing to prevent solder bridging, and conducts electrical signals. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity
3Ease of manufacture
If standard flux is used without predetermined pattern, then manufacturing process is simpler, but tilting occurs during reflow
Solution Approach 1:
The flux is applied with local quality variation through a predetermined pattern that concentrates flux in specific areas. This localized flux distribution provides differential adhesion forces that counteract the tilting moment during reflow, ensuring proper alignment of the InFO package with the PCB while maintaining manufacturing feasibility
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 conductive spacers effectively prevent solder bridging by maintaining a consistent distance and ensuring proper alignment, enhancing the reliability and yield of the packaging process.
Implementation Method 1
Due to a mismatch in the coefficient of thermal expansion (CTE) of the various materials in the InFO package, warpage can cause bowing in the InFO package
Implementation Method 2
a flux is applied to attach the one or more than one conductive spacer to the InFO package, where the flux includes a pre-determined pattern with a gap underneath the one or more than one conductive spacer for avoiding the tilting of the one or more than one conductive spacer during a reflowing process
Implementation Method 3
the conductive spacers simultaneously serve as a spacer and an electrical connector between the InFO package and the PCB
Data Source
AI summary
A package structure includes a first package, a second package, a conductive spacer, and a flux portion. The first package includes a semiconductor die. The second package is stacked to the first package. The conductive spacer is disposed between and electrically couples the first package and the second package. The flux portion is disposed between and electrically couples the first package and the conductive spacer, where the flux portion includes a first portion and a second portion separating from the first portion by a gap, and the first portion and the second portion are symmetric about an extending direction of the gap. The gap is overlapped with the conductive spacer.