Magnetic Retention for Laminate Flatness During Chip Joining
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Solution Overview
Problem
Thermal stress during the reflow process causes laminate warpage, leading to undesirable effects such as opens, shorts, cracking, and separation of dielectric layers, which can result in module failure due to increased warpage.
Innovation Solution
Applying a magnetic force to a laminate using magnets placed above a ferromagnetic back plate to maintain laminate flatness, either through attractive or repulsive forces, preventing warpage during the chip-joining process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal stress is applied during reflow process to join chip to laminate, then electrical connection is improved, but laminate warpage increases
Solution Approach 1:
Magnetic force is applied as a counteracting force to balance the thermal stress-induced warpage. Magnets positioned above and below the laminate generate attractive forces that counterbalance the warping tendency, maintaining laminate flatness during the reflow process while allowing solder balls to melt and create electrical connections.
Solution Approach 2:
The magnetic field strength and temperature are controlled as parameters to achieve the desired effect. The magnetic force is adjusted to be sufficient to prevent warpage but not so strong as to interfere with the joining process. The temperature is controlled to melt solder balls while maintaining laminate flatness through the magnetic constraint.
2Volume of moving object
If laminate thickness is reduced to improve device integration, then device size is improved, but laminate warpage increases
Solution Approach 1:
Magnetic force serves as a counteracting force that compensates for the increased warpage susceptibility of thinner laminates. The magnetic attraction between magnets positioned above and below the laminate provides the necessary constraint to maintain flatness despite the reduced structural rigidity of thinner materials.
Solution Approach 2:
Mechanical clamping or fixation systems are replaced with a magnetic field-based constraint system. The magnetic field provides non-contact force application that maintains laminate flatness without requiring physical contact or mechanical fasteners, enabling better control over thin laminate structures.
3Shape
If magnetic force is applied to maintain laminate flatness, then laminate flatness is improved, but device complexity increases
Solution Approach 1:
The magnetic constraint system is divided into multiple independent magnets positioned at specific locations above and below the laminate. This segmentation allows for distributed force application across the laminate surface, providing uniform flatness maintenance while simplifying the overall system design compared to a single complex magnetic assembly.
Solution Approach 2:
The magnetic system is designed to automatically maintain laminate flatness throughout the reflow process without requiring active control or adjustment. The magnets are positioned to generate self-balancing forces that naturally counteract warpage as it develops, eliminating the need for complex control systems or real-time 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
Prevents laminate warpage, ensuring reliable electrical connections and maintaining module co-planarity by holding the laminate flat against the back plate during solder reflow, thereby reducing the risk of opens, shorts, and cracking.
Implementation Method 1
applying a magnetic force to the laminate using a first magnet so that the magnetic force holds the laminate flat against the back plate
Implementation Method 2
an attractive force generated between the first magnet and a ferromagnetic region of the back plate pulls the first magnet against the laminate
Implementation Method 3
a repulsive force generated between the first magnet and the magnet pushes the first magnet against the laminate
Data Source
AI summary
Methods for preventing warpage of a laminate may include placing the laminate on a back plate and applying a magnetic force to the laminate to hold the laminate flat against the back plate. In some embodiments, the magnetic force may be applied by placing a first magnet above the laminate so that an attractive force generated between the first magnet and a ferromagnetic region of the back plate pulls the first magnet against the laminate, thereby holding the laminate flat against the back plate. In other embodiments, the magnetic force may be applied by placing a first magnet above the laminate and placing a second magnet above the first magnet so that a repulsive force generated between the first magnet and the magnet pushes the first magnet against the laminate, thereby holding the laminate flat against the back plate.