Flexible Transfer Mask for Micro-Ball Mounting
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Solution Overview
Problem
In micro-ball mounting for surface-mount semiconductor devices like BGA and CSP packages, existing methods face challenges with inconsistent gap distances between the transfer mask and the substrate, leading to inaccurate positioning and connection defects due to substrate warping caused by thermal contraction, which affects yield and increases production costs.
Innovation Solution
A thin plate transfer mask with slits formed along its length and width directions is used, allowing for flexibility and maintaining a constant gap distance with the substrate, ensuring accurate positioning of conductive balls onto terminal areas through a combination of vacuum adhesion and magnetic attraction, and reflow soldering for secure connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the transfer mask is made rigid to maintain structural stability, then the mask strength is improved, but the gap between the mask and substrate becomes nonuniform due to substrate warping
Solution Approach 1:
The transfer mask employs a flexible thin plate structure that can elastically deform to conform to substrate warping. This flexibility allows the mask to maintain a substantially uniform gap distance across the substrate surface even when the substrate warps, while still providing sufficient strength for vacuum adhesion and micro-ball transfer operations.
Solution Approach 2:
The mask design changes the physical parameters of the mask plate by incorporating slits that reduce overall rigidity while maintaining structural integrity. This parameter modification enables the mask to adapt its shape to substrate warping, ensuring uniform gap maintenance without sacrificing the vacuum adhesion capability.
2Manufacturing precision
If the transfer mask is made flexible to accommodate substrate warping, then the gap uniformity is improved, but the mask rigidity decreases making it difficult to maintain vacuum adhesion
Solution Approach 1:
The thin plate mask with integrated slits provides the optimal balance between flexibility and rigidity. The slits allow the mask to flexibly conform to substrate warping patterns while the overall continuous plate structure maintains sufficient rigidity for vacuum adhesion and positional stability during the micro-ball transfer process.
Solution Approach 2:
The mask plate is segmented by incorporating slits that divide the continuous structure into regions that can independently deform. This segmentation allows localized flexibility to accommodate warping while the connected structure maintains overall rigidity and vacuum adhesion capability.
3Adaptability or versatility
If the gap between transfer mask and substrate is increased to accommodate warping, then the adaptability to substrate deformation is improved, but the positioning accuracy of micro-balls deteriorates
Solution Approach 1:
The mask transitions from a static rigid structure to a dynamic flexible structure that can adapt its shape to substrate warping. This dynamic capability allows the mask to maintain optimal positioning accuracy by conforming to the substrate surface while preserving the through-hole alignment with terminal areas.
Solution Approach 2:
The flexible thin plate mask maintains a substantially uniform and small gap distance across the substrate by elastically deforming to match substrate warping patterns. This ensures that through-holes remain properly aligned with terminal areas for accurate micro-ball positioning while accommodating substrate deformation.
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 solution improves the accuracy and reliability of micro-ball placement, reduces connection defects, and enhances the yield and cost-effectiveness of semiconductor device manufacturing by maintaining a consistent gap and accommodating substrate warping, thereby improving the overall manufacturing process.
Implementation Method 1
A transfer mask (200) is registered on the substrate (100), and the perimeter of the transfer mask (200) is affixed by vacuum adhesion
Implementation Method 2
a magnet is arranged inside the stage (310), so that the center of the transfer mask (200) is drawn toward the stage (310) by the magnetic force of the magnet (330)
Implementation Method 3
The micro-balls (380) and terminal areas (108) are subsequently connected by reflow soldering
Data Source
AI summary
The objective of this invention is to provide a transfer mask that is able to accurately pass micro-balls onto terminal areas on a substrate. A thin plate transfer mask 200 is arranged facing a substrate 100, and possesses a plurality of through-holes 242 for the purpose of passing micro-balls (solder balls) onto a plurality of terminal areas 108 formed on one surface of a substrate 100. Slits 230, 232, 234, 236 formed in the surface of the transfer mask 200 extending in the length direction and the width direction of the transfer mask 200, inside the substrate edge P1 and outside the area in which the plurality of through-holes 242 is formed when it is facing the substrate 100.