Laser Bonding of Bare Chip Dies on Flexible Substrates
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Solution Overview
Problem
Current methods for bonding bare die chip components on flexible substrates lack high resolution and reliability, are prone to thermal shock, and cannot handle non-flat surfaces or web deformations, limiting their effectiveness in miniature electrical interconnects.
Innovation Solution
A direct write method using a laser to transfer thermosettable or thermoplastic adhesives or flux-containing solder pastes with controlled laser timing and energy, ensuring the bonding material remains intact and suitable for bonding, allowing for high-resolution spot sizes smaller than conventional methods and enabling flexible substrate handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If screen printing or stencil printing is used for bonding bare dies, then high productivity is achieved, but manufacturing precision deteriorates due to insufficient resolution (100 μm approx.) and web deformation on flexible substrates
Solution Approach 1:
The patent replaces mechanical contact printing methods (screen printing, stencil printing) with a laser-based direct write system. The laser beam selectively cures adhesive material deposited on the substrate without mechanical contact, eliminating web deformation issues and achieving sub-100 μm resolution while maintaining high throughput through rapid scanning capabilities.
Solution Approach 2:
The system employs dynamic laser scanning with programmable beam paths that can adapt to substrate movements and deformations in real-time. The laser parameters (power, speed, pattern) are dynamically adjusted during the bonding process to maintain precision on flexible substrates that may not be perfectly flat or stationary.
2Productivity
If contact mode printing is used, then high productivity is achieved, but reliability deteriorates due to damage to fragile substrates and dislocation from web movements
Solution Approach 1:
The patent eliminates mechanical contact between the deposition system and the substrate by using a laser-based direct write approach. The adhesive material is deposited and cured through non-contact laser energy, completely avoiding mechanical damage to fragile flexible substrates while maintaining high deposition speeds.
3Productivity
If laser energy is increased to improve transfer efficiency, then productivity is improved, but thermal shock increases which degrades adhesive properties and causes flux activation
Solution Approach 1:
The system uses pulsed laser delivery with carefully controlled duty cycles and pulse durations. By delivering energy in short, periodic pulses rather than continuous high power, the system achieves rapid adhesive curing and material transfer while allowing thermal diffusion to prevent excessive heat accumulation and thermal shock to the substrate and adhesive.
Solution Approach 2:
The laser energy is highly localized to the immediate bonding area through focused beam delivery and selective scanning patterns. This concentrates the thermal energy only where needed for adhesive curing, minimizing the thermal affected zone and preventing thermal shock to surrounding areas, flux activation, and substrate damage while maintaining fast transfer speeds.
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 method achieves robust bonding with electrical connectivity exceeding 1 MPa shear strength, suitable for large-scale industry use, and is cost-effective with high-speed, high-resolution deposition capabilities, overcoming limitations of existing techniques.
Implementation Method 1
impinging a laser beam on a dynamic release layer provided on a donor film in such a way that the dynamic release layer is activated to cover a selected part of the connection pads or the connection pad structure with bonding material transferred from the donor film
Implementation Method 2
the laser beam is restricted in timing and energy, in such a way that the transferred solder paste includes flux consisting of more than 10 % volume percent of flux
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3A~3B
AI summary
A method is provided for assembly of a micro-electronic component comprising the steps of: providing a conductive die bonding material comprising of a conductive thermosettable resin material or flux based solder and a dynamic release layer adjacent to the conductive thermoplastic material die bonding material layer; and impinging a laser beam on the dynamic release layer adjacent to the die bonding material layer; in such a way that the dynamic release layer is activated to direct conductive die bonding material matter towards the pad structure to be treated to cover a selected part of the pad structure with a transferred conductive die bonding material; and wherein the laser beam is restricted in timing and energy, in such a way that the die bonding material matter remains thermosetting. Accordingly adhesive matter can be transferred while preventing that the adhesive is rendered ineffective by thermal overexposure in the transferring process.