Reactive Multilayer Foil Bonding for Low-Temperature LED Assembly
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Solution Overview
Problem
Conventional high-temperature solder reflow processes damage temperature-sensitive semiconductor devices and components, such as LEDs, during bonding to substrates, leading to poor thermal, electronic, and optical performance due to excessive heat exposure.
Innovation Solution
A method using reactive multilayer foils to generate thermal energy for bonding by initiating an exothermic reaction, allowing for the formation of electrically and thermally conductive bonds without damaging sensitive components, by sandwiching the foils between bonding materials like solder and applying pressure to melt the bonding material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature solder reflow process is used to bond LED package to substrate, then bonding strength is improved, but temperature-sensitive components are damaged
Solution Approach 1:
A bonding layer comprising reactive multilayer foil and solder material is introduced as an intermediary between the LED package and substrate. The reactive multilayer foil generates localized heat through exothermic reaction to melt the solder material, which then bonds the components together without requiring high temperature reflow that would damage temperature-sensitive components
Solution Approach 2:
The solder material undergoes phase transition from solid to liquid through the heat generated by the reactive multilayer foil, enabling it to flow and form bonds between the LED package and substrate. The reactive multilayer foil itself undergoes exothermic phase transition to generate the necessary heat for this process
2Reliability
If solder reflow cycle is extended to ensure adequate melting, then bonding quality is improved, but thermal damage to components increases
Solution Approach 1:
The reactive multilayer foil acts as a localized heat generator that provides sufficient thermal energy to melt the solder material quickly, eliminating the need for extended reflow cycles. This intermediary enables complete solder melting and reliable bonding while keeping the overall process time short and component temperature exposure low
Solution Approach 2:
The bonding process uses a brief, intense heat pulse from the exothermic reaction of the reactive multilayer foil rather than prolonged heating. This periodic, concentrated thermal action achieves complete solder melting in a short time, ensuring bonding quality without extended temperature exposure that would damage components
3Temperature
If thermally conductive adhesive is used to attach center slug, then bonding at low temperature is achieved, but thermal conductivity is insufficient
Solution Approach 1:
The bonding structure uses a composite of reactive multilayer foil and solder material instead of conventional thermally conductive adhesive. This composite provides both the low-temperature bonding capability (through controlled exothermic reaction) and superior thermal conductivity (through the metallic solder and foil layers), outperforming single-material adhesive solutions
Solution Approach 2:
The patent replaces the thermal conduction mechanism of adhesives with a metallurgical bonding mechanism using solder. The reactive multilayer foil generates heat to melt the solder, which then forms strong, highly conductive metallic bonds between the center slug and substrate, replacing the weaker thermal conduction path provided by polymeric adhesives
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 uniform and reliable bonding with controlled heat generation, maintaining component temperatures near ambient, thus enhancing thermal and electrical conductivity while preventing damage from excessive heat.
Implementation Method 1
initiating an exothermic reaction in the reactive multilayer foil to generate sufficient thermal energy to melt the bonding material
Implementation Method 2
applying a pressure to the contacts in the bonding region and initiating an exothermic reaction in the reactive multilayer foil to generate sufficient thermal energy to melt the bonding material
Data Source
AI summary
A method for bonding an LED assembly (71) or other electronic package (31) to a substrate PCB containing a heat-sink (52), which utilizes layers of reactive multilayer foil (51) disposed between contacts (32, 34) of the electronic package 31 and the associated contact pads (55) on the supporting substrate PCB. By initiating an exothermic reaction in the reactive multilayer foil (51), together with an application of pressure, sufficient heat is generated between the contacts (32, 34) and the associated contact pads (55) to melt adjacent bonding material (54) to obtain good electrically and thermally conductive bonds between the contacts 32, 34 and contact pads (55) without thermally damaging the electronic package (31), heat-sensitive components (35) associated with the electronic package (31), or other the supporting substrate PCB.