Flip Chip Bonding Alloys for Multi-Die Reflow Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing flip chip bonding techniques using solder alloys face issues with bond failure when reflowing additional dies, as the solder can melt and spread, potentially damaging existing bonds and causing shorts between adjacent dies, especially in applications where efficient IC real estate usage is critical.
Innovation Solution
The use of metal alloys with higher reflow temperatures than traditional solder, such as silver-tin and nickel-titanium combinations, which form alloys that harden at lower temperatures and maintain a higher melting point than the reflow temperature, preventing subsequent melting and ensuring stable bonding during subsequent reflow processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solder alloys are used for flip chip bonding, then bonding is achieved at lower temperatures, but the solder melts and spreads during subsequent reflow processes causing bond failure and shorts
Solution Approach 1:
The patent changes the material parameter of the bonding alloy from traditional low-melting-point solder to high-melting-point alloys (such as gold-silver-copper or nickel-based alloys) that maintain structural integrity at reflow temperatures. This parameter change allows the bonding material to withstand subsequent reflow processes without melting, thereby preventing bond failure and shorts while maintaining reliable electrical connections.
Solution Approach 2:
The patent employs composite alloy compositions (e.g., gold-silver-copper alloys or nickel-based intermetallic compounds) that combine multiple elements to achieve both high melting points and good bonding characteristics. These composite materials provide thermal stability during reflow while maintaining adequate wetting and adhesion properties for reliable flip chip bonding.
2Reliability
If sufficient spacing is provided between dies to prevent solder spread, then bond reliability is maintained, but IC real estate usage efficiency decreases
Solution Approach 1:
By changing the melting point parameter of the bonding material to a higher value (above reflow temperature), the patent enables closer spacing between dies. The high-melting-point alloys remain solid during reflow processes, preventing unwanted solder flow between adjacent bond pads, thereby allowing more compact die arrangements and improved board area utilization while maintaining bond reliability.
3Reliability
If lead or gold is used to achieve higher reflow temperature, then bond stability during reflow is improved, but health issues or cost increase
Solution Approach 1:
The patent replaces expensive or problematic materials (lead with health concerns, gold with high cost) with more economical alternatives such as nickel-based alloys or other base metal compositions that achieve the required high melting point. These alternative materials provide comparable or sufficient bonding stability during reflow at lower material costs without the health and environmental issues associated with lead.
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 approach ensures that the flip chips remain securely bonded, allowing for closer spacing without the risk of solder flow between adjacent dies, enabling efficient integration of multiple dies on a single board while maintaining the integrity of existing bonds.
Implementation Method 1
the metals will melt or diffuse to mix with the solder paste to create a new alloy that has a melting temperature above the reflow temperature
Implementation Method 2
the metals will melt or diffuse to mix with the solder paste to create a new alloy
Data Source
AI summary
A method of bonding a plurality of die having first and second metal layers on a die surface to a board, comprising placing a first die onto a board comprising one of a ceramic or substrate board or metal lead frame having a solderable surface and placing the first die and the board into a reflow oven. The method includes reflowing at a first reflow temperature for a first period until the first metal board layer and at least one of the first and second metal die layers of the first die form an alloy to adhere the first die to the board. The newly formed alloy has a higher melting temperature than the first reflow temperature. Accordingly, additional die may be reflowed and attached to the board without causing the bonding of the first die to the board to fail if the same reflow temperature is used.