Flip Chip Interconnection Using Thermode-Controlled Underfill Gel
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Solution Overview
Problem
Conventional flip chip technology faces limitations in reducing interconnection pitch due to solder bump shorting during reflow bonding, high costs associated with multilayer substrates, and electrical parasitics from routing patterns, which hinder its adoption in mainstream products.
Innovation Solution
The method employs a thermode tool to apply heat and pressure, controlling the underfill material to form a gel stage that secures bumps to interconnect sites, allowing for reflow without a solder mask, thereby preventing void formation and enabling finer pitch interconnections with simpler substrate designs and reduced manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reflow bonding is used to form flip chip interconnections, then electrical connections are established between bumps and interconnect sites, but adjacent solder bumps short during the reflow bonding operation
Solution Approach 1:
A gel-forming material is applied to the interconnect sites on the substrate before bump placement. This material acts as an intermediary that forms a gel during reflow bonding, physically separating adjacent solder bumps and preventing them from shorting while still allowing electrical connection through the gel medium. The gel material is positioned between the bumps and provides the necessary isolation.
Solution Approach 2:
The material on the interconnect sites undergoes a parameter change from solid to gel state during the reflow bonding process. This phase change occurs at the melting point of the gel-forming material, transforming it into a gel that provides bump separation. The parameter change enables the material to transition from a rigid state during assembly to a gel state during reflow that prevents shorting.
2Manufacturing precision
If conventional flip chip packaging is used, then interconnections are formed, but the interconnection pitch cannot be reduced due to bump shorting propensity
Solution Approach 1:
The gel-forming material serves as a mediator that enables finer pitch interconnections by preventing bump shorting. It allows the bumps to be placed closer together than conventional methods permit, as the gel material physically separates adjacent bumps during reflow bonding, enabling manufacturing precision improvement without encountering the bump shorting problem.
3Ease of manufacture
If conventional substrates with solder mask are used, then capture pads are exposed for bump bonding, but the substrate design becomes complex and costly
Solution Approach 1:
Instead of using a solder mask to expose capture pads (conventional approach), the invention inverts the approach by applying a gel-forming material directly to the interconnect sites on the substrate. This eliminates the need for complex solder mask patterns and multilayer substrate designs, simplifying manufacturing while maintaining reliable bump-to-pad connections through the gel material.
4Ease of manufacture
If conventional capillary underfill is used, then underfill material flows into the space between die and substrate, but the process requires precise control and may trap air
Solution Approach 1:
The gel-forming material is applied to the interconnect sites before bump placement and reflow bonding. This preliminary action ensures the material is in position to form a gel that will prevent void formation during subsequent processing steps. The material is pre-positioned to facilitate underfill flow and prevent air trapping, improving reliability without requiring precise real-time control during underfill application.
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 allows for finer pitch interconnects, reduces manufacturing costs, and improves connection yields by ensuring reliable bump-pads mating, while eliminating the need for complex multilayer substrates and minimizing electrical parasitics.
Implementation Method 1
The underfill includes a material that is thermally cured; that is, raising the temperature of the underfill material can result in progressive curing of the underfill through stages including a gel stage and a fully cured stage
Implementation Method 2
the semiconductor chip is carried by a thermode, which is employed to control the temperature of the assembly in a specified way
Implementation Method 3
raising the temperature of the bumps to a temperature at which the fusible portion of the bump (the entire bump in some embodiments) melts
Implementation Method 4
applying the underfill material in a liquid form to the narrow space between the die and the substrate near an edge of the die, whereupon the underfill material is permitted to flow by capillary action into the space
Data Source
AI summary
Methods for forming flip chip interconnection, in which the bump interconnect is defined at least in part by an underfill. The underfill includes a material that is thermally cured; that is, raising the temperature of the underfill material can result in progressive curing of the underfill through stages including a gel stage and a fully cured stage. According to the invention, during at least an early stage in the process the semiconductor chip is carried by a thermode, which is employed to control the temperature of the assembly in a specified way. Also, flip chip interconnections and flip chip packages made according to the methods of invention.