Flip-Chip Solder Joint Assembly Using Arc Welding Reflow
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Solution Overview
Problem
Flipchip semiconductor packages face reliability issues due to non-wet or insufficient solder joint connections caused by solder flux dry up and solder inactivation during the die attach process, attributed to a long window between die attach and solder reflow.
Innovation Solution
The method involves placing a semiconductor die with solder paste on bond pads onto a package substrate and using arc welding with a biased electrode to melt the solder paste, forming a solder connection without the need for a separate solder reflow step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a long window of time is allowed between die attach and solder reflow, then the assembly process is more flexible, but solder flux dry up and solder inactivation occur causing unreliable solder joints
Solution Approach 1:
The patent combines the die attach and solder reflow operations into a single integrated process step. The die is attached to the substrate using solder paste as the bonding material, and the same solder paste is subsequently reflowed to create reliable solder joints. This merging eliminates the long time window between die attach and solder reflow that causes flux dry up and solder inactivation, thereby maintaining solder joint reliability while preserving process flexibility.
2Reliability
If traditional solder reflow process is used, then the solder joint is formed, but solder flux dry up and inactivation occur during the long process window
Solution Approach 1:
The patent applies preliminary action by applying solder paste to the bond pads before die attach, and then immediately performing the reflow operation in the same process window. The solder paste is prepared and positioned in advance on the substrate, and the die is attached directly onto it without allowing the paste to sit exposed to air for an extended period. This preliminary preparation followed by immediate reflow prevents flux dry up and solder inactivation that would occur with traditional separate processes.
3Ease of manufacture
If separate die attach and solder reflow steps are used, then process control is easier, but solder flux dry up occurs reducing solder joint quality
Solution Approach 1:
The patent merges die attach and solder reflow into a single integrated process step where solder paste serves dual purposes as both the bonding material for die attach and the material for forming solder joints. This integration eliminates the harmful time window that causes flux dry up and solder inactivation, thereby maintaining high solder joint quality. The process control is maintained through precise control of the combined process parameters including die attach pressure, temperature profile during reflow, and timing synchronization.
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 reliable solder connections by eliminating the risk of solder flux dry up and inactivation, thereby enhancing the reliability and efficiency of the flipchip semiconductor package assembly process.
Implementation Method 1
Arc welding is utilized using an arc welding apparatus comprising an arm and a biased electrode having a tip spaced apart from the solder paste, wherein electrical current generated by the arc welding melts the solder to provide a solder connection.
Data Source
AI summary
A method of assembling a flipchip semiconductor package, includes placing a semiconductor die having circuitry electrically coupled to bond pads with bumps having solder paste thereon onto bonding features of a package substrate. Arc welding is used using an arc welding apparatus including a biased electrode having a tip spaced apart from the solder paste, wherein electrical current generated by the arc welding melts the solder paste to provide a solder connection.