Tamper-Resistant Flip Chip Solder Joints via Transient Liquid Phase Bonding
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Solution Overview
Problem
Current tamper-resistant semiconductor packaging methods are costly, difficult to apply consistently, and can compromise component reliability, as they often require time-consuming specialized coatings that may interfere with component cooling and are challenging to perform on a large scale.
Innovation Solution
The use of flip chip solder joints formed through a transient liquid phase (TLP) bonding process, where a metal with a lower melting point is diffused into a metal with a higher melting point to create an alloy with a melting point above the maximum temperature the semiconductor can withstand, making it difficult to remove the semiconductor without damaging it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a specialized coating is applied to the semiconductor die to prevent removal, then tamper resistance is improved, but manufacturing time and cost increase
Solution Approach 1:
The invention changes the melting point parameter of the solder joint alloy to be higher than the maximum temperature the semiconductor can withstand. This creates a temperature parameter mismatch where removing the semiconductor would require temperatures that destroy the device, providing tamper resistance without requiring additional coating processes.
Solution Approach 2:
The invention uses a composite solder joint structure formed by TLP bonding, combining a base metal (e.g., gold) with a sacrificial metal (e.g., tin) to create an intermetallic compound with elevated melting point. This composite material approach achieves the desired high melting point while maintaining bonding reliability through the transient liquid phase process.
2Reliability
If a specialized coating is applied to the semiconductor die, then tamper resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The invention merges the bonding function and tamper resistance function into a single solder joint structure. The same TLP-bonded solder joint that provides electrical and mechanical connection also provides tamper resistance through its high melting point, eliminating the need for separate coating processes and reducing overall manufacturing complexity.
Solution Approach 2:
The solder joint is designed to serve multiple functions: electrical connection, mechanical bonding, and tamper resistance. By making the solder joint alloy melting point higher than the semiconductor's maximum temperature, a single component structure achieves three critical functions, simplifying the overall manufacturing process.
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 provides a cost-efficient, reliable, and dense packaging solution that enhances tamper resistance by ensuring that attempting to remove the semiconductor through heating will destroy its functionality, thereby protecting proprietary aspects of the semiconductor package.
Implementation Method 1
a first metal in the liquid state is diffused into a second metal while the second metal is in the solid state
Implementation Method 2
The flip chip solder joints are formed using a transient liquid phase (TLP) bonding process
Implementation Method 3
The flip chip solder joints are formed of an alloy having a higher melting point than the maximum allowable temperature of the semiconductor device
Data Source
AI summary
A tamper resistant semiconductor package includes a surface having flip chip electrical contacts. A flip chip semiconductor of the package also has flip chip electrical contacts. The flip chip semiconductor has a maximum temperature to which it can be exposed before being damaged. Flip chip solder joints physically couple and electrically connect the flip chip electrical contacts of the flip chip semiconductor to the flip chip electrical contacts of the surface. The flip chip solder joints are formed of an alloy having a higher melting point than the maximum temperature such that removal of the flip chip semiconductor from the surface by heating will destroy the functionality of the flip chip semiconductor.