Intermetallic Solder Joint Bonding With Laser Heating to Reduce Thermal Stress
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Solution Overview
Problem
The conventional heat pression process for fabricating semiconductor packages leads to increased thermal stress due to differences in thermal expansion coefficients between the lower and upper elements.
Innovation Solution
A method involving a laser beam bonding process, where a lower element with a UBM layer, reducing agent layer, and optional curing agent and base material layers is bonded to an upper element with a solder bump layer, using conductive heat to form an intermetallic compound layer, thereby minimizing thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a heat pression process is used to fabricate semiconductor packages, then the bonding process is simple and straightforward, but thermal stress increases due to difference in thermal expansion coefficient between lower and upper elements
Solution Approach 1:
The patent replaces the conventional thermal bonding process with a laser-based bonding process. Instead of using heat and pressure to bond the upper and lower elements, a laser beam is used to locally heat and melt the solder bump layer, forming intermetallic compounds that bond the elements together. This substitution eliminates the need for overall thermal heating, thereby reducing thermal stress while maintaining bonding effectiveness.
Solution Approach 2:
The laser bonding process applies heat locally only to the solder bump layer at the bonding interface, rather than heating the entire semiconductor package structure. This localized heating approach minimizes thermal stress in non-bonding areas while achieving effective bonding where needed, resolving the contradiction between bonding effectiveness and thermal stress reduction.
2Stress or pressure
If a laser beam bonding process is used, then thermal stress is reduced, but the process complexity increases
Solution Approach 1:
The patent introduces several intermediary layers between the lower element and the solder bump layer, including a reducing agent layer, curing agent layer, and base material layer. These intermediaries facilitate the laser bonding process by controlling heat distribution, preventing oxidation, and enabling proper intermetallic compound formation, thereby simplifying the overall process control while maintaining low thermal stress.
Solution Approach 2:
The patent carefully controls and optimizes various process parameters including laser beam power, scanning speed, wavelength, and the composition/thickness of intermediary layers. By precisely adjusting these parameters, the complex laser bonding process becomes controllable and repeatable, reducing thermal stress while managing process complexity through systematic parameter optimization.
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 effectively reduces thermal stress between the lower and upper elements, enhancing the mechanical reliability of the semiconductor package by forming a strong intermetallic compound layer through the controlled application of conductive heat.
Implementation Method 1
providing a laser beam passing through the pressing member to the upper substrate to form the UBM layer, the reducing agent layer, and the solder bump layer as an intermetallic compound layer by using conductive heat of the upper substrate and the upper electrode
Implementation Method 2
providing a laser beam passing through the pressing member to the upper substrate to form the UBM layer, the reducing agent layer, and the solder bump layer as an intermetallic compound layer
Data Source
AI summary
Provided is a method of fabricating a semiconductor package. The method of fabricating the semiconductor package include preparing a lower element including a lower substrate, a lower electrode, an UBM layer, and a reducing agent layer, providing an upper element including an upper substrate, an upper electrode, and a solder bump layer, providing a pressing member on the upper substrate to press the upper substrate to the lower substrate, and providing a laser beam passing through the pressing member to bond the upper element to the lower element.