Engineered Solder Preforms for Low-Residue Semiconductor Reflow
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Solution Overview
Problem
Existing soldering processes for power modules in semiconductor packaging face issues such as voiding, residue from liquid flux, contamination of reflow ovens, improper alignment, and the need for bulky fixturing, leading to defects and reduced throughput.
Innovation Solution
The use of a tacky material with low reflow residual weight to temporarily join and align semiconductor components during reflow, eliminating the need for mechanical fixturing and liquid flux, and ensuring proper alignment without leaving residue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder paste is used in high power semiconductor packaging, then the soldering process can be completed, but voiding occurs in the solder joints due to solvent evaporation during reflow
Solution Approach 1:
The patent changes the physical state parameter of the solder material from paste (containing solvent) to solid preform (flux-free). This parameter change eliminates the solvent evaporation process that causes voiding, thereby improving solder joint quality without compromising the soldering functionality
Solution Approach 2:
The patent employs disposable solid solder preforms that are consumed during the soldering process. These preforms are single-use components that eliminate the need for reusable flux coatings, thereby preventing voiding issues associated with solvent-based solder pastes while maintaining effective solder joint formation
2Reliability
If liquid flux is used to coat solder preforms, then oxide removal and wetting are improved, but residue is left on the PCB and parts requiring post-process cleaning
Solution Approach 1:
The patent extracts and removes the liquid flux component from the soldering process by using flux-free solid solder preforms. This extraction eliminates the source of residue contamination while maintaining oxide removal capability through the solid preform's inherent properties, thereby preventing PCB contamination without sacrificing wetting quality
Solution Approach 2:
The patent converts the potential harm of requiring flux coating into a benefit by designing solid preforms that inherently provide oxide removal and wetting capabilities without needing liquid flux. This transformation eliminates residue issues while maintaining or improving solder joint quality through the preform's engineered composition
3Productivity
If liquid flux is used during reflow, then the soldering process can proceed, but the reflow oven interior becomes contaminated requiring periodic shutdowns for cleaning
Solution Approach 1:
The patent extracts the liquid flux substance from the soldering process by implementing flux-free solid preforms. This removal eliminates the contamination source that causes reflow oven interior fouling, thereby maintaining continuous production operations without periodic shutdowns for oven cleaning while preserving effective solder joint formation
4Manufacturing precision
If bulky fixturing is used to hold assembly during reflow, then alignment is maintained, but the reducing atmosphere cannot penetrate the assembly to clean oxides from surfaces
Solution Approach 1:
The patent extracts and eliminates the bulky mechanical fixturing component by using self-aligning solid solder preforms with inherent positioning features. This extraction opens up the assembly structure, allowing reducing atmosphere penetration to effectively remove oxides from surfaces while maintaining alignment precision through the preform's engineered geometry
Solution Approach 2:
The patent replaces the mechanical fixturing system with a chemical/atmospheric-based solution where the reducing atmosphere performs the oxide removal function that was previously hindered by mechanical fixtures. The solid preform's structural design enables atmospheric access while maintaining alignment, substituting mechanical constraint with atmospheric action
5Reliability
If fixturing is used during reflow, then assembly is held together, but the footprint in the reflow oven limits the number of devices that can be reflowed in a single batch
Solution Approach 1:
The patent extracts and removes the bulky fixturing components that occupy valuable reflow oven space. By using compact solid solder preforms with self-holding capabilities, the patent eliminates the need for space-consuming mechanical fixtures, thereby increasing the number of devices that can be processed in each batch while maintaining assembly stability through the preform's inherent structural properties
6Ease of manufacture
If solder paste is used, then the soldering process can be completed, but volatile components coat the inside of the oven during reflow causing frequent production stops
Solution Approach 1:
The patent extracts and eliminates the volatile solvent components from the soldering process by using solid flux-free solder preforms. This extraction removes the source of oven interior contamination, thereby maintaining ease of manufacture through effective solder joint formation while eliminating production stoppages for oven cleaning and improving overall productivity
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 reduces defects, simplifies the manufacturing process, enhances throughput, and eliminates the need for post-process cleaning, while maintaining reliable bonding and alignment of semiconductor components.
Implementation Method 1
a first tacky material configured to cause a surface of the first device to adhere to a first surface of the first solder preform, and a first surface of the second device to adhere to a second surface of the first solder preform
Implementation Method 2
reflowing the semiconductor assembly at a temperature above a solidus temperature of the first solder preform to bond, via at least the first solder preform, the first device to the second device
Implementation Method 3
reflowing the semiconductor assembly at a temperature above a solidus temperature of the first solder preform to bond, via at least the first solder preform, the first device to the second device
Data Source
AI summary
Some implementations of the disclosure are directed to a method including: placing a first solder preform and a first tacky material between a first device and a second device to form a semiconductor assembly, the first tacky material configured to cause a surface of the first device to adhere to a first surface of the first solder preform, and a first surface of the second device to adhere to a second surface of the first solder preform opposite the first surface; and reflowing the semiconductor assembly at a temperature above a solidus temperature of the first solder preform to bond, via at least the first solder preform, the first device to the second device. The first tacky material has a reflow residual weight of less than 1% of the weight of the first tacky material before reflowing the semiconductor assembly.