Solder Preform Gaps for Void Reduction and Thermal Conductivity
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Solution Overview
Problem
High thermal resistance in solder interfaces due to voiding, caused by trapped gases and metal oxides, leads to heat dissipation bottlenecks and electrical resistance issues in high-frequency or high-power devices.
Innovation Solution
Solder preforms with strategically designed gaps extending from the boundary towards the center, which close during reflow, allowing flux and gases to escape, and channels on the surface for enhanced oxygen purging and increased surface area, facilitating the removal of trapped oxides and gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solid solder preforms are used, then the solder interface is simple and easy to manufacture, but voids form during reflow due to trapped gases and flux, increasing thermal resistance and reducing reliability
Solution Approach 1:
The solder preform is segmented into multiple regions including solid solder portions and void portions (gaps, channels, cavities) that extend from the boundary toward the center. These void portions create escape pathways for flux and gases during reflow, preventing void formation in the bonded interface while maintaining structural integrity.
Solution Approach 2:
The void portions are pre-formed in the solder preform before the reflow process. This preliminary structure ensures that flux and gases have predetermined escape routes available before heating begins, allowing them to evacuate during reflow without becoming trapped and forming defects.
2Reliability
If flux is applied to remove metal oxides, then solder bonding is improved, but flux becomes trapped in the interface creating high thermal resistance areas
Solution Approach 1:
The void portions (gaps, channels, cavities) are strategically positioned to extract and remove flux and gases from the solder interface during reflow. These structures actively take out the harmful materials that would otherwise become trapped and create thermal resistance, allowing flux to perform its oxide-removing function without leaving residual harmful byproducts.
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
The solution effectively reduces voiding, enhancing thermal and electrical conductivity by ensuring efficient evacuation of gases and oxides, thereby improving heat dissipation and device reliability.
Implementation Method 1
During reflow soldering, the gaps close from the center towards the boundary. This allows flux and gasses to escape the interface between the solder and the substrate.
Implementation Method 2
the channels increase the effectiveness of oxygen purging using inert or reducing gasses in the reflow chamber
Implementation Method 3
Metal solders are frequently used for mechanical bonding and heat dissipation through an interface between a heat source and cooling mechanism
Implementation Method 4
The thermal conductivity of Sn63Pb37 solder is 50 W/mK. Accordingly, this solder is able to effectively conduct the heat and electricity through the interface
Implementation Method 5
The most common method for removing metal oxides is to use a flux. Ideally, the flux removes the oxide film and takes it into the main flux body.
Data Source
AI summary
A solder preform has gaps extending from the boundary of preform towards the preform center. During reflow soldering, the gaps close from the center towards the boundary. This allows flux and gasses to escape the interface between the solder and the substrate. Particularly, flux accumulates in the spaces formed by the gaps and is forced to the edge of the solder preform as the gap closes. In further embodiments, channels are formed on one or both surfaces of the solder preform. In addition to further assisting in the escape of gas and flux during reflow, the channels and gaps increase the effectiveness of oxygen purging using inert or reducing gasses in the reflow chamber. Additionally, the channels and gaps increase the effectiveness of vacuum solder.