Mixed Alloy Solder Paste for Multi-Reflow Bridging Prevention
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Solution Overview
Problem
In the packaging process of MEMS sensors, the remelting of solder paste during multiple reflow soldering stages can cause bridging between soldering points, leading to product failure.
Innovation Solution
A mixed alloy solder paste comprising a first solder alloy powder with a solidus temperature of 200° C. to 260° C., such as Sn—Cu or Sn—Cu—Ag, and a second solder alloy powder with a lower solidus temperature, typically below 250° C., including alloys like Sn—Ag or Sn—Ag—Cu, is used, along with a solder flux, to inhibit remelting and enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-temperature solder is used for first-stage packaging, then bonding strength is improved, but solder paste remelting occurs in subsequent reflow soldering causing bridging
Solution Approach 1:
The patent changes the melting point parameter of the solder paste by creating a mixed alloy composition. The solder paste contains a first solder alloy (Sn-Cu or Sn-Cu-Ag with solidus temperature 200-260°C) and a second solder alloy (Sn or Sn-based alloy with solidus temperature below 250°C). This dual-alloy composition enables the solder paste to have different melting characteristics at different temperature stages, preventing remelting during subsequent reflow soldering while maintaining strong bonding.
Solution Approach 2:
The patent uses a composite solder paste material composed of two different solder alloys with distinct melting characteristics. The first solder alloy (Sn-90Cu-10 or Sn-87Cu-11Ag-2) provides high-temperature bonding strength, while the second solder alloy (Sn-99.3 or Sn-96.5Ag-3.5) prevents remelting at lower temperatures. This composite material approach resolves the contradiction between achieving strong bonding and preventing bridging.
2Device complexity
If multiple reflow soldering processes are performed, then assembly complexity is reduced, but solder paste remelting causes functional failure
Solution Approach 1:
The patent modifies the thermal parameter (melting point) of the solder paste to enable multi-stage reflow soldering. By incorporating a first solder alloy with solidus temperature of 200-260°C and a second solder alloy with solidus temperature below 250°C, the solder paste remains stable during subsequent reflow processes, allowing integrated packaging without causing bridging or functional failure.
3Reliability
If solder paste with lower melting point is used, then remelting is inhibited in subsequent reflow, but bonding strength at first-stage packaging is reduced
Solution Approach 1:
The patent optimizes the melting point parameters of the solder paste components. The first solder alloy (Sn-90Cu-10 or Sn-87Cu-11Ag-2) with solidus temperature of 200-260°C ensures strong bonding at high temperature, while the second solder alloy (Sn-99.3 or Sn-96.5Ag-3.5) with solidus temperature below 250°C prevents remelting during subsequent reflow. The specific compositional ratios are carefully controlled to balance bonding strength and remelting resistance.
Solution Approach 2:
The patent creates a composite solder paste where the first solder alloy (providing bonding strength) and second solder alloy (providing remelting resistance) work synergistically. The mixed alloy composition enables the solder paste to exhibit both strong bonding characteristics at high temperature and resistance to remelting at lower temperatures, resolving the contradiction between bonding strength and remelting resistance.
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 mixed alloy solder paste achieves a variable melting point, preventing bridging and ensuring reliable assembly and packaging by forming a soldering seam with improved bonding and a higher melting point, thus preventing functional failure during multiple reflow soldering processes.
Implementation Method 1
a first solder alloy powder in an amount ranging from 30% to 95% by weight, the first solder alloy powder including a first solder alloy with a solidus temperature of 200° C. to 260° C.
Implementation Method 2
heating to melt the solder paste using the reflow soldering process to form a soldering seam connecting the first device and the second device
Data Source
AI summary
A solder paste includes a first solder alloy powder in an amount ranging from 30% to 95% by weight. The first solder alloy powder includes a first solder alloy with a solidus temperature of 200° C. to 260° C. The first solder alloy includes an Sn—Cu alloy or an Sn—Cu—Ag alloy. The solder paste further includes a second solder alloy powder in an amount ranging from 5% to 70% by weight, and a solder flux. The second solder alloy powder includes a second solder alloy with a solidus temperature below 250° C. The solder paste has a variable melting point. In multiple reflow soldering, a remelting of the solder paste is inhibited under different temperature conditions so that no functional failure occurs during assembly and/or packaging of PCBs or electronic devices due to melting of solder.