SnBi Solder Paste with Preform Diffusion for Drop Impact Resistance
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Solution Overview
Problem
The use of low-temperature lead-free solders for printed circuit boards, such as SnBi eutectic solder compositions, results in brittle solder joints that are prone to failure under drop impacts in small electronic devices, and existing methods to enhance strength either require higher reflow temperatures or do not effectively reduce power consumption.
Innovation Solution
A soldering method using a SnBi-based low-temperature solder paste with a preform composition of Sn-Ag, Sn-Cu, or Sn-Ag-Cu, where the preform is added in a specific ratio to the solder paste to diffuse into the SnBi solder, forming a stronger intermetallic compound layer instead of a Bi-rich layer, allowing for reflow under lower energy conditions and improved impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If SnBi-based low-temperature solder paste is used, then power consumption is reduced and low heat resistance electronic parts can be used, but the solder joints become brittle and have low resistance to drop impacts
Solution Approach 1:
The patent applies composite materials by combining SnBi-based solder paste with preforms made of Sn-Ag, Sn-Cu, or Sn-Ag-Cu alloys. This creates a composite solder joint structure where the SnBi matrix provides low melting point and power savings, while the dispersed preform particles contribute Ag, Cu, or Sn that react to form intermetallic compounds, enhancing the strength and impact resistance of the otherwise brittle SnBi solder joint.
Solution Approach 2:
The patent changes the chemical composition parameters of the solder joint by controlling the diffusion of Ag, Cu, or Sn from the preforms into the SnBi solder paste during reflow. By adjusting the preform composition and quantity, the patent modifies the intermetallic compound layer formation to achieve optimal balance between low-temperature processing and mechanical strength.
2Temperature
If Sn-Bi solder composition is used, then melting temperature is reduced enabling low heat resistance parts to be used, but the solder joints fracture at the bonding interface under drop impacts
Solution Approach 1:
The patent creates a composite solder structure by embedding preform particles (Sn-Ag, Sn-Cu, or Sn-Ag-Cu) within the SnBi solder matrix. During reflow, the preforms partially dissolve and react with the SnBi to form intermetallic compounds at the bonding interface, creating a reinforced composite structure that maintains the low melting point of SnBi while significantly improving reliability under mechanical stress.
Solution Approach 2:
The preforms act as intermediaries that facilitate the formation of intermetallic compound layers between the solder and the bonding surfaces. These preforms serve as a mediator that transforms the inherently brittle SnBi solder into a more reliable joint by introducing reactive elements (Ag, Cu, Sn) that form strengthening intermetallic phases during the soldering process.
3Strength
If preform is added to solder paste, then intermetallic compound layer is formed improving strength, but reflow temperature must be higher than without preform
Solution Approach 1:
The patent optimizes the reflow temperature parameter by selecting preform materials (Sn-Ag, Sn-Cu, or Sn-Ag-Cu) and quantities that enable intermetallic compound formation at temperatures compatible with low-heat-resistance electronic components. The composition and amount of preform are carefully controlled to achieve sufficient intermetallic layer formation without requiring excessive temperature increases beyond the SnBi melting point.
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 achieves solder joints with resistance to drop impacts comparable to SnAgCu solders, reducing power consumption and enabling the use of low-heat resistance electronic parts while maintaining reflow under standard conditions.
Implementation Method 1
to diffuse at least one solder composition selected from a Sn-Ag, a Sn-Cu, and a Sn-Ag-Cu solder composition into a SnBi-based low-temperature solder
Data Source
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AI summary
Problem: Even if the strength of a solder composition close to a SnBi eutectic composition was improved, it was brittle, so when it was used for small electronic devices such as mobile phones or notebook computers, the resistance to drop impacts when the small electronic equipment was dropped was low. Therefore, interface peeling often took place between the soldered surface and a printed circuit board, resulting in the devices being destroyed. Means for Solving the Problem: When soldering using a solder paste containing a SnBi-based low-temperature solder, at least one type of solder composition selected from a Sn-Ag, a Sn-Cu, and a Sn-Ag-Cu solder composition is diffused into the solder paste by simultaneously supplying at least one type of preform selected from a Sn-Ag, a Sn-Cu, and a Sn-Ag-Cu solder composition, whereby resistance to drop impacts is improved.