Lead-Free Conductive Paste Composition for Solder Dissolution Resistance
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Solution Overview
Problem
Conductive pastes used for forming electrodes on ceramic electronic components face issues with excessive crystallization of glass frits, leading to decreased fluidity and inadequate adherence and adhesion between fired films and substrates, especially when exposed to high soldering temperatures and acidic plating solutions.
Innovation Solution
A lead-free conductive paste composition comprising a silver-based conductive powder and an aluminoborosilicate-based glass frit with specific oxide content ratios (B2O3, SiO2, Al2O3, MgO, BaO, ZnO, and TiO2) is developed, which enhances resistance to solder dissolution and acid resistance while maintaining moderate fluidity and adherence to substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free glass frits are used in conductive paste to improve environmental compatibility, then acid resistance and solder dissolution resistance are improved, but excessive crystallization occurs during firing leading to decreased fluidity and inadequate adherence to substrates
Solution Approach 1:
The patent modifies the chemical composition parameters of the glass frit by incorporating specific amounts of ZnO (0-10 wt%) and TiO2 (0-5 wt%) along with the base aluminoborosilicate composition. These compositional parameter changes adjust the crystallization behavior and melting characteristics of the glass frit, enabling it to maintain adequate fluidity during firing while still providing excellent acid and solder dissolution resistance in the final fired state.
Solution Approach 2:
The patent creates a composite glass frit system combining aluminoborosilicate base glass with zinc oxide and titanium oxide additives. This composite material approach allows the glass frit to exhibit multiple functions: the base glass provides acid and solder resistance, while the ZnO and TiO2 components modulate the crystallization process to maintain fluidity and improve adherence to ceramic substrates during the firing process.
2Reliability
If high-melting-point lead-free solders are used to improve environmental compatibility, then solder dissolution of conductive powder increases at high temperatures
Solution Approach 1:
The glass frit acts as an intermediary protective layer between the conductive powder (silver-based) and the high-melting-point solder. The specific glass composition with ZnO and TiO2 creates a more stable interface that reduces the chemical interaction and dissolution of conductive powder into the solder, even at high soldering temperatures, while maintaining environmental compatibility through lead-free formulation.
3Reliability
If glass frit crystallization is increased to improve acid resistance, then fluidity during firing decreases and adherence to substrate becomes insufficient
Solution Approach 1:
The patent carefully controls the crystallization parameters of the glass frit by adjusting the ZnO and TiO2 content within specific ranges. This controlled parameter change allows the glass frit to develop sufficient crystalline structure for acid resistance while preventing excessive crystallization that would harm fluidity and substrate adherence during the firing process.
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 conductive paste achieves excellent resistance to solder dissolution and acid resistance, with improved adherence and adhesion to substrates, even when using high-melting-point solders, and forms dense metal-glass fired films with high adhesive strength.
Implementation Method 1
crystallization of glass frit is facilitated in firing the conductive pastes, fine crystals precipitate in a network form on a conductor film to densify the film structure of the conductor film
Implementation Method 2
the conductive paste is applied by various methods such as screen printing, dipping, and brush coating so as to form a predetermined pattern form onto a terminal part of a ceramic electronic component or the like and then fired at a high temperature of approximately 700 to 950°C to thereby form a conductor film
Implementation Method 3
Use of a solder having a high melting point causes a metal contained as a conductive powder in a conductive paste to diffuse and dissolve in the melted solder
Data Source
Figure 1
AI summary
A conductive paste comprising a conductive powder, a glass frit substantially free of lead, and an organic vehicle, wherein the glass frit contains 25 to 50 mol% B in terms of B2O3, 25 to 50 mol% Si in terms of SiO2, 7 to 23 mol% Al in terms of Al2O3, 2 to 15 mol% Mg in terms of MgO, 2 to 5 mol% Ba in terms of BaO, one or two selected from the group consisting of 3 to 18 mol% Zn in terms of ZnO, and 3 to 8 mol% Ti in terms of TiO2, based on the total number of moles in terms of the above oxides. According to the present invention, it is possible to provide a lead-free conductive paste having excellent resistance to dissolution in solder and acid resistance as well as being capable of forming fired films having excellent adherence and adhesion to a substrate.