Sn-Ag-Cu-Sb-Ni Solder Bonding for Back Metal Separation Control
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Solution Overview
Problem
In electronic component bonding, the Ni layer in the back metal diffuses into the solder alloy during melting, leading to separation issues between the back metal and the solder alloy, resulting in poor wetting and potential chip cracking due to stress and void formation, especially under varying environmental conditions.
Innovation Solution
A method using an Sn-Ag-Cu-Sb-Ni solder alloy with controlled cooling and pressure reduction steps to prevent the coarsening of Sn-Sb intermetallic compounds, ensuring the solder alloy layer remains between intermetallic compound layers, thereby relaxing stress and preventing separation, non-wetting, and chip cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the liquidus temperature of the solder alloy is increased by adding a large amount of Sb, then the solder alloy can prevent melting during mounting, but the solder alloy may be softened at temperatures near the liquidus temperature causing resistance value changes
Solution Approach 1:
The patent changes the chemical composition parameters of the solder alloy by adding Ni (0.01-1 mass%) and Cu (0.1-5 mass%) to the Sn-Sb system. This modifies the phase diagram and solidification characteristics, allowing the alloy to maintain high strength at temperatures near the liquidus point while preventing softening, thus resolving the contradiction between high liquidus temperature and resistance stability.
2Strength
If a Ni layer is provided on the barrier layer to improve wettability, then adhesion strength is enhanced, but Ni diffuses into the solder alloy during melting causing separation between back metal and solder alloy
Solution Approach 1:
The patent introduces Cu as an intermediary element between Ni and the Sn-Sb solder alloy. The Cu layer acts as a diffusion barrier that prevents Ni from dissolving into the solder during melting, while still allowing wetting to occur. This resolves the contradiction by maintaining adhesion strength through the Ni-Cu-Sn-Sb system while preserving back metal layer stability.
Solution Approach 2:
The patent creates a composite back metal structure with multiple layers (barrier layer, Ni layer, Cu layer) that work together. The composite structure allows each layer to perform its specific function: barrier layer prevents Si diffusion, Ni layer provides wettability, and Cu layer prevents Ni dissolution into solder, thus resolving the contradiction between adhesion and compositional stability.
3Stability of the object's composition
If the back metal layer is multilayered to prevent Ni diffusion, then diffusion is reduced, but separation between back metal layers or between back metal and solder alloy occurs
Solution Approach 1:
The Cu layer serves as an intermediary between the Ni layer and the Sn-Sb solder alloy, preventing direct contact and separation. It acts as a buffer zone that maintains bonding strength while preventing the formation of brittle intermetallic compounds that cause separation, thus resolving the contradiction between compositional stability and bonding strength.
4Reliability
If Sn-Sb-based solder alloy is used to prevent melting during mounting, then high liquidus temperature is achieved, but void formation and non-wetting occur due to poor wettability
Solution Approach 1:
The patent modifies the compositional parameters of the Sn-Sb alloy by adding Ni and Cu, which changes the wetting characteristics and solidification behavior. The modified alloy composition promotes better wetting of the back metal layers while maintaining high liquidus temperature, thereby preventing void formation and non-wetting issues.
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 method effectively prevents separation of the back metal from the solder alloy, ensuring reliable bonding and improved heat dissipation by maintaining the Ni layer and reducing void formation, thus enhancing the reliability and durability of the solder joint.
Implementation Method 1
heating the substrate above which the electronic component has been placed via the solder alloy at a temperature in a heating temperature region being at least 10°C higher than a liquidus temperature of the solder alloy, such that the solder alloy turns from a semi-molten state to a molten state and the molten solder sufficiently wets and spreads over the back metal
Implementation Method 2
the molten solder sufficiently wets and spreads over the back metal of the electronic component and the Ni plating of the substrate
Implementation Method 3
cooling in a temperature region of from precipitation start temperature of an Sn-Sb intermetallic compound phase to 230°C for 5 seconds or more and 2 minutes or less
Implementation Method 4
improving heat dissipation by maintaining the Ni layer and reducing void formation, thus enhancing the reliability and durability of the solder joint
Data Source
Figure 1(a)~1(d)
Figure 2
Figure 3(a)~3(d)
AI summary
Provided are: a soldered joint which suppresses detachment between a back metal and a solder alloy during formation of the soldered joint, and which offers higher reliability by suppressing non-wetting of the solder alloy, splashing of molten solder, and breakage of an electronic component due to chip cracking; and a method for forming such a soldered joint. In this soldered joint, an electronic component equipped with a back metal is bonded to a substrate via a solder alloy. The solder alloy has: a solder alloy layer having an alloy composition comprising, in mass%, 2-4% of Ag, 0.6-2% of Cu, 9.0-12% of Sb, 0.005-1% of Ni with the remainder being Sn; a Sn-Sb intermetallic compound phase; a back metal-side intermetallic compound layer; and a substrate-side intermetallic compound layer. The solder alloy layer is interposed between the Sn-Sb intermetallic compound phase and the back metal-side intermetallic compound layer and/or between the Sn-Sb intermetallic compound phase and the substrate-side intermetallic compound layer.