Indium is commonly used to suppress the melting point of various alloys. These low-temp indium alloys range in solidus temperature from 157°C to 7°C. That’s right; some of the alloys melt below room temperature!
For this very same reason, indium is also used in higher temperature solder alloys and even braze alloys. The addition of indium allows us to use alloy families that would normally be too high temperature for certain applications. One such alloy family is the Silver-Copper braze system.
The Silver-Copper family of brazes has two main indium-containing variations:
- 61.5%Ag/24%Cu/14.5%In (which has a solidus temp of 625°C and a liquidus temp of 730°C)
- 63%Ag/27%Cu/10%In (which has a solidus temp of 685°C and a liquidus temp of 730°C)
Non-indium alternatives can be used (including cadmium, zinc, lead, and phosphorus), although indium is a superior additive in Ag/Cu brazes because it is:
- non-toxic
- ROHS compliant
- a low vapor element (important for vacuum furnace applications)
Although braze alloys are higher temperature materials than solders, even brazing can benefit from lowered process temperatures (due to the addition of indium). Here's why:
1) Less stress on parts
Less heat in any soldering or brazing application translates to less stress for the components involved. This is due to less thermal expansion during the bonding process.
2) Improved wetting of ferrous alloys
The addition of indium into the Silver-Copper system is known to improve wetting to ferrous metals.
3) A usable plastic range
Since there is a gap between the temperatures that these alloys start melting and turn completely liquid, they are especially useful for brazing applications with uneven surfaces where a fully liquid braze may start dripping away from the joint area.
4) Increased profits
This is due to reduced energy consumption, reduced rework (due to less stress on parts), and reduced field failures.
If you’d like to explore using an indium-contained braze material in your application, you can reach one of our knowledgeable Applications Engineers here: AskUs@Indium.com
~Jim