Indium for Bonding Non-Metallic Materials
Indium and high indium alloys will coat non-metallic materials when the molten metal is gently rubbed against the surface of the non-metal. Materials on which this coating ability can be utilized include glass, mica, quartz, glazed ceramics and certain metallic oxides.
Surface Preparation
Adhesion to the substrate occurs due to formation of a connecting layer of indium suboxide during the soldering process. Therefore, flux is not used during the final soldering operation since that would prevent formation of the critical suboxide.
Before bonding, thoroughly clean the non-metallic substrate with a strong alkaline cleaner. Rinse with distilled water and then with electronics grade acetone or alcohol. In the case of glass, quartz or glazed ceramics, adhesion is enhanced by heating the material to about 350°C then cooling to about 200°C. At this time, apply indium to the heated non-metal using an indium applicator. Rub gently until the non-metal is coated with a thin film of indium.
To bond two non-metallic substrates together, precoat each surface with indium as described above. Bring the two pretinned substrates in contact with each other and reflow at 20-30°C above the liquidus temperature of the solder used to pretin.
To bond a non-metallic substrate to a metallic substrate, precoat the non-metallic surface as described above. Pretin the metallic surface with the same indium alloy as used on the non-metallic surface, using an appropriate flux. Completely remove the flux residue. Bring the two pretinned surfaces in contact with each other and reflow at 20-30°C over the liquidus temperature of the solder used to pretin.
In most cases, ultrasonic energy like that generated by an ultrasonic soldering iron or pot is effective in promoting wetting of the surface. Bond strengths of 400-700 lbs/sq in. are typical of this bonding technique.
See our Wire Selector Kit for a choice of alloys to test in your application. Or call one of our Applications Engineers for more information.
Bonding Procedure
In the case of glass, quartz or glazed ceramics, adhesion is enhanced by first heating the material to about 350°C (to drive off contaminates) and then cooling the material to 20°C to 30°C above the liquidus temperature of the selected solder, at which time the solder should be applied. Use an indium plated nickel felt (included in kit) or similar applicator and apply the solder by rubbing it gently until wetting occurs.
After the surface is coated, it is joined to the second surface at the soldering temperature and then allowed to cool to room temperature. In some instances, an ultrasonic soldering iron is effective in promoting initial wetting of the surface. Bond strengths between 400 and 700 PSI can be expected using this technique.
| Indalloy # |
Temperature °C | Tensile Strength (PSI) |
Electrical Conductivity % of Copper |
Thermal Coefficient of Expansion Micro in / C at 20°C |
Thermal Conductivity Watts / Cm C at 85°C |
Comp. | |
|---|---|---|---|---|---|---|---|
| Liquidus | Solidus | ||||||
| IE* | 118 | 118 | 1720 | 11.7 | 20 | 0.34 | 52In 48Sn |
| 3 | 237 | 143 | 1650 | 22.1 | 15 | 0.67 | 90In 10Ag |
| 4 | 157 | MP | 273 | 24.0 | 29 | 0.86 | 100In |
| 290* | 143 | 143 | 800 | 23.0 | 22 | 0.73 | 97In 3Ag |
| ( * Eutectic ) , ( MP = Melting Point ) | |||||||
