NanoBond®
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NanoBond® is RNT’s patented process for bonding components utilizing NanoFoil®. Activated by a small pulse of energy, in a fraction of a second, NanoFoil® delivers the necessary amount of heat and energy to reflow solder or braze and create a strong, true metallic joint. The process enables high strength, high conductivity bonds between most combinations of materials making it ideal for many joining and assembly operations.
RNT has developed and tailored its patented NanoBond® process with each of its customers in mind. The multilayer foil is placed between two components to be bonded, along with two layers of solder, either pre-applied to the components or freestanding. Pressure is applied to prevent the components from moving, and the chemical reaction between the Al and Ni layers in the foil is activated. Heat from the NanoFoil’s reaction melts the solder or brazed layers and enables metallic bonding at room temperature in fractions (thousandths) of a second.
Our Applications: Please visit our Applications pages to find out how RNT can meet your specific application’s needs, or contact our applications engineering team directly with your technical questions.
NanoBond®: The Process for Using NanoFoil®
NanoBond® is the process of bonding two components with solder using NanoFoil® as a heat source. When activated, the foil creates a self sustaining reaction that acts as a rapid and controllable localized heat source to melt adjoining solder layers, bonding components together. Processing details vary with components, but some basic bonding details are:
- NanoFoil® selection and sizing
- The 3Ps - plating, planarity, and pressure
- NanoFoil® activation
NanoFoil® Selection and Sizing
NanoFoil® is available as:
- Standard NanoFoil® - a localized heat source that, when combined with solder performs or a solder-coated surface (<450°C), can be used to join two materials together.
- Tin-Plated NanoFoil® - standard NanoFoil® coated with 10μm of pure tin on both sides. Tin-plated NanoFoil® only requires solderable surfaces to create a bond.
The NanoFoil® should match the size and shape of your bondline, with the exception of exposed foil for activation if necessary (see the section on NanoFoil® Activation below). The foil should be oversized 1mm for any holes, or undersized 1mm for any edges that need to be clear of solder to prevent overspray of solder and foil material. Thicker NanoFoil® can be used to join materials in the brazing range of 450°-700°C.
NanoFoil® Availability and Properties*
| Standard Thicknesses (μm) | 40, 60, 80 |
|---|---|
| Tin Plated Thickness (μm) | 40, 60, 80 |
| Minimum Available Size | 1mm x 1mm |
| Composition After Reaction | Ni50Al50 |
| Heat of Reaction | 1050-1250 J/g |
| Maximum Reaction Temp | 1350-1500°C |
| Thermal Conductivity | 35-50 W/mK |
*Please contact Indium Corporation for safety and handling
The 3 ps: plating, planarity, and pressure
Plating: Two Solderable Surfaces
A solderable surface is a surface to which solder will flow and wet without the help of flux. a solderable surface
is necessary for both standard and tin-plated NanoFoil®. Some recommended solderable finishes are:
- ENIG >1micron
- Gold- or silver-plating: 1-15μm
- Solder-plating: 10-15μm
- Hot plate soldering: 10-250μm
This table matches the component surface finishes with the recommended NanoFoil® types. NanoFoil® thickness is determined based on solder and component type, composition and sensitivity.
| Recommended NanoFoil® | Component 1 Plating | Component 2 Plating |
|---|---|---|
| Tin-plated | ENIG, Au, Ag | ENIG, Au, Ag |
| Tin-plated | ENIG, Au, Ag | Solder-plated |
| Standard using solder preforms* | ENIG, Au, Ag | ENIG, Au, Ag |
| Standard | Solder-plated | Solder-plated |
*Solder preforms can be used with NanoFoil® and appropriate surfaces
Planarity: Two Flat Surfaces
Another key component for a successful NanoBond® is the planarity of the components relative to one another and to the NanoFoil®. NanoFoil® can accommodate bowing up to 0.1% of the overall length in one or both of the components. Since the NanoFoil® reaction occurs in less than 5 milliseconds, flatter bonding surfaces will ensure better contact with the foil and prevent voiding or uneven bonding. In addition, flatter components will require less applied pressure to create a good bond (see image).
Pressure and Alignment
The pressure application requires three components: adequate pressure, uniform pressure, and constant pressure.
- Adequate Pressure: A spacer should be used to step the pressure to the size of parts being joined; actual pressure depends on planarity and part sensitivity. (i.e. a solid metal component may need 50psi, but a sensitive die may only be able to withstand 0.5 psi)
- Uniform Pressure: A compliant layer, such as foam, should be used to spread the load. We recommend 2# EVA Foam from Rubberlite.
- Constant Pressure: since solder will be molten for a few milliseconds during activation, constant feedback pressure from a hydraulic, air-driven or mechanical- driven (spring) press or fixture is required.
Alignment is also an important part of the activation process as parts can shift during if they are not properly aligned. (See Figure 1)
NanoFoil® Activation
NanoFoil® can be activated with a small pulse of local energy applied using optical, electrical, or thermal sources. Applying energy at a local point is just as important as the amount of energy applied.
- Thermal: soldering iron or 250°C temperature
- Electrical: resistance soldering iron or a battery (50 watts of power)
- Optical: laser
NanoFoil® must be in direct contact with the energy source when activated. In most cases, this requires oversizing the foil or cutting a tab in the foil. However, once activated, foil outside of the bond will leave a brittle metallic alloy that may need to be cleaned. Sizing the NanoFoil® to the exact bondline and activating it with a laser or fine wire will eliminate this post reaction material.
Application Highlight
Power Amplifier Packages can be bonded with the NanoBond® process. Using existing ENIG-coated packages with flanges for attach allow for the use of tin-plated NanoFoil® without oversizing, with access to the foil through the flange. Bonding details below:
- Solderable surfaces:
- Power amp - ENIG
- Heat-sink - gold
- NanoFoil®: 40μm tin-plated
- Sizing: footprint of bond including flanges
- Planarity: parts measured .05% of total length
- Pressure
- 500lb hand spring press
- 1⁄4" thick foam
- 50 psi
- Activation
- American Beauty resistance soldering iron
