Precision Brazing Services

By applying a force during precision brazing, we can reduce the uncertainty of whether or not the mating surfaces are predictably seated against one another. The force can be applied through the use of a deadweight, hydrostatic pressure, differential thermal expansion effects, or an active force from a hydraulic ram.

With increasing frequency, there are instances where the design of a brazed joint is constrained by assembly features that would render the assembly “not brazeable” if conventional design criteria were applied. We have found that these assembly features are driven by factors that include:

• Component geometries that are becoming much smaller
• Materials innovations
• Market competitiveness
• New machining innovations

Thin film metalized ceramics for miniature feed-throughs used in medical devices require the use of specific biocompatible materials. Yesterday’s materials choices are not acceptable in these applications. Biomaterials are often reactive and limiting; accurately controlling the time-at-temperature makes some designs suitable that would otherwise not work.

A key factor in precision brazing is capillary action, which ensures proper filler metal distribution. It is of particular importance when brazing assemblies that incorporate microchannels and other small features.

These processes can provide a brief period of liquid at the joint interface, helping to achieve intimate contact. The liquid will solidify isothermally under correct processing to achieve high-strength bonds.

In conventional brazing, “in-stock” or “inventoried off-the-shelf” forms of filler alloy are used for the sake of convenience. In precision brazing, the alloy chemistry appropriate for the application is selected or developed to meet strength and environmental/service requirements.

In precision brazing, serious consideration is given to determining how much filler alloy should be used for a given assembly. The rule of thumb of using 125% to 150% of joint volume as the amount of filler alloy to employ is challenged.

Precise placement of the filler alloy is achieved using precision-fabricated pre-forms produced by EDM methods. They are used to help keep the filler alloy away from capillaries. These may be applied by:

• Foil, wire, and powder—by hand, pneumatic, or robotic techniques
• Wet plating
• PVD coatings

To impede the flow of filler alloy, channels (or even sharp corners) may be used.

Filler alloys may react to form lower-melting eutectics with consequences that are often difficult to predict. When performing precision brazing services, we frequently make use of metallurgical reactions to obtain optimal brazing results.

Knowing the joint volume is important in determining the amount of filler alloy to use. Our design engineers review assembly tolerances to assure that the assembly performs as intended in service and that an optimal amount of brazing filler metal is utilized.

Undesirable brittle inter-metallic reactions can be avoided by using rapid brazing processes.

With a time-temperature-applied force profile, fundamental parameters have the capacity to alter metallurgical reactions. VPE considers the role of each parameter carefully when designing critical assemblies.

• Interface chemistry
• Production tooling design
• Selective enabling or limiting capillary action
• Service environment—hermeticity, corrosive, temperature, stress, life, creep, and fatigue
• Temperature profile design