FAQ

S-Bond solders can be ordered in a variety of Kits or in bulk. S-Bond 220, 220-50, 220M are available in wire, pellet, or ingot form and in foil upon special request. S-Bond 400 is available as wire and all other alloys are developmental and are only available in small ingots or in other forms by special order. Contact us for S-Bond bulk alloy pricing and availability.

Active solders have elements added to their base compositions which react with oxides and other compounds that form naturally on metal and ceramic surfaces. Current S-Bond solders are specifically made active with the addition of Ti and rare earth elements to Sn or Zn based solders. These reactive elemental additions enable the soldering of most metals and ceramics to, without flux, promote wetting and adherence to many metal and ceramic surfaces, provided the oxides on the melting solders are disrupted in the joining process. The key feature of active solders is that they are “self fluxing” as they are melted and join a wide range of base materials without the need for added chemical fluxes or plating.

All S-Bond solders are lead (Pb) -free unless one requests a special Pb-containing active solder formulation. For additional safety information check our Material Safety Data Sheets (MSDS).

S-Bond joints (solder joints) shear strengths run from 3,000 – 6,500 psi (20 – 45MPa), as compared to braze joints which may be 5 – 10 x stronger. S-Bond joints are soft solder joints but unlike conventional solders, S-Bond joins a wide range of metals and ceramics, all without flux, and result in excellent solder joint strengths. S-Bond solders, with their Ti additions, contain fine hard phase dispersions that act to increase the higher temperature strengths [ 70% of RT tensile strength to 190°C] and increases the creep resistance of the S-Bond filler metal.

S-Bond joining can be very cost effective. The cost effectiveness does depend on the application, the bond area and the materials being joined. Although the cost of bulk S-Bond solders can be over 6x the cost of conventional solders, the joining process does not require flux or pre-plating, thus eliminating post solder cleaning to remove flux and plating costs thus lowering overall joining cost. When joining ceramics to metals, S-Bond joining processes have fewer processing steps and is a more reliable and re-workable, thus lowering the cost of ceramic metal joining.

The issues to consider are 1) expected service temperature and temperature cycles, 2) expected service environment (gases, chemicals, etc.) , 3) expected service stress , 4) chemical compatibility of the adjoining metals (for example, uncoated aluminum to graphite … is an electrochemical battery cell) and the mismatch in coefficients of expansion (CTE).

S-Bond alloys are good in service from at least -50 C to 380C, depending on the S-Bond alloy. S-Bond alloys are either Sn or Zn based and in certain environments are subject to corrosion and other chemical attack. S-Bond strengths are like those of other soft solders (see above).

Finally and perhaps most importantly, S-Bond can reduce but not totally solve the issue of mismatch of thermal expansion when joining dissimilar materials. S-Bond processes will heat component to join them in their melting ranges, from 115 – 450°C. Upon cooling from the joining temperature, the differential of thermal contraction must be able to be accommodated by design or the part will either distort, the ceramic will crack or the solder joint will fracture. Solder interfaces must be minimized by making smaller bonded areas and perhaps breaking components into tiles to better adjust the strain differences. See our blog or contact us for design guidance.

Mechanical activation of active solders is the process by which S-Bond solders wet and adhere to metal and ceramic surfaces. The activation process our fluxless procedure used to break up the oxide films that exist on and/or form continually during the melting of S-Bond active solders. The breaking up process is akin to the breaking of an eggshell. When the thin oxide shell is disrupted, the molten S-Bond spreads and contacts the metal and/or ceramic surfaces to which the S-Bond adheres and/or metallurgically interacts. Mechanical activation processes include brushing, rubbing, sliding, or ultrasonic agitation.

Aluminum and copper are readily joined by S-Bond soldering. Since the S-Bond process is fluxless the copper and aluminum can readily joined and aggressive chemical used to flux aluminum for conventional soldering to not interfere with the copper solder adherence. The process works by coating (brushing, wiping, or ultrasonic agitation) the copper, aluminum or both with molten S-Bond. Once coated, these “tinned” surfaces are slid or pressed together, while the S-Bond solder is still, after which a light load is applied and the joint area is cooled to solidify the joint.

Molten metals such as solders do not readily wet and adhere to graphite and/or ceramics due to the chemical characteristics of their surfaces. To promote wetting and adhesion, S-Bond has developed a proprietary procedure to S-Bond metallize materials such graphite, carbon, carbide and all ceramic surfaces prior to soldering. This process incorporates a high temperature vacuum treatment process to react S-Bond alloys’ active elements with the bonding surfaces. The procedure melts and reacts S-Bond to their surfaces in preparation for a post treatment S-Bond, mechanically activated joining process at much lower “soldering” temperatures. This process yield excellent, strong and hermetic joints… more on graphite joining… more on ceramic joining.