S-Bond® Solders At the Interface of the NanoBond® Process

January 27th, 2012
NonoBond heating process1 300x149 S Bond® Solders At the Interface of the NanoBond® Process

Figure 1. Illustration of the NanoBond® / NanoFoil® heating process® (from www.indiumcorp.com)

S-Bond active solder layers have been shown in many applications to be the key ingredient that permits many ceramics and refractory metals to be bonded to largely coefficient of thermal expansion (CTE) mismatched metals such as aluminum and copper. Indium Corporation offers a NanoBond® process that uses NanoFoil ® as local heat source to remelt preplaced solder layers without the need for the bulk heating of assembled components that have large CTE mismatch. Active S-Bond solders are applied as prelayers and have Ti, Ce, Ga and Mg additions that permit them to wet any ceramic or metal surface. Once the S-Bond pre-layers are applied to ceramic and/or metallic surfaces, conventional solders can be reflowed onto the S-Bond layer to create the preplaced solder layers that are remelted and bonded via the heat emitted from an ignited NanoFoil®. Figure 1 illustrates how temperatures of over 1,400 K are generated by an ignited nano-engineered foil.

Figure 2 illustrates the use of S-Bond in the NanoBond® process in bonding sputter targets.

s bond applied nanobond process S Bond® Solders At the Interface of the NanoBond® Process

Figure 2. An illustration of S-Bond being applied in the NanoBond® process

NanoFoil® , sold by Indium Corporation, is used on the Nanobond® process as a heat source to only locally reheat a pre-soldered interface with an instantaneous release of heat energy for joining applications. NanoFoil® is a nano-engineered material fabricated by vapor-depositing thousands of alternating nanoscale layers of Aluminum (Al) and Nickel (Ni), as shown in Figure 1. When activated by a small pulse of local energy from electrical, optical or thermal sources, the foil reacts to precisely deliver localized heat up to temperatures of 1500°C in fractions (thousandths) of a second. As a sacrificial heat source in soldering and brazing applications, NanoFoil® is ideal for high-temperature applications. NanoFoil® becomes a non-functional part of the solder or braze joint, eliminating the need for an oven or furnace and allowing for the use of higher temperature solders.

NanoFoil® works by acting as a local heat source to melt adjacent solder layers without heating the target or backing plate materials. This allows the bonding of nearly any combination of sputter target material and backing plate material, including ceramics to metals, irrespective of the difference in coefficient of thermal expansion (CTE). S-Bond solders enable the NanoBond® process in many applications by providing an “activated / bonded layer” on the ceramic or metal interface to which conventional solders can wet and adhere.

Contact us for more information on how S-Bond can assist your NanoBond® applications.

NanoFoil® and NanoBond® are registered trademarks of Indium Corporation.

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S-Bond Joining of High Brightness LEDs

January 27th, 2012

S-Bond active solder joining is emerging as an effective method to bond heat sinks to the back of High Brightness Light Emitting Diodes (HBLEDs). Active solders can wet and adhere to many of the thermally conductive ceramics (AlN, BeO, etc.) that are being used in HBLED’s and enable effective and thermally stable and conductive joints.

schematic hbled heat sink 300x170 S Bond Joining of High Brightness LEDs

Figure 1. Shcematic of HBLED with Heat Sink

Light-emitting diodes (LEDs) are semiconductor light sources used as indicator lamps in many devices and are increasingly used for lighting. LEDs were introduced as a practical electronic components in 1962 and now many versions are available across the visible, ultraviolet, and infrared wavelengths, and with very high brightness.

LEDs are created by depositing two thin layers of materials onto a substrate, one with an excess of electrons and the other having “holes” and needing electrons to achieve a more stable state. When a potential is applied across the device, the electrons and holes move in the opposite directions. This causes light to be emitted with a wavelength and color determined by the energy released when the electrons and holes combine.

High-brightness LEDs (HBLED) are a more recent development made possible by special deposition techniques. Such HBLEBs can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for regular LEDs. Some can emit over a thousand lumens. Since overheating is destructive, the HBLEDs must be mounted on heat sinks to allow for heat dissipation and to prevent device failure. See Figure 1 above that shows the elements on a HBLED.

hbled S Bond Joining of High Brightness LEDs

Figure 2. Picture of HBLED

One HBLED can now replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp. This opens up many new applications such as backlighting for displays, automotive lighting and new consumer products like flash for camera phones or compact projectors.

With the growing application of HBLED’s, the need for effective heat sink to device bonding increases. S-Bond active soldering processes offer one step, fluxless joining of these components without the need to preplate the ceramic with Ti, Ni, and/or Au. S-Bond can join directly to ceramics such as AlN and BeO heat sink substrates and then bond these heat sinks to copper and aluminum heat spreaders as indicated in Figure 2.

Contact us to see how S-Bond can be a solution for your HBLED joining requirements

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Fluxless Soldering of Sputter Targets

January 27th, 2012
schematic sputtering process Fluxless Soldering of Sputter Targets

Figure 1. Schematic of sputtering process

S-Bond soldering is seeing increased application for the solder bonding of sputter targets. Sputter targets are used in a wide range of applications for making thing films used in making electronic chips, solar cells, sensors, TV screens, optical components, electrical devices, and on and on… Sputter targets support a very large physical vapor deposition (PVD) and diverse technological base that is wide ranging and pervasive. Sputter targets under ion bombardment release target material atoms into a high vacuum chamber that under an electric field can be accelerated and deposited onto the component surface where the arriving atoms arrange themselves into a contiguous thin film. Figure 1 schematically illustrates the sputtering process. Ion bombardment is a high energy collisional process that can heat target materials to their melting points unless cooled; hence most sputter targets are bonded to a water cooled backing plate. Backing plates are made normally made from copper and are mounted to a water cooling manifold. Other metallic backing materials are also used. See Figures 2-3 for examples of bonded sputter targets.

sputter targets Fluxless Soldering of Sputter Targets

Figure 2. Example Sputter Targets

To manufacture sputter targets, the target materials, such as W, Ti, Cr, Al, Si, InSnO (ITO), Ce, Ga, Au, Pd, Ag, etc. need to be bonded to metallic backing plate. Soldering or diffusion bonding normally are used since a metallic joint is required in order to provide an electrically and thermally conductive structural joint. The soldering process has been a major bonding technique since soldering is simpler and more versatile and can bond a wider range of materials. For ceramic targets such as Indium Tim Oxide (ITO) and other ceramics and intermetallic targets, Indium solders have used. Indium is a mildly “active” metal that can interact with oxide surfaces and can bond a range of metals without extensive use of flux. Most Sn based conventional solders use flux to clean the backing plate surface and/or the plated target materials, but in the wide bond areas required for many sputter targets, flux is trapped in the interface, later causing contamination in high vacuum sputtering systems. Hence, fluxless soldering is desired. S-Bond and indium solders fit this requirement; however, Indium re-melts at 157°C where S-Bond begins to remelt at 220°C. This increased remelt temperature permits higher power inputs translating to higher sputter rates).

S-Bond solder joining is an active, fluxless process where the Ti, Mg, Ce and Ga in the S-Bond solders enable the solder to interact and wet directly to all metals including Cu, Al, Mo, Ti, W, and Si as well as most compounds and ceramics. Since S-Bond joining requires no plating nor does it use flux, the bonding is direct and complete with no flux filled voids.

sputter bond sputter targets Fluxless Soldering of Sputter Targets

Figure 3. Picture of a range of sputter bonded sputter targets

As sputter targets get larger and larger for applications such as 300 mm wafers and TV screens, large differences in coefficients of thermal expansion (CTE) make diffusion bonding impossible as cooling from the bonding temperatures distort and many times crack the targets. Soldering is preferred and the lower the temperature of the joining process the better. For conventional soldering of larger targets, Indium solder is preferred when since the lower melting temperature (157°C) of indium and its mildly active nature creates a bond with less CTE mismatch stresses. However, indium solders to lower the power input ratings and lowers the effective sputtering rates. As such, active Sn-Ag solders such as S-Bond can be used to create stronger bonds and higher temperature (remelts at 233°C) target operation.

In the last few years a new bonding process has emerged which improves the solder bonding of large sputter targets that have large CTE mismatch such as CIGS and ITO used in flat panel displays and in solar panels. The process is NanoBond®. It is a “no temperature” process and in combination with S-Bond as a “tinning layer” to wet the ceramics and refractory metals and in combination with Sn-Ag solder, large targets can be bonded. The NanoBond® process using S-Bond is described more fully in another blog article on this website, but in summary, using patented exothermically reactive foils, the heat generated by the preplaced Nanofoils® into bond interfaces that have been pre-tinned with solder, remelts the solder and bonds the target to the backing plated without bulk heating of the target / backing material.

The NanBond® process is sold through the Indium Corporation and they provide bonding services, materials and license their customers to utilize the NanoBond® process in combination with S-Bond solders to make larger sputter targets of widely mismatched CTE materials.

Contact us for more information on S-Bond solders and how we can improve your sputter target manufacturing processes.

NanoBond®; registered trademark of Indium Corporation.

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Soldering Silicon Carbide (SiC) for Electronics and Optics

January 27th, 2012
s bond joined sic 191x300 Soldering Silicon Carbide (SiC) for Electronics and Optics

Figure 1. Steel fitting S-Bond joined to SIC

S-Bond active soldering of silicon carbide (SiC) has recently been demonstrated on a range of electronic and optical components, providing for metal to SiC joints in plug, mounting and/or water cooling fittings. Silicon carbide is ceramic semiconductor with good thermal conductivity (120 W/mK) and low thermal expansion ( 4 ppm / °C). Thermal conductivity is comparable to aluminum with 1/8 of aluminum’s thermal expansion coefficient (CTE), making it a very stable material. The manufacture techniques for SiC and Si:SiC have recently developed to permit more complex SiC based components. As a ceramic, SiC is very difficult to machine so normally powder sintering and infiltration and/or slip casting and sintering followed by infiltration is used making for making complex shapes. Because of its thermal, electrical and optical properties, SiC and SiC composites are seeing increased industrial application in electronics and optics thus driving an interest for robust SiC joining methods. For high temperature SiC applications vacuum active brazing has proven effective; however, for lower temperature electronic and optical applications, there has been interest in solder joining methods.

The solder joining of SiC and SiC composites to metals have been a focus of S-Bond Technologies and it has developed

bonding ss fitting sic 150x150 Soldering Silicon Carbide (SiC) for Electronics and Optics

Figure 2. Another configuration bonding stainles steel fitting to SIC

bonding methods that incorporate the use of it active solders to bond SiC, ceramics and metals. S-Bond has successfully

bonded SiC and Si:SiC to metals such as stainless steel, Kovar, aluminum and copper to make mechanical connections, plugs and water fittings. Figures 1-2 below illustrate several stainless steel water fitting connections on SiC. The process starts with placing “S-Bond

metallization paste” onto the SiC areas that will require bonding and firing the paste at elevated temperature in vacuum. The elevated temperature causes the active elements in S-Bond paste to react with the SiC surfaces and produces a chemical (metallurgical) bond to the SiC surface that prepares the SiC surface for soldering [for other information on ceramic S-Bond joining, Click Here] .

Figure 3 shows the “as reacted” paste on the surface of a SiC feed through area where a metal fitting is to be bonded. The S-Bond metallization process is complete when the excess reacted solder paste is “scraped” off, exposing a shine S-Bond

metalized sic surface 150x150 Soldering Silicon Carbide (SiC) for Electronics and Optics

Figure 3. S-Bond metalized SIC surface after firing

metallized layer on the SiC surface, as seen in Figure 4. This metallized surface then can be soldered by adding a fresh layer of S-Bond 220 or other solders then bonding a “S-Bond (solder) tinned” metal surface.

These SiC to stainless steel joints are as strong as any solder joint and the joints are hermetic. Within the constraints of coefficient of thermal expansion (CTE) mismatch, any metal can be joined to SiC using the S-Bond active solders and processes. S-Bond active soldering has been demonstrated in a range of applications, showing that S-Bond can meet

many exacting bonding requirements in electronics and optics.

metalized sic surface final 150x150 Soldering Silicon Carbide (SiC) for Electronics and Optics

Figure 4. S-Bond metalized SIC surface after final preparation for soldering

For further information, Contact Us.

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Ultrasonic Soldering & Active Solders

October 10th, 2011

S-Bond® active solders are very effective in combination with ultrasonic soldering for a range of applications. Ultrasonic (U/S) soldering is a fuxless soldering process and is finding growing application in soldering of metals and ceramics from solar photovoltaics and medical shape memory alloys to specialized electronic and senor packages. U/S soldering has been reported since 1955 as a method to solder aluminum and other metals without the use of flux. The reason for expanding usage is that ultrasonic soldering is a fluxless process.

U/S soldering uses either ultrasonically coupled (piezoelectric ) heated solder iron tips (0.5 – 10 mm) or solder baths. These devices generate high frequency (20 – 60 kHz) acoustic waves to mechanically disrupt oxides that form on the molten solder surfaces and/or initiates cavitation in the solder pool which also mechanically disrupt oxide layers that naturally formed on metal surfaces being joined. Cavitation in the molten solder pool can be very effective in disrupting the oxide on many metals, however, it is not effective when soldering to ceramics and glass since they themselves are oxides or other non-metal compound that cannot be disrupted since they are the base materials. A schematic of the U/S soldering process is illustrated below.

ultrasonic soldering Ultrasonic Soldering & Active Solders

U/S soldering consists of heated soldering tips coupled to a piezoelectric crystal that is powered by an acoustic amplifier operating at 20 – 60 KHz. The tips for U/S soldering irons are also coupled to a heating element while the piezoelectric crystal is thermally isolated, not to degrade the piezoelectric element. The tip thus can heat (up to 450°C) and mechanically oscillate at 20 – 60 KHz. This soldering tip can melt solder filler metals as acoustic vibrations are induced in the molten solder pool. The vibration and cavitation in the molten solder then permits solders to wet and adhere to many metal surfaces. Initially, U/S soldering aimed at joining aluminum and other metals; however, with the emergence of active solders, much wider range of materials can be soldered c using ultrasonics as a form of mechanical activation.

U/S soldering is now expanding in application, since fluxless active solders are increasingly being requested for joining assemblies where either corrosive flux can be trapped or otherwise disrupt operation or contaminate clean production environments or there are dissimilar materials / metals / ceramic/ glasses being joined. In this expanded list of materials, active solders’ own nascent oxide on melting need to be disrupted and U/S agitation is well suited.

ultrasonic soldering dissimilar materials Ultrasonic Soldering & Active Solders

Active solders such as S-Bond and other activated solders that use rare earth elements, Ti, Hf, Zr or even indium all form a tenacious oxide on their molten surfaces and conventional solder fluxes to not disrupt these. In applications where the area of the solder joint is a small or band, U/S soldering using 1 – 10 mm tips can be very effective since the volume of molten metal is small and can effectively be agitated by the 1 – 10 mm U/S soldering iron tips. The figures in this article show the U/S soldering equipment (power supply and soldering tools-tips) and the application of solder to glass using U/S solder iron tips. In other larger surface bonding application, as shown in the image below, wide, heated U/S tips are being used to spread and wet active solders on large aluminum surfaces (and is applicable to other metal, ceramic and glass surfaces.

ultrasonic soldering surface bonding Ultrasonic Soldering & Active Solders

One can see that with the commercial introduction of active solders, such as S-Bond®, U/S soldering has expanded well past it use to aluminum and is finding wider and wider application. S-Bond Technologies maintains a U/S soldering development laboratory and offers both development and production services. Contact Us to evaluate if U/S soldering can be beneficial and applicable in your applications.

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S-Bond® 220M Developed for Silicon/Silicate Joining

October 10th, 2011

The direct solder joining of silicon is difficult posing solder wetting and adherence challenges for many applications including electronic “die” packages, sensor chips and solar panels. The direct solder bonding to silicon (Si) has been limited by the wetting resistance of angstrom thick nascent silicon dioxide (SiO2) layers that naturally forms on silicon. To combat these solder bonding challenges, metal plating (vapor deposition of Ti and Ni) has been used. To address this challenge, S-Bond Technologies has developed and has recently been awarded a patent for its S-Bond 220M alloy which is a Sn-Ag-Ti-Ce-Ga + Mg alloy that has been optimized for direct Si solder bonding without flux nor plating. The new alloy bonds well to silicon, silica, and glass silicates based on a solder formulation that adds magnesium (Mg) in low enough levels that does not change the solder melt behavior but enhances the “active” nature of S-Bond alloys to interact with oxides of silicon and many other metals even more effectively than other active solders. These Mg modified active solders wet and adhere very well to silicon based on mechanical activation used in other active solders.

In wetting tests the mechanism of Si adherence for S-Bond 220M was observed to be on the micro-scale, and can be seen as a metallurgical interaction on the Si surface with the Ti modified Sn-Ag phases. See the image below.

s bond reaction zone1 S Bond® 220M Developed for Silicon/Silicate Joining

In addition to direct solder bonding to Si, S-Bond 220M has been found to enhance the direct solder bonding of a wide range of metals to many ceramics, glasses and refractory metals. Due to its versatility and bonding to Si, silicates, ceramics and metals, S-Bond 220M is finding wide acceptance in solar panel manufacturing and sputter target bonding . Contact Us to discuss your needs to direct solder to silicon, silicates and other glass-ceramic-metals.

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Metal Soldering with Active Solders

October 10th, 2011

Active solders such as S-Bond have wide application in joining a wide variety of metals including aluminum, copper, stainless steel, titanium, all based on S-Bond alloys’ ability to directly wet and adhere to the metallic surface compounds. Using mechanical activation active solders such as S-Bond successfully join like and dissimilar metal combinations in a wide variety of applications, from heat sinks and sensors to medical/surgical devices.

Soldering of metals has always depended on the “disruption” of surface oxide or other compounds that naturally form on metals. These surface oxides need to be removed for molten solders to permit the liquid solder to “wet” and adhere to metallic surfaces. Thus in soldering, the major process component of soldering is removal of these compounds such that the molten solder can adhere and react with the underlying clean metal surface. In conventional soldering, chemical fluxes are used to remove surface oxides as the solder filler metals melt and flow onto to the surface the flux has just cleaned. Fluxes are nominally acids of differing activity, depending on the metals being soldered and the stability of the oxides that have formed on the metal.

Metals such as copper, nickel and iron naturally form oxides that are not as stable at the oxides that form on aluminum, stainless steel, and titanium and thus the fluxes and/or surface preparations prior to soldering differ. Copper and nickel are easily soldered with milder fluxes and/or rosins. Their oxides are easily reduced. On the other hand, aluminum, stainless steels and titanium, all known for their corrosion resistance (due to their stable surface oxides) are difficult to solder and either employ aggressive acidic fluxes or plating with either nickel or copper prior to soldering. After plating, then these corrosion resistant metals can be soldered with milder fluxes.

S-Bond’s active solders eliminate the flux requirement and the need for plating. With just mechanical activation, S-Bond alloys wet and adhere to all metals. There are two main mechanisms active solders adhere. These mechanisms are illustrated below.

active soders mechanisms Metal Soldering with Active Solders

On copper, copper alloys, aluminum and nickel metallurgical bonding occurs as the “active elements (Ti, Ce, Ga and/or Mg) interact with the base metals’ surface oxides, disrupt them and then the S-Bond elements react with the underlying metals to form intermetallic zones that provide the basis for adherence.

In more corrosion resistant alloys such as Ti and/or stainless steel S-Bond adherence is based in atomic attraction at the very local level. The surface oxide layers are not disrupted, but the “atmospheres” of the active elements in the S-Bond solders interact across the oxide layer and create attractive forces. The images below show the microstructural differences between these two “operative” S-Bond joining mechanisms. The aluminum / S-Bond image illustrates the S-Al-Ag phase that forms at the interface. The Ti / S-Bond interface shows excellent interface conformance but no resolvable reaction zone.

s bond interface adherence Metal Soldering with Active Solders
With these two metal bonding mechanisms, S-Bond active solders can join all metals with varying bond strengths. Bond lap shear strengths range from 2,000 – 8,000 psi (14-56 MPa). The bonding is metallic and offers good electrical and thermal conductivity. Another advantage of active soldering is the ability to directly solder dissimilar metals. When conventionally soldering, dissimilar metal joining presents challenges in selecting a compatible flux that can remove oxides on copper and aluminum at the same time while the solder reacts with the surface and many times only plating both sides of the joint is effective for soldering. In S-Bond active soldering the two different adhesion mechanisms operate in parallel on opposite sides of the joint, at the same time without flux, thus S-Bond is a one step process. Additionally, S-Bond joining is done at lower soldering temperatures and thus the process can mitigate the negative effects of thermal expansion mismatch when a soldered assembly cools from the soldering temperatures.

If you would like to evaluate S-Bond for your metal joining applications you may order a Test Kit or Contact Us to discuss the application and/or have us quote making prototype parts.

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Soldering vs. Brazing

July 8th, 2011

We receive many inquiries to silver solder, solder or braze components and many times there is confusion over this terminology and the various materials and processes used to bond metals, ceramic and/or glasses. This short article offers some clarification to the distinctions between soldering and brazing such that you can make informed decisions about your needs.

Brazing is a process where a molten metal is the joining agent (filler) between to materials where during the bonding process only the filler metal is melted. These molten fillers react with and adhere to the adjoining surfaces. AWS (American Welding Society) defines a material to be a braze filler when it melts over 450C°C (842°F). Example braze fillers include but are not exclusive to copper, copper-silver, Cu-P, and all copper alloys, Al-Si, NiCrBSi, Ni-P, FeCrBSi, gold, silver, palladium, etc.

Soldering is a related process to brazing and also employs molten metal fillers, with the exception (according to AWS definitions) that solder fillers melt below 450°C. Such fillers include lead-tin (Pb-Sn), Sn-Ag, Sn-Bi, Sn-Sb, Zinc, Zinc-Al, etc… these solders are used in electronics, plumbing, structural low temperature components, heat sinks and cold plates, sputter targets, etc.

Note there is some confusion over the term “silver solder”… in reality silver solder is a braze but this term has been adopted commercially since the fillers use copper-silver (Cu-Ag) alloys. These silver-solders are also associated with the term “hard solder” vs. soft solder… All “silver solders” are technically brazes since their melting temperatures are over 750°C (1382°F) and employ braze processes to make bonded components.

Is soldering or brazing more suitable? …. The answer is “it depends” on…

  • Strength requirements… brazed joints can be 3 – 10x the strength of soldered joints
  • Corrosion resistance… solders are generally more susceptible to oxidation and degradation from chemicals and salt since the fillers are Sn, Zn or Pb based.
  • Temperature assemblies can be exposed to… solders melt from 100 – 250°C and are generally used in electronics and other temperature sensitive parts.
  • Thermal expansion… differing CTE assembly materials benefit from soldering since lower joining temperature lowers distortion upon cooling and “softer” filler metals permit CTE mismatch to be accommodated.
  • Cost… soldering is generally a lower cost process with the filler metals being less expensive and the lower temperatures processing reduced post joining clean-up lowers overall joining costs.

So, chose the processes and filler metals most suited to your assemblies and their expected service temperatures, remembering soldering is generally less expensive and less sensitive to thermal expansion mismatch.

When comparing soldering to brazing and their related filler alloys, one begins to see the processing changes made necessary by the significantly different processing temperatures (100 – 450°C) for solders and 450-1,600°C) for brazing. The higher temperatures needed to melt brazing fillers makes oxidation of the filler metals and the base materials (being joined) much more of a concern and problem. Since oxidation and the subsequent oxides formed interfere with wetting and adherence, oxidation must be minimized and a means to remove any formed oxides must be used. Chemical fluxes are commonly used and the most effective fluxes melt and flow just before the melting temperatures of the filler metal and are not thermally decomposed in the range of temperatures where the filler metals melt. For solder filler metals, fluxes are normally rosin based or low temperature acidic compounds that when melted can react with tin, lead, silver, copper or nickel oxides.  For brazes, fluxes are normally organometallic salts, or higher temperature salts that when melted are acid and reduce the oxides forming on materials such as brass, steel, stainless steel and even aluminum. Normally to flux the more oxidation resistant materials (stainless steel and/or aluminum) very acidic and corrosive fluoride based acid are required.  Soldering fluxes, as a result of their composition, are much less aggressive and generally less corrosive than the fluxes used in brazing.

Alternatively, brazing is also commercial done in furnaces… and those furnaces can either produce a “fluxing atmosphere” such as in cracked ammonia (reduces oxygen activity while reducing oxide scales formed in steel and copper based materials).  Other furnaces exclude oxygen altogether by pumping the atmosphere out with vacuum pumps, then backfilling with inert or reducing gases (N2, Ar, or H2) pumping to high vacuum where the high vacuum really excludes oxygen and can in many metals reduce and/or evaporate the surface oxides on part. Thus “furnace brazing” many times is a preferred method over torch brazing due to temperature uniformity and part cleanliness after brazing.

Structural soldering (non-electronic) is generally not practiced in ovens since soldering temperatures are low.  Soldering irons (hot metal tips), propane torches (in brazing MAP and even acetylene torches are used for their higher heating capacity), hot air guns and hot surface plates are used. In high volume soldering for electronics, batch or continuous flow (belt) furnaces are employed to re-flow solder pastes that consist of a decomposable organic carrier, a flux and the solder filler metal powder. When heated in a “reflow” oven, reducing gases or more inert gases such as N2 can also be used, however, if mildly acidic or no clean fluxes are uses, air solder reflow ovens can be used.

The bottom line, once you have the terminology down, is to choose the most compatible (technically and economically) filler metal (solder vs. braze) then select the most suitable process compatible with that filler metal in combination with the assemblies’ components.

Feel free to Contact Us to assist in your selection process. We can evaluate the most suitable filler metals followed by the most appropriate process.

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Solar Panel Assembly

July 8th, 2011

S-Bond has demonstrated the assembly (stringing) of photovoltaic (PV) solar panels bonding aluminum or copper buss bars using their active solders (S-Bond) in combination with thermosonic bonding. Thermosonic bonding is the simultaneous application of ultrasonic agitation, pressure and heat, normally applied using commercially available ultrasonic soldering irons.

Commercial polycrystalline silicon photovoltaic (PV) cells currently utilize an aluminum powder applied metallization as the current collector for the electrons released by the incident solar energy collects at the aluminized surfaces. Commercial PV cells then require that a conductor strip be bonded to the aluminized cell back in order to transmit the electrons (current) from the cell to the adjacent cells that make up a solar power module in a solar panel assembly. The challenge has been electrically bonding to the aluminized (or otherwise coated) PV materials. Many times silver paint / plated pads has been applied to the coated PV cell followed by conventional flux soldering of pre-tinned thin copper strip to the silver pad

The S-Bond active solder process eliminates the need for pre-coating of silver (lowering cost) to the coated cell surfaces and eliminates the need to use flux (lowering cleaning costs while improving the working environment with no flux off gases). The figures below show how thermosonic bonding of S-Bond coated copper (or even aluminum) buss strip can be used to “string” PV cells together into solar panel modules. S-Bond can provide S-Bond alloys tinned with Copper (or aluminum) buss using an ultrasonic solder pot as illustrated below. For aluminum powder metallized PV cells, the ultrasonic tip is used to “burnish” and densify the areas for buss strip attachment. This treatments makes a dense well adhered, directly S-Bond solderable surface. Using a heated ultrasonically activated soldering tip, the tip can be robotically manipulated to press heat and activate the S-Bond solder in order to locally reheat, reflow and mechanically disrupt the local oxides on the melting solders such that a metallurgical bond is made direct to the coated PV surfaces.

S-Bond has demonstrated this same thermosonic method for bonding to a range of different coated PV materials including Mo coated CIGS and even bonding ceramics to the back of concentrated solar PC cells (CPV’s). Contact us and see how S-Bond thermosonic boding might be used in your solar panel manufacturing processes. To see how robotics and thermosonic bonding can be integrated with robotics take a look at http://www.japanunix.co.jp/ju_en/products/video_unisonik.html .

Please Contact Us to inquire how S-Bond active solders and thermosonic bonding may be used in the manufacture your solar modules.

Pic1 Solar Panel Assembly

Pic2 Solar Panel Assembly

Pic3 Solar Panel Assembly

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Active Solder… What-Why-How

July 8th, 2011

What is meant by “active solder”?  The term evolves from active brazing; I assume that does not really help you…. But it is true that active brazing was the key technology that led to the development of active solders.

Most important in the brazing/soldering sense what does “active” really denote. By practice, active brazes and solders have elements added to their base compositions that are reactive with surface oxides and other compounds that form naturally and can, when thermally activated (heated to reaction temperatures), these reactive elements can interact and substitute themselves into the chemical structure of surface compounds (oxide layers,  solid oxides  or other ceramics) in a way that the new interface compounds form which are well bonded to the surface of a material being joined.

For example, elements such as titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb) and tantalum (Ta) have an electronic outer shell structure that enable them to more easily react with many compounds and can thus integrate themselves (when thermally activated) into many compounds found in surface films on metals, semiconductors and ceramics. Thirty years ago or so, with the advent of vacuum metallurgy and vacuum brazing, the integration of such “reactive” elements into brazing filler metals became commercially viable. Wesgo Metals (division of Morgan Advanced Ceramics) and Degussa (now BrazeTec) pioneered such reactive element additions to braze filler metals.  These reactive metal additions to braze fillers are “active” (typically in low concentrations, 0.1 – 2 w/o) since upon melting, the elements diffuse to the braze interface and “reduce” the local oxide (or ceramic) and enter into the bonding structure. Thus the reactive elements become a “active” participant in the chemical constituency of the interface compounds that the term “active braze” stuck and these braze filler metals have been termed “active braze alloys”. Mostly Ti, Hf, Zr or V are being commercially added to Cu-Ag, Au, and Ni alloys. However due to the “activity” of these braze fillers brazing the active braze process is exclusively done high vacuum in order to exclude any oxygen or nitrogen that might react the Ti, Hf, Zr or V elements, preventing sufficient reactive element activity to diffuse and react with surface compounds.  It has also been observed that elevated temperatures, normally over 800°C, have been required to thermally activate the substitution process of the reactive elements with interface compounds in brazed assemblies in order to effect a braze joint.

The extension of “active” brazing to soldering and to be active at soldering temperatures (below 450°C) was a goal of investigators at Euromat and S-Bond Technologies. In 1996 their first “active” solders were patented. Before this time the element indium was the only active commercially available solder. Note that Ti and Hf additions had been made to Sn-Ag base solders but the soldering required heating these filler metals to over 800°C in a vacuum to get the reactive element “Ti” to react with surface compounds and bond. The discovery by S-Bond Technologies of small additions of rare earth elements (e.g. Ce, La, and Lu) gallium and titanium together in solder filler bases  (Sn-Ag, Pb-Sn, Sn-Sb, Sn-Bi, etc.) enabled the “active” soldering phenomena to occur when soldering  most metals and many ceramics at solder melting temperatures (from 115°C to 420°C). The addition of rare earth elements and gallium enabled these Ti containing “active” molten solders to wet and adhere to many metal and ceramic surfaces with using flux. A key part of active solders is that they are “self fluxing” as they are melted and bond to a wide range of base materials without the need for added chemical fluxes or plating…. A key attribute of active solders (and/or brazes).

It was found; however, that the active soldering behavior (wetting and bonding without flux) required that “mechanical activation” be used in conjunction with the active solders patented by S-Bond and Euromat. This process is a means, again without chemical fluxes, to break up the stable solder oxide film that forms when the active solders melt. With the addition of Ti and rare earth elements into Sn-Ag and other solder bases, the rare earth element modifying the melting surfaces’ oxides forming a protective layer for the molten solder, but encasing the other active elements from coming into contact with the base materials. Once the thin oxide film is broken in a continuous way, Ti, Ce and Ga interact with the base materials’ surface compound and bonds to or breaks up these compound layers. Click this link to see how active solders (S-Bond) works on aluminum to provide metallurgical bonds with the need for aggressive chemical fluxes.

So for active solders…

The What: Solders that when melted can wet and adhere to metals, ceramics and glasses without the use of chemical fluxes

The Why: To join at soldering temperatures, without flux and eliminate contamination and entrapment associated with flux usage. Also is enables solder joining of metals, ceramics, carbon/carbides

The How: With Ti, rare earth and gallium additions, many solder bases can be made “active” provided the active solder compositions are used in conjunction with mechanical activation that effectively disrupts the oxide films that form constantly on molten active solders.

If you have further questions about active solders and would like to know more about how they could benefit the assembly of your components [flux free and no plating] then Contact Us.

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Posted in Active Soldering, Aluminum Soldering, Ceramic-Metal Bonding, Graphite Bonding, Soldering & Brazing | No Comments »

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