Epoxy Bond vs. Solder Bond Applications

Bond assembly can be done via 1) mechanical attachment, 2) adhesive bonding of which epoxy bonding is one form of adhesive, 3) soldering bonding using lower melting filler metals (< 450˚C), 4) brazing using filler metals melting above 450˚C, and 5) welding such as resistance welding bonding, ultrasonic welding and friction weld bonding that uses locally melted parent metal.

Bonding is done for a variety of technical reasons a) mechanical attachment, b) thermal contact, c) electrical contact d) gas or liquid seal, or e) any or all combinations thereof. The choice of bonding method will then depend on the intrinsic properties of the bonding filler materials ( i.e. hermetic, electrical conductance, thermal conductance, thermal coefficient of expansion, adhesive bond strength related to the intrinsic fillers’ mechanical properties, and their adhesive and cohesive strengths). Read more about Epoxy Bond vs. Solder Bond Applications

Metal to Metal Bonding

Metal to metal bonding is used in many applications for fabricating components where the metallic parts are too large or too complex to make from one piece of metal or the assembly contains dissimilar metals for various functions, such as: 1) physical properties such as electrical or thermal conductivity, 2) differences in thermal coefficient of expansion, 3) differences in corrosion, 4) differences in strength and/or modulus. For designers to utilize the optimum combination of metal properties, it is useful to have metal to metal bonding properties that optimally combine metals in an assembly.

Bonding technologies include: 1)Mechanical fastening, 2) Epoxy bond, 3) other Metal Adhesives, 4) Diffusion Bonding, 5) Explosive Bonding, 6) Weld & Weld Cladding, 7) Ultrasonic Welding, 8) Brazing and Soldering and 9) specialized active solder bonding. For strength mechanical fastening and welding are favored… for low cost, epoxy and other adhesive metal bonding are best but have limitations with regard to sealing, thermal conductivity, and stability over time. Diffusion and explosive bonding perhaps provides the best strength and interfaces between metals. However; for the best combination of bond properties and the least effect on base metal properties; ultrasonic welding, brazing, or soldering are the processes of choice. The choice of bonding process also entails the area of bond required, the joints’ physical properties and the effect the bonding process has on the base metal properties… all these are considerations when selecting bonding process. Read more about Metal to Metal Bonding

Solder Bond vs. Epoxy Bond as Thermal Interface Materials

Thermal interface materials are materials used in creating heat conductive paths at interfaces between components and thus reduce thermal interface resistance. These materials permit more effective heat flow between separate components where heat is being generated to a heat dissipation components such as solid state transistors to heat sink or a high frequency device connected to a heat spreader. Thermal interface materials’ purpose is to fill the air gap that occurs at contact interfaces with more thermally conductive compounds to permit more effective heat flow than poorly conductive air.

There is a wide variety of thermal interface materials (TIM’s); thermal greases, phase change polymers, thermal tapes, gap filling pads, filled epoxies and solders. All having various costs, performance and manufacturing challenges. Read more about Solder Bond vs. Epoxy Bond as Thermal Interface Materials

Solar Panel Assembly

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 https://www.japanunix.com/en/products/unit/unit_ultra_sonic.php.

 Solar Panel AssemblyPic2Solar Panel Assembly

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

Aluminum Bonding and Heat Management in Manufacturing

Abstract CPUThink of the smartphone you hold in your hand, or of your tablet or laptop. The amount of processing power they contain dwarfs offerings from just a few years ago. Theoretically, the parts should be much hotter from doing so many more operations. They are not and one of the biggest reasons why is aluminum soldering and aluminum bonding applications.

Basics of Thermal Management in Manufacturing

Many of the advancements for electronics manufacturing, and other industries that benefit from aluminum soldering, revolve around miniaturization. Parts are smaller, which in some cases mean they are more fragile. In the case of solid-state lighting and LEDs, the advancement in efficiency comes at a price as well: the area of the product where the light is created can hit high temperatures of up to 150 degrees Celsius at the absolute maximum, according to Cree LED data sheets. Read more about Aluminum Bonding and Heat Management in Manufacturing

Myths Regarding Lead-Free Solder Products and Joining Techniques

Soldering Techniques - Joing Methods

Brush Application

While it has been several years since manufacturers began moving to lead-free solder procedures, in part due to the European Union’s Restriction of Hazardous Substances Directive, some still believe myths that have long been inaccurate regarding the use of alloy joining materials that do not require flux and are based on lead and tin.

Temperatures Can Be Enough to Destroy Components

The first round of lead-free solder options to join metals and other materials were comprised of tin, silver and copper, which do have a slightly higher melting point of 217 degrees Celsius compared to existing solder’s 183 degrees Celsius. That disparity could cause problems regarding PC board damage.

However, newer products including several offered by S-Bond have significantly lower melting points that make it easier to join metals like aluminum. At the lowest temperatures, some materials can be joined at just 115 degrees Celsius.

Issues Regarding Silicon Will Require Other Materials

Read more about Myths Regarding Lead-Free Solder Products and Joining Techniques

Accounting for Material Thermal Expansion and Torsional, Tensile Strength

S-Bond material joining applications enable engineers to use multiple materials, such as materials and ceramics, in a variety of applications. However, just because aluminum and steel can be joined, as one example, does not mean that the joining process cannot introduce deformations or other issues.

Thermal Expansion Concerns in Bonding

When soldering two different types of metal together, both surfaces have to be heated in S-Bond can effectively assemble a wide variety of components with its unique bonding attributes - See more at: http://www.s-bond.com/solutions-and-service/s-bond-joined-components/#sthash.6FQ20NgZ.dpuforder for the solder to bond to both components. Materials expand as they heat, and different metals do so at a different rate. This can create problems as the joining site cools back down.

Two examples of materials that react easily to heat are aluminum and magnesium, which can expand at twice the rate of carbon steel and iron. If an aluminum sheet is soldered to a sheet of carbon steel, during the cool-down period the combined piece will warp with a slight curve. With more brittle components such as those made with ceramics, the combined part can shatter based on expansion during bonding and later cooling.

Solutions for Dissimilar Coefficients of Thermal Expansion

Read more about Accounting for Material Thermal Expansion and Torsional, Tensile Strength

Solder Bond vs. Epoxy Bond as Thermal Interface Materials (TIM)

Thermal interface materials are materials used in creating heat conductive paths at interfaces between components and thus reduce thermal interface resistance. These materials permit more effective heat flow between separate components where heat is being generated to a heat dissipation components such as solid state transistors to heat sink or a high frequency device connected to a heat spreader. Thermal interface materials’ purpose is to fill the air gap that occurs at contact interfaces with more thermally conductive compounds to permit more effective heat flow than poorly conductive air.

There is a wide variety of thermal interface materials (TIM’s); thermal greases, phase change polymers, thermal tapes, gap filling pads, filled epoxies and solders. All having various costs, performance and manufacturing challenges.

S-Bond Thermal Interface

Figure 1. Illustration of thermal grease filling an interface
between a heat generating device and a heat sink.

Thermal greases are viscous fluid substance which increase the thermal conductivity of a thermal interface “gap by filling microscopic air-gaps present due to the imperfectly flat and smooth surfaces of the components as seen in Figure 1.

Thermal grease compounds have far greater thermal conductivity than air (but far less than metals). They are used in electronics, as depicted in Figure 2, to improve the heat flow from lower power electronic devices thus lowering the components temperature and increasing its life.

Read more about Solder Bond vs. Epoxy Bond as Thermal Interface Materials (TIM)

Epoxy Bond vs. Solder Bond Applications

Bond assembly can be done via 1) mechanical attachment, 2) adhesive bonding of which epoxy bonding is one form of adhesive, 3) soldering bonding using lower melting filler metals (< 450˚C), 4) brazing using filler metals melting above 450˚C and 5) welding such as resistance welding bonding, ultrasonic welding and friction weld bonding that uses locally melted parent metal.

Bonding is done for a variety of technical reasons a) mechanical attachment, b) thermal contact, c) electrical contact d) gas or liquid seal, or e) any of all combinations of a – d. The choice of bonding method will then depend on the intrinsic properties of the bonding filler materials (hermetic, electrical conductance, thermal conductance, thermal coefficient of expansion, adhesive bond strength related to the intrinsic fillers’ mechanical properties and their adhesive and cohesive strengths…

With all these variables and design considerations how does one choose? The three main guiding principles are:

1. Cost of filler and Cost of bonding processes

2. Performance in Service (based on the properties of the bond and bonding materials)

3. Compatibility with Manufacturing Sequence.

To compare epoxy bonds to solder bonds one has to ask the purpose of the bond… Is strictly a mechanical bond ? Is cost a large factor? If cost drives the choice then many times epoxy is the bonding material of choice. Epoxies are generally low cost thermosetting polymers, that are mixed chemicals which are thermally or UV cured to achieve hardness and adherence. Epoxy by far is the lower cost material over solder metal fillers and thus if low cost is the driving aim of the bond, then epoxy will be the bonding material selected.
Figures 1-2 illustrate typical epoxy bonded applications


When bonds have to be thermally conductive or electrically conductive solders are usually the bonding material of choice. Solder are metal fillers melt below 450˚C are normally alloys of Sn, Ag, Pb, In, or Bi with the Pb-free alloys being preferred for environmental reasons. As metals, these materials are intrinsically 10 – 100 time more conductive than epoxy bonds. In recent year epoxy bonds have been filled with aluminum or silver particles to increase the epoxy bond filler conductivity to values of 3 – 5 W/m-K from 0.5 – 2 W/m-K. When compared to solder bond metals with conductivities of 40 – 400 W-m-K, one can see for thermal bonded components that solder bonding would be preferred. S-Bond Technologies makes active solder alloys that bond to metals, ceramics, glass and their combinations without the need for flux or plating and are many times selected over epoxy bonds for their improved thermal characteristics.
Figures 3 – 4 illustrate typical solder bond applications.

Figures 5-7 show the solder bond process being used to make a heat exchanger.


Bonding for electrical resistance or conductance will many times determine the choice of epoxy bonds over solder or active solders. If the bond joint has to provide electrical isolation, then epoxy has much higher dielectric strength and resistivity, hence are excellent at isolating electrical components from their base materials. However, if the bond has to be electrically conductive solder bonds are preferred.

Bonding for seals are a mixed choice… in the short term epoxy seals can perform and create a sufficient seal for liquids and many gases. However, in applications for long term use epoxy bonds are permeable to certain gases and moisture and are not used in seals that require high hermetic seal integrity. Metals are impervious to moisture and gases thus solder bonds are the preferred bonding materials for high integrity hermetic seals.

Epoxy bonds are “permanent” and less resistant to thermal cycle and temperatures as well as UV exposures (can degrade with time). Solders on the other hand being metallic can be remelted repeatedly to renew or rework the bond. Additionally, as metals, solders are resistant to cracking being ductile and tough and are not susceptible to UV degradation.

Finally, the issue of compatibility with manufacturing sequences and the choice of solder bond vs. epoxy one has to select the bonding materials that will suit not only cost but the sequence of manufacturing operations. The bond has to have the properties that will take the exposure to all the assemblies operations. Bonding is many times completed after machining and fabrication but before plating or coating. If an electrical package the bonding has to be done in a compatible sequence with the electrical soldering operations. For example if a printed circuit board needs to bonded to a heat sink solder bonding the circuit board has to be done a temperatures below the solder reflow temperature on the circuit, for example below 200˚C or one has to epoxy bond the circuit board with a thermally filled epoxy. Compared to solder bonding, epoxy bonds can be less expensive in a manufacturing operation with no need for heating and reflowing solders. On the other hands solders “cure” as soon as the heating is off, while epoxy bonds need “setting time” to cure, which in some high volume applications provide some problems. When electroplating a full assembly, the bonded parts need to be bonded electrically hence solder bonding is the choice, while if powder coating, the epoxy bond may be the bond of choice.

This blog discussed how the choice of epoxy bond vs. solder bond is determined by a host of factors that need to be considered. We hope the discussion has been useful.

If you need help in making the choice of epoxy bond vs. solder please contact us, we can offer the proper counsel for making the right choice and we also offer alternative

S-Bond Joining of SiC Tiles in Microwave Beam Dampers (Absorbers)

Argonne National Laboratories selected S-Bond active solder technology to make water cooled high power microwave beam dump in its Advanced Photon Source which is a user-facility to producing extremely brilliant x-ray photon beams. The Advanced Photon Source uses high energy microwave beams to steer and create such x-ray photon beams. These beams once started cannot be shut down or restarted easily, so to facilitate the use the various beam lines, the microwave beams are diverted to beam dumps. These beam dumps consist of microwave cavities that are lined with SiC tiles bonded to water cooled rectangular copper enclosures that are heavy water cooled. SiC is a well know high efficiency absorber of microwave energy and thus is used in dampers.

The challenge faced by the Argonne engineers and physicists was to find a stable process for bonding the SiC tiles to copper bases that would provide thermal and electrically conductive interface and be able to take the thermal expansion mismatch during the bonding processes and in service. Active brazing and active soldering were considered since active brazes and solders are able to form metallurgical bonds with the SiC tiles. Active brazing, using Cu-Ag-Ti was tested and it was found the residual stresses stemming from the coefficient of thermal expansion (CTE) mismatch of SiC and copper led to the fracture of the SiC tiles upon cooling from the 860˚C brazing temperature to room temperature. S-Bond active soldering was selected as good alternative to active brazing since the solder bonding temperature of 250˚C yielded much lower CTE derived stresses and created a more compliant bond line that would better accommodate the heating and cooling stresses in service.

Figure 1 below show the S-Bond joined SiC tiles being bonded into one half of the microwave beam damper cavity indicating how S-Bond successfully joins SiC to copper. Figure 2 is an ultrasonic C-Scan of the bonded interfaces under each tile in the damper half

Contact us to see how S-Bond joining can solve your ceramic to metal bonding challenges.