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Knowledge Base | Kester

Within the Knowledge Base you will find a wealth of information about processing materials and process information on solder and other assembly materials.

Advanced Assembly Materials

Reflow Encapsulants

Anti-collapse Reflow Encapsulant Technology for FCOF

Slide presentation on anti-collapse reflow encapsulant technology for flip chip on flex.
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Development Aspects for Single Pass High Reliability FC Reflow Encapsulants

A summary of developmental work done in the field of single pass high reliability Flip Chip Reflow Encapsulants.
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Reflow Profiling

Standard Reflow Profile

The standard reflow profile for leaded and lead-free products.
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Alloys

Alloy Temperature Chart

This chart lists the alloys that are available from Kester. Along with the alloys the alloy melting temperature or plastic range is listed. Also listed for each alloy are the forms it is available in.

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Alloy Properties

Strength properties of some of the more common alloys. Shear strength, tensile strength and density values for some of the common alloys. Additional alloy properties including information on conductivity, brinell, hardness, elastic modulus, surface tension.

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2% Silver

When a silver alloy is recommended. The 2% silver is required when soldering to silver or silver plated components/leads. The small percent of silver in the solder prevents the silver on the leads from migrating into the solder resulting in a weak or brittle solder connection.


Dross

What is dross? Dross is an oxide that is formed of the tin and lead in the solder. Dross is generated by a combination of heat and agitation. The hotter the solder pot is, the faster the dross is generated. Also, the more agitation the solder sees, the more dross will be formed. A nitrogen blanket will prevent oxygen from reaching the surface of the solder and the dross generation will be greatly diminished or eliminated. There are also chemical dross reducing agents such as the Kester #5744 Dross Eliminator. These chemical compounds react with the tin and lead oxides reducing them back to the base metal and releasing the oxygen to the air. Follow the instructions on the Product Data Sheet when using chemical reducing agents.


Sn60 vs. Sn63

When is the use of one of these two alloys more appropriate than the other? The Sn60Pb40 has a plastic range and puts down a slightly thicker coating of solder. Sn60 is often preferred for lead tinning and other solder coating applications. Sn63Pb37 is eutectic and as such has no plastic range. Generally it flows better than the Sn60 and is the preferred alloy for wave soldering and surface mount applications.


Gold Colored Solder

Assemblers are often concerned when they see a gold color on the surface of a solder pot. The gold color is tin oxide. When the surface of the molten solder is exposed to air it oxidizes and turns gold; sometimes the tin oxide is a purple-blue color. This is normal and can only be prevented by using an anti-oxidant powder or pellet. The discoloration is a cosmetic defect and in no way degrades the reliability of the solder. Kester offers the #5744 Dross eliminator for this purpose.

Shelf Life

Shelf Life of Kester Products

The shelf life policy for Kester’s solders and other non-chemical products can be found here.
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Flux

Flux Residue Removal

Removing No-Clean Flux Residues

Suggestions of how to remove the residues from no-clean fluxes: To remove the residues of no-clean fluxes most solvents will work. The mild solvents such as alcohol’s (Kester # 5315) work slowly, the stronger solvents (Kester #5240) work faster. The best results are achieved by removing the residues in an aqueous spray cleaner. The spray cleaner can be either a batch type or an in-line type. The addition of a saponifier (Kester # 5768) and hot water, about 130°F will completely remove the flux residues.


Removing Organic Acid (OA) Flux Residues

It is required to remove the residues of OA fluxes? You will get corrosion if you do not fully remove all the flux residues. The flux residues from organic fluxes are hygroscopic, they contain organic acids and they may contain halides. Over time the residues will absorb moisture and the halides will become mobile and corrosive. This will lead to ‘catastrophic failure’ of the assembly in question. We recommend cleaning with an aqueous cleaning system, it can be either batch type or in-line. The water temperature should be between 120-140°F. The important thing is to have lots of rinsing and flushing to completely remove all the flux residues.


White Residue

Identification and categorization of white residues often found on cleaned circuit assemblies.
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Flux Thinning

Soldering fluxes loose solvent and need additions of thinner. Flux is composed of solids dissolved in a solvent base. Over time the solvent evaporates. As the solvent evaporates the solids concentrate and eventually crystallize out. You will need to add thinner on a regular basis to prevent the flux from crystallizing. A hydrometer is used to measure the specific gravity of the flux. Normally the specific gravity (density) is checked 2 or 3 times a day. Thinner is then added to return the flux to its correct density. Hydrometers can be purchased from any scientific supply house. Kester has flux density control Data Sheets (also called nomographs) for the rosin and higher solid content fluxes. Using the nomograph you can determine how much thinner needs to be added. We sell test kits for the low residue fluxes. The test kits indicate how much thinner to add to the flux pot.


What Does No-Clean Mean?

There is some apprehension at the description, ‘no-clean’. What does it mean? The flux category called “no-clean” . Many fluxes fall into this category because the flux residues are not harmful to assemblies. It does not mean there will be no residues. All fluxes leave residues (the solids are the active portion of the flux that does all the work). Some flux residues are conductive or corrosive and must be removed. Other fluxes like the no-clean fluxes leave residues that do not need to be removed.


Flux Test Kit

The PS-20 and PS-22 test kits are used for flux control of low residue(no-clean) fluxes. The PS-20 and PS-22 test kits are acid titration kits. As solvent evaporates, the acids in the flux become more and more concentrated. The kit is used to determine the acid number of the flux. The test is a simple drop test with an indicator for the endpoint (similar to a swimming pool test). You count the drops and then go to a chart. From the chart you determine how much thinner to add to bring the acid number back down to spec. Traditionally flux control is maintained by measuring the density of the flux and adding thinner as the flux thickens. This is a good method for fluxes with high solids contents. A slight change in density corresponds to a small change in the flux. The no-clean fluxes have low solids percents (typically 2 or 3 %) so a small change in the flux density could reflect the change in solids of 25-30%. This would put the acid level unacceptably high. The test kits are more accurate than using density measurements as a way to monitor the flux.


VOC-Free Flux Wave Soldering Profile

A general profile setting up a wave solder machine to optimize reflow using an alcohol base flux.
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VOC-Free Flux Considerations

Process changes that will have to be considered when changing from an alcohol based to a VOC-Free flux technology.
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Flux Deposition

How much no-clean flux should be applied to a PCB and how does one determine the deposition rate?
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Rosin Flux

Saponification

Saponifiers in an aqueous cleaner can be used to remove rosin flux residues. What the Bio-Kleen #5768 saponifier does is react with the outside layer of flux and soften it up, lLiterally turning it into a soap. You need a spray cleaner so that this soap layer will be washed away which then allows the Bio-Kleen to react with the next layer. Rinse that layer off, etc. The problem with ultrasonic removal is that the outer layer is slightly dissolved and that is the end of the reaction. In the meantime the solder is being exposed to an alkaline condition. The exposed solder turns a dull gray as the surface shine is etched off by the caustic solution.


Thinner Calculation

A calculation that can be used to determine how much thinner needs to be added to the flux to maintain a specified specific gravity. The following formula can be used to determine how much Kester # 4662 thinner to add to the Kester # 2235 flux to bring it back to the recommended specific gravity (density). For your information this formula can be used for any Kester flux that utilizes the # 4662 thinner. V = ( x – y ) 128 Y – 0.783 Where V = ounces of # 4662 thinner to be added per gallon of flux. X = present flux density Y = desired flux density For example: The flux is at 0.875 and it should be at 0.856 V = ( 0.875-0.856 ) 128 or V = 2.432 or V = 33.3 ounces of thinner per gallon of flux 0.856 – 0.783 .073


Storage of Flammable Materials

Most rosin fluxes are flammable materials. This is a general guide to storage of flammable materials. Kester does not have a required temperature and humidity for storage of flammable liquid chemicals. From a safety standpoint we recommend storage at room temperature and humidity. For flammable materials we recommend storage in an approved flammable materials storage cabinet. Storage above normal room temperature can be risky as the material (alcohol) will build up pressure in the container. There is a risk the material will spew out of the container when opened.


Flux Thinning

Soldering fluxes lose solvent and need additions of thinner. Flux is composed of solids dissolved in a solvent base. Over time the solvent evaporates. As the solvent evaporates the solids concentrate and eventually crystallize out. You will need to add thinner on a regular basis to prevent the flux from crystallizing. A hydrometer is used to measure the specific gravity of the flux. Normally the specific gravity (density) is checked 2 or 3 times a day. Thinner is then added to return the flux to its correct density. Hydrometers can be purchased from any scientific supply house. Kester has flux density control Data Sheets (also called nomographs) for the rosin and higher solid content fluxes. Using the nomograph you can determine how much thinner needs to be added. We sell test kits for the low residue fluxes. The test kits indicate how much thinner to add to the flux pot.


Rosin Flux Removal

Do rosin flux residues need to be removed? Rosin flux residues are non-conductive and non-corrosive. Under normal circumstances they do not have to be removed from a printed circuit assembly. Rosin residue removal would be for cosmetic considerations. In an environment where the working temperature of the assembly will exceed 200°F the rosin residues will melt and become conductive, in these situations flux removal is required.


Alcohol based flux wave soldering profile

A general profile setting up a wave solder machine to optimize reflow using an alcohol base flux.
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Green Corrosion?

Rosin fluxes react with copper (especially on braided cables underneath the insulation) to form a green by-product that is not corrosion.
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Water-Soluble (OA) Flux

Thinner Calculation

A calculation that can be used to determine how much thinner needs to be added to the flux to maintain a specified specific gravity. The following formula can be used to determine how much Kester # 4662 thinner to add to the Kester # 2235 flux to bring it back to the recommended specific gravity (density). For your information this formula can be used for any Kester flux that utilizes the # 4662 thinner. V = ( x – y ) 128 Y – 0.783 Where V = ounces of # 4662 thinner to be added per gallon of flux. X = present flux density Y = desired flux density For example: The flux is at 0.875 and it should be at 0.856 V = ( 0.875-0.856 ) 128 or V = 2.432 or V = 33.3 ounces of thinner per gallon of flux 0.856 – 0.783 .073


Flux Thinning

Soldering fluxes lose solvent and need additions of thinner. Flux is composed of solids dissolved in a solvent base. Over time the solvent evaporates. As the solvent evaporates the solids concentrate and eventually crystallize out. You will need to add thinner on a regular basis to prevent the flux from crystallizing. A hydrometer is used to measure the specific gravity of the flux. Normally the specific gravity (density) is checked 2 or 3 times a day. Thinner is then added to return the flux to its correct density. Hydrometers can be purchased from any scientific supply house. Kester has flux density control Data Sheets (also called nomographs) for the rosin and higher solid content fluxes. Using the nomograph you can determine how much thinner needs to be added. We sell test kits for the low residue fluxes. The test kits indicate how much thinner to add to the flux pot.


Removing OA Flux Residues

Is it required to remove the residues of OA fluxes? You will get corrosion if you do not fully remove all the flux residues. The flux residues from organic fluxes are hygroscopic, they contain organic acids and they may contain halides. Over time the residues will absorb moisture and the halides will become mobile and corrosive. This will lead to ‘catastrophic failure’ of the assembly in question. We recommend cleaning with an aqueous cleaning system, it can be either batch type or in-line. The water temperature should be between 120-140°F. The important thing is to have lots of rinsing and flushing to completely remove all the flux residues.


Alcohol based flux wave soldering profile

A general profile setting up a wave solder machine to optimize reflow using an alcohol base flux.
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VOC-Free Flux Wave Soldering Profile

A general profile setting up a wave solder machine to optimize reflow using an alcohol base flux.
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VOC-Free Flux Considerations

Process changes that will have to be considered when changing from an alcohol based to a VOC-Free flux technology.
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Solder Paste

No-Clean Solder Paste

What Does No-Clean Mean? Many fluxes fall into this category because the flux residues are not harmful to assemblies. It does not mean there will be no residues. All fluxes leave residues (the solids are the active portion of the flux that does all the work). Some flux residues are conductive or corrosive and must be removed. Other fluxes like the no-clean fluxes leave residues that do not need to be removed.


Organic Acid (Water-Soluble) Solder Paste

It is required to remove the residues of OA fluxes? You will get corrosion if you do not fully remove all the flux residues. The flux residues from organic fluxes are hygroscopic, they contain organic acids and they may contain halides. Over time the residues will absorb moisture and the halides will become mobile and corrosive. This will lead to ‘catastrophic failure’ of the assembly in question. We recommend cleaning with an aqueous cleaning system, it can be either batch type or in-line. The water temperature should be between 120-140°F. The important thing is to have lots of rinsing and flushing to completely remove all the flux residues.


Process Information

Syringable Paste Needle Size

Syringable solder paste requires a needle and plunger for application. The 100 g paste comes in a standard 30cc. syringe. 35 g samples come in a standard 10 cc syringe. Most distributors carry plungers and needles. Scientific supply companies such as Fisher Scientific (www.fishersci.com) and Cole Parmer (www.coleparmer.com) also carry plungers and needles. For dispensing SMT solder paste a 20 gauge needle is the smallest that is usable.


10 Solder Tips

Tips for successfully soldering surface mount applications.

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SMT Process recommendations

Key competitive advantages can be obtained through the minimization of process defects and disruptions. In today’s electronic manufacturing processes there are many variables to optimize.

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Solder Beads

What are solder beads? Why do they appear on SMT assemblies? What you can do to minimize their presence?

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Standard Reflow Profile

The recommended reflow profile for Kester solder pastes manufactured with standard tin/lead alloys.

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Solder Paste Volume Percents

What are the volume percents for flux and metals for a typical solder paste?

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Solder Paste Handling

This document will explain how to handle solder paste after it leaves Kester's facilities?

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Solderability

Soldering to gold

When soldering to a gold plated surface the thickness of the gold is important. If the gold is thicker than 40-50 micro-inches, the solder most likely may not dissolve all the gold and bond to it. The solder will be dull looking and, if the gold content in the solder exceeds about 5%, the solder joint will be brittle. If the gold is thin, less than 20 micro-inches, it easily dissolves into the solder, making the solder joint look grainy. If the metal that was under the gold is not oxidized, the gold-contaminated solder will bond to it. However, as gold plates usually in a columnar structure, the gold should be at least 10 micro-inches thick to protect the base metal (in most cases nickel) from oxidation.
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Soldering to stainless steel

Stainless steel is a difficult metal to solder to.
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2% Silver

When is a silver alloy is recommended? The 2% silver is required when soldering to silver or silver plated components/leads. The small percent of silver in the solder prevents the silver on the leads from migrating into the solder resulting in a weak or brittle solder connection.


Soldering to Aluminum

Aluminum is an extremely difficult metal to solder to. Kester does not have any products for soldering to aluminum.


Soldering Thermocouple Wires

Thermocouple materials are not solderable. It is possible to surround the thermocouple wire (encapsulate it) with solder but you cannot make a metallurgical bond to it. It is important to note that even if you could solder the two wires back together the thermocouple still will not work. A thermocouple works by measuring the change in resistance of the two dissimilar metals joined in the welded bead. If one were to join the metals with a solder inter-connect the thermocouple would give meaningless numbers. The way to fix a broken thermocouple is to re-weld the thermocouple bead. If you wish to attach a thermocouple to a printed circuit board for reflow profiling, you can use a high temperature alloy to encapsulate it or use a cyano-acrylate adhesive to stick it to the board.


Questions About Solderability

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Creating Solder Joint Reliability with SnCu Based Solders

Tin-copper systems with lead-free wave and selective soldering are a growing option. This paper shows how to implement a reliable process using K100LD SnCu based solders.
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Hand Soldering

Lead-Free Hand Soldering – Ending the Nightmares

Hand soldering with lead-free solders can be challenging but not if the points in this article are understood.
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Case Study on the Validation of SAC305 and SnCu-based Solders in SMT Wave and Hand Soldering

This paper describes the work done at a contract assembler who implemented a successful process to build over 500,000 assemblies using both Kester K100LD and SAC305 solders.
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Technical Papers

White Residue

This article discusses the identification and categorization of white residues often found on cleaned circuit assemblies.
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Developing a Reliable Lead-Free SMT Assembly Process

This article offers valuable information to be used during the successful lead-free reflow process implementation.
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How do you create a RoHS Compliancy-Lead-Free Roadmap?

This article describes the various considerations in the transition to lead-free but also RoHS compliancy.
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How do you ready a solder pot for lead-free solder?

This article in designed for those cleaning a leaded solder pot to convert it to lead-free solder. It insures the solder is not contaminated with lead during the switchover.
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Implementation of Reliable Lead-free Wave and SMT Processes

This article describes the points to consider in transitioning to lead-free wave and reflow soldering.
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Lead-Free Hand Soldering – Ending the Nightmares

Hand soldering with lead-free solders can be challenging but not if the points in this article are understood.
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Lead-Free Reliability – Building it right the First Time

This article describes the comparison done in reference to lead-free and leaded solder joints. The article also gives insight on the points to improve overall reliability with lead-free solders.
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Lead-Free SMT Soldering Defects How to Prevent Them

This paper shows how avoid soldering defects with lead-free solder pastes. Process control is emphasized to reduce defects.
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Lead-Free Wave Soldering

This article shows the impact to wave soldering with lead-free materials and how to create a reliable defect free process.
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Creating Solder Joint Reliability with SnCu Based Solders

Tin-copper systems with lead-free wave and selective soldering are a growing option. This paper shows how to implement a reliable process using K100LD SnCu based solders.
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Tin-copper based solder options for lead-free assembly

This article details the process changes associated with K100LD solder systems.
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Case Study on the Validation of SAC305 and SnCu-based Solders in SMT Wave and Hand Soldering

This paper describes the work done at a contract assembler who implemented a successful process to build over 500,000 assemblies using both Kester K100LD and SAC305 solders.
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Wave Soldering

Wave Soldering Guideline

Important process parameters to consider when setting up a wave soldering process.
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Alcohol-Based Flux Wave Soldering Profile

A general profile setting up a wave solder machine to optimize reflow using an alcohol-based flux.
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VOC-Free Flux Wave Soldering Profile

A general profile setting up a wave solder machine to optimize reflow using an alcohol-based flux.
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Effects of Metallic Impurities on the Wetting Properties of Solder

Effects that small amount of metallic impurities can have on the wetting properties of solder in a wave solder machine.
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VOC-Free Flux Considerations

Process changes that will have to be considered when changing from an alcohol based to a VOC-free flux technology.
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Flux Deposition

How much no-clean flux should be applied to a PCB and how does one determine the deposition rate?
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Implementation of Reliable Lead-free Wave and SMT Processes

This article describes the points to consider in transitioning to lead-free wave and reflow soldering.
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Lead-free Wave Soldering

This article shows the impact to wave soldering with lead-free materials and how to create a reliable defect free process.
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Case Study on the Validation of SAC305 and SnCu-based Solders in SMT Wave and Hand Soldering

This paper describes the work done at a contract assembler who implemented a successful process to build over 500,000 assemblies using both Kester K100LD and SAC305 solders.
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Lead-Free

Lead-Free Reflow Profile

Recommended reflow profile for Kester solder paste formulations containing the Sn96.5Ag3.5 and Sn96.5Ag3.0Cu0.5 alloys.
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K100LD & K100 Case Studies Summary

This PowerPoint pictorial examines a successful implementation of K100LD and K100 lead-free alloys at SMT Dynamics and Ayrshire Electronics.
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Lead-Free Technical Papers

Standard Reflow Profile

The recommended reflow profile for Kester solder pastes manufactured with standard tin/lead alloys.
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K100 Implementation at SMT Dynamics

This paper shows results obtained at a contractor in successful builds using SAC305 for reflow soldering and K100 solder for wave assembly.
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Developing a Reliable Lead-free SMT Assembly Process

This article offers valuable information to be used during the successful lead-free reflow process implementation.
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How do you create a RoHS Compliancy-Lead-free Roadmap?

This article describes the various considerations in the transition to lead-free but also RoHS compliancy.
Download Article


How do you ready a solder pot for lead-free solder?

This article in designed for those cleaning a leaded solder pot to convert it to lead-free solder. It insures the solder is not contaminated with lead during the switchover.
Download Article


Implementation of Reliable Lead-free Wave and SMT Processes

This article describes the points to consider in transitioning to lead-free wave and reflow soldering.
Download Article


Lead-free Hand Soldering – Ending the Nightmares

Hand soldering with lead-free solders can be challenging but not if the points in this article are understood.
Download Article


Lead-free Reliability – Building it right the First Time

This article describes the comparison done in reference to lead-free and leaded solder joints. The article also gives insight on the points to improve overall reliability with lead-free solders.
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Lead-free SMT Soldering Defects How to Prevent Them

This paper shows how avoid soldering defects with lead-free solder pastes. Process control is emphasized to reduce defects.
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Lead-free Wave Soldering

This article shows the impact to wave soldering with lead-free materials and how to create a reliable defect free process.
Download Article


Creating Solder Joint Reliability with SnCu Based Solders

Tin-copper systems with lead-free wave and selective soldering are a growing option. This paper shows how to implement a reliable process using K100LD SnCu based solders.
Download Article


Tin-copper based solder options for lead-free assembly

This article details the process changes associated with K100LD solder systems.
Download Article


Case Study on the Validation of SAC305 and SnCu-based Solders in SMT Wave and Hand Soldering

This paper describes the work done at a contract assembler who implemented a successful process to build over 500,000 assemblies using both Kester K100LD and SAC305 solders.
Download Article