Knowledge Base

Reflow Encapsulants

Anti-collapse Reflow Encapsulant Technology for FCOF
Slide preesentation 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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Standard Reflow Profile
The recommended reflow profile for Kester solder pastes manufactured with standard tin/lead alloys.

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Alloy Temperature Chart
This chart lists the alloys that are available from Kester. Along with the alloys the alloy melting temperature or plasticc range is listed. Also listed for each alloy are the forms it is avaiable 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.

Effects of Metallic Impurities on the Wetting Properties of Solder
Effects that small amount of metallic impurities can have on the wetting properies of solder in a wave solder machine.

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Shelf Life of Solder

Shelf life policy for solders and other non chemical products. Attached is the Kester Shelf Life Policy for solder and other Kester products.

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Shelf Life of Solder

Shelf life policy for solders and other non chemical products. Attached is the Kester Shelf Life Policy for solder and other Kester products.

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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 O.A. 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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No Clean Flux

Flux Pens
Flux Dispensing Pens.

Flux dispensing onto a small area has always been problematical for assembly operation. The fluxes usually gum-up the flux applicators. To simplify flux application for these situations Kester has come out with flux pens. These are like marking pens with a pump action felt tips that only deliver flux as needed. When the felt tips wear down, others are also available from Kester.

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. Literally 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, etc. The problem with ultrasonic removal is that the outer layer is slightly dissolved and that is the end of the reaction. In the mean time 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 Pens
Flux Dispensing Pens.

Flux dispensing onto a small area has always been problematical for assembly operation. The fluxes usually gum-up the flux applicators. To simplify flux application for these situations Kester has come out with flux pens. These are like marking pens with a pump action felt tips that only deliver flux as needed. When the felt tips wear down, others are also available from Kester.

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.

Rosin Flux Removal
The question that frequently comes up is, 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 (O.A.) 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 Pens
Flux Dispensing Pens.

Flux dispensing onto a small area has always been problematical for assembly operation. The fluxes usually gum-up the flux applicators. To simplify flux application for these situations Kester has come out with flux pens. These are like marking pens with a pump action felt tips that only deliver flux as needed. When the felt tips wear down, others are also available from Kester.

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.

Removing O.A. 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.

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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No Clean Solder Paste

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.

Organic Acid (Water Soluble) Solder Paste

Removing O.A. 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.

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 succesfully 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 and what you can do to minimize thier 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

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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Questions About Flux

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Questions About Hand Soldering

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Questions About Solder Paste

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Applying Solderpaste to Surface Mount Assemblies

Questions About Solderability

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Questions About Industry Specifications

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Shelf Life for Chemical Products
The shelf life of chemical products and the dated of manufacture are printed on the product label.

The shelf life of chemical products including fluxes, thinners, cleaners and other liquids is printed on the product label. Along with the shelf life is the date of manufacture (DOM).

Shelf Life of Solder
Shelf life policy for solders and other non chemical products.

Attached is the Kester Shelf Life Policy for solder and other Kester products.

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Soldering to gold
The importance of gold plating thickness.

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 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 extrremely difficult metal to solder to.

Kester does not have any products for soldering to aluminum.

Soldering Thermocouple Wires
Thermocouple wire materials are not solderable.

Thermocouple materials are not solderable. It is possible to surround the thermocouple wire (encapsulate it) with solder but you can not 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 K100 or K100LD SnCu based solders.

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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.

"44" Flux Residues
The question is frequently asked are "44" flux residues harmful to an assembly.

The “44” flux residues are non-conductive and non-corrosive. Residue removal would normally be for cosmetic reasons. If the assembly is in a heated environment and sees temperatures of over 160°F the flux residues will re-melt. When liquid (at high temperatures) the residues are conductive.

Tip Temperatures
What is the recommended soldering iron tip temperature?

When hand soldering with a rosin flux such as the Kester #44 or the # 285 the recommended iron tip temperature is 750°F. If you are soldering with a low residue no clean solder such as the #245or # 275 we recommend a tip temperature of 600-650°F.

Tip Maintenance
Proper soldering iron tip maintenance is important to extend the life if iron tips.

Tip maintenance is important to extend the life of soldering iron tips. Keep the tips tinned by frequently melting a small length of rosin core solder directly on the tip and then wiping off the excess with a damp (not wet) sponge. Kester offers “Tip Tinners”. These are available through our distributors. The Tip Tinners are small containers of solder in powder form with a special tinning flux. Wipe the hot soldering iron tip on the surface of the tip tinner, melting some of the solder on the tip. Wipe off any excess on a damp sponge.

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

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 K100 and SAC305 solders.

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White Residue
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 comnpliancy.

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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.

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 K100 or 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 K100 or 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 K100 and SAC305 solders.

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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 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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Effects of Metallic Impurities on the Wetting Properties of Solder
Effects that small amount of metallic impurities can have on the wetting properies 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 K100 and SAC305 solders.

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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 comnpliancy.

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.

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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 K100 or K100LD SnCu based solders.

Download Article

Tin-copper based solder options for lead-free assembly
This article details the process changes associated with K100 or 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 K100 and SAC305 solders.

Download Article