Soldering

Soldering Materials

Solder

Solder Alloys

There are a wide variety of solder alloys for varying uses as shown by this table below, which also gives the solidification and liquifaction points together with their uses.

Ag = Silver

Cd = Cadmium

Cu =Copper

PB = Lead

Sn = Tin

Sb = Antimony

2%Sn/2%Sb/96%Pb Solidus 305°C Liquidus 315 °C Uses: High Temperature, High Creep Strength

5%Sn/93.5%Sb/1.5%Pb Solidus 296 °C Liquidus 301°C Uses: High Melting Point

95/5%Sn/4.5%Pb Solidus 236°C Liquidus 243°C Uses: High Melting Point

100%Sn Solidus 232°C Liquidus 232°C Uses: Lead Free

15%Sn/85%Pb Solidus 225°C Liquidus 290°C Uses: Lamps

96% Sn/4%Ag Solidus 221°C Liquidus 221°C Uses: Stainless Steel, Bright, Strong Non Toxic

20%Sn/80%Pb Solidus 183°C Liquidus 275°C Uses: Lamps

30%Sn/70%Pb Solidus 183°C Liquidus 255°C Uses: Lamps, Motors

31.2%Sn/67Pb/1.8%Sb Solidus 185°C Liquidus 243°C Uses: Radiators, General Purpose Non Electrical

40%Sn/60%Pb Solidus 183°C Liquidus 234°C Uses: General Purpose

45%Sn/55%/Pb Solidus 183°C Liquidus 224°C General Purpose

50%Sn/48.5%Pb/1.5%Cu Solidus 183°C Liquidus 215°C Uses: Saves Copper Erosion

50%Sn/49.7%Pb/0.3%Sb Solidus 183°C Liquidus 212°C Uses: General Purpose

50%Sn/50%Pb Solidus 183°C Liquidus 212°C Uses: General Purpose

60%Sn/39.7%Pb/0.3%Sb Solidus 183°C Liquidus 188°C Uses: General Purpose

60%Sn/40%Pb Solidus 183°C Liquidus 188°C Uses: Electrical

63%Sn/36.7%Pb/0.3%Sb Solidus 183°C Liquidus 183°C Uses: Electrical

62%Sn/35.7%Pb/2%Sb/0.3%Ag Solidus 179°C Liquidus 179°C Uses: Silver - Plated Surfaces

62%Sn/36%Pb/2%Ag Solidus 179°C Liquidus 179°C Uses: Silver - Plated Surfaces

18%Sn/80.1%Pb/1.9%Ag Solidus 178°C Liquidus 270°C Uses: Aluminium

50%Sn/32%Pb/18%Cd Solidus 145°C Liquidus 145°C Uses: Low melting point, Soldering on Gold

70%Sn/30%Zn Solidus 196°C Liquidus 307°C Uses: Spray Wire for Metal Film capacitors

80%Sn/20%Zn Solidus 196°C Liquidus 268°C Uses: Spray Wire for Metal Film capacitors

30%Sn/70%Cd Solidus 176°C Liquidus 240°C Uses: Low Thermal EMF Solder

Common Solder Compositions for Stained Glass

The table above shows what a large variety of compositions there are for various soldering purposes.

The common solders for stained glass are mixtures of tin and lead, respectively:

63/37: melts at 183°C (362°F)

60/40: melts between 183°C (362°F) and 188°C (376°F)

50/50: melts between 183°C (362°F) and 212°C (421°F)

40/60: melts between 183°C (362°F) and 234°C (454°F)

lead-free solder (useful in jewellery, eating containers, and other environmental uses): melts between 118°C (245°F) and 220°C (428°F), depending on composition.

The 63/37 and 60/40 solders are most often used in copper foil work because of their narrower melting range. This allows the solder to set more quickly than the solders with higher lead content. They tend to give smoother beads also.

 50/50 and 40/60 solders are more often used in leaded panel work. Their wider range of melting temperatures allows the solder to spread and become flat.

Hard Solder

As used for brazing, hard solder is generally a copper/zinc or copper/silver alloy, and melts at higher temperatures than tin/lead compositions.

In silversmithing or jewellery making, special hard solders are used that will pass assay. They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders also come in a variety of hardnesses, known as 'enamelling', 'hard', 'medium' and 'easy'. Enamelling solder has a high melting point, close to that of the material itself, to prevent the joint de-soldering during firing in the enamelling process. The remaining solder types are used in decreasing order of hardness during the process of making an item, to prevent a previously soldered seam or joint de-soldering while soldering a new joint. Easy solder is also often used for repair work for the same reason. Flux or rouge is also used to prevent joints de-soldering

Flux Core Solder

A tube of multi-core electronics solder is used for manual soldering in the electronics industry - the flux is contained in cores within the solder itself.

Solder often comes pre-mixed with, or is used with, flux, a reducing agent designed to help remove impurities (specifically oxidised metals) from the points of contact to improve the electrical connection. For convenience, solder is often manufactured as a hollow tube and filled with flux. Most cold solder is soft enough to be rolled and packaged as a coil, making for a convenient and compact solder/flux package.

The two principal types of flux are acid flux, used for metal mending; and rosin flux, used in electronics, where the corrosiveness of the vapours that arise when acid flux is heated could damage components. Due to concerns over atmospheric pollution and hazardous waste disposal, the electronics industry has been gradually shifting from rosin flux to water-soluble flux, which can be removed with de-ionised water and detergent, instead of hydrocarbon solvents.

Lead-Free Solder

Most of the advice in the stained glass community about lead free solder is to avoid using it. However, lead-free solder is essential for making jewellery (which may have skin contact) or any project that may be in contact with food.

Lead-free solder does require a hotter iron than lead bearing solders, plus it does not flow easily. It has a pasty state between solid and liquid that is prone to lumps and spikes. If this is not bad enough, it also does not take patina designed for lead bearing solders well.

Those using rheostats with their soldering irons, should get rid of the rheostat, as they limit the ability of the iron to recover the soldering temperature. The best iron to use with lead free solders is a temperature controlled iron of 100W or 200W. You can get tips that run at 800F to replace the standard 700F tips. This helps with the higher temperatures needed for the lead free solder. But you should not be vaporizing the solder as the fumes are a health hazard.

Consider the effects of the flux that you are using. Experimenting with various kinds (see below) can lead you to one that works better than the others.

As always, good hygiene and good ventilation are required when soldering. Also you should wash your hands well and frequently, and eat in a separate room.

Flux

An Introduction

Flux is a key contributor to most soldering applications. It is a compound that is used to lift tarnish films from a metal's surface, keep the surface clean during the soldering process, and aid in the wetting and spreading action of the solder. There are many different types and brands of flux available on the market; check with the manufacturer or reseller of your flux to ensure that it is appropriate for your application, taking into consideration both the solder being used and the two metals involved in the process. Although there are many types of flux available, each will include two basic parts, chemicals and solvents.

The chemical part includes the active portion, while the solvent is the carrying agent. The flux does not become a part of the soldered joint, but retains the captured oxides and lies inert on the joint's finished surface until properly removed. It is usually the solvent that determines the cleaning method required to remove the remaining residue after the soldering is completed. It should be noted that while flux is used to remove the tarnish film from a metal's surface, it will not (and should not be expected to) remove paint, grease, varnish, dirt or other types of inert matter. A thorough cleaning of the metal's surface is necessary to remove these types of contaminates. This will greatly improve the fluxing efficiency and also aid in the soldering methods and techniques being used.

Courtesy of American Beauty Tools

The Action of Fluxes

All common untreated metals and metal alloys (including solders) are subject to an environmental attack in which their bare surfaces become covered with a non-metallic film, commonly referred to as tarnish. This tarnish layer consists of oxides, sulphides, carbonates, or other corrosion products and is an effective insulating barrier that will prevent any direct contact with the clean metal surface which lies beneath. When metal parts are joined together by soldering, a metallic continuity is established as a result of the interface between the solder and the surfaces of the two metals. As long as the tarnish layer remains, the solder and metal interface cannot take place, because without being able to make direct contact it is impossible to effectively wet the metal's surface with solder.

The surface tarnishes that form on metal are generally not soluble in - and cannot be removed by - most conventional cleaning solvents. They must, therefore be acted upon chemically, or mechanically, in order to be removed. The required chemical reaction is most often accomplished by the use of soldering fluxes. These soldering fluxes will displace the atmospheric gas layer on the metal’s surface and upon heating will chemically react to remove the tarnish layer from the fluxed metals and maintain the clean metal surface throughout the soldering process.

Chemical reactions


The chemical reaction that is required to remove the tarnish layer will usually be one of two basic types.

It can be a reaction where the tarnish and flux combine forming a third compound that is soluble in either the flux or its carrier.

An example of this type of reaction takes place between water-white rosin and copper oxides. Water-white rosin, when used as a flux is usually in an isopropyl alcohol carrier and consists mainly of abietic acid and other isomeric diterpene acids that are soluble in several organic solvents. When applied to an oxidized copper surface and heated, the copper oxides will combine with the abietic acid forming a copper abiet (which mixes easily with the un-reacted rosin) leaving a clean metallic surface for solder wetting. The hot molten solder displaces the rosin flux and the copper abiet, which can then be removed by conventional cleaning methods.

Another type of reaction is one that causes the tarnish film, or oxidized layer to return to its original metallic state restoring the metals clean surface.

An example of this type of reaction takes place when soldering under a blanket of heated hydrogen. At elevated temperatures (the temperature that is required for the intended reaction to take place is unique to each type of base metal) the hydrogen removes the oxides from the surface, forming water and restoring the metallic surface, which the solder will then wet. There are several other variations and combinations that are based on these two types of reactions.

Flux as a temporary protective coating

Once the desired chemical reaction has taken place (lifting or dissolving the tarnish layer) the fluxing agent must provide a protective coating on the cleaned metal surface until it is displaced by the molten solder. This is due to the elevated temperatures required for soldering causing the increased likelihood that the metal’s surface may rapidly re-oxidize if not properly coated. Any compound that can be used to create one of the required types of chemical reactions, under the operating conditions necessary for soldering, might be considered for use as a fluxing material. However, most organic and inorganic compounds will not hold up under the high temperature conditions that are required for proper soldering. That is why one of the more important considerations is a compounds thermal stability, or its ability to withstand the high temperatures that are required for soldering without burning, breaking down, or evaporating.

When evaluating all of the requirements necessary for a compound to be considered as a fluxing agent, it is important to consider the various soldering methods, techniques and processes available and the wide range of materials and temperatures they may require. A certain flux may perform well on a specific surface using one method of soldering and yet not be at all suitable for that same surface using a different soldering method. When in doubt it never hurts to check with the flux, or solder manufacturer for recommendations.

Courtesy of American Beauty Tools

Flux Categories

A. Rosin Fluxes

Rosin based fluxes are made from rosin which is extracted from pine sap. The purified product is known as "Water White Rosin". The active ingredient is an organic acid, abietic acid and may contain homologues such as dehydro abietic acid and leviopmaric acid.

In addition to rosin other activators may be present at different levels to increase the ability to clean and de oxidise. Activators are compounds that decompose at soldering temperatures yielding ammonia or hydrochloric acid in the process. Flux activity is categorised as R (rosin only), RMA (rosin mildly activated) and RA (rosin activated). A low boiling solvent such as isopropanol is used as the vehicle so they are flammable.

Type R containing only rosin is the least active and is recommended for surfaces very clean to start with. It leaves virtually no residue behind. Thus this is the best rosin based flux for copper foil and lead cames.

Type RMA contains a small amount of additional activator to enhance cleaning and de-oxidisation leaving only a minimum amount of inert residue behind. A characteristic of RMA fluxes is that the remaining residue be non-corrosive, tack free, and exhibit a high degree of freedom from ionic contamination after cleaning. These fluxes are acceptable, but more difficult to clean. They are not acceptable for conservation work.

Type RA are most active of the rosin fluxes, and leave the most residue, however the residues can be removed with appropriate flux cleaners. The residues are really difficult to remove in decorative glass work circumstances and should not be used.

B. Water Soluble Fluxes

These are called water-soluble, as the residue left after soldering is water soluble, although the flux is not. The so-called water-soluble fluxes are divided into two categories, organic and inorganic based on composition. Organic fluxes are more active than RA rosin, and inorganic are the most active of all. Both of these are the best of all fluxes to use in decorative glass work, as the residues are water soluble making clean-up easier, and they are more effective in wetting and keeping the copper and lead free from oxidisation at soldering temperatures.

Other articles in this series are:
Processes
Tools