"The Solder Shop"

Discussion in 'The Academy' started by rcline, Feb 16, 2005.

  1. rcline

    rcline Member

    Welcome to “The Solder Shop”. Please post no replies here. Every few days I will be adding
    more and more to the solder shop. Also I will start a thread that we will call the “The solder Shop Q/A”. Under that thread I will answer all your questions on a one on one basis.

    The idea of the solder shop is to “lightly” cover several different areas of the soldering field.
    What is solder and rosin. How the two work together. and to give you a new out look on soldering.

    So let’s get started!

    Solder is an alloy composed of two different metals, which are Tin and lead. The melting point of lead is 621 degrees F. While the melting point of tin is at 450 degrees F. When the two alloys are mixed together to form solder, it now has a melting point of 361 degrees F. The alloy Solder is identified by its tin / lead percentage weight ratios. The tin content is always listed first, as in this ratio figure. Sn 60/40 ( Sn – the symbol for tin and 60 for representing 60% by weight, therefore 40 represents 40% lead by weight ratio).

    All solder starts to melt at 361 degrees F. and all solder, ( except Sn 63/37 ) goes through 3 different states. First is the solid, then at 361 degrees it starts to melt and goes into what is called the plastics or putty range, and after it heats up a little more, then it becomes a liquid. Sn 60/40 becomes a liquid at 370 degrees F. Upon cooling down the process is reversed. It goes from a liquid to a putty and then to a solid.

    Sn 63/37 starts to melt at 361 degrees F. and then at 361.5 degrees F. it is a liquid. Sn 63/37 is what we call Eutectic solder. It has no plastics or putty range. ( This is the only solder that I use because I don’t have to be as careful while holding my soldered connections in place while I’m waiting for the solder to cool down).

    Principals of Soldering:

    1. Soldering is in a group of welding processes which produce a joining of material by heating them to a suitable temperature and using a filler material having a liquidus ( melting temperature ) of “less” than 800 degrees F. The filler material is distributed between the closely fitted surfaces by capillary action and wetting. When molten solder leaves a continuous, permanent film and an intermetallic zone on a base metal, (meaning,when the molecules of the solder melt into and mix with the molecules of the base metal ) it is said to wet the surface. Without wetting there can be no soldering (welding) action. In order for wetting to occur there must be a surface mixing of the solder atoms and the base metal atoms. This surface mixing yields the intermetallic zone. The intermetallic zone is a new alloy composed of the solder metals plus the base metals.

    2. Intermetallic reactions usually take place at the interface between the base metal and the solder. This reaction is partly chemical in nature. The liquid solder works as a solvent on the base metal, somewhat like water on a salt block. Small amounts of the base metal are dissolved and mix with the solder, while some of the solder soaks into the base metal and mixes with its molecules. Since the wetting process has mixed the base metal with the solder, a new alloy has been formed. If the base metal is copper, then the resultant alloy (intermetallic zone) is one of lead, tin and copper, having physical characteristics different from the solder or the copper.

    3. Since heat is applied to facilitate the wetting process, care must be taken to avoid to much heat or an excessive amount of time that the heat is applied. Excessive intermetallic reactions may cause brittleness in the joint being soldered.

    4. Wetting is a liquid actually touching or adhering to a solid surface. Wetting is facilitated by the ability of solder to alloy with the base metal. For example, pure lead does not readily wet to copper or steel, where as solder readily wets both. Some other metals increase the wetting properties even farther.

    5. The forces of capillary action and interfacial tension assist solder to wet and spread along a base metal. Capillary action is the force of adhesion between a solid and a liquid. The capillary action in soldering is the drawing of a liquid between closely spaced solids, a consequence of surface tension, cohesion and adhesion.

    6. Cohesion is the molecular attraction by which the particles of a body are united throughout the mass and Adhesion is the molecular attraction exerted between the surfaces of the bodies in contact.


    1. Solder solvent action and the corresponding wetting cannot occur unless the base metal is free of all oils, greases, dirt and any chemical reactions. All metals and metal alloys, when exposed to air at room temperatures, are constantly under going chemical reactions. These reactions are primarily oxidations, the combining of an element with oxygen. Small amounts of nitrides, sulfides, and carbides are also forming depending on the ambient conditions. ( This is the main reason for our tracks getting dirty)

    2. Oxides of aluminum, magnesium and stainless steel are very hard and act as a shield for the metal, protecting it from further chemical attack. Copper, silver and lead oxides fortunately are easier to remove, therefore soldering to these metals can be facilitated by the use of mild fluxs.

    Flux Core Solder

    1. One restrictive feature about soft solder fluxes is that they are generally unsuited to sustained high temperature applications due to a fundamental thermal instability. For instaintance, no soldering flux possesses the stability or resistance to thermal decomposition to remain continuously active at the temperatureof a soldering iron, which normally runs from about 600 degrees to 800 degrees F.

    2. Organic and Resin type fluxes, in which the naturally organic solvents are singularly prone to volatilize at low temperatures. However, in addition to loss of solvent and subsequent decrease in ionic behavior, the organic and resin fluxes themselves are highly subject to thermal decomposistion, carbonization, or volatilization at temperatures not far greater than the boiling point of any solvent that may be employed.

    "The Golden Rule of Soldering"

    1. Briefly this rule stipulates that the cored solder strand must be applied at the exact junction between the flat surface of the adequately heated soldering iron and the metal being soldered, ( except when soldering pretinned conductors and componet leads ) inorder that solder and flux may be simultaneously liberated at the exact point where solder adhesion is desired. The soldering flux, unlike molten solder, will not flow down the side of a hot soldering iron.

    2. In general, as heating proceeds, an insulating film of oxide rapidly forms over the surface of both metals which retards the flow of thermal engery, and it is at this point that the application of flux becomes important. As the strand of solder melts, the released flux removes the oxide films so that the intervening space is immediately filled with a conductive colum of solder to the unit being soldered.

    3. In addition, there must be a thermally conductive colum of molten solder, between the two hot surfaces in order to secure successful and efficient soldering.


    1. Flux can be a solid, paste or putty, a liquid or even a gaseous material, which when heated is capable of providing or accelerating wetting of a material by solder.

    Purpose of flux

    1. It cleans, removes and excludes oxides and other impurities from the joint being soldered.
    2. Prevents re-oxidation. (The molten flux flowing on the joint excludes air from the joint.)
    3. Aids in the wetting action.

    Classes of Flux

    1. Corrosive --------- Inorganic salts and acids
    2. Non-Corrosive -- Natural rosins only, which sometimes has mild additives

    Types of Flux

    1. Type R ----------- Rosin
    2. Type RMA ----- Rosin mildly activated
    3. Type RA -------- Rosin highly activated

    Forms of Fluxs
    symbol form
    1. S Solid (meaning solid metal with no flux)
    2. L Liquid
    3. P Paste or Plastics
    4. D Powder or Pellets

    Flux Percentage

    Solder which has flux manufactured into it has a percentage rating. The percentage of the flux that is manufactured into the solder is based on weight. Meaning that "X" amount of solder has "X" amount of flux in it. The flux percentage symbols are: 1, 2, 3, 4 and 6. The percentage amounts are as follows:
    percentage symbol flux percentage
    1 --------------------- 0.8 thru 1.5
    2 --------------------- 1.6 ------ 2.6
    3 --------------------- 2.7 ------ 3.9
    4 --------------------- 4.0 ------ 5.0
    6 --------------------- 6.0 ------ 7.0

    Properties of Rosin Flux

    1. Melts at 260 degrees F. and remains active in molten state to 600 degrees F.
    2. Will decompose and char at 545 degrees F.
    3. Active constituent of rosin is abietic acid.
    4. Abietic Acid:
    A. Inert in solid state
    B. Active when molten
    C. Becomes inert (inactive) when it cools
    5. Activators added are organic chlorides:
    A. Primarily, Amine Hydrochloride
    B. At soldering temperatures, hydrogen chloride is released to do chemical cleaning
    (at disassociation temperatures)
    C. It will recombine upon cooling leaving non-corrosive residues.

    Forms of Solder:
    Solder comes in several different types of forms and these forms are noted by a single
    1. - B -- Bar
    2. - I -- Ingot
    3. - P -- Powder
    4. - R -- Ribon
    5. - W - Wire
    6. - S -- Special ( includes pellets and preforms )

    Now that we have covered several different forms of solder and flux, lets take a look at a spool of solder to see just what type of solder it is and weather or not it has a flux core center. When reading the label on the side of a spool of solder, I see the following code: Sn60 W R 2
    From what we learned above, we know that Sn60 is showing us that the solder is made up of
    60% tin and 40% lead. The "W" is showing that the solder form is of wire type. The "R" is showing that the wire solder has a rosin center core and the "2" is showing that the rosin flux percentage is "1.6 - 2.6".
    If we see: Sn60 W S, we know that the solder is 60% tin and is of wire form and it is solid wire with out a rosin core center.
    If we see: Sn60-W-R-P2, we know that the solder is 60% tin and is of wire form and it has a rosin core center and that the rosin is a paste or putty with a percentage rating of 2.
  2. rcline

    rcline Member

    Soldering Irons:
    The most fundamental skill needed to assemble any electronic project is that of soldering. It takes some practice to make the perfect joint, but, like riding a bicycle, once learned is never forgotten! The idea is simple: to join electrical parts together to form an electrical connection, using a molten mixture of lead and tin (solder) with a soldering iron. A large range of soldering irons is available - which one is suitable for you depends on your budget and how serious your interest in electronics is.

    Voltage: Most irons run from the mains at 120V (240v.over the great waters). However, low voltage types (e.g. 12V or 24V) generally form part of a "soldering station" and are designed to be used with a special controller made by the same manufacturer.
    Wattage: Typically, they may have a power rating of between 15-25 watts or so, which is fine for most work. A higher wattage does not mean that the iron runs hotter - it simply means that there is more power in reserve for coping with larger joints. This also depends partly on the design of the "bit" (the tip of the iron). Consider a higher wattage iron simply as being more "unstoppable" when it comes to heavier-duty work, because it won't cool down so quickly.

    Temperature Control: the simplest and cheapest types don't have any form of temperature regulation. (I use an $8 special from Radio Shack and it works just fine for all my hobby needs!) Simply plug them in and switch them on! Thermal regulation is "designed in" (by physics, not electronics!): they may be described as "thermally balanced" so that they have some degree of temperature "matching" but their output will otherwise not be controlled. Unregulated irons form an ideal general purpose iron for most users, and they generally cope well with printed circuit board soldering and general interwiring. Most of these "miniature" types of iron will be of little use when attempting to solder large joints (e.g. very large terminals or very thick wires) because the component being soldered will "sink" heat away from the tip of the iron, cooling it down too much. (This is where a higher wattage comes in useful.)
    A proper temperature-controlled iron will be quite a lot more expensive and will have some form of built-in thermostatic control, to ensure that the temperature of the bit (the tip of the iron) is maintained at a fixed level (within limits). This is desirable especially during more frequent use, since it helps to ensure that the temperature does not "overshoot" in between times, and also guarantees that the output will be relatively stable. Some irons have a bimetallic strip thermostat built into the handle which gives an audible "click" in use: other types use all-electronic controllers, and some may be adjustable using a screwdriver.

    soldering stations consist of a complete bench-top control unit into which a special low-voltage soldering iron is plugged. Some versions might have a built-in digital temperature readout, and will have a control knob to enable you to vary the setting. The temperature could be boosted for soldering larger joints, for example, or for using higher melting-point solders (e.g. silver solder). These are designed for the most discerning users, or for continuous production line/ professional use. The best stations have irons which are well balanced, with comfort-grip handles which remain cool all day. A thermocouple will be built into the tip or shaft, which monitors temperature.

    Anti-static protection: if you're interested in soldering a lot of static-sensitive parts (e.g. CMOS chips or MOSFET transistors), more advanced and expensive soldering iron stations use static-dissipative materials in their construction to ensure that static does not build up on the iron itself. You may see these listed as "ESD safe" (electrostatic discharge proof). The cheapest irons won't necessarily be ESD-safe but never the less will still probably perform perfectly well in most hobby or educational applications, if you take the usual anti-static precautions when handling the components. The tip would need to be well earthed (grounded) in these circumstances.
    Bits: it's useful to have a small selection of manufacturer's bits (soldering iron tips) available with different diameters or shapes, which can be changed depending on the type of work in hand. You'll probably find that you become accustomed to, and work best with, a particular shape of tip. Often, tips are iron-coated to preserve their life, or they may be bright-plated instead. Copper tips are seldom seen these days.

    Spare parts: it's nice to know that spare parts may be available, so if the element blows, you don't need to replace the entire iron. This is especially so with expensive irons. Check through some of the larger mail-order catalogues.

    You will occasionally see gas-powered soldering irons which use butane rather than the mains electrical supply to operate. They have a catalytic element which, once warmed up, continues to glow hot when gas passes over them. Service engineers use them for working on repairs where there may be no power available, or where a joint is tricky to reach with a normal iron, so they are really for occasional "on the spot" use for quick repairs, rather than for mainstream construction or assembly work. A solder gun is a pistol-shaped iron, typically running at 100W or more, and is completely unsuitable for soldering modern electronic components: they're too hot, heavy and unwieldy for micro-electronics use. Plumbing, maybe..!

    Soldering irons are best used along with a heat-resistant bench-type holder, so that the hot iron can be safely parked in between use. Soldering stations already have this feature, otherwise a separate soldering iron stand is essential, preferably one with a holder for tip-cleaning sponges. Now let's look at how to use soldering irons properly, and how to put things right when a joint goes wrong.

    Turning to the actual techniques of soldering, firstly it's best to secure the work somehow so that it doesn't move during soldering and affect your accuracy. In the case of a printed circuit board, various holding frames are fairly popular especially with densely populated boards: the idea is to insert all the parts on one side ("stuffing the board"), hold them in place with a special foam pad to prevent them falling out, turn the board over and then snip off the wires with cutters before making the joints. The frame saves an awful lot of turning the board over and over, especially with large boards. Other parts could be held firm in a modeller's small vice, for example.

    Solder joints may need to possess some degree of mechanical strength in some cases, especially with wires soldered to, say, potentiometer or switch tags, and this means that the wire should be looped through the tag and secured before solder is applied. The down side is that it is more difficult to de-solder the joint (see later) and remove the wire afterwards, if required. Otherwise, in the case of an ordinary circuit board, components' wires are bent to fit through the board, inserted flush against the board's surface, splayed outwards a little so that the part grips the board, and then soldered.

    Methods of Heat Transfer:

    Soldering Iron Tips-
    1. The efficiency of a soldering iron in transferring heat to the assembly to be soldered is controlled by 3 factors:
    (A) The soldering tip should have a high thermal conductivity in order that the heat transfer may be rapid and effective.
    (B) The tip should be capable of ready tinning in order that there may always be a completely metallic path through which the conducted heat, which accumlates at the tips surface, may be readily transmitted to the assembly.
    (C) The tip should have a low solubility in molten solder in order to prevent excess pitting due to solvent action of the solder.

    Next to silver, copper has by far the highest thermal conductivity of the metals, it is this property, coupled with its ready ease of tinning, that accounts for its unusual efficiency as a soldering tip. However coppeer pits and dissolves quite repidly and requires frequent and periodic dressing. ( When dressing of the tip is needed, use a fine flat file and lightly file the tip until all pits are removed, then retin with solder ) This pitting of the soldering tip is not due, (as some people think) to errosion or to corrosion by the flux, but is due to metal solvent action of the molten solder on the metal tip. Steel, on the other hand, is virtually insoluble to molten solder, therefore, they are not subject to pitting and have a longer operating life span.

    The perfectly soldered joint will be nice and shiny looking, and will prove reliable in service.

    Definitions of solder joint defects:

    1. Cold Joints - A cold joint will appear full, round, piled up and will usually be shiny.
    The solder will not have the characteristic feathered out low fiiet of a good joint.

    2. Overheated Joint - The joint will appear dull, chalky and granular. This condition is caused by excessive iron temperature allowing the iron tip to remain on the connection to long, or the remelting of the soldered connection several times.

    3. Fractured Joint - This joint will resemble the dull, chalky or granular appearance to the overheated joint, but in addition will have a crack between the conductors. This condition results from moving the wire or conductor before the solder solidifies.

    4. Improperly Bonded Joint - This joint will usually have a demarcation line between the conductors. This condition is often caused by oxidized, dirty, greasy or otherwise contaminated conductors or componet leads.

    5. Pitted or Porosity Joint- This joint will show evidence of pits, pin holes or small craters in the solder. This joint can be caused by oxidization, the type of plating material used on conductors (gold plating will cause this condition) or other foreign matter not compatible with solder. This joint may also appear dull, depending on the amount of contamination present.

    6. Excess Solder - The contour of the wire or conductor will be covered by solder to the extent that a visual inspection will not determine if a proper bond has been achieved. (Meaning that there is so much solder that the strands of the conductor
    cannot be seen at all and there is no feathering out of the edges of the solder)

    7. Insufficient Solder - Conductors with insufficient solder will have the apperance of being tinned and/or sweated together with no apparent fillet. A joint should have
    sufficient solder to produce a low fillet between the conductors.
  3. rcline

    rcline Member

    New info added to first post.

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