Solderability

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The solderability of a substrate is a measure of the ease with which a soldered joint can be made to that material. Good solderability requires wetting (low contact angle) of the substrate by the solder. [1]

Contents

Of metals

Solderability varies depending on the type of solder alloy under discussion. The discussion that follows applies only to unspecified electronic solders [2] (which may include solders that contain lead, now banned for use in nearly all electronic equipment made or sold in the EU). Solderability when using lead-free alloys can differ significantly from solderability when using lead based alloys.

Noble metals may be easy to solder but they have brittle joints. The metals in the good category require a large amount of heat therefore oxidation is an issue. To overcome this a flux is required. For carbon steel, low alloy steel, zinc, and nickel the presence of sulfur creates a brittle joint; lower temperatures are used to minimize this problem. The oxides on the surface of aluminium cause wetting issues and special solders must be used to prevent galvanic corrosion issues. Stainless steel and high alloy steel have a low solderability because the chromium alloying element creates oxides that require aggressive fluxes. The only way that the final category of metals can be soldered is by pre-plating them in a metal that is solderable. [2]

Solderability of various metals [2]
Solderability          Metal          Remarks
Excellent Tin
Cadmium
Gold
Silver
Palladium
Rhodium
Noble metals dissolve easily in solders, resulting in brittle joints.
Good Copper
Bronze
Brass
Lead
Nickel silver
Beryllium copper
High thermal conductivity of these metals requires high heat input during soldering. Oxidizes quickly so proper flux must be used.
Fair Carbon steel
Low alloy steel
Zinc
Nickel
Solder joints become brittle in sulfur-rich environments. Avoid higher temperatures in the presence of lubricants (which contain sulfur).
Poor Aluminium
Aluminium bronze
Tough oxides on the surface prevent wetting (formation of the inter-metallic layers). Solders have to be specially selected to avoid galvanic corrosion problems. Tin-zinc solders have proven to be reliable in joining aluminum to aluminum and aluminum to copper. [3] They most often require flux and brushing with a stainless steel brush to break oxide coating to achieve proper bond.
Difficult High alloy steel
Stainless steels
Too much chromium oxide. The surface needs to be cleaned with an aggressive flux.
Very Difficult Cast iron
Chromium
Titanium
Tantalum
Magnesium
May require pre-plating, or pre-tinning, [4] with a solderable metal or will require the use of a specialized solder. [5]

Testing solderability

Both quantitative and qualitative tests for solderability exist. [6] The two most common testing methods are the 'dip and look' method and wetting balance analysis. In both of these tests, the soldered pieces undergo an accelerated aging process before being tested for solderability, to take into consideration the time a component was in storage prior to mounting to final assembly. The dip and look method is a qualitative test. One form of it is specified as Mil-Std-883 Method 2003. On the other hand, the wetting balance analysis is a quantitative test that measures the wetting forces between molten solder and the test surface as a function of time.

Related Research Articles

<span class="mw-page-title-main">Soldering iron</span> A hand tool for soldering

A soldering iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two workpieces.

<span class="mw-page-title-main">Solder</span> Alloy used to join metal pieces

Solder is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.

<span class="mw-page-title-main">Hot-dip galvanization</span> Process of coating iron or steel with molten zinc

Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and is considered superior in terms of cost and life-cycle. It can be identified by the crystallization patterning on the surface (often called a "spangle").

<span class="mw-page-title-main">Brazing</span> High-temperature soldering; metal-joining technique by high-temperature molten metal filling

Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.

<span class="mw-page-title-main">Flux (metallurgy)</span> Chemical used in metallurgy for cleaning or purifying molten metal

In metallurgy, a flux is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time. They are used in both extractive metallurgy and metal joining.

Forge welding (FOW), also called fire welding, is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces. The process is one of the simplest methods of joining metals and has been used since ancient times, being a staple of traditional blacksmithing. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical welding and gas welding methods during the Industrial Revolution, manual forge-welding has been largely replaced, although automated forge-welding is a common manufacturing process.

<span class="mw-page-title-main">Desoldering</span>

In electronics, desoldering is the removal of solder and components from a circuit board for troubleshooting, repair, replacement, and salvage.

<span class="mw-page-title-main">Wave soldering</span>

Wave soldering is a bulk soldering process used for the manufacturing of printed circuit boards. The circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave. As the circuit board makes contact with this wave, the components become soldered to the board. Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued onto the surface of a printed circuit board (PCB) by placement equipment, before being run through the molten solder wave. Wave soldering is mainly used in soldering of through hole components.

<span class="mw-page-title-main">Gold plating</span>

Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver, by chemical or electrochemical plating. This article covers plating methods used in the modern electronics industry; for more traditional methods, often used for much larger objects, see gilding.

<span class="mw-page-title-main">Reflow soldering</span> Attachment of electronic components

Reflow soldering is a process in which a solder paste is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subjected to controlled heat. The solder paste reflows in a molten state, creating permanent solder joints. Heating may be accomplished by passing the assembly through a reflow oven, under an infrared lamp, or (unconventionally) by soldering individual joints with a desoldering hot air pencil.

A filler metal is a metal added in the making of a joint through welding, brazing, or soldering.

Solder paste is used in the manufacture of printed circuit boards to connect surface mount components to pads on the board. It is also possible to solder through-hole pin in paste components by printing solder paste in and over the holes. The sticky paste temporarily holds components in place; the board is then heated, melting the paste and forming a mechanical bond as well as an electrical connection. The paste is applied to the board by jet printing, stencil printing or syringe; then the components are put in place by a pick-and-place machine or by hand.

<span class="mw-page-title-main">Selective soldering</span>

Selective soldering is the process of selectively soldering components to printed circuit boards and molded modules that could be damaged by the heat of a reflow oven or wave soldering in a traditional surface-mount technology (SMT) or through-hole technology assembly processes. This usually follows an SMT oven reflow process; parts to be selectively soldered are usually surrounded by parts that have been previously soldered in a surface-mount reflow process, and the selective-solder process must be sufficiently precise to avoid damaging them.

<span class="mw-page-title-main">Dip soldering</span>

Dip soldering is a small-scale soldering process by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly. The solder wets to the exposed metallic areas of the board, creating a reliable mechanical and electrical connection.

<span class="mw-page-title-main">Glass-to-metal seal</span>

Glass-to-metal seals are a very important element of the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass encapsulated semiconductor diodes, reed switches, pressure tight glass windows in metal cases, and metal or ceramic packages of electronic components.

<span class="mw-page-title-main">Soldering</span> Process of joining metal pieces with heated filler metal

Soldering is a process in which two or more item are joined by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Unlike welding, soldering does not involve melting the work pieces. In brazing, the work piece metal also does not melt, but the filler metal is one that melts at a higher temperature than in soldering. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes.

Tin-silver-copper, is a lead-free (Pb-free) alloy commonly used for electronic solder. It is the main choice for lead-free surface-mount technology (SMT) assembly in the industry, as it is near eutectic, with adequate thermal fatigue properties, strength, and wettability. Lead-free solder is gaining much attention as the environmental effects of lead in industrial products is recognized, and as a result of Europe's RoHS legislation to remove lead and other hazardous materials from electronics. Japanese electronics companies have also looked at Pb-free solder for its industrial advantages.

<span class="mw-page-title-main">Wiped joint</span> Form of soldered joint used

A wiped joint is a form of soldered joint used to join lead pipework.

<span class="mw-page-title-main">Aluminium joining</span>

Aluminium alloys are often chosen due to their high strength-to-weight ratio, corrosion resistance, low cost, high thermal and electrical conductivity. There are a variety of techniques to join aluminium including mechanical fasteners, welding, adhesive bonding, brazing, soldering and friction stir welding (FSW), etc. Various techniques are used based on the cost and strength required for the joint. In addition, process combinations can be performed to provide means for difficult to join assemblies and to reduce certain process limitations.

<span class="mw-page-title-main">Solder alloys</span>

Solder is a metallic material that is used to connect metal workpieces. The choice of specific solder alloys depends on their melting point, chemical reactivity, mechanical properties, toxicity, and other properties. Hence a wide range of solder alloys exist, and only major ones are listed below. Since early 2000s the use of lead in solder alloys is discouraged by several governmental guidelines in the European Union, Japan and other countries, such as Restriction of Hazardous Substances Directive and Waste Electrical and Electronic Equipment Directive.

References

  1. Solders, fluxes, and solderability Section 5: Solderability , www.tutorialsweb.com
  2. 1 2 3 Solderability , retrieved 2009-11-30.
  3. Kapp Alloy. "KappAloy". Kapp Alloy & Wire, Inc. Retrieved 23 October 2012.
  4. Kapp Alloy. "Kappa Tinning Compound". Kapp Alloy & Wire, Inc. Retrieved 4 April 2013.
  5. Kapp Alloy GalvRepair. "Kapp GalvRepair". Kapp Alloy & Wire, Inc. Retrieved 23 October 2012.
  6. Solderability Testing www.eesemi.com