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.
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Of metals
Solderability varies depending on the type of solder alloy under discussion. The discussion that follows applies only to unspecified electronic solders
{| class="wikitable" align="center"
|+Solderability of various metals
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! Solderability !! Metal !! Remarks
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| Excellent || Tin<br />Cadmium<br />Gold<br />Silver<br />Palladium<br />Rhodium || Noble metals dissolve easily in solders, resulting in brittle joints.
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| Good || Copper<br />Bronze<br />Brass<br />Lead<br />Nickel silver<br />Beryllium copper || High thermal conductivity of these metals requires high heat input during soldering. Oxidizes quickly so proper flux must be used.
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| Fair || Carbon steel<br />Low alloy steel<br />Zinc<br />Nickel || Solder joints become brittle in sulfur-rich environments. Avoid higher temperatures in the presence of lubricants (which contain sulfur).
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| Poor || Aluminium<br />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. They most often require flux and brushing with a stainless steel brush to break oxide coating to achieve proper bond.
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| Difficult || High alloy steel<br />Stainless steels || Too much chromium oxide. The surface needs to be cleaned with an aggressive flux.
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| Very Difficult || Cast iron<br />Chromium<br />Titanium<br />Tantalum<br />Magnesium || May require pre-plating, or pre-tinning, with a solderable metal or will require the use of a specialized solder.
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Testing solderability
Both quantitative and qualitative tests for solderability exist.
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.