Solder Dictionary of Terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Activator
The chemically reactive portion of a Flux. Activator cleans metal surfaces of oxides and contaminants, promoting wetting of Solder Alloy. Activator is consumed by heat over time.
Alloy
A substance composed of two or more metal elements. Example: Sn96.5 Ag3.0 Cu0.5 is 96.5% Tin, 3.0% Silver, and 0.5% Copper. Generally, alloys will have different properties than those exhibited by their individual elements (e.g. tensile strength, melting temperatures).
Area Array Package
A surface-mount component with a grid of connection points on the bottom.
Ball Grid Array (BGA)
A surface-mount component containing a processor, and sometimes additional components, where the bottom has a grid of connection points with solder balls attached. BGA packages, and other area array packages, allow for higher connection counts and connection density than other surface-mount packages.
Brazing
A method of joining metals that involves the use of a filler metal or alloy that melts over 450° C (842° F) and below the melting temperature of substrate materials. Brazing differs from soldering by the melting temperature of the alloy (greater than 450° C for brazing and less than 450° C for soldering.)
Brazing Alloy
Alloy used as the filler metal in the brazing process. Some typical brazing alloys include copper-zinc, copper-gold, copper-phosphorous, and silver-based alloys. The melting temperatures for brazing alloys range from 450° C (852° F) to 1100° C (2012° F).
Bridging
Formation of a solder alloy connection between two or more adjacent contacts.
Bumped Circuit Boards
Bare printed circuit boards that have had solder paste deposited and reflowed on the pads prior to component installation.
Burn In
The functional operation of components or assemblies, as a test for defects or failure prior to putting into use.
Capillary Action
The ability of a liquid to flow in narrow spaces independent of external forces like gravity. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces.
Cold Solder Joint
A solder connection that was made with insufficient heat. The possible causes include too short contact time or low soldering temperature. This is evident by poor wetting, a non-smooth surface, and/or a chalky or grainy appearance.
Compacting
Solder alloy in solder paste that has been compressed into a dense, low-flowing or non-flowing condition caused by repeated pressure cycles, flow restriction, vibration, and/or high temperatures. Compacting during solder paste dispensing, can be observed in the dispense tip and all other sections of the flow path.
Copper Mirror Test
IPC–TM-650 2.3.32: The test method designed to determine the removal effect the flux has, if any, on the bright copper mirror film, which has been vacuum deposited on clear glass.
Dendrites (dendritic growths)
Branch or snowflake-like patterns of metal that grow on surfaces between conductors. It requires a chemical reaction capable of dissolving the metal into a solution of metal ions, which are then redeposited by electro-migration in the presence of an electromagnetic field.
De-soldering
The removal of solder and components from a circuit, usually for purposes of repair.
De-wetting
A condition where molten solder has coated a surface and then receded, leaving irregularly shaped mounds of solder separated by areas covered with a thin solder film.
Dissolution
The chemical change that takes place as solid materials dissolve into liquid materials. This is NOT a function of all the materials melting, but rather a dissolving of one material into another. This is like dissolving sugar into water. The sugar has not reached its melting temperature, but readily dissolves into liquid water.
Disturbed Solder Joint
A solder fillet that solidified while the solder joint was moving. The result is a distorted fillet with an irregular surface texture.
Drawbridging
See Tombstoning.
ENIG
Surface finishing process of electroless nickel followed by immersion gold. During soldering the gold is dissolved into the solder joint.
Eutectic
An alloy composition where the alloy melts and solidifies at a single temperature. Ex: Sn63 Pb37 alloy melts and solidifies at 183° C (361° F).
Fillet
Solder formation at the intersection of surfaces of a solder connection.
Fine Pitch
Centerline spacing of leads 0.5 mm (20 mils) or less.
Flux
A material that cleans metal surfaces of absorbed gases, oxide films, and other surface contaminants. Flux comes in three forms: solid, paste, and liquid. Solid flux is most often found inside flux core solder wire. Paste flux is used for precise flux application. It can be used by itself or combined with powdered solder alloy to form solder paste. Liquid flux is used in low precision and large area fluxing, such as wave soldering. See Nordson EFD flux products.
Halide or Halides
Positive ionic compound that contains a halogen. Halides may be found in flux activators. See Halogen. See Halides and Halogens white paper.
Halide Free
Solder flux containing less than 0.05% quantitative halide.
Halogen
Elements in the 17th column of the periodic table: Fluorine, Chlorine, Bromine, Iodine, and Astatine. See Halides and Halogens white paper.
Halogen Free
Solder flux containing less than 900 ppm each of Chlorine and Bromine with a total of less than 1500 ppm of halogen of flux solids.
High Temperature Alloy
Refers to a solder alloy with a solidus temperature above 230° C (446° F). See Solidus.
Hygroscopic
The capacity of a material or compound to absorb and retain moisture from its environment.
Icicle
An unacceptable sharp point of solder that protrudes out of a solder joint. Icicles are formed when a soldering iron is withdrawn from the solder joint and either the joint is too cold or all flux activity has been exhausted.
Intermetallic Layer
An intermediary layer of metal at the interface of solder and a wetted surface that is a mixture (alloy) of the solder metal and the base metals. This is formed through diffusion, not a melting of component metals.
J-Standard
Joint Industry Standard published by the Institute of Interconnecting and Packaging Electronic Circuits (IPC).
Leaching
(In soldering terms) The migration of base metal into a solder alloy through the process of dissolution.
Liquidus Temperature
Temperature above which a non-eutectic alloy is completely liquid.
Low Temperature Alloy
Refers to a solder alloy with a liquidus temperature below 183° C (361° F). See Liquidus.
Manhattan Effect
See Tombstoning.
Mask (Solder Mask)
A material that is used to protect selected areas of a printed circuit board (PCB) from being soldered.
Melting Point
Temperature at which a pure elemental metal, such as tin, becomes liquid.
Molten
The condition where a material that is solid at room temperature is liquid.
No Clean (NC)
Category of flux designed to be left on a product after soldering, as opposed to cleaning it off.
Non-Wetting
A defect condition where part, or all, of a surface did not wet during the soldering process. Non-wetting is recognized by the fact that the bare base metal is visible (different from de-wetting). It is usually due to the presence of an interference layer (oxidation or contamination) on the surface to be soldered.
Oxidation
Reaction of a metal surface with oxygen forming a metal oxide. The resulting oxidized surface is more difficult to wet.
Oxide
A binary compound of oxygen with another element or group. Metal oxides are more chemically stable than pure metals, which are highly reactive.
Particle Size Distribution (PSD)
Solder alloy powder is classified into types 1 through 7 based on the distribution of powder diameter as detailed in IPC J-STD-005A.
Pitch
The center-to-center spacing of adjacent pads on a surface-mount board or leads on an electrical component.
Plating
A metal coating applied to a surface. There are different plating processes used to produce different thickness including electroless and electrolytic plating.
Popcorning
A term used to describe the effect of water turning into steam inside electrical components during reflow. The pressure caused by the steam can crack the components with some cracks being so severe they propagate to the exterior.
Preheat
The process of stabilizing the work to be soldered at a temperature below the solder melting point. Excessive preheat can reduce flux effectiveness.
Printing
A process for transferring solder to a surface by forcing solder paste through a stencil or screen with a squeegee.
Reflow
A term used to describe the heating and melting of solder alloy that allows it to flow as liquid again.
Reflow Profile
A graph of temperature over time experienced by a product during a reflow process. Reflow profiles are most commonly associated with printed circuit boards heated in reflow ovens.
Residue
The portion of flux that remains after solder paste has been reflowed.
Rosin Activated (RA)
Consists of rosin, solvent, and aggressive activators. RA flux has higher activity than RMA for moderately oxidized surfaces. Most RA flux residues are corrosive and should be removed. Maximum safe time before cleaning is product dependent. Residue may be removed with an appropriate solvent.
Rosin Mildly Activated (RMA)
Consists of rosin, solvent, and a small amount of activator. Most RMA flux is best suited to easily solderable surfaces. RMA flux residue is clear, soft, non-corrosive, and non-conductive. Cleaning is optional. Residue may be removed with an appropriate solvent.
Rosin/Resin (R)
Natural or modified pine tree sap. Resins are processed Rosins. Rosin is the mildly acidic sap found in pine trees and was the first fluxing agent used in the Bronze Age.
Shelf Life
Duration of time a product remains fit for use.
Surface Insulation Resistance (SIR)
Test defined in IPC TM-650 2.6.3.3 used to classify flux. Flux is reflowed on a set of interdigitated traces and an electrical potential is supplied. A passing test maintains a resistance value of 1x108 Ω or greater.
Slump
Test defined in IPC TM-650 2.4.35 to measure the change in shape of solder paste after deposition and before reflow.
Solder Balls
Small spheres of solder that have separated from a solder deposit during reflow.
Solderability
The ability of metal to be wetted by solder during the reflow process.
Solder Paste
Homogenous mixture of powdered solder alloy and paste flux. Solder pastes are formulated for application to a product using printing, dispensing, dipping, and jetting processes. See Nordson EFD solder paste products.
Solidus Temperature
Temperature below which a solder alloy is completely solid.
Spatter or Splatter
The dispersion of flux and alloy away from a solder paste deposit due to explosive vaporization of low boiling point materials in the flux, which can include absorbed or condensed water.
Step Soldering
A process by which successive soldering operations are performed using a different solder alloy at each temperature “step.” The solidus of the higher temperature alloy is higher than the liquidus of the lower temperature alloy. Example: Sn10Pb88Ag2 melts from 268° C (514° F) to 290° C (554° F). A second operation using Sn96.3Ag3.7 that melts at 221° C (430° F) will not disturb the higher temperature joints.
Tackiness
Ability of solder paste to hold surface-mount components in place after placement.
Tensile Strength
Characteristic of a material that describes its resistance to fracture when the material is under tension.
Through hole
A plated hole in a circuit board. Through hole components have leads that are inserted into and soldered to plated through holes.
Tin Whiskers
Whiskers are crystalline, electrically conductive, hair-like structures that grow from metal surfaces. They are thought to be a function of induced stresses. Lead, bismuth, and antimony have been used to decrease the frequency and size of whiskers in tin-bearing alloys.
Tinning
The pre-application of a thin coating of tin or tin-based alloy on the area of a part to be soldered. This coating helps protect the surface from oxidation, promote wettability, and control flow when the solder joint is produced. The tin coating is dissolved into the solder joint during reflow, changing the solder alloy composition.
Tombstoning
Also referred to as “Drawbridging” or the “Manhattan Effect,” tombstoning is the raising up of one end of a leadless component from solder paste as a result of torque applied by the surface tension of liquid solder as it wets. This is usually a function of an imbalance in the wetting forces during reflow. This imbalance can be attributed to many causes. See Tombstone Troubleshooting white paper.
Viscosity
The measure of a material’s resistance to shear. Viscosity is measured in 1000s of centipoises (kcPs).
Voids
Cavities inside a solder joint containing liquids and gases trapped during reflow.
Water Soluble Paste (WS)
A mixture of organic acids, thixotrope, and solvent. WS flux comes in a wide range of activity levels for soldering to even the most difficult surfaces. WS flux residue is corrosive and should be removed as soon as possible after reflow to avoid damage to your assembly. Maximum safe time before cleaning is product dependent.
Wave Soldering
A process of soldering through hole and surface-mount components to printed circuit boards by exposing the lower side to a wave of molten solder.
Wetting
The ability of a liquid to spread across a surface as opposed to drawing into itself. Wetting occurs when the attractive surface energy of the pad, or component lead, is greater than the surface energy of the solder.
Zero Halogen
Solder flux manufactured with no intentionally added halogens.
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