SMT term explanation

Activator

The activator is the key to providing good electrical contact. It remains relatively stable at low temperatures, but as soon as it enters the oven, it becomes very active and begins to act as an acid, eroding the metal surface. This can effectively "scrub" all metal surfaces to remove oxides, oils and other contaminants, allowing metal alloys to properly wet other surfaces (circuit board gaskets, component leads, wires, etc.).

alloy

A compound composed of two or three metal elements. Generally speaking, the properties of alloys are different from those shown by individual elements (such as melting point).

Spherical grid arrangement

A high-density packaging method for surface mount components.

brazing

A method of welding metals, where the metal includes a wire or alloy with a melting point over 444.4°C.

Brazing alloy

    Alloys 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 444.4-1111°C.

Overlap

A harmful substance formed in the heat transfer path of the solder paste between two joints.

Raised circuit board

Bare printed circuit board, this circuit board has been deposited solder paste on the solder joints before the component is mounted, and the solder paste has been reflowed.

Burn in

At high temperatures, run the device for a long time to test the failure rate of the edge components.

Capillary action

The interaction between the liquid and the solid channel or opening with a small diameter. When the liquid wets both sides of the solid channel, the surface tension moves the liquid along the capillary channel.

Cold welded joints

A welding head, made with very little heat (due to too short contact time or low temperature welding). This indicates that the wettability is poor, the surface is not smooth, and the appearance is chalky or grainy.

suppress

A location where repeated pressure cycles, vibrations or high temperatures force the welding alloy to form a dense profile. The pressing slows down the flow of solder paste and blocks the needle.

Bronze mirror test

A flux test method for determining corrosiveness.

Dendrites

Dendritic crystals or dendritic growths are snowflakes that look like patterns that can grow along the surface of metals and alloys, rather than sticking out like whiskers. This growth mechanism is well understood, and a chemical reaction is required to dissolve the metal into a solution of metal ions, and then redistribute the metal ions through the electron migration that occurs in the electromagnetic field.

Desoldering

The solder paste and components are removed from the circuit, usually for repair purposes.

Dehumidification

A state created when a layer of molten solder paste is applied to the surface, and then centrifuged, leaving an irregularly shaped pile of solder paste separated by the area covered by the thin solder paste layer.

Dissolve

Dissolution is the chemical change that occurs when a solid substance is dissolved into a liquid substance. This is not a function of the melting of all substances, but the dissolution of one substance in another substance. It's like sugar dissolving in water (for example: sugar does not reach its melting point, but easily dissolves into exactly the same liquid water.)

Disturbed solder joint

One solder foot. When one or two metals to be welded vibrates, this welding foot becomes hard. The result is an uneven joint with a grained surface fabric.

Eutectic

An alloy composition in which all alloys change from solid to liquid at the same temperature.

Solder foot

Solder joints. Metal adhesive tape.

Fine pitch

The centerline spacing of leads of 0.5mm (20 mils) or less.

Flux

A substance that can remove adsorbed gas, oxide film and other surface pollutants on metal surfaces. The flux can enhance the wetting ability of the solder paste by reducing the surface tension between the solder paste and the substrate.

halide

This substance can be found in some flux activators. Halides include: chloride, bromide, fluoride and iodide.

Superalloy

See welding alloys whose liquidus temperature exceeds 183°C.

Hygroscopicity

The ability of a substance or compound to absorb moisture and retain moisture comes from its surrounding environment.

icicle

An unacceptable sharp point of solder paste, which is protruding from the solder joint, but is not in contact with other conductors. When the soldering iron is removed from the solder joint and the solder joint is too cold or all the flux activity is used up, icicles will form.

Intermetallic layer

An intermetallic layer, which is a mixture of solder paste metal and substrate or metal components. This is generally due to diffusion, rather than melting of all metal components. Care must be taken to ensure that a strong, non-breakable structure is formed.

standard

The soldering industry standard prepared by the Electronic Circuit Interconnect and Packaging Association for specific requirements.

Leaching

(In welding terminology) Alkali metals move into the welding alloy, often through a dissolution process.

Liquidus

Above this temperature, the non-eutectic alloy melts completely.

Low temperature alloy

See welding alloys with a liquidus temperature below 183°C.

Manhattan effect

See tombstone

Shelter

A coating substance used to protect selected areas of printed circuit boards from being soldered.

Melting point

At this temperature, a pure element metal such as tin becomes liquid. As far as pure elements or eutectic alloys are concerned, there is only a precise melting point.

melt

Melting is the process of heating a solid substance to the point where it becomes a liquid. An object that has been melted is also melted at the same time.

No cleaning or low residue

These substances only leave a thin transparent film, which is non-conductive and harmless to the end product. No need to clean the finished product.

Non-wetting

A defect condition in which part or all of the surface is not wetted during the welding process. Non-wetting is recognized by the fact that the bare alkali metal is clearly visible (this is not the same as de-wetting). It is usually due to the presence of an interference layer on the surface being welded.

Degassing

Over time, gas or steam is released. Release gases trapped or frozen in some substances. Not to be confused with sublimation or boiling, they are the phase change of matter into gas.

oxidation

Degradation of the metal surface due to oxygen corrosion. This result is more difficult for wetted surfaces.

the size of granule

The specified diameter range of solder powder (generally 45~75 microns, usually reported in the form of particle size -200/+325)

spacing

The centerline distance between two soldering points on the surface mount board or wire of the electronic component.

plating

A metal coating method for parts. There are different plating processes used to produce coatings of different thicknesses, including electroless plating or electrolytic processes.

Popcorn

"Popcorn" is a term used to describe the effect of turning water into steam within an element. The pressure caused by the steam can cause the component to break. In some cases where the fracture is severe, they extend to the outside.

Warm up

The process of increasing the soldering work below the melting point of the solder paste to reduce the thermal shock of the components.

print

A process that transfers the solder paste to the surface by applying the solder paste to the entire stencil/screen with an applicator.

Section view

Diagram of the relationship between time and temperature.

Active flux (RA)

It is composed of resin, solvent and corrosive activator. For moderately oxidized surfaces, RA flux has higher activity than RMA. The residue of RA flux is corrosive and should be removed as soon as possible after reflow to avoid damage to your parts. The longest safe time before cleaning depends on the product. The residue can be removed with a suitable solvent.

Backflow

A term used to describe the heating and melting process of pre-alloyed solder paste.

the remains

The part of the flux remaining after the solder paste has flowed away.

Low activity flux (RMA)

It is composed of resin, solvent and a small amount of activator. Most RMA fluxes are quite low in activity and are most suitable for surfaces that are easy to solder. RMA flux residue is transparent, soft, non-corrosive and non-conductive. Can be cleaned arbitrarily. The residue can be removed with a suitable solvent.

Rosin/resin (R)

Raw material or mildly processed tree sap. The resin is processed into rosin. Rosin is a mildly acidic sap found in pine trees and was the first flux used in the Bronze Age.

Surface Insulation Resistance (SIR)

A test used to classify flux. The flux is reflowed on a set of rails arranged at an angle to each other, and voltage is supplied. A resistance value of 1x108 Ω is reserved for a passing test.

Collapse degree

The spread of solder paste after deposition and before drying can cause loss of clarity.

Solder ball

The small ball of solder paste has been separated from the main body of the solder paste.

Solderability

The metal ability to treat solder paste as a soldering agent.

Solder paste

A homogeneous mixture of powdered solder alloy and solder paste. Through printing, drip coating, dipping and spraying methods, different solder pastes can be applied to one product.

Solid line

Below this temperature, the welding alloy becomes completely solid. .

Solvent

A liquid chemical used to turn solid rosin or resin into solder paste. The solvent will evaporate when exposed to air, reducing the physical properties of the solder paste.

Splash

Due to the explosive evaporation of absorbed water or other low-boiling substances, the flux and alloy are dispersed away from the solder paste deposits.

Graded welding

A process in which different welding alloys are used for continuous welding operations at each "graded" temperature. The solidus of high-temperature alloys is higher than the liquidus of low-temperature alloys. For example: the melting temperature of Sn10Pb88Ag2 is 268ºC～290ºC. Another operation using Sn96.3Ag3.7 melted at 221ºC will interfere with high temperature solder joints.

viscosity

After placement, the ability of solder paste to hold surface mount components in place.

tensile strength

The properties of a substance are used to describe the resistance to rupture of a substance under tension.

Through hole

A plated hole on the circuit board. The through-hole component has wires inserted and soldered to the plated through-holes.

Tin whisker

Whiskers are crystalline electrical conductors that resemble hair and grow from the surface of metals and alloys. Think of them as a kind of inducing stress. In tin whisker alloys, lead, bismuth, and antimony have been used to reduce the frequency and size of whiskers.

Tinned

Pre-coat a thin layer of tin or wrap a layer of tin base alloy on the surface of the parts to be welded. When forming solder joints, this coating helps accelerate wettability and control flow.

Monument

Also known as the "suspension bridge effect" or "Manhattan effect". Tombstone refers to the torque generated by the surface tension of the solder paste when wetting, which lifts one end of the wireless component from the solder paste. This is usually caused by an imbalance in the wetting force during reflow. This imbalance may be due to many reasons.

Viscosity

A measure of the resistance of a substance to flow. In solder paste, it refers to thickness. The viscosity is measured in centipoise in 1000's (kcps).

Hollow

During reflow, the gas creates a cavity in the solder joint.

Water-soluble solder paste (WS)

It is composed of organic acid, thixotropic glue and solvent. WS flux provides a wide range of active levels for solder paste to flatten the most difficult surfaces. WS flux residue is corrosive and should be removed as soon as possible after reflow to avoid damage to your device. The longest safety time before cleaning depends on the product. Under a pressure of 40 psi, the residue can be easily removed with water at 60°C (140°F).

Wave welding

A process in which printed circuit boards are welded by wave-like melting of solder paste.

Wetting

The ability of liquid metal to flow across the metal surface when the metal is pulled in the opposite direction. When the suction surface energy of the pad or component lead is greater than the surface energy of the solder paste, wetting occurs. This results in the automatic formation of a thin solder paste surface. The heat reduces the surface energy of the solder paste, allowing it to wet further in the thinner layer. Heat also causes surface oxidation, slowing down wetting.