SMT: Glossary Of Terms - S Stage
Glossary of terms
Saponifier
An alkaline chemical added to water to improve its ability to dissolve rosin flux residues.
Secondary Side
That side of the packaging and interconnecting structure furthest from layer #1 .This is commonly referred as the “solder side†when using though-hole component mounting technology. In SMT, the secondary side may be either reflow soldered (active component) or wave soldered (passive component).
Self-alignment
Due to the surface tension of molten solder, the tendency of slightly misaligned components (during placement) to self align with respect to their land pattern during reflow soldering. This kind of correction may take care of any minor mis-alignment only.
Shadowing (Infrared Reflow)
A condition in which component bodies block radiated infrared energy from striking certain areas of the board directly. Shadowed areas receive less energy than their surroundings and may not reach desired temperatures.
Shadowing (Solder)
A condition in which solder fails to wet the surface mount device leads during the wave soldering process. Generally the trailing terminations of a component are affected, because the component body blocks the proper flow of solder. Requires proper component orientation during wave soldering to correct the problem. The body of the component may also cause “shadowing†of the terminations of another component.
Silk Screen
A screen of a closely woven solid mesh stretched over a frame and used to hold an emulsion outlining a circuit pattern. Silk screens are used in screen printing solder paste. The term is used generically to describe any screen (stainless steel or nylon) used for screen printing.
Single -Layer Board
A printed wiring board that contains metallized conductors on only one side of the board. Though-hole are unplated.
Single-Sided Assembly
A packaging and interconnecting structure with components mounted only on the primary side.
SMA, Surface Mounted Assembly
Trademark by AWI. A circuit assembly being primarily (60%) or wholly constructed using surface mount components.
SMC, Surface Mounted Components
A component designed to be mounted and soldered to lands on the surface of a packaging and interconnecting structure rather than inserted into though-holes in the structure.
SMD, Surface Mount Device
Registered trade mark of North American Philips Corporation to denote resistor, capacitor, SOIC, and SOT. The term is similar to SMC, surface mount component.
SMT, Surface Mount Technology
A method of assembling printed wiring boards or hybrid circuits, where components are mounted onto the planar surface rather than inserted into through-holes.
Snap-Off Distance
The height the stencil or screen set above the top surface of the board (substrate) for an “off-contact†printing, which determines the amount of deflection that occurs during the snap-back action of the stencil. Snap-off distance is typically in the range of 0.003 to 0.050â€. On-contact printing would have a zero snap-off distance.
SO, Small Outline
Similar to miniature dual in-line package, but with gull wing lead forms for surface mounting. Typical lead spacing:0.050â€.
SOIC, Small Outline Integrated Circuit
An integrated circuit surface mount package with two parallel rows of gull wing leads, with standard spacing between leads and rows.
SOJ, Small Outline J Leaded
An integrated circuit surface mount package with two parallel rows of J-leads, with standard spacing between leads and rows. Generally used for memory devices.
Solder
A metallic alloy which has a melting temperature below 427C(800F)
Solder Balls
Small spheres of solder that remain on the board after wave or reflow soldering adhering to laminate, mask, or conductors. Solder balls are most often associated with the use of solder paste containing oxides or may be due to excessive moisture content. Baking of paste may minimize formation of solder balls, but overbaking may cause excessive balling. They are sources of electrical shorts.
Solder Bridge
An electrical short circuit between two conductors by solder that “bridges†above the dielectric.
Solder Connection
An electrical/mechanical connection which employs solder for the joining of two or more metal parts.
Solder Connection, Disturbed
Cold solder joint resulting from motion between the joined members when the solder was solidifying.
