Editor note; All the PWB terms are listed below. The alphabetic links above will switch to the main glossary, so scroll down the page for definitions related to Printed Wiring Boards.
Tented Via. A via with dry film solder mask which completely covers both the via pad and its plated-through hole. In some cases this may also be referred to as a Capped Via or Cap plating, although the phrase tented via is much more common.
Test Coupon. A printed circuit card used to test the quality of the fabrication process used to develop PWBs. Test Coupons are fabricated on the same panel as the PWB being developed, normally at the edges of the panel. There are a number of different styles of test coupons each with a different trace pattern. Test Coupon 'E' is shown to the right.
Test Pads: In many cases Test Pads are added to the layout to assist in circuit debug and trouble-shooting. In this case square pads are added to the PCB to break-out pins on a small pitch surface mount IC. The pads may be on pins that are being used or placed on a test or unused interface to determine the health of the IC. Because no vias are evident these pads are bringing out signals on the IC that are not used by the IC to function. Also see Automated Test Pads.
PCB IC Test Pads
Test Points. Plated vias used by automated testers such as a clam-shell bed-of-nails test or flying probes, which test the continuity of circuits. Note the use of Test Pads [TP] located next to automated test points in the graphic to the right. The terms test point and test pad may be interchangeable.
Thermal Relief: A spoke added to a plated via to reduce the amount of copper attached to the via to aid in soldering to the via's. Thermal reliefs are not required on a via that will not be soldered to. The graphic to the right shows four via's with thermal relief. Note the via is in the center of the pad, but not shown.
Thermal Resistance: The resistance of a substance to the conductivity to heat. Refer to FR4 Thermal Resistance x Pad Area for a graph.
Thermal VIA: A via in the Printed Wiring Board [PWB] to effectively transfer heat from the top copper layer of the Printed Circuit Board [PCB] to the inner or bottom copper layers. The thermal vias should make their connection to the internal ground plane with a complete connection around the entire circumference of the plated through hole. Do not use a thermal relief web or spoke connection which impedes the conduction path into the inner copper layer.
Tinning: The process of applying a thin coat of solder to materials prior to their being soldered; for example, application of a light coat of solder to the filaments of a conductor to hold the filaments in place prior to soldering of the conductor.
Tin Plating: See Plating. Reference; MIL-T-10727C - Tin Plating: Electro-Deposited or Hot-Dipped, for Ferrous and Non-ferrous metals.
Tin whiskers: Term located on the Tin whiskers definition page.
Through-Hole Device: A component that attaches to a printed wiring board [PWB] using leads that pass-through the PWB. Any component may be a through-Hole device. Unless required for mechanical stability do not select through-hole devices. When possible use surface mount devices to lower lead inductance and reduce the size of the component.
Tombstoned: A two leaded surface mount device that has been turned up on end so that only one side physically bounds to the PWB. The other side of the component is attached to the PWB via a wire.
Trace: A strip of metal making an electrical connection
between two or more points on a PCB. The trace carries signals
between these points. Traces are normally copper.
Trace Separation: The distance between to Signal traces. Note there are different guidelines between two traces comprising a differential trace pair, and the trace separation between a single ended trace and a differential pair [refer to the graphic below].
Separation of Traces
Trace Termination: The terminating load applied to a trace to reduce reflections on a signal trace [line]. When to Terminate a Trace
Type of PWB. There are five different types of Printed wiring boards as defined by the IPC or Military; Types 1 to 5. Refer to PWB Types.
Vendor: A Printed Wiring Board production house. PWB Design Services [Layout, Fabrication, Compliance Testing].
Vertical Mount: A component that is mounted standing up, instead of being mounted horizontally which would normally be the case. Vertical Mounting only applies to through-hole components.
Via. A plated-thru hole in a printed wiring board. A via may exist between one or more adjacent board layers, or through the entire board. A blind via runs vertically between the top [or bottom] side and through one or more adjacent board layers, but not through the entire board. A buried via runs between one or more adjacent internal layers, but does not run to the top or bottom layer. Also refer to PWB Design.
Via Stub. the portion of the via that is not in series with the signal. When a signal pin does not traverse the entire via, or when the signal layer using the via is not the bottom layer of the PWB. Two methods may be used to over come a via stub; Counter Boring, and Blind Vias, in both cases the via is terminated at its destination and not allowed to continue to the other side of the PWB. Read more about Via Stubs.
Wagon Wheel. The pattern generated when thermal reliefs are added to a via.
Wave Soldering: A process wherein PWAs are brought in contact with the surface of continuously flowing and circulating solder.
Wicking. A flow of molten solder, flux, or cleaning solution by capillary action.
Zero Ohm Resistor: A resistor that has a resistance of zero ohms; however, these components do have a tolerance, so the actual value may be something other than zero. Zero Ohm Resistors are used as jumpers or 'select as needed' components. Note a zero ohm resistor is the same as a jumper wire, but when you specify a zero ohm resistor, pads are placed on the PCB will will accept any other resistor value. Also refer to the Dictionary of Resistor Terms, which leaves this section.