Dictionary U


See "upper byte".



See "universal asynchronous receiver transmitter".



See "upper-byte enable".



See “uncorrectable bit-error rate”. References:


See “under-bump metal” and  “under-bump metallurgy”. References:


See "unijunction transistor".


ultraviolet-erasable programmable read-only memory (UV-EPROM)

Synonym for "erasable programmable read-only memory (EPROM)".


JESD100-B, 12/99

uncased device

A device with some portion of the die exposed.

NOTE Usually the chip has bonding pads, bumps, etc. that may be bonded to pads or lands on a lead-frame, tape, substrate, or printed wiring board.


JESD30D, 7/06

uncommitted logic array

Synonym for "gate array integrated circuit".


uncorrectable bit-error rate (UBER)

A metric for data corruption rate equal to the number of data errors per bit read after applying any specified error-correction method. References:

JESD22-A117B, 3/09

under-bump metal (UBM)

The metal layers located between the solder bump or column and the die. References:

JEP156, 3/09

under-bump metallization (UBM)

A patterned, thin-film stack of material that provides 1) an electrical connection from the silicon die to a solder bump; 2) a barrier function to limit unwanted diffusion from the bump to the silicon die; and 3) a mechanical interconnection of the solder bump to the die through adhesion to the die passivation and attachment to a solder bump pad. References:

JEP154, 1/08

under-bump metallurgy (UBM)

The metal layers located between the solder bump and the die. References:

JESD22-B109A, 1/09


The reduction of the cross section of a material caused by etching action spreading beneath the edge of the photoresist or other masking films.


JESD99B, 5/07


The adhesive material applied between the solder bump side of the flip chip die and the substrate.


JESD22-B109, 6/02


Plated layers between the base metal and the outer surface finish.


JESD201, 3/06

undetectable fault

A functional fault for which no test pattern can be created that will cause the effects of the fault to be observable at an externally accessible node.


JESD12-5, 8/88

undetected fault

A functional fault that causes effects that are not observed at an externally accessible node when the circuit is exercised by the existing test pattern.


JESD12-5, 8/88

unidirectional ABD

A two-terminal ABD with a voltage-current avalanche breakdown characteristic in one direction and either a forward or a blocking characteristic in the other

NOTE    Large transient currents will be clamped for positive cathode-to-anode voltages when driven into the avalanche breakdown region with one or more p-n junctions placed in series or parallel with each junction connected in the same direction. Large transient currents may also be clamped for negative cathode-to-anode voltages at significantly lower voltages with the typical forward-conducting characteristics of a single p-n junction (or of multiple p-n junctions connected in the same direction). The most common type of unidirectional ABD has a forward-conducting characteristic.


Unidirectional-conducting ABD                                               Unidirectional-blocking ABD References:

JESD77C, 10/09
JESD210, 12/07

unidirectional thyristor surge protective device

A thyristor surge protective device (TSPD) that can switch in only one quadrant.

NOTE The two types are forward-conducting TSPDs and reverse-blocking TSPDs.


JESD77-B, 2/00