- questions most frequently asked by visitors of www.EESemi.com
Rel Test Preconditioning
What is the purpose of preconditioning before reliability testing?
preconditioning the same as SHRT?
Resistance Test (SHRT)
is a reliability testing step performed to determine the ability of a
device to withstand the
stresses of the board mounting or
process. It is also known by other names, such as RTSH (Resistance to
Solder Heat). See SHRT.
refers to SHRT that's performed on rel samples as a 'preparatory' step before the
samples are subjected
to a major reliability test
Temp Cycle, etc.). Preconditioning
exposes the rel samples to thermally stressful
equivalent to thermal conditions experienced by units during board
of preconditioning is therefore to simulate the board mounting or board soldering process
that a device undergoes before they are used in the field. The
major rel test that follows preconditioning, on the other hand,
simulates the thermo-mechanical stresses that the device experiences
while operating in the field.
subjecting parts directly to reliability testing without preconditioning
is like testing the reliability of parts that have not been mounted on
the board. In other words, preconditioning must be done on samples
prior to a major reliability test to reflect the actual 'use' conditions
of the units on the customer side, i.e., they must first be mounted on
boards (a thermally stressful process) before they are put into field
Preconditioning ensures that inherently weak parts that are susceptible
to popcorn cracking during board mounting will fail and consequently be
detected. It will also aggravate marginalities within a package,
such that these 'weaknesses' will translate into actual failures during
the reliability test succeeding the preconditioning. For example,
preconditioning can cause die-to-package delamination in weak parts,
which in turn can lead to corrosion during HAST or neck breaks during
TCT. Without preconditioning, these corrosion or neck break
mechanisms might not occur during the actual HAST or TCT, since no delam
was induced in the absence of precon.
Preconditioning generally consists of three distinct steps: 1)
drives away all the internal moisture within the samples; 2)
which drives controlled amounts of moisture into the package; and 3)
some form of
which simulates the board soldering process itself.
The bake and
soak steps must be done according to industry standards since these two
steps determine the level of internal moisture when the shock is
performed. The thermal
shock, which may be provided by a
heating, or a
of IR and convection heating, must likewise conform to industry-standard
SHRT; Reliability Testing
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