Accelerated Stress Test (HAST)
The acronym "HAST"
stands for "Highly Accelerated
Temperature/Humidity Stress Test."
It was developed as a shorter alternative to Temperature Humidity Bias
Testing. If THB testing takes 1000 hours to complete, HAST results
are available within 96-100 hours. Because of this, the popularity
of HAST has continuously increased in recent years, to the extent that
some companies have totally replaced THB testing with HAST.
Figure 1 shows an example of a HAST system - the Trio Tech 6000X.
THB testing, HAST accelerates corrosion, particularly that of the die
metal lines and thin film resistors. HAST requires
and is conducted with electrical bias
at 130 deg C and 85% RH for 96-100
Example of a HAST system: the Trio Tech 6000X
bias during HAST stressing must be defined based on the following
must be minimized to ensure that moisture is always present at the die
pins must be
subjected to opposite bias (low voltage versus high voltage) as much as
potential differences between the various metallizations
on the die must be maximized; 4) the operating
for the device must also be maximized,
as long as the power dissipation is kept under control.
samples for HAST stressing are loaded into
prior to loading into the HAST chamber. HAST boards are designed
to withstand the severe test conditions of HAST and are, therefore,
The HAST boards are then inserted into
Fig. 2) inside the chamber of the HAST system.
A look inside the chamber of the Trio Tech 6000X
is recommended for the
any change that can potentially affect the
of the product. Thus, a new fab process, a new
package, or a new fab/assembly site definitely requires HAST data. HAST is also recommended for changes
in the die glassivation, metallization or thin film resistors, as well
as changes in the molding compound. It is also used for the
reliability assessment of lots suspected to be prone to corrosion due to
One may refer to
for more details on this reliability test.
Test or PCT; Temperature
Heat Resistance Test (SHRT);
Reliability Modeling; Qualification
Package Failures; Die
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