3 Reliability Test
3.1 Purpose of Reliability Test
This test is implemented to verify the appropriate ability of the semiconductor device to withstand stress in customer’s manufacturing through transportation and at the market, and to maintain and improve reliability.
- Description of Reliability Test
The reliability test is broadly divided into three types. The test is implemented at the design development, pre-production, and mass production start time to verify that there are no problems.
- Reliability Test Method
Various methods of the reliability test are standardized in the “Japanese Industrial Standards (JIS), “standards of the Japan Electronics and Information Technology Industries Association (JEITA),” “Military Specifications and Standards (MIL),” “International Electrotechnical Commission (IEC) standards” and other standards. We implement the reliability test according to the JEITA standards.
3.2 Reliability Test Method
1) New Process Development Stage
Narrowing down problems by only evaluating an actual product for all internal elements is inefficient and uneconomical for improvement in reliability with the recent trend toward smaller design feature and more complicated integrated-circuit (IC) products. Therefore, commonly known wafer level life tests (HCI, TDDB, BTI, EM, SM) are performed, in order to ensure the products reach the life expectancy. Also, it is required to fully evaluate and grasp the reliabiliy at the levels of individual elements such as active element (transistor), passive elements (dioide, capacitor, resistor) and metallization comprising the IC. Especially during new process development with smaller design feature, it is verified that there are no basic problems in reliability using the TEG (Test Element Group).
2) Individual Product Development Stage
At this stage, product prototyping occurs roughly twice. Verification is performed focusing on the following two points:
- Prototyping after design: Verification that characteristics and reliability designed at the stage of development planning are met.
- Pre-production: Verification as to the following through prototyping using the mass production line:
－ Verification of countermeasure effects where there is any problem in the prototyping after design.
－ Verification that there are no problems in mass production.
Reliability is basically evaluated at each prototyping.
3) Periodic Reliability Evaluation
Reliability is periodically evaluated by sampling mass-produced products to verify that the reliability level designed at the stage of development is continuously maintained after mass production. Typical products are determined in consideration of the combination of the wafer process, assembly process, manufacturing place and other factors to perform evaluation.
3.3 Standards Related to Reliability Test
|JEITA Standard||Test Method||Category and Title|
||Application guide of the accelerated life test for semiconductor devices|
||Guideline for IC reliability qualification plan|
||Guideline for discrete semiconductor device feliability qualification plan|
||Procedure of the test time and the sample size determination for the life tests|
Wafer Level Reliability test methods for semiconductor devices
|A101||Hot carrier injection test for MOSFET|
|A102||Bias temperature instability test for MOSFET|
|A104||Time dependant dielectric breakdown (TDDB) test|
|B101||Constant current electromigration test|
|B102||Copper stress migration test|
Life Test I
|101A||High temperature operating life|
|101A||High temperature bias|
|102A||Temperature humidity bias|
|103A||Temperature humidity storage|
|104A||Moisture soaking and soldering heat stress series test|
|106A||Intermittent operating life|
Life test Ⅱ
|201A||High temperature storage|
Stress Test Ⅰ
|301D||Resistance to soldering heat for surface mount devices|
|302A||Resistance to soldering heat for through hole mount devices|
|304A||Human body model electrostatic discharge (HBM / ESD)|
|305C||Charged device model electrostatic discharge (CDM / ESD)|
Stress Test Ⅱ
|405||Acceleration (Steady state)|
|501A||Permanence of marking|
Specific Test for Discrete Semiconductors
|601||Power cycling test (Molding type)|
|602||Power cycling test (Non-molding type / short time)|
|603||Power cycling test (Non-molding type /long time)|
|Test Standard||Test Method|
|JISC60068-2-82||Whisker test methods for electronic and electric components|
|IEC 60749-43||Guidelines for IC reliability qualification plans|
3.4 Acceleration Models and Derating
The reliability of semiconductor devices greatly varies according to the degree of derating even in use with the absolute maximum rating or within the working range specified individually. It is requested to perform appropriate derating allowing for satisfactory safety in your designing equipment. The reliability verification is performed according to the general assumed operating environment of the quality grade defined in JEITA EDR-4708B/EDR-4711A.
The following describes derating based on the temperature acceleration model, temperature difference acceleration model, and humidity acceleration model, which are often used for the estimation of a market life from the reliability test result.
Electric stress can be applied to temperature acceleration or temperature difference acceleration by self-heating. Where there is especially abrupt stress application or if there is concern about other stresses, contact us.
Temperature Acceleration Model (Arrhenius Model)
The Arrhenius model is a model to predict the speed of a chemical reaction at a given temperature, which was proposed by Arrhenius, a scientist from Sweden. It is most often used for estimation of the life of semiconductor devices.
Ea=Activation energy (eV)
k=Boltzmann constant 8.6173×10-5[eV/K]
T=Absolute temperature (K)
Where a life at a derating temperature T1 is L1 and an implementation time at a reliability test temperature T2, an acceleration factor α is obtained as follows:
The following shows an example of the temperature derating curve with our experimental values based on the above idea:
Example of a life of intermetallic compound formation (Kirkendall void) between Au wire and Al electrode
(derived from experimental results of high-temperature storage at 150℃, 160℃ and 175℃)
Temperature Acceleration Model (Eyring Model)
As for a temperature difference acceleration model, the Eyring model proposed by the American theoretical chemist is adopted.
The temperature difference repeatedly applied and the life cycle number are expressed by the following expression:
n=Temperature difference factor
Where a life cycle number is L1 with a derating temperature difference (⊿T1) and an implementation cycle number is L2 with a reliability test temperature difference (⊿T2) in the above expression, a temperature difference acceleration factor (α⊿T) can be obtained as follows:
The following shows an example of the temperature difference derating curve with our experimental values based on the above idea:
Example of chip connection part (solder deterioration) life
(derived from experimental results at the power cycle with ⊿70℃, ⊿90℃, and ⊿100℃)
Humidity Acceleration Model
Various models have been proposed for humidity acceleration. Among those, the absolute vapor pressure model and relative humidity model are described below.
● Absolute Vapor Pressure Model / Vapor Acceleration Factor
This model correlates the time leading up to a constant cumulative failure rate (L) with a vapor pressure (Vp).<
n:2 (reference value)
Where a vapor pressure and life in the derating status are respectively Vp1 and L1 and those in a reliability test status are respectively Vp2 and L2 in the above expression, a vapor pressure acceleration factor (αVp) can be expressed by the following expression:
A saturated vapor pressure e(T) at a given temperature (T) can be obtained approximately by using the expression of Tetens:
● Relative Humidity Model / Humidity Acceleration Factor
This model correlates the time leading up to a constant cumulative failure rate (L) with a relative humidity (RH%) and temperature T(℃).
A:Constant, Ea=Activation energy (eV)
Where a relative humidity and life in a normal state are respectively RH1 and L1 and those in an acceleration state are RH2 and L2 in the above expression, a humidity acceleration factor (αH) can be expressed by the following expression:
Based on the above idea, the following show examples of relative curves of the absolute vapor pressure model and relative humidity model for the pressure cooker test (121℃, 100%, 100 hrs.):