Reliability Testing Acceleration Testing
Most semiconductor devices have lifetimes that extend over many years at normal use. However, we cannot wait years to study a device; we have to increase the applied stress. Applied stresses enhance or accelerate potential fail mechanisms, help identify the root cause, and help labcompanion take actions to prevent the failure mode.
In semiconductor devices, some common accelerants are temperature, humidity, voltage, and current. In most cases, the accelerated testing does not change the physics of the failure, but it does shift the time for observation. The shift between accelerated and use condition is known as ‘derating.’
Highly accelerated testing is a key part of JEDEC based qualification tests. The tests below reflect highly accelerated conditions based on JEDEC spec JESD47. If the product passes these tests, the devices are acceptable for most use cases.
Temperature Cycle
Per the JESD22-A104 standard, temperature cycling (TC) subjects the units to extreme high and low temperatures transitions between the two. The test is performed by cycling the unit's exposure to these conditions for a predetermined number of cycles.
High Temperature Operating Life (HTOL)
HTOL is used to determine the reliability of a device at high temperature while under operating conditions. The test is usually run over an extended period of time according to the JESD22-A108 standard.
Temperature Humidity Bias/Biased Highly Accelerated Stress Test (BHAST)
According to the JESD22-A110 standard, THB and BHAST subject a device to high temperature and high humidity conditions while under a voltage bias with the goal of accelerating corrosion within the device. THB and BHAST serve the same purpose, but BHAST conditions and testing procedures enable the reliability team to test much faster than THB.
Autoclave/Unbiased HAST
Autoclave and Unbiased HAST determine the reliability of a device under high temperature and high humidity conditions. Like THB and BHAST, it is performed to accelerate corrosion. Unlike those tests, however, the units are not stressed under a bias.
High Temperature Storage
HTS (also called Bake or HTSL) serves to determine long-term reliability of a device under high temperatures. Unlike HTOL, the device is not under operating conditions for the duration of the test.
Electrostatic Discharge (ESD)
Static charge is an unbalanced electrical charge at rest. Typically, it is created by insulator surfaces rubbing together or pulling apart; one surface gains electrons, while the other surface loses electrons. The result is an unbalanced electrical condition known as static charge.
When a static charge moves from one surface to another, it becomes Electrostatic Discharge (ESD) and moves between the two surfaces in a form of a miniature lightning bolt.
When a static charge moves, it becomes a current that can damage or destroy gate oxide, metal layers, and junctions.
JEDEC tests ESD in two different ways:
1. Human Body Mode (HBM)
A component level stress developed to simulate the action of a human body discharging accumulated static charge through a device to ground.
2. Charged Device Model (CDM)
A component level stress that simulates charging and discharging events that occur in production equipment and processes, per the JEDEC JESD22-C101 specification.
Solar Module Test
Solar energy is a kind of renewable energy, refers to the sun's thermal radiation energy, the main performance is often said that the sun rays, in the modern generally used for power generation or to provide energy for water heaters. In the case of decreasing fossil fuels, solar energy has become an important part of human energy use and continues to develop. The use of solar energy has two ways of photothermal conversion, solar power generation is an emerging renewable energy, so the related solar energy research and application industry has also stepped up the pace of development. In the research and production process of the solar module, the relevant reliability test and environmental test specifications have been formulated to ensure that the solar module can be durable for more than 20 to 30 years and its power generation conversion rate when used in outdoor environment.
Solar module HAST and PCT test illustration
Temperature and humidity test IEC61215-10-13:
Temperature and humidity test conditions are 85℃/85%R.H., time: 1000 hours, to determine the ability of the module to resist long-term moisture penetration, through the temperature and humidity test can be found defects: CELL delamination, EVA(delamination, discoloration, bubble generation, atomization, Browning), string line blackening, TCO corrosion, solder joint corrosion, Thin-film yellow discoloration, junction box degumming off... However, according to the test results of relevant Solar plants,1000 hours is not enough, and the actual situation finds that the test time to enable the module to find the problem needs to be at least 3000 to 5000 hours.
Test method of HAST [Highly Accelerated Temperature and Humidity Stress Test]:
HAST is short for Highly Accelerated Temperature and Humidity Stress Test in English. The highly accelerated humidity resistance evaluation test method is based on the environmental parameters of temperature and humidity. HAST and PCT [Pressure Cooker Test] are different from the two tests, HAST is called unsaturated test, while PCT is saturated humidity test, and the biggest difference from the general humidity evaluation test method is that it is in the field of temperature and humidity above 100℃, and is in the high-density water vapor environment test. The purpose of HAST is to accelerate the test of humidity intrusion into the sample for humidity resistance evaluation by taking advantage of the fact that the water vapor pressure in the test tank is much higher than the water vapor partial pressure inside the sample.
Test specifications and conditions of JESD22-A118[Accelerated Moisture Resistance-Unbiased](HAST unbiased test) :
It is used to evaluate the reliability of the device in wet environment, that is, the penetration of harsh temperature, humidity and increased water vapor pressure through the external protective material (encapsulation or sealing material) or along the interface of the external protective material and metal conductor, the failure mechanism is the same as that of the [85℃/85%RH] high temperature and high humidity steady-state humidity life test (JESD22-A101-B). In this test process, no bias is applied to ensure that the failure mechanism is not covered by bias, and this test is used to determine the failure mechanism in the package. The sample is in a non-condense humidity environment, only the temperature is increased a little, and the failure mechanism is the same as the [85℃/85%RH] high temperature and high humidity steady-state humidity life test without bias. It should be noted that, Since absorbed water vapor reduces the glass transition temperature of most polymer materials, an unreal failure mode may occur when the temperature is higher than the glass transition temperature.
85℃/85%/1000H(JESD22-A101)→110 ℃/85%/264H(JESD22-A110, A118)
Specifications: JEDEC22-A110(with bias), JEDEC22-A118(without bias)
Common conditions: 110℃/85%R.H./264h Applicable: PET, EVA, modules
Test method of PCT [Pressure Cooker Test]:
Generally known as the pressure cooker cooking test or saturated steam test, the most important is to test the product under harsh temperature, saturated humidity (100%R.H.)[saturated water vapor] and pressure environment, test the high humidity resistance of the test product, for solar packaging materials or modules, used for material moisture absorption test, high pressure cooking... For the purpose of the test, if the product to be tested is a Cell, it is used to test the moisture resistance of the Cell. The product to be tested is placed in a harsh temperature, humidity and pressure environment for testing. If the package is not well packaged, moisture will penetrate into the package along the colloid or the interface between the colloid and the wire frame. Popcorn effect, open circuit caused by metal wire corrosion, short circuit caused by contamination between package pins... And other related issues, and HAST accelerated aging is not the same.
Test specifications and conditions of PCT JESD22-A102:
To evaluate the integrity of non-airtight packaged devices against water vapor in a condensed or saturated water vapor environment, the sample is placed in a condensed, high-humidity environment under high pressure to allow water vapor to enter the package, exposing weaknesses in the package, such as delamination and metallization layer corrosion. The test is used to evaluate the new package structure or the update of the material and design in the package body. It should be noted that some internal or external failure mechanisms will appear in the test which are not consistent with the actual application situation. Since absorbed water vapor reduces the glass transition temperature of most polymer materials, an unreal failure mode may occur when the temperature is higher than the glass transition temperature.
Test conditions: 121℃/100%R.H./80h(COVEME), 200h[toyalSolar]
Applicable: PET, EVA, modules
Pressure cookers (PCTS) and Highly Accelerated Life Test Equipment (HAST) :
At present, most solar materials and modules can withstand long-term DHB(temperature and humidity + bias) test without failure, in order to improve the test efficiency and shorten the test time, the pressure cooker test method is used. Pressure cooker test methods are mainly divided into two types: That is, PCT and HAST, if the defects of solar packaging materials and modules can be found through HAST tests, and the degradation can be reduced by 1%, the LCOE[Levelized Cost of Electricity(actual energy output value, power generation cost per KWH)] will be reduced by 10%. The purpose of the PCT test is to increase the ambient stress (temperature & humidity), and to evaluate the sealing effect of the module and the moisture absorption of the backplane by exposing it to a wetting vapor pressure of more than one atmosphere.
Accelerated Test of Die Casting at High Temperature and High Humidity
Die casting is a precision casting method, the principle is to melt the better metal [zinc, tin, lead, copper, magnesium, aluminum]... Six kinds of alloy melting, with rapid high pressure mechanical properties into the metal mold, the use of steel mold low temperature rapid solidification molding casting method, die casting is a pressure casting parts, can be manufactured into auto parts, locomotive parts, LED lamps and LED street lights, consumer electronics parts, cameras, mobile phones, communications... In order to confirm whether the die-casting parts can be satisfied with the outdoor environment for a long time and whether there will be related defects, relevant tests need to be carried out through the HAST highly accelerated life testing machine.
Common defects in die casting: cold insulation, cracks, holes
List of common specifications for die casting:
ASTM B85: Standard for pressed Film Casting of aluminum alloys
ASTM B86: Zinc and zinc aluminum alloys
ASTM B176: Copper Alloy die castings
ASTM B894: Zinc-Copper-Aluminum Alloy die casting
ASTM E155: Standard Reference Radiographs for the inspection of Aluminum & Magnesium castings
ASTM B94: Magnesium Alloy mold standard
GB5680: high manganese steel casting
GB9438: Aluminum alloy casting
GB15114: Aluminum alloy die casting
QC273: Technical specifications for automotive zinc alloy aluminum alloy copper alloy die casting parts
YL-J021201: die casting of aluminum alloy cover plate for machine cooler
Die casting test items: metallographic test, mechanical ability, bending test, hardness test, impact test, tensile test, high temperature and high humidity, chemical composition, non-damage inspection (X-ray, fluorescence), residual element analysis, surface defects, dimensional tolerance, microstructure, weight tolerance, air tightness test
Die casting Performance test - high temperature and high humidity accelerated test:
PCT condition: 120℃/100%R.H.
HAST condition: 130℃/85%R.H.
Common missing after high temperature and high humidity accelerated test of die casting:
Die casting in the manufacturing process, if the cleaning is not true, resulting in residual release agent, cutting fluid, saponification fluid on the surface... Such corrosive substances, or other pollutants, under certain temperature and humidity conditions, it is easy to accelerate oxidation or mold, die-casting test product surface with a layer of white powder or yellow, black are oxidation phenomenon.
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