Temperature and Humidity Terms
Dew Point temperature Td, in the air water vapor content unchanged, maintain a certain pressure, so that the air cooling to reach saturation temperature called dew point temperature, referred to as dew point, the unit is expressed in ° C or ℉. It's actually the temperature at which water vapor and water are in equilibrium. The difference between the actual temperature (t) and the dew point temperature (Td) indicates how far the air is saturated. When t>Td, it means that the air is not saturated, when t=Td, it is saturated, and when t<Td, it is supersaturated.
dew is the liquid water in the air that condenses on the ground. In the evening or at night, due to the radiation cooling of the ground or ground objects, the air layer close to the surface will also cool down. When the temperature drops below the dew point, that is, when the water vapor content in the air is susaturated, there will be condensation of water vapor on the surface of the ground or ground objects. If the dew point temperature is above 0 ° C at this time, tiny water droplets appear on the ground or ground objects, which are called dew.
frost refers to the white ice crystals formed on the ground or objects after the air close to the ground is cooled to the frost point (meaning the dew point is below 0) under the influence of radiation cooling on the ground.
fog refers to the condensation of water vapor suspended in the atmosphere near the Earth's surface, composed of small water droplets or ice crystals. When the temperature reaches the dew point temperature (or is close to the dew point), the water vapor in the air condenses to form fog.
snow is solid water in the form of snowflakes that falls to the ground from mixed clouds. Precipitation consisting of a large number of white opaque ice crystals (snow crystals) and their polymers (snow masses). Snow is the natural phenomenon of water condensing and falling in the air, or falling snow;
There is a limit to the amount of water vapor that can be contained in a unit volume of air under a certain pressure and a certain temperature. If the water vapor contained in the volume of air exceeds this limit, the water vapor will condense and produce precipitation, and the actual value of water vapor in the volume of air. In terms of absolute humidity. The more water vapor there is, the higher the absolute humidity of the air.
Relative Humidity refers to the percentage of water vapor pressure in the air and saturated water vapor pressure at the same temperature, or the ratio of the absolute humidity of wet air to the maximum absolute humidity that can be reached at the same temperature, and can also be expressed as the ratio of the partial pressure of water vapor in wet air to the saturation pressure of water at the same temperature.
Humidity: wet and dry bulb measurement
The dry and wet bulb thermometer is used to detect the [relative humidity] in the air, the dry bulb temperature is the temperature measured by the general temperature sensor, and the wet bulb temperature is tied on the temperature sensor with a wet cloth, and then soaked in a small cup of water, so that the water is wrapped in the whole sensor, because the relative humidity in the air must be less than or equal to 100% (the water vapor in the air is not saturated). Therefore, the moisture of the wet bulb will be evaporated, and the heat will be taken away during evaporation, resulting in a drop in the wet bulb temperature (the dry bulb temperature is the real air temperature), which means that the greater the difference in the readings of the dry and wet bulb thermometer, the more vigorous the evaporation of water, and the smaller the relative humidity in the air, as long as the temperature of the dry and wet bulb is measured, Then compare [relative humidity table] you can know the relative humidity of the environment at that time.
Temperature Cyclic Stress Screening (1)
Environmental Stress Screening (ESS)
Stress screening is the use of acceleration techniques and environmental stress under the design strength limit, such as: burn in, temperature cycling, random vibration, power cycle... By accelerating the stress, the potential defects in the product emerge [potential parts material defects, design defects, process defects, process defects], and eliminate electronic or mechanical residual stress, as well as eliminate stray capacitors between multi-layer circuit boards, the early death stage of the product in the bath curve is removed and repaired in advance, so that the product through moderate screening, Save the normal period and decline period of the bathtub curve to avoid the product in the process of use, the test of environmental stress sometimes lead to failure, resulting in unnecessary losses. Although the use of ESS stress screening will increase the cost and time, for improving the product delivery yield and reduce the number of repairs, there is a significant effect, but for the total cost will be reduced. In addition, customer trust will also be improved, generally for electronic parts of the stress screening methods are pre-burning, temperature cycle, high temperature, low temperature, PCB printed circuit board stress screening method is temperature cycle, for the electronic cost of the stress screening is: Power pre-burning, temperature cycling, random vibration, in addition to the stress screen itself is a process stage, rather than a test, screening is 100% of the product procedure.
Stress screening applicable product stage: R & D stage, mass production stage, before delivery (screening test can be carried out in components, devices, connectors and other products or the whole machine system, according to different requirements can have different screening stress)
Stress screening comparison:
a. Constant high temperature pre-burning (Burn in) stress screening, is the current electronic IT industry commonly used method to precipitate electronic components defects, but this method is not suitable for screening parts (PCB, IC, resistor, capacitor), According to statistics, the number of companies in the United States that use temperature cycling to screen parts is five times more than the number of companies that use constant high temperature prefiring to screen components.
B. GJB/DZ34 indicates the proportion of temperature cycle and random vibrating screen selection defects, temperature accounted for about 80%, vibration accounted for about 20% of the defects in various products.
c. The United States has conducted a survey of 42 enterprises, random vibration stress can screen out 15 to 25% of the defects, while the temperature cycle can screen out 75 to 85%, if the combination of the two can reach 90%.
d. The proportion of product defect types detected by temperature cycling: insufficient design margin: 5%, production and workmanship errors: 33%, defective parts: 62%
Description of fault induction of temperature cyclic stress screening:
The cause of product failure induced by temperature cycling is: when the temperature is cycled within the upper and lower extremal temperatures, the product produces alternating expansion and contraction, resulting in thermal stress and strain in the product. If there is a transient thermal ladder (temperature non-uniformity) within the product, or the thermal expansion coefficients of adjacent materials within the product do not match each other, these thermal stresses and strains will be more drastic. This stress and strain is greatest at the defect, and this cycle causes the defect to grow so large that it can eventually cause structural failure and generate electrical failure. For example, a cracked electroplated through-hole eventually cracks completely around it, causing an open circuit. Thermal cycling enables soldering and plating through holes on printed circuit boards... Temperature cyclic stress screening is especially suitable for electronic products with printed circuit board structure.
The fault mode triggered by the temperature cycle or the impact on the product is as follows:
a. The expansion of various microscopic cracks in the coating, material or wire
b. Loosen poorly bonded joints
c. Loosen improperly connected or riveted joints
d. Relax the pressed fittings with insufficient mechanical tension
e. Increase the contact resistance of poor quality solder joints or cause an open circuit
f. Particle, chemical pollution
g. Seal failure
h. Packaging issues, such as bonding of protective coatings
i. Short circuit or open circuit of the transformer and coil
j. The potentiometer is defective
k. Poor connection of welding and welding points
l. Cold welding contact
m. Multi-layer board due to improper handling of open circuit, short circuit
n. Short circuit of power transistor
o. Capacitor, transistor bad
p. Dual row integrated circuit failure
q. A box or cable that is nearly short-circuited due to damage or improper assembly
r. Breakage, breakage, scoring of material due to improper handling... Etc.
s. out-of-tolerance parts and materials
t. resistor ruptured due to lack of synthetic rubber buffer coating
u. The transistor hair is involved in the grounding of the metal strip
v. Mica insulation gasket rupture, resulting in short circuit transistor
w. Improper fixing of the metal plate of the regulating coil leads to irregular output
x. The bipolar vacuum tube is open internally at low temperature
y. Coil indirect short circuit
z. Ungrounded terminals
a1. Component parameter drift
a2. Components are improperly installed
a3. Misused components
a4. Seal failure
Introduction of stress parameters for temperature cyclic stress screening:
The stress parameters of temperature cyclic stress screening mainly include the following: high and low temperature extremum range, dwell time, temperature variability, cycle number
High and low temperature extremal range: the larger the range of high and low temperature extremal, the fewer cycles required, the lower the cost, but can not exceed the product can withstand the limit, do not cause new fault principle, the difference between the upper and lower limits of temperature change is not less than 88°C, the typical range of change is -54°C to 55°C.
Dwell time: In addition, the dwell time can not be too short, otherwise it is too late to make the product under test produce thermal expansion and contraction stress changes, as for the dwell time, the dwell time of different products is different, you can refer to the relevant specification requirements.
Number of cycles: As for the number of cycles of temperature cyclic stress screening, it is also determined by considering product characteristics, complexity, upper and lower limits of temperature and screening rate, and the screening number should not be exceeded, otherwise it will cause unnecessary harm to the product and cannot improve the screening rate. The number of temperature cycles ranges from 1 to 10 cycles [ordinary screening, primary screening] to 20 to 60 cycles [precision screening, secondary screening], for the removal of the most likely workmanship defects, about 6 to 10 cycles can be effectively removed, in addition to the effectiveness of the temperature cycle, Mainly depends on the temperature variation of the product surface, rather than the temperature variation inside the test box.
There are seven main influencing parameters of temperature cycle:
(1) Temperature Range
(2) Number of Cycles
(3) Temperature Rate of Chang
(4) Dwell Time
(5) Airflow Velocities
(6) Uniformity of Stress
(7) Function test or not (Product Operating Condition)
Temperature Cycling Test
Temperature Cycling, in order to simulate the temperature conditions encountered by different electronic components in the actual use environment, changing the ambient temperature difference range and rapid rise and fall temperature change can provide a more stringent test environment, but it must be noted that additional effects may be caused to material testing. For the relevant international standard test conditions of temperature cycle test, there are two ways to set the temperature change. Macroshow Technology provides an intuitive setting interface, which is convenient for users to set according to the specification. You can choose the total Ramp time or set the rise and cooling rate with the temperature change rate per minute.
List of international specifications for temperature cycling tests:
Total Ramp time (min) : JESD22-A104, MIL-STD-8831, CR200315
Temperature variation per minute (℃/min) : IEC 60749, IPC-9701, Bellcore-GR-468, MIL-2164
Example: Lead-free solder joint reliability test
Instructions: For the reliability test of lead-free solder joints, different test conditions will also be different in terms of the temperature change setting mode. For example, (JEDEC JESD22-A104) will specify the temperature change time with the total time [10min], while other conditions will specify the temperature change rate with [10℃/ min], such as from 100 ℃ to 0℃. With a temperature change of 10 degrees per minute, that is to say, the total temperature change time is 10 minutes.
100℃ [10min]←→0℃[10min], Ramp: 10℃/ min, 6500cycle
-40℃[5min]←→125℃ [5min], Ramp: 10min,
200cycle check once, 2000cycle tensile test [JEDEC JESD22-A104]
-40℃(15min)←→125℃(15min), Ramp: 15min, 2000cycle
Example: LED Automotive lighting (High Power LED)
The temperature cycle test condition of LED car lights is -40 ° C to 100 ° C for 30 minutes, the total temperature change time is 5 minutes, if converted into temperature change rate, it is 28 degrees per minute (28 ° C /min).
Test conditions: -40℃(30min)←→100℃(30min), Ramp: 5min
Надежность оборудования для испытаний на воздействие окружающей среды в сочетании с многоканальными системами контроля и обнаружения температурыОборудование для испытаний на воздействие окружающей среды включает в себя испытательную камеру с постоянной температурой и влажностью, камеру для испытаний на горячий и холодный удар, камеру для испытаний на температурный цикл, безветренную печь... Все это испытательное оборудование находится в смоделированной среде температуры и воздействия влажности на продукт, чтобы выяснить В процессе проектирования, производства, хранения, транспортировки и использования могут возникнуть дефекты продукции, ранее только моделировалась температура воздуха в испытательной зоне, но в новых международных стандартах и новых условиях испытаний на международном заводе начинаются требования, основанные на температуре воздуха. нет. Это температура поверхности испытуемого продукта. Кроме того, температуру поверхности также следует измерять и фиксировать синхронно во время процесса испытаний для последующего анализа. Соответствующее оборудование для испытаний на воздействие окружающей среды должно сочетаться с контролем температуры поверхности, а применение измерения температуры поверхности обобщается следующим образом. Применение определения температуры испытательной камеры с постоянной температурой и влажностью: Описание: Испытательная камера с постоянной температурой и влажностью в процессе испытаний в сочетании с многоканальным обнаружением температуры, высокой температурой и влажностью, конденсацией (конденсатом), комбинированной температурой и влажностью, медленным температурным циклом... Во время процесса испытания датчик прикрепленный к поверхности тестируемого продукта, который можно использовать для измерения температуры поверхности или внутренней температуры тестируемого продукта. С помощью этого многодорожечного модуля определения температуры заданные условия, фактическая температура и влажность, температура поверхности тестируемого продукта, а также те же измерения и записи могут быть интегрированы в файл синхронной кривой для последующего хранения и анализа.Применение контроля и обнаружения температуры поверхности камеры для испытаний на термический удар: [время выдержки на основе контроля температуры поверхности], [запись измерения температуры поверхности в процессе температурного удара] Описание: 8-канальный датчик температуры крепится к поверхности тестируемого продукта и применяется в процессе температурного шока. Время пребывания можно отсчитывать в обратном направлении по достижению температуры поверхности. Во время процесса удара условия настройки, температура испытания, температура поверхности испытуемого продукта, а также те же измерения и записи могут быть интегрированы в синхронную кривую.Приложение для контроля и обнаружения температуры поверхности испытательной камеры с температурным циклом: [Изменчивость температуры температурного цикла и время выдержки контролируются в зависимости от температуры поверхности тестируемого продукта] Описание: Испытание на температурный цикл отличается от испытания на температурный шок. Испытание на температурный шок использует максимальную энергию системы для изменения температуры между высокими и низкими температурами, а скорость изменения температуры достигает 30 ~ 40 ℃ / мин. Испытание температурного цикла требует процесса изменения высоких и низких температур, и его изменчивость температуры можно устанавливать и контролировать. Однако новые спецификации и условия испытаний международных производителей начали требовать, чтобы изменчивость температуры относилась к температуре поверхности тестируемого продукта, а не к температуре воздуха, а также к контролю изменчивости температуры в соответствии со спецификациями текущего температурного цикла. Согласно характеристикам поверхности испытательного продукта [JEDEC-22A-104F, IEC60749-25, IPC9701, ISO16750, AEC-Q100, LV124, GMW3172]... Кроме того, время пребывания при высоких и низких температурах также может быть основано на испытательной поверхности, а не температуры воздуха.Применения контроля и обнаружения температуры поверхности испытательной камеры для циклического стресс-скрининга: Инструкции: Машина для испытания на стресс-скрининг с температурным циклом в сочетании с многорельсовым измерением температуры. При изменении температуры стресс-скрининга вы можете использовать [температуру воздуха] или [температуру поверхности испытуемого продукта] для контроля изменчивости температуры, кроме того, В резидентном процессе с высокой и низкой температурой обратную величину времени также можно контролировать в зависимости от поверхности испытуемого продукта. В соответствии с соответствующими спецификациями (GJB1032, IEST) и требованиями международных организаций, в соответствии с определением GJB1032 в точке измерения времени воздействия и температуры при стресс-скрининге, 1. Количество термопар, закрепленных на изделии, должно быть не менее 3, а точка измерения температуры системы охлаждения должна быть не менее 6, 2. Убедитесь, что температура 2/3 термопар на изделии установлена на уровне ± 10 ℃, кроме того, в соответствии с требованиями IEST (Международного Ассоциация по экологическим наукам и технологиям) время пребывания должно достигать времени стабилизации температуры плюс 5 минут или времени испытания производительности. Приложение для определения температуры поверхности без воздушной печи (испытательная камера с естественной конвекцией): Описание: Благодаря сочетанию безветренной печи (испытательная камера с естественной конвекцией) и многоканального модуля определения температуры создается температурная среда без вентилятора (естественная конвекция) и интегрирован соответствующий тест определения температуры. Это решение может применяться для реальных испытаний электронных продуктов при температуре окружающей среды (таких как: облачный сервер, 5G, салон электромобиля, помещение без кондиционирования воздуха, солнечный инвертор, большой ЖК-телевизор, домашний интернет-распределитель, офис 3C, ноутбук, настольный компьютер). , игровая консоль....... и т. д.).
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