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
Equipo de prueba ambiental de confiabilidad combinado con aplicaciones de detección y control de temperatura de múltiples pistasEl equipo de prueba ambiental incluye una cámara de prueba de temperatura y humedad constante, una cámara de prueba de choque frío y caliente, una cámara de prueba de ciclo de temperatura, un horno sin viento... Todos estos equipos de prueba se encuentran en un entorno simulado de temperatura y humedad que impactan en el producto, para averiguarlo. El proceso de diseño, producción, almacenamiento, transporte y uso puede aparecer defectos del producto, anteriormente solo se simulaba la temperatura del aire del área de prueba, pero en los nuevos estándares internacionales y las nuevas condiciones de prueba de la fábrica internacional, el comienzo de los requisitos basados en la temperatura del aire. no lo es. Es la temperatura de la superficie del producto de prueba. Además, la temperatura de la superficie también debe medirse y registrarse sincrónicamente durante el proceso de prueba para el análisis posterior a la prueba. El equipo de prueba ambiental relevante debe combinarse con el control de la temperatura de la superficie y la aplicación de la medición de la temperatura de la superficie se resume a continuación. Aplicación de detección de temperatura de la mesa de prueba de la cámara de prueba de temperatura y humedad constantes: Descripción: Cámara de prueba de temperatura y humedad constantes en el proceso de prueba, combinada con detección de temperatura multipista, alta temperatura y humedad, condensación (condensación), temperatura y humedad combinadas, ciclo de temperatura lento... Durante el proceso de prueba, el sensor fijado a la superficie del producto de prueba, que se puede utilizar para medir la temperatura de la superficie o la temperatura interna del producto de prueba. A través de este módulo de detección de temperatura de múltiples pistas, las condiciones establecidas, la temperatura y humedad reales, la temperatura de la superficie del producto de prueba y la misma medición y registro se pueden integrar en un archivo de curva sincrónico para su posterior almacenamiento y análisis.Aplicaciones de detección y control de temperatura de la superficie de la cámara de prueba de choque térmico: [tiempo de permanencia basado en el control de la temperatura de la superficie], [registro de medición de la temperatura de la superficie del proceso de choque de temperatura] Descripción: El sensor de temperatura de 8 rieles se fija a la superficie del producto de prueba y se aplica al proceso de choque de temperatura. El tiempo de permanencia se puede contar hacia atrás según la llegada de la temperatura superficial. Durante el proceso de impacto, las condiciones de fraguado, la temperatura de prueba, la temperatura de la superficie del producto de prueba y la misma medición y registro se pueden integrar en una curva sincrónica.Aplicación de detección y control de temperatura de la superficie de la cámara de prueba del ciclo de temperatura: [La variabilidad de la temperatura del ciclo de temperatura y el tiempo de permanencia se controlan de acuerdo con la temperatura de la superficie del producto de prueba] Descripción: La prueba del ciclo de temperatura es diferente de la prueba de choque de temperatura. La prueba de choque de temperatura utiliza la energía máxima del sistema para realizar cambios de temperatura entre temperaturas altas y bajas, y su tasa de cambio de temperatura es tan alta como 30 ~ 40 ℃ /min. La prueba del ciclo de temperatura requiere un proceso de cambios de temperatura alta y baja, y su variabilidad de temperatura se puede configurar y controlar. Sin embargo, las nuevas especificaciones y las condiciones de prueba de los fabricantes internacionales han comenzado a exigir que la variabilidad de la temperatura se refiera a la temperatura de la superficie del producto de prueba, no a la temperatura del aire, y el control de variabilidad de la temperatura de la especificación del ciclo de temperatura actual. Según las especificaciones de la superficie del producto de prueba son [JEDEC-22A-104F, IEC60749-25, IPC9701, ISO16750, AEC-Q100, LV124, GMW3172]... Además, el tiempo de residencia de temperaturas altas y bajas también puede basarse en la superficie de prueba, en lugar de la temperatura del aire.Aplicaciones de detección y control de temperatura de la superficie de la cámara de prueba de detección de estrés cíclico de temperatura: Instrucciones: Máquina de prueba de detección de tensión por ciclo de temperatura, combinada con medición de temperatura de múltiples rieles, en la variabilidad de temperatura de la detección de tensión, puede optar por usar [temperatura del aire] o [temperatura de la superficie del producto de prueba] para controlar la variabilidad de la temperatura, además, En el proceso residente de alta y baja temperatura, el tiempo recíproco también se puede controlar según la superficie del producto de prueba. De acuerdo con las especificaciones pertinentes (GJB1032, IEST) y los requisitos de las organizaciones internacionales, de acuerdo con la definición de GJB1032 en el punto de medición de temperatura y tiempo de residencia de detección de tensión, 1. El número de termopares fijados en el producto no será inferior a 3, y el punto de medición de temperatura del sistema de enfriamiento no deberá ser inferior a 6, 2. Asegúrese de que la temperatura de 2/3 de los termopares del producto esté establecida en ±10 ℃, además, de acuerdo con los requisitos de IEST (Internacional Association for Environmental Science and Technology), el tiempo de residencia debe alcanzar el tiempo de estabilización de temperatura más 5 minutos o el tiempo de prueba de rendimiento. Aplicación de detección de temperatura de superficie sin horno de aire (cámara de prueba de convección natural): Descripción: Mediante la combinación de un horno sin viento (cámara de prueba de convección natural) y un módulo de detección de temperatura multipista, se genera la temperatura ambiente sin ventilador (convección natural) y se integra la prueba de detección de temperatura relevante. Esta solución se puede aplicar a la prueba de temperatura ambiente real de productos electrónicos (como: servidor en la nube, 5G, interior de vehículos eléctricos, ambiente interior sin aire acondicionado, inversor solar, televisor LCD grande, compartidor de Internet en el hogar, oficina 3C, computadora portátil, computadora de escritorio). , consola de juegos....... Etc.).
Consigue una cotización
Red IPv6 compatible
