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
Équipement de test environnemental de fiabilité combiné à des applications de contrôle et de détection de température multi-pistesL'équipement de test environnemental comprend une chambre d'essai à température et humidité constantes, une chambre d'essai de choc chaud et froid, une chambre d'essai de cycle de température, pas de four à vent... Ces équipements de test sont tous dans l'environnement simulé de la température, de l'impact de l'humidité sur le produit, pour le savoir. la conception, la production, le stockage, le transport et le processus d'utilisation peuvent apparaître des défauts du produit, auparavant seulement la température de l'air de la zone de test simulée, mais dans les nouvelles normes internationales et les nouvelles conditions de test de l'usine internationale, le début des exigences basées sur la température de l'air ne l'est pas. C'est la température de surface du produit testé. De plus, la température de surface doit également être mesurée et enregistrée de manière synchrone pendant le processus de test pour une analyse post-test. L'équipement d'essai environnemental pertinent doit être combiné avec le contrôle de la température de surface et l'application de la mesure de la température de surface est résumée comme suit. Application de détection de température de table d'essai de chambre d'essai de température et d'humidité constantes : Description : Chambre de test de température et d'humidité constantes dans le processus de test, combinée à une détection de température multipiste, une température et une humidité élevées, une condensation (condensation), une température et une humidité combinées, un cycle de température lent... Pendant le processus de test, le capteur est apposé sur la surface du produit testé, qui peut être utilisé pour mesurer la température de surface ou la température interne du produit testé. Grâce à ce module de détection de température multipiste, les conditions définies, la température et l'humidité réelles, la température de surface du produit testé, ainsi que les mêmes mesures et enregistrements peuvent être intégrés dans un fichier de courbe synchrone pour un stockage et une analyse ultérieurs.Applications de contrôle et de détection de la température de surface de la chambre d'essai de choc thermique : [temps de séjour basé sur le contrôle de la température de surface], [enregistrement de mesure de la température de surface du processus de choc thermique] Description : Le capteur de température à 8 rails est fixé à la surface du produit testé et appliqué au processus de choc thermique. Le temps de séjour peut être décompté en fonction de l'arrivée de la température de surface. Pendant le processus d'impact, les conditions de prise, la température de test, la température de surface du produit de test, ainsi que les mêmes mesures et enregistrements peuvent être intégrés dans une courbe synchrone.Application de contrôle et de détection de la température de surface de la chambre d'essai de cycle de température : [La variabilité de la température du cycle de température et le temps de séjour sont contrôlés en fonction de la température de surface du produit testé] Description : Le test de cycle de température est différent du test de choc thermique. Le test de choc thermique utilise l'énergie maximale du système pour effectuer des changements de température entre des températures élevées et basses, et son taux de changement de température peut atteindre 30 ~ 40 ℃/min. Le test du cycle de température nécessite un processus de changements de température élevés et faibles, et sa variabilité de température peut être réglée et contrôlée. Cependant, les nouvelles spécifications et les conditions de test des fabricants internationaux ont commencé à exiger que la variabilité de la température se réfère à la température de surface du produit testé, et non à la température de l'air, et au contrôle actuel de la variabilité de la température des spécifications du cycle de température. Selon les spécifications de surface du produit testé sont [JEDEC-22A-104F, IEC60749-25, IPC9701, ISO16750, AEC-Q100, LV124, GMW3172]... De plus, le temps de séjour des températures élevées et basses peut également être basé sur la surface d’essai, plutôt que la température de l’air.Applications de contrôle et de détection de la température de surface de la chambre d'essai de dépistage des contraintes cycliques en température : Instructions : Machine d'essai de dépistage des contraintes du cycle de température, combinée à une mesure de température multi-rails, dans la variabilité de la température du dépistage des contraintes, vous pouvez choisir d'utiliser [température de l'air] ou [température de la surface du produit testé] pour contrôler la variabilité de la température, en plus, dans le processus résident à haute et basse température, le temps réciproque peut également être contrôlé en fonction de la surface du produit testé. Conformément aux spécifications pertinentes (GJB1032, IEST) et aux exigences des organisations internationales, selon la définition de GJB1032 dans le temps de séjour et le point de mesure de la température de dépistage des contraintes, 1. Le nombre de thermocouples fixés sur le produit ne doit pas être inférieur à 3, et le point de mesure de la température du système de refroidissement ne doit pas être inférieur à 6, 2. Assurez-vous que la température des 2/3 des thermocouples sur le produit est réglée à ± 10 ℃, en outre, conformément aux exigences de l'IEST (International Association for Environmental Science and Technology), le temps de séjour doit atteindre le temps de stabilisation de la température plus 5 minutes ou le temps de test de performance. Application de détection de température de surface sans four à air (chambre d'essai à convection naturelle) : Description : Grâce à la combinaison d'un four sans vent (chambre d'essai à convection naturelle) et d'un module de détection de température multipiste, l'environnement de température sans ventilateur (convection naturelle) est généré et le test de détection de température pertinent est intégré. Cette solution peut être appliquée au test de température ambiante réelle des produits électroniques (tels que : serveur Cloud, 5G, intérieur de véhicule électrique, intérieur sans environnement de climatisation, onduleur solaire, grand téléviseur LCD, partage Internet domestique, bureau 3C, ordinateur portable, ordinateur de bureau. , console de jeux....... Etc.).
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