Concentrator Solar Cell
A concentrating solar cell is a combination of [Concentrator Photovoltaic]+[Fresnel Lenes]+[Sun Tracker]. Its solar energy conversion efficiency can reach 31% ~ 40.7%, although the conversion efficiency is high, but due to the long sunward time, it has been used in the space industry in the past, and now it can be used in the power generation industry with sunlight tracker, which is not suitable for general families. The main material of concentrating solar cells is gallium arsenide (GaAs), that is, the three five group (III-V) materials. General silicon crystal materials can only absorb the energy of 400 ~ 1,100nm wavelength in the solar spectrum, and the concentrator is different from silicon wafer solar technology, through the multi-junction compound semiconductor can absorb a wider range of solar spectrum energy, and the current development of three-junction InGaP/GaAs/Ge concentrator solar cells can greatly improve the conversion efficiency. The three-junction concentrating solar cell can absorb energy of 300 ~ 1900nm wavelength relative to its conversion efficiency can be greatly improved, and the heat resistance of concentrating solar cells is higher than that of general wafer-type solar cells.
Conduction Zone of Heat
Thermal conductivity
It is the thermal conductivity of a substance, passing from high temperature to low temperature within the same substance. Also known as: thermal conductivity, thermal conductivity, thermal conductivity, heat transfer coefficient, heat transfer, thermal conductivity, thermal conductivity, thermal conductivity, thermal conductivity.
Thermal conductivity formula
k = (Q/t) *L/(A*T) k: thermal conductivity, Q: heat, t: time, L: length, A: area, T: temperature difference in SI units, the unit of thermal conductivity is W/(m*K), in imperial units, is Btu · ft/(h · ft2 · °F)
Heat transfer coefficient
In thermodynamics, mechanical engineering and chemical engineering, the heat conductivity is used to calculate the heat conduction, mainly the heat conduction of convection or the phase transformation between fluid and solid, which is defined as the heat through the unit area per unit time under the unit temperature difference, called the heat conduction coefficient of the substance, if the thickness of the mass of L, the measurement value to be multiplied by L, The resulting value is the coefficient of thermal conductivity, usually denoted as k.
Unit conversion of heat conduction coefficient
1 (CAL) = 4.186 (j), 1 (CAL/s) = 4.186 (j/s) = 4.186 (W).
The impact of high temperature on electronic products:
The rise in temperature will cause the resistance value of the resistor to decrease, but also shorten the service life of the capacitor, in addition, the high temperature will cause the transformer, the performance of the related insulation materials to decrease, the temperature is too high will also cause the solder joint alloy structure on the PCB board to change: IMC thickens, solder joints become brittle, tin whisker increases, mechanical strength decreases, junction temperature increases, the current amplification ratio of transistor increases rapidly, resulting in collector current increases, junction temperature further increases, and finally component failure.
Explanation of proper terms:
Junction Temperature: The actual temperature of a semiconductor in an electronic device. In operation, it is usually higher than the Case Temperature of the package, and the temperature difference is equal to the heat flow multiplied by the thermal resistance. Free convection (natural convection) : Radiation (radiation) : Forced Air(gas cooling) : Forced Liquid (gas cooling) : Liquid Evaporation: Surface Surroundings Surroundings
Common simple considerations for thermal design:
1 Simple and reliable cooling methods such as heat conduction, natural convection and radiation should be used to reduce costs and failures.
2 Shorten the heat transfer path as much as possible, and increase the heat exchange area.
3 When installing components, the influence of radiation heat exchange of peripheral components should be fully considered, and the thermal sensitive devices should be kept away from the heat source or find a way to use the protective measures of the heat shield to isolate the components from the heat source.
4 There should be sufficient distance between the air inlet and the exhaust port to avoid hot air reflux.
5 The temperature difference between the incoming air and the outgoing air should be less than 14 ° C.
6 It should be noted that the direction of forced ventilation and natural ventilation should be consistent as far as possible.
7 Devices with large heat should be installed as close as possible to the surface that is easy to dissipate heat (such as the inner surface of the metal casing, metal base and metal bracket, etc.), and there is good contact heat conduction between the surface.
8 Power supply part of the high-power tube and rectifier bridge pile belong to the heating device, it is best to install directly on the housing to increase the heat dissipation area. In the layout of the printed board, more copper layers should be left on the board surface around the larger power transistor to improve the heat dissipation capacity of the bottom plate.
9 When using free convection, avoid using heat sinks that are too dense.
10 The thermal design should be considered to ensure that the current carrying capacity of the wire, the diameter of the selected wire must be suitable for the conduction of the current, without causing more than the allowable temperature rise and pressure drop.
11 If the heat distribution is uniform, the spacing of the components should be uniform to make the wind flow evenly through each heat source.
12 When using forced convection cooling (fans), place the temperature-sensitive components closest to the air intake.
13 The use of free convection cooling equipment to avoid arranging other parts above the high power consumption parts, the correct approach should be uneven horizontal arrangement.
14 If the heat distribution is not uniform, the components should be sparsely arranged in the area with large heat generation, and the component layout in the area with small heat generation should be slightly denser, or add a diversion bar, so that the wind energy can effectively flow to the key heating devices.
15 The structural design principle of the air inlet: on the one hand, try to minimize its resistance to the air flow, on the other hand, consider dust prevention, and comprehensively consider the impact of the two.
16 Power consumption components should be spaced as far apart as possible.
17 Avoid crowding temperature sensitive parts together or arranging them next to high power consuming parts or hot spots.
18 The use of free convection cooling equipment to avoid arranging other parts above the high power consumption parts, the correct practice should be uneven horizontal arrangement.
Temperature Cyclic Stress Screening (2)
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)
Stress screening fatigue classification:
The general classification of Fatigue research can be divided into High-cycle Fatigue, Low-cycle Fatigue and Fatigue Crack Growth. In the aspect of low cycle Fatigue, it can be subdivided into Thermal Fatigue and Isothermal Fatigue.
Stress screening acronyms:
ESS: Environmental stress screening
FBT: Function board tester
ICA: Circuit analyzer
ICT: Circuit tester
LBS: load board short-circuit tester
MTBF: mean time between failures
Time of temperature cycles:
a.MIL-STD-2164(GJB 1302-90) : In the defect removal test, the number of temperature cycles is 10, 12 times, and in the trouble-free detection it is 10 ~ 20 times or 12 ~ 24 times. In order to remove the most likely workmanship defects, about 6 ~ 10 cycles are needed to effectively remove them. 1 ~ 10 cycles [general screening, primary screening], 20 ~ 60 cycles [precision screening, secondary screening].
B.od-hdbk-344 (GJB/DZ34) Initial screening equipment and unit level uses 10 to 20 loops (usually ≧10), component level uses 20 to 40 loops (usually ≧25).
Temperature variability:
a.MIL-STD-2164(GJB1032) clearly states: [Temperature change rate of temperature cycle 5℃/min]
B.od-hdbk-344 (GJB/DZ34) Component level 15 ° C /min, system 5 ° C /min
c. Temperature cyclic stress screening is generally not specified temperature variability, and its commonly used degree variation rate is usually 5°C/min
IEC-60068-2 Combined Test of Condensation and Temperature and Humidity
Difference of IEC60068-2 damp heat test specifications
In the IEC60068-2 specification, there are a total of five kinds of humid heat tests, in addition to the common 85℃/85%R.H., 40℃/93%R.H. In addition to fixed-point high temperature and high humidity, there are two more special tests [IEC60068-2-30, IEC60068-2-38], these two are alternating wet and humid cycle and temperature and humidity combined cycle, so the test process will change temperature and humidity, and even multiple groups of program links and cycles, applied in IC semiconductors, parts, equipment, etc. To simulate the outdoor condensation phenomenon, evaluate the material's ability to prevent water and gas diffusion, and accelerate the product's tolerance to deterioration, the five specifications were organized into a comparison table of the differences in the wet and heat test specifications, and the test points were explained in detail for the wet and heat combined cycle test, and the test conditions and points of GJB in the wet and heat test were supplemented.
IEC60068-2-30 alternating humid heat cycle test
This test uses the test technique of maintaining humidity and temperature alternating to make moisture penetrate into the sample and cause condensation (condensation) on the surface of the product to be tested, so as to confirm the adaptability of the component, equipment or other products in use, transportation and storage under the combination of high humidity and temperature and humidity cyclic changes. This specification is also suitable for large test samples. If the equipment and the test process need to keep the power heating components for this test, the effect will be better than IEC60068-2-38, the high temperature used in this test has two (40 ° C, 55 ° C), the 40 ° C is to meet most of the world's high temperature environment, while 55 ° C meets all the world's high temperature environment, the test conditions are also divided into [cycle 1, cycle 2], In terms of severity, [Cycle 1] is higher than [Cycle 2].
Suitable for side products: components, equipment, various types of products to be tested
Test environment: the combination of high humidity and temperature cyclic changes produces condensation, and three kinds of environments can be tested [use, storage, transportation ([packaging is optional)]
Test stress: Breathing causes water vapor to invade
Whether power is available: Yes
Not suitable for: parts that are too light and too small
Test process and post-test inspection and observation: check the electrical changes after moisture [do not take out the intermediate inspection]
Test conditions: Humidity: 95%R.H.[Temperature change after high humidity maintenance](low temperature 25±3℃←→ high temperature 40℃ or 55℃)
Rising and cooling rate: heating (0.14℃/min), cooling (0.08 ~ 0.16℃/min)
Cycle 1: Where absorption and respiratory effects are important features, the test sample is more complex [humidity not less than 90%R.H.]
Cycle 2: In the case of less obvious absorption and respiratory effects, the test sample is simpler [humidity is not less than 80%R.H.]
IEC60068-2 damp heat test specification difference comparison table
For component type parts products, a combination test method is used to accelerate the confirmation of the test sample's resistance to degradation under high temperature, high humidity and low temperature conditions. This test method is different from the product defects caused by respiration [dew, moisture absorption] of IEC60068-2-30. The severity of this test is higher than that of other humid heat cycle tests, because there are more temperature changes and [respiration] during the test, the cycle temperature range is larger [from 55℃ to 65℃], and the temperature change rate of the temperature cycle is faster [temperature rise: 0.14 ° C /min becomes 0.38 ° C /min, 0.08 ° C /min becomes 1.16 ° C /min], in addition, different from the general humid heat cycle, the low temperature cycle condition of -10 ° C is added to accelerate the breathing rate and make the water condensed in the gap of the substitute freeze, which is the characteristic of this test specification. The test process allows the power test and the applied load power test, but it can not affect the test conditions (temperature and humidity fluctuation, rising and cooling rate) because of the heating of the side product after power. Due to the change of temperature and humidity during the test process, there can not be condensation water droplets on the top of the test chamber to the side product.
Suitable for side products: components, metal components sealing, lead end sealing
Test environment: combination of high temperature, high humidity and low temperature conditions
Test stress: accelerated breathing + frozen water
Whether it can be powered on: it can be powered on and external electric load (it can not affect the conditions of the test chamber because of power heating)
Not applicable: Can not replace moist heat and alternating humid heat, this test is used to produce defects different from respiration
Test process and post-test inspection and observation: check the electrical changes after moisture [check under high humidity conditions and take out after test]
Test conditions: damp heat cycle (25 please - 65 + 2 ℃ / 93 + / - 3% R.H.) please - low temperature cycle (25 please - 65 + 2 ℃ / 93 + 3% R.H. - - 10 + 2 ℃) X5cycle = 10 cycle
Rising and cooling rate: heating (0.38℃/min), cooling (1.16 ℃/min)
Heat and humidity cycle (25←→65±2℃/93±3%R.H.)
Low temperature cycle (25←→65±2℃/93±3%R.H. →-10±2℃)
GJB150-09 damp heat test
Instructions: The wet and heat test of GJB150-09 is to confirm the ability of equipment to withstand the influence of hot and humid atmosphere, suitable for equipment stored and used in hot and humid environments, equipment prone to high humidity, or equipment that may have potential problems related to heat and humidity. Hot and humid locations can occur throughout the year in the tropics, seasonally in mid-latitudes, and in equipment subjected to combined pressure, temperature and humidity changes, with special emphasis on 60 ° C /95%R.H. This high temperature and humidity does not occur in nature, nor does it simulate the dampness and heat effect after solar radiation, but it can find the parts of the equipment with potential problems, but it cannot reproduce the complex temperature and humidity environment, evaluate the long-term effect, and can not reproduce the humidity impact related to the low humidity environment.
Relevant equipment for condensation, wet freezing, wet heat combined cycle test: constant temperature and humidity test chamber
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