Basic troubleshooting methods for high and low temperature test chambers:
1、 High and low temperature testing equipment. In high temperature testing, if the temperature change does not reach the test temperature value, the electrical system can be checked and the faults can be eliminated one by one. If the temperature rises slowly, you need to check the air circulation system to see if the regulating baffle of the air circulation is open normally. Otherwise, check the motor of the air circulation
Is the operation normal. If the temperature overshoot is severe, it is necessary to adjust the PID setting parameters. If the temperature rises directly and is protected against overheating, the controller will malfunction and the control instrument must be replaced.
2、 When the high and low temperature test equipment suddenly malfunctions during the test operation, the corresponding fault display prompt and audible alarm prompt will appear on the control instrument. The operator can quickly identify which type of fault it belongs to by referring to the troubleshooting chapter in the operation and use of the equipment, and then ask professional personnel to quickly troubleshoot it to ensure the normal progress of the experiment. Other environmental testing equipment may experience other phenomena during use, so it is necessary to analyze and eliminate them specifically. Regular maintenance and upkeep of environmental testing equipment, regular cleaning of the condenser in the refrigeration system, lubrication of moving parts according to the instructions, and regular maintenance and inspection of the electrical control system are essential tasks
3、 If the low temperature of the high and low temperature testing instrument cannot meet the test indicators, then you need to observe the temperature changes, whether the temperature drops very slowly or there is a trend of temperature recovery after reaching a certain value. The former needs to check whether the working chamber is dried before conducting the low temperature test, so that the working chamber can be kept dry before putting the test sample into the working chamber for further testing. If there are too many test samples placed in the working chamber, which prevent the air in the working chamber from fully circulating, after ruling out the above reasons, you need to consider whether it is a fault in the refrigeration system. In this case, you need to hire professional personnel from the Lab Companion manufacturer for maintenance. The latter phenomenon is caused by poor usage environment of the equipment. The temperature and location of the equipment placement (distance between the box and the wall) must meet the requirements (as specified in the equipment operation instructions).
At present, the company's main products include: high and low temperature test chambers, rapid temperature change test chambers, constant temperature and humidity test chambers, and high and low temperature impact test chambers.
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.
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
AEC-Q100- Failure Mechanism Based on Integrated Circuit Stress Test Certification
With the progress of automotive electronic technology, there are many complicated data management control systems in today's cars, and through many independent circuits, to transmit the required signals between each module, the system inside the car is like the "master-slave architecture" of the computer network, in the main control unit and each peripheral module, automotive electronic parts are divided into three categories. Including IC, discrete semiconductor, passive components three categories, in order to ensure that these automotive electronic components meet the highest standards of automotive anquan, the American Automotive Electronics Association (AEC, The Automotive Electronics Council is a set of standards [AEC-Q100] designed for active parts [microcontrollers and integrated circuits...] and [[AEC-Q200] designed for passive components, which specifies the product quality and reliability that must be achieved for passive parts. Aec-q100 is the vehicle reliability test standard formulated by the AEC organization, which is an important entry for 3C and IC manufacturers into the international auto factory module, and also an important technology to improve the reliability quality of Taiwan IC. In addition, the international auto factory has passed the anquan standard (ISO-26262). AEC-Q100 is the basic requirement to pass this standard.
List of automotive electronic parts required to pass AECQ-100:
Automotive disposable memory, Power Supply step-down regulator, Automotive photocoupler, three-axis accelerometer sensor, video jiema device, rectifier, ambient light sensor, non-volatile ferroelectric memory, power management IC, embedded flash memory, DC/DC regulator, Vehicle gauge network communication device, LCD driver IC, Single power Supply differential Amplifier, Capacitive proximity switch Off, high brightness LED driver, asynchronous switcher, 600V IC, GPS IC, ADAS Advanced Driver Assistance System Chip, GNSS Receiver, GNSS front-end amplifier... Let's wait.
AEC-Q100 Categories and Tests:
Description: AEC-Q100 specification 7 major categories a total of 41 tests
Group A- ACCELERATED ENVIRONMENT STRESS TESTS consists of 6 tests: PC, THB, HAST, AC, UHST, TH, TC, PTC, HTSL
Group B- ACCELERATED LIFETIME SIMULATION TESTS consists of three tests: HTOL, ELFR, and EDR
PACKAGE ASSEMBLY INTEGRITY TESTS consists of 6 tests: WBS, WBP, SD, PD, SBS, LI
Group D- DIE FABRICATION RELIABILITY Test consists of 5 TESTS: EM, TDDB, HCI, NBTI, SM
The group ELECTRICAL VERIFICATION TESTS consist of 11 tests, including TEST, FG, HBM/MM, CDM, LU, ED, CHAR, GL, EMC, SC and SER
Cluster F-Defect SCREENING TESTS: 11 tests, including: PAT, SBA
The CAVITY PACKAGE INTEGRITY TESTS consist of 8 tests, including: MS, VFV, CA, GFL, DROP, LT, DS, IWV
Short description of test items:
AC: Pressure cooker
CA: constant acceleration
CDM: electrostatic discharge charged device mode
CHAR: indicates the feature description
DROP: The package falls
DS: chip shear test
ED: Electrical distribution
EDR: non-failure-prone storage durability, data retention, working life
ELFR: Early life failure rate
EM: electromigration
EMC: Electromagnetic compatibility
FG: fault level
GFL: Coarse/fine air leakage test
GL: Gate leakage caused by thermoelectric effect
HBM: indicates the human mode of electrostatic discharge
HTSL: High temperature storage life
HTOL: High temperature working life
HCL: hot carrier injection effect
IWV: Internal hygroscopic test
LI: Pin integrity
LT: Cover plate torque test
LU: Latching effect
MM: indicates the mechanical mode of electrostatic discharge
MS: Mechanical shock
NBTI: rich bias temperature instability
PAT: Process average test
PC: Preprocessing
PD: physical size
PTC: power temperature cycle
SBA: Statistical yield analysis
SBS: tin ball shearing
SC: Short circuit feature
SD: weldability
SER: Soft error rate
SM: Stress migration
TC: temperature cycle
TDDB: Time through dielectric breakdown
TEST: Function parameters before and after stress test
TH: damp and heat without bias
THB, HAST: Temperature, humidity or high accelerated stress tests with applied bias
UHST: High acceleration stress test without bias
VFV: random vibration
WBS: welding wire cutting
WBP: welding wire tension
Temperature and humidity test conditions finishing:
THB(temperature and humidity with applied bias, according to JESD22 A101) : 85℃/85%R.H./1000h/bias
HAST(High Accelerated stress test according to JESD22 A110) : 130℃/85%R.H./96h/bias, 110℃/85%R.H./264h/bias
AC pressure cooker, according to JEDS22-A102:121 ℃/100%R.H./96h
UHST High acceleration stress test without bias, according to JEDS22-A118, equipment: HAST-S) : 110℃/85%R.H./264h
TH no bias damp heat, according to JEDS22-A101, equipment: THS) : 85℃/85%R.H./1000h
TC(temperature cycle, according to JEDS22-A104, equipment: TSK, TC) :
Level 0: -50℃←→150℃/2000cycles
Level 1: -50℃←→150℃/1000cycles
Level 2: -50℃←→150℃/500cycles
Level 3: -50℃←→125℃/500cycles
Level 4: -10℃←→105℃/500cycles
PTC(power temperature cycle, according to JEDS22-A105, equipment: TSK) :
Level 0: -40℃←→150℃/1000cycles
Level 1: -65℃←→125℃/1000cycles
Level 2 to 4: -65℃←→105℃/500cycles
HTSL(High temperature storage life, JEDS22-A103, device: OVEN) :
Plastic package parts: Grade 0:150 ℃/2000h
Grade 1:150 ℃/1000h
Grade 2 to 4:125 ℃/1000h or 150℃/5000h
Ceramic package parts: 200℃/72h
HTOL(High temperature working life, JEDS22-A108, equipment: OVEN) :
Grade 0:150 ℃/1000h
Class 1:150℃/408h or 125℃/1000h
Grade 2:125℃/408h or 105℃/1000h
Grade 3:105℃/408h or 85℃/1000h
Class 4:90℃/408h or 70℃/1000h
ELFR(Early Life failure Rate, AEC-Q100-008) : Devices that pass this stress test can be used for other stress tests, general data can be used, and tests before and after ELFR are performed under mild and high temperature conditions.
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
Reliability Environmental Test Equipment Combined with Multi-track Temperature Control and Detection Applications
Environmental test equipment includes constant temperature and humidity test chamber, hot and cold shock test chamber, temperature cycle test chamber, no wind oven... These test equipment are all in the simulated environment of temperature, humidity impact on the product, to find out the design, production, storage, transportation, use process may appear product defects, previously only simulated test area air temperature, but in the new international standards and the new test conditions of the international factory, the beginning of the requirements based on the air temperature is not. It is the surface temperature of the test product. In addition, the surface temperature should also be measured and recorded synchronously during the test process for post-test analysis. The relevant environmental test equipment should be combined with surface temperature control and the application of surface temperature measurement is summarized as follows.
Constant temperature and humidity test chamber test table temperature detection application:
Description: Constant temperature and humidity test chamber in the test process, combined with multi-track temperature detection, high temperature and humidity, condensation (condensation), combined temperature and humidity, slow temperature cycle... During the test process, the sensor is affixed to the surface of the test product, which can be used to measure the surface temperature or internal temperature of the test product. Through this multi-track temperature detection module, the set conditions, actual temperature and humidity, the surface temperature of the test product, and the same measurement and record can be integrated into a synchronous curve file for subsequent storage and analysis.
Thermal shock test chamber surface temperature control and detection applications: [dwell time based on surface temperature control], [temperature shock process surface temperature measurement record]
Description: The 8-rail temperature sensor is attached to the surface of the test product and applied to the temperature shock process. The dwell time can be counted backward according to the arrival of the surface temperature. During the impact process, the setting conditions, the test temperature, the surface temperature of the test product, and the same measurement and record can be integrated into a synchronous curve.
Temperature cycle test chamber surface temperature control and detection application: [Temperature cycle temperature variability and dwell time are controlled according to the test product surface temperature]
Description: Temperature cycle test is different from temperature shock test. Temperature shock test uses the maximum energy of the system to carry out temperature changes between high and low temperatures, and its temperature change rate is as high as 30 ~ 40℃ /min. Temperature cycle test requires a process of high and low temperature changes, and its temperature variability can be set and controlled. However, the new specification and the test conditions of international manufacturers have begun to require that the temperature variability refers to the surface temperature of the test product, not the air temperature, and the current temperature cycle specification temperature variability control. According to the test product surface specifications are [JEDEC-22A-104F, IEC60749-25, IPC9701, ISO16750, AEC-Q100, LV124, GMW3172]... In addition, the residence time of high and low temperatures can also be based on the test surface, rather than the air temperature.
Temperature cyclic stress screening test chamber surface temperature control and detection applications:
Instructions: Temperature cycle stress screening testing machine, combined with multi-rail temperature measurement, in the temperature variability of stress screening, you can choose to use [air temperature] or [test product surface temperature] to control the temperature variability, in addition, in the high and low temperature resident process, the time reciprocal can also be controlled according to the surface of the test product. In accordance with the relevant specifications (GJB1032, IEST) and the requirements of international organizations, according to the definition of GJB1032 in the stress screening residence time and temperature measurement point, 1. The number of thermocouples fixed on the product shall not be less than 3, and the temperature measurement point of the cooling system shall not be less than 6, 2. Ensure that the temperature of 2/3 thermocouples on the product is set at ±10℃, in addition, according to the requirements of IEST(International Association for Environmental Science and Technology), the residence time should reach the temperature stabilization time plus 5min or performance test time.
No air oven (natural convection test chamber) surface temperature detection application:
Description: Through the combination of a windless oven (natural convection test chamber) and a multi-track temperature detection module, the temperature environment without fan (natural convection) is generated, and the relevant temperature detection test is integrated. This solution can be applied to the actual ambient temperature test of electronic products (such as: Cloud server, 5G, electric vehicle interior, indoor without air conditioning environment, solar inverter, large LCD TV, home Internet sharer, office 3C, laptop, desktop, game console....... Etc.).
Comparison of Natural Convection Test Chamber, Constant Temperature and Humidity Test Chamber and High Temperature Oven
Instructions:
Home entertainment audio-visual equipment and automotive electronics are one of the key products of many manufacturers, and the product in the development process must simulate the adaptability of the product to temperature and electronic characteristics at different temperatures. However, when using a general oven or thermal and humidity chamber to simulate the temperature environment, either the oven or thermal and humidity chamber has a test area equipped with a circulating fan, so there will be wind speed problems in the test area.
During the test, the temperature uniformity is balanced by rotating the circulating fan. Although the temperature uniformity of the test area can be achieved through the wind circulation, the heat of the product to be tested will also be taken away by the circulating air, which will be significantly inconsistent with the actual product in the wind-free use environment (such as the living room, indoor).
Because of the relationship of wind circulation, the temperature difference of the product to be tested will be nearly 10℃. In order to simulate the actual use of environmental conditions, many people will misunderstand that only the test chamber can produce temperature (such as: oven, constant temperature humidity chamber) can carry out natural convection test. In fact, this is not the case. In the specification, there are special requirements for wind speed, and a test environment without wind speed is required. Through the natural convection test equipment and software, the temperature environment without passing through the fan (natural convection) is generated, and the test integration test is performed for the temperature detection of the product under test. This solution can be used for home related electronics or real-world ambient temperature testing in confined Spaces (e.g., large LCD TV, car cockpits, automotive electronics, laptops, desktops, game consoles, stereos, etc.).
Unforced air circulation test specification :IEC-68-2-2, GB2423.2, GB2423.2-89 3.31 The difference between the test environment with or without wind circulation and the test of products to be tested:
Instructions:
If the product to be tested is not energized, the product to be tested will not heat itself, its heat source only absorbs the air heat in the test furnace, and if the product to be tested is energized and heated, the wind circulation in the test furnace will take away the heat of the product to be tested. Every 1 meter increase in wind speed, its heat will be reduced by about 10%. Suppose to simulate the temperature characteristics of electronic products in an indoor environment without air conditioning. If an oven or a constant temperature humidifier is used to simulate 35 °C, although the environment can be controlled within 35 °C through electric heating and compressor, the wind circulation of the oven and the thermal and humidify test chamber will take away the heat of the product to be tested. So that the actual temperature of the product to be tested is lower than the temperature under the real windless state. It is necessary to use a natural convection test chamber without wind speed to effectively simulate the actual windless environment (indoor, no starting car cockpit, instrument chassis, outdoor waterproof chamber... Such environment).
Comparison table of wind speed and IC product to be tested:
Description: When the ambient wind speed is faster, the IC surface temperature will also take away the IC surface heat due to the wind cycle, resulting in the faster the wind speed and the lower the temperature.
Comparison of Climatic Test and Environmental Test
Climate environment test -- constant temperature and humidity test chamber, high and low temperature test chamber, cold and hot shock test chamber, wet and heat alternating test chamber, rapid temperature change test chamber, linear temperature change test chamber, walk-in constant temperature and humidity test chamber, etc. They all involve temperature control.
Because there are multiple temperature control points to choose from, the climate chamber temperature control method also has three solutions: inlet temperature control, product temperature control and "cascade" temperature control. The first two are single-point temperature control, and the third is two-parameter temperature control.
Single point temperature control method has been very mature and widely used.
Most of the early control methods were "ping-pong" switch control, commonly known as heating when it's cold and cooling when it's hot. This control mode is a feedback control mode. When the temperature of the circulating air flow is higher than the set temperature, the electromagnetic valve of refrigeration is opened to deliver cold volume to the circulating air flow and reduce the temperature of the air flow. Otherwise, the circuit switch of the heating device is switched on to directly heat the circulating air flow. Raise the temperature of the air stream. This control mode requires that the refrigeration device and heating components of the test chamber are always in a standby working state, which not only wastes a lot of energy, but also the controlled parameter (temperature) is always in an "oscillation" state, and the control accuracy is not high.
Now the single-point temperature control method is mostly changed to the universal proportional differential integral (PID) control method, which can give the controlled temperature correction according to the past change of the controlled parameter (integral control) and the change trend (differential control), which not only saves energy, but also the "oscillation" amplitude is small and the control accuracy is high.
Dual-parameter temperature control is to collect the temperature value of the air inlet of the test chamber and the temperature value near the product at the same time. The air inlet of the test chamber is very close to the installation position of the evaporator and heater in the air modulation room, and its magnitude directly reflects the air modulation result. Using this temperature value as the feedback control parameter has the advantage of quickly modulating the status parameters of the circulating air.
The temperature value near the product indicates the real temperature environmental conditions suffered by the product, which is the requirement of the environmental test specification. Using this temperature value as the parameter of feedback control can ensure the effectiveness and credibility of the temperature environmental test, so this approach takes into account the advantages of both and the requirements of the actual test. The dual-parameter temperature control strategy can be the independent "time-sharing control" of the two groups of temperature data, or the weighted two temperature values can be combined into one temperature value as a feedback control signal according to a certain weighting coefficient, and the value of the weighting coefficient is related to the size of the test chamber, the wind speed of the circulating air flow, the size of the temperature change rate, the heat output of the product work and other parameters.
Because heat transfer is a complex dynamic physical process, and is greatly affected by the atmospheric environment conditions around the test chamber, the working state of the tested sample itself, and the complexity of the structure, it is difficult to establish a perfect mathematical model for the temperature and humidity control of the test chamber. In order to improve the stability and accuracy of control, fuzzy logic control theory and method are introduced in the control of some temperature test chambers. In the control process, the thinking mode of human is simulated, and the predictive control is adopted to control the temperature and humidity space field more quickly.
Compared with the temperature, the selection of humidity measurement and control points is relatively simple. During the circulation flow of the well-regulated humid air into the high and low temperature cycle test chamber, the exchange of water molecules between the wet air and the test piece and the four walls of the test chamber is very small. As long as the temperature of the circulating air is stable, the circulating air flow from entering the test chamber to exiting the test chamber is in the process. The moisture content of wet air changes very little. Therefore, the relative humidity value of the detected air at any point of the circulating air flow field in the test box, such as the inlet, the middle stream of the flow field or the return air outlet, is basically the same. Because of this, in many test chambers that use the wet and dry bulb method to measure humidity, the wet and dry bulb sensor is installed at the return air outlet of the test chamber. Moreover, from the structural design of the test box and the convenience of maintenance in use, the wet and dry bulb sensor used for relative humidity measurement and control is placed at the return air inlet for easy installation, and also helps to regularly replace the wet bulb gauze and clean the temperature sensing head of the resistance PT100, and according to the requirements of the GJB150.9A wet heat test 6.1.3. The wind speed passing through the wet-bulb sensor should not be lower than 4.6m/s. The wet-bulb sensor with a small fan is installed at the return air outlet for easier maintenance and use.
Bellcore GR78-CORE is one of the specifications used in early surface insulation resistance measurement (such as IPC-650). The relevant precautions in this test are organized for reference of personnel who need to carry out this test, and we can also have a preliminary understanding of this specification.
Test purpose:
Surface Insulation Resistance Testing
1. Constant temperature and humidity test chamber: the minimum test conditions are 35°C±2°C/85%R.H., 85 ±2°C/85% R.H.
2. Ion migration measurement system: Allowing insulation resistance of the test circuit to be measured under these conditions, a power supply will be able to provide 10 Vdc / 100μA.
Test procedure:
a. The test object is tested after 24 hours at 23°C (73.4° F)/50%R.H. environment
b. Place limited Test patterns on an appropriate rack and keep the test circuits at least 0.5 inches apart, without obstructing air flow, and the rack in the furnace until the end of the experiment.
c. Place the shelf in the center of the constant temperature and humidity test chamber, align and parallel the test board with the air flow in the chamber, and lead the line to outside of the chamber, so that the wiring is far away from the test circuit.
d. Close the furnace door and set the condition to 35 ±2°C, at least 85%R.H. and allow the furnace to spend several hours stabilizing
e. After 4 days, the insulation resistance will be measured and the measured value will be recorded periodically between 1 and 2,2 and 3,3 and 4, 4 and 5 using an applied voltage of 45 ~ 100 Vdc. Under the test conditions, the test is sent out the measured voltage to the circuit after 1 minute. 2 and 4 are periodically at an identical potential. And 5 periodically at opposite potentials.
f. This condition only applies to transparent or translucent materials, such as solder masks and conformal coatings.
g. As for multilayer printed circuit boards required for insulation resistance testing, the only normal procedure will be used for insulation resistance testing circuit products. Extra cleaning procedures are not allowed.
Related test chamber： temperature and humidity chamber
Method of conformity determination:
1. After the electron migration test is completed, the test sample is removed from the test furnace, illuminated from the back and tested at 10 x magnification, and will not be found to reduce the electron migration (filamental growth) phenomenon by more than 20% between the conductors.
2. adhesives will not be used as a basis for republication when determining compliance with the 2.6.11 test method of IPC-TM-650[8] to examine appearance and surface item by item.
Insulation resistance does not meet the requirements of the reasons:
1. Contaminants weld the cells like wires on insulating surface of substrate, or are dropped by water of test furnace (chamber)
2. Incompletely etched circuits will reduce insulation distance between conductors by more than permitted design requirements
3. Chafes, breaks, or significantly damages the insulation between conductors
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