Instructions:
Early temperature cycle tests only look at the air temperature of the test furnace. At present, according to the requirements of relevant international norms, the temperature variability of the temperature cycle test refers not to the air temperature but the surface temperature of the product to be tested (such as the air temperature variability of the test furnace is 15°C/min, but the actual temperature variability measured on the surface of the product to be tested may only be 10~11°C/min), and the temperature variability that will rise and cool down also needs symmetry, repeatability (the rise and cooling waveform of each cycle is the same), and linear (the temperature change and cooling speed of different loads is the same). In addition, lead-free solder joints and part life assessment in advanced semiconductor manufacturing processes also have many requirements for temperature cycle testing and temperature shock, so its importance can be seen (such as: JEDEC-22A-104F-2020, IPC9701A-2006, MIL-883K-2016). The relevant international specifications for electric vehicles and automotive electronics, their main test are also based on the temperature cycle test of the surface of the product (such as :S016750, AEC-0100, LV124, GMW3172).
Specification for the product to be tested surface temperature cycle control requirements:
1. The smaller the difference between the sample surface temperature and the air temperature, the better.
2. Temperature cycle rise and fall must be over temperature (exceed the set value, but not exceed the upper limit required by the specification).
3. The surface of the sample is immersed in the shortest time. Time (soaking time is different from residence time).
Thermal stress testing machine (TSC)of LAB COMPANION in the temperature cycle test of the product to be tested surface temperature control features:
1. You can choose [air temperature] or [temperature control of the product to be tested] to meet the requirements of different specifications.
2. The temperature change rate can be selected [equal temperature] or [average temperature], which meets the requirements of different specifications.
3. The deviation of temperature variability between heating and cooling can be set separately.
4. Overtemperature deviation can be set to meet the requirements of the specification.
5.[temperature cycle] and [temperature shock] can be selected table temperature control.
IPC requirements for temperature cycle test of products:
PCB requirements: The maximum temperature of the temperature cycle should be 25°C lower than the glass transfer point temperature (Tg) value of the PCB board.
PCBA requirements: The temperature variability is 15°C/min.
Requirements for solder:
1. When the temperature cycle is below -20 °C, above 110 °C, or contains the above two conditions at the same time, more than one damage mechanism may occur to the solder lead welding connection. These mechanisms tend to accelerate each other, leading to early failure.
2. In the process of slow temperature change, the difference between the sample temperature and the air temperature in the test area should be within a few degrees.
Requirements for vehicle regulations: According to AECQ-104, TC3(40°C←→+125°C) or TC4(-55°C←→+125°C) is used in accordance with the environment of the engine room of the car.
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
Burn-in is an electrical stress test that employs voltage and temperature to accelerate the electrical failure of a device. Burn-in essentially simulates the operating life of the device, since the electrical excitation applied during burn-in may mirror the worst-case bias that the device will be subjected to in the course of its use able life. Depending on the burn-in duration used, the reliability information obtained may pertain to the device's early life or its wear-out. Burn-in may be used as a reliability monitor or as a production screen to weed out potential infant mortalities from the lot.
Burn-in is usually done at 125 deg C, with electrical excitation applied to the samples. The burn-in process is facilitated by using burn-in boards (see Fig. 1) where the samples are loaded. These burn-in boards are then inserted into the burn-in oven (see Fig. 2), which supplies the necessary voltages to the samples while maintaining the oven temperature at 125 deg C. The electrical bias applied may either be static or dynamic, depending on the failure mechanism being accelerated.
Figure 1. Photo of Bare and Socket-populated Burn-in Boards
The operating life cycle distribution of a population of devices may be modeled as a bath tub curve, if the failures are plotted on the y-axis against the operating life in the x-axis. The bath tub curve shows that the highest failure rates experienced by a population of devices occur during the early stage of the life cycle, or early life, and during the wear-out period of the life cycle. Between the early life and wear-out stages is a long period wherein the devices fail very sparingly.
Figure 2. Two examples of burn-in ovens
Early life failure (ELF) monitor burn-in, as the name implies, is performed to screen out potential early life failures. It is conducted for a duration of 168 hours or less, and normally for only 48 hours. Electrical failures after ELF monitor burn-in are known as early life failures or infant mortality, which means that these units will fail prematurely if they were used in their normal operation.
High Temperature Operating Life (HTOL) Test is the opposite of ELF monitor burn-in, testing the reliability of the samples in their wear-out phase. HTOL is conducted for a duration of 1000 hours, with intermediate read points at 168 H and 500 H.
Although the electrical excitation applied to the samples are often defined in terms of voltages, failure mechanisms accelerated by current (such as electromigration) and electric fields (such as dielectric rupture) are understandably accelerated by burn-in as well.
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