The concept of PCB aging
The PCB aging we usually say is that after the circuit board is powered on for a certain period of time under certain conditions, some component parameters on the circuit board will change. This change is related to the time the circuit board is used. For some special-purpose circuits It is absolutely not allowed for the circuit board, so many circuit boards will be anti-aging before leaving the factory to stabilize the circuit before use. This can greatly improve reliability and security.
Practice of PCB aging test
In general industrial refrigerators, the single-piece non-welding parts are used in a fixed way, and the temperature generally changes alternately between -40°C~+55°C. During this process, the lower temperature should be kept for 1 hour, and then Slowly return to room temperature. Keep it for 4 hours without room temperature. After 4 hours, slowly raise the temperature to the highest set temperature. This state should also be kept for 2 hours, and then slowly drop to room temperature. At this time, it also needs to be kept for 2 hours. Hours, remove, check the health of the minimum line and cut with vias. This process has to do two cycles to be more guaranteed.
General rules for aging of instrumentation circuit boards
The following Senyan circuit board manufacturer will introduce a general procedure for the aging of instrumentation circuit boards. We need to divide this procedure into several covers, and these aspects include:
1. Subject content and scope of application
2. Definition
3. Purpose
4. Check the environmental conditions
5. Requirements before aging
6. Aging equipment
7. Aging
8. Recovery
9. Final inspection
Let's talk about these nine points separately.
Subject content and scope of application
This standard specifies the basic content and requirements for aging screening of instrumentation functional circuit boards. This standard is applicable to the aging screening of various single-loop regulators and functional circuit boards of various digital instruments in the instrumentation industry.
definition
Instrumentation functional circuit board (hereinafter referred to as functional board) refers to a printed circuit board that has been installed with components or components in the instrumentation; it can complete certain functions.
Purpose
Make the functional board experience the change of air temperature in a thermal aging equipment with temperature changes. Through the combined effects of high temperature, low temperature, high and low temperature changes, and electric power, the defects of the functional board are exposed, such as poor welding, mismatched component parameters, and temperature drift. As well as the faults caused during the debugging process, in order to eliminate them, it will play a role in stabilizing the parameters of the non-defective function board.
Detect environmental conditions
The test should be carried out under the following environmental conditions: Temperature: 15~35°C Relative humidity: 45%~75% Atmospheric pressure: 86~106Kpa
Requirements before aging
The old circuit board also has two requirements, these two requirements are:
1. Electrical parameter testing All functional boards to be aged need to be tested for electrical parameters, and functional boards whose parameters do not meet the requirements should be rejected.
2. Appearance inspection All functional boards to be aged need to be visually inspected first. For functional boards with obvious defects, such as short circuit, open circuit, wrong component installation, missing parts and other defective functional boards should be rejected.
aging equipment
Any point in the working space of the thermal aging equipment shall meet the following requirements:
1. The low temperature required for thermal aging can be maintained.
2. It can maintain the high temperature required for thermal aging.
3. The change process from high temperature to low temperature or from low temperature to high temperature can be carried out according to the temperature change rate required by aging.
Function board installation and support
1. The function board should be installed on the bracket in the normal use position.
2. The support of the functional board should be insulated to ensure that there is no leakage between the tested functional board and the support.
3. The heat conduction of the bracket of the functional board should be low, so that the functional board and the bracket are actually heat-insulated.
Electrical power aging equipment
1. The electric power aging equipment should ensure that during the aging process, it should not stop midway due to the aging equipment.
2. The electric power aging equipment should guarantee to provide the voltage and current required by the aging function board, and can provide variable input signals, and can detect each function board at any time.
Ageing
heat aging conditions
1. The thermal aging time is at least 72 hours.
2. If there is no other regulation, the temperature cycle range should be: 0~60°C or -10~60°C, which can be selected by yourself.
3. Temperature change rate (the average value during the change process from low temperature to high temperature or from high temperature to low temperature) 1±0.5°C/min.
aging method
The method of aging is generally divided into seven steps; these seven steps are:
1. Put the functional board at the ambient temperature into the thermal aging equipment at the same temperature.
2. The function board is in running state.
3. Then the temperature inside the equipment should be lowered to room temperature at a specified rate.
4. Then the temperature inside the equipment should be raised to the specified temperature at the specified rate.
5. Then the temperature inside the equipment should decrease to the specified temperature value at the specified rate.
6. When the temperature inside the equipment is stable, the functional board should be exposed to high temperature for 2 hours.
7. When the temperature inside the equipment is stable, the functional board should be exposed to low temperature for 2 hours.
8. Repeat 3 to 7 continuously. Until the specified aging time, and measure and record the functional board once according to the specified aging time.
9. The function board should be taken out of the box after the temperature in the equipment reaches room temperature and is stable.
recover
After the functional board is taken out, it should be placed under the specified conditions and allowed to reach a stable temperature, and the recovery time should be at least 1h.
final test
Under the specified conditions, the electrical parameters of the function board are tested, and those that do not meet the requirements are rejected.
Through the above nine steps, it is generally possible to do a good job in the detection of circuit board aging, but some special circumstances still need to be excluded, which requires everyone to learn to use it flexibly.
