PCB, commonly known as printed circuit board, is an indispensable part of electronic components and plays a central role.
In a series of production processes of PCB, there are many matching points. If the board is not careful, there will be defects, which will affect the whole body. The quality problems of PCB will emerge one after another.
Therefore, after the circuit board is made and formed, the inspection test becomes an essential link.
Let's share with you the faults of PCB circuit board and their solutions.
1. Reasons for stratification often occur in the use of PCB boards :(1)Supplier material or process issues (2)Poor design material selection and copper surface distribution (3)
The storage time is too long, exceeding the storage period, and the PCB board is affected with damp (4)
Improper packaging or storage, moisture response measures: Select the packaging, use constant temperature and humidity equipment for storage.
Do a good job in the factory reliability test of PCB, for example, in the thermal stress test of PCB reliability test, the supplier is responsible for taking no delamination for more than 5 times as the standard, confirmation will be carried out at the sample stage and every cycle of mass production, while the general manufacturer may only require twice and will confirm once in several months.
The IR test of analog mounting can also prevent the outflow of defective products, which is a must for excellent PCB factories.
In addition, PCB sheet Tg should be selected above 145 ℃, so as to be safer.
Reliability test equipment: constant temperature and humidity box, stress screening type cold and hot impact test box, special equipment for PCB reliability test 2. Poor soldering property of PCB board reasons: too long storage time leads to moisture absorption, the layout is polluted and oxidized, black nickel is abnormal, and welding SCUM (Shadow), Anti-welding PAD.
Solution: when purchasing, we should strictly pay attention to the quality control plan of PCB factory and the standards for maintenance.
For example, black nickel, need to see whether the PCB board production plant has the gold out, whether the concentration of the gold wire is stable, whether the analysis frequency is sufficient, whether the regular gold stripping test and phosphorus content test are set to detect, whether the internal soldering test is well performed, etc.
3. Reasons for PCB board bending: unreasonable selection of materials by suppliers, poor control of heavy industry, improper storage, abnormal operation assembly line, obvious difference in copper area of each layer, and insufficient firmness of broken holes.
Countermeasures: compress the thin plate with wood pulp board and then pack and ship it to avoid deformation in the future. If necessary, add a clamp on the patch to prevent the device from bending the plate.
Before packaging, the PCB needs to be tested under simulated IR conditions to avoid the bad phenomenon of bending after passing through the furnace.
4. Reasons for poor PCB impedance: the impedance difference between PCB batches is relatively large.
Countermeasures: require manufacturers to attach batch test reports and impedance strips when delivering goods, and provide comparative data of wire diameter inside the board and wire diameter at the edge of the board when necessary.
5. Causes of anti-welding blistering/Shedding: the selection of anti-welding ink is different, the anti-welding process of PCB board is abnormal, and the temperature of heavy industry or patch is too high.
Countermeasures: PCB suppliers should formulate reliability test requirements for PCB boards and control them in different production processes.
6. Reason for methylvani effect: electrons will dissolve into copper ions in OSP and large gold surface process, resulting in a difference in potential between gold and copper.
Countermeasures: manufacturers need to pay close attention to the control of the potential difference between gold and copper in the production process.
