PCB printed circuit board common fault dialysis
PCB, commonly known as printed circuit board, is an indispensable part of electronic components and plays a central role. In a series of PCB production processes, there are a lot of matching points. If you are not careful, the board will be flawed, and the quality of the PCB will end up in an endless stream. Therefore, after the circuit board is formed, the test is an indispensable part. Let's share with you the failure of the PCB board and its solutions.
1, PCB board often stratifies in use
Reasons: (1) Supplier material or process issues
(2) poor design and poor copper distribution
(3) The storage time is too long, exceeds the storage period, and the PCB board is damp.
(4) improper packaging or preservation, damp
Response: Choose the package and store it with constant temperature and humidity equipment. Do a good job in the factory reliability test of the PCB, for example: the thermal stress test in the PCB reliability test, the supplier is responsible for the 5 or more non-layering as the standard, and will be confirmed in each stage of the sample stage and mass production. The average manufacturer may only request 2 times and will only confirm it once in a few months. The IR test of the analog placement can also prevent the outflow of defective products, which is a must for an excellent PCB factory. In addition, the PCB plate Tg should be selected above 145 ° C, so it is safer.
Reliability test equipment: constant temperature and humidity chamber, stress screening type thermal shock test chamber, special equipment for PCB reliability test
2, PCB board solderability is poor
Cause: The placement time is too long, resulting in moisture absorption, the layout is contaminated, oxidized, black nickel is abnormal, solder-proof SCUM (shadow), and anti-solder PAD.
Solution: Pay attention to the quality control plan of the PCB factory and the standards for maintenance. For example, black nickel, need to see whether the PCB board production plant has no gold outburst, whether the chemical concentration of the gold line is stable, whether the analysis frequency is sufficient, whether regular gold stripping test and phosphorus content test are set to detect, whether the internal soldering test is Have good execution and so on.
Reason: The supplier's material selection is unreasonable, the heavy industry is poorly controlled, the storage is improper, the operation pipeline is abnormal, the copper area of each layer is obviously different, and the fracture hole is not made firmly.
Responsive measures: press the board 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 over-bending the board. The PCB needs to be simulated before the packaging to simulate the placement of IR conditions, so as to avoid the phenomenon of plate bending after the furnace.
4, PCB board impedance is poor
Cause: The impedance difference between PCB batches is relatively large.
Response measures: Manufacturers are required to attach a batch test report and impedance bar when delivering, and if necessary, provide comparison data between the board diameter and the board edge diameter.
5, anti-weld foaming / shedding
Reason: There is a difference in the selection of solder resist inks. The PCB board anti-welding process is abnormal, and the heavy work or patch temperature is too high.
Response: PCB suppliers should develop PCB board (multilayer PCB manufacturer in china)reliability testing requirements and control them in different production processes.
6, the Cavalier effect
Cause: The electrons dissolve into copper ions in the process of OSP and large gold surface, resulting in a difference in potential between gold and copper.
Response: Manufacturers need to pay close attention to the potential difference between gold and copper in the production process.