PCB Technical - PCB print circuit board fault and its solution

PCB boardis often layered in use

Cause:
(1) Supplier material or process issues
(2) Poor material selection and copper distribution
(3) If the storage time is too long, the PCB board is affected by moisture
(4) Improper packing or storage, damp

Solution: select a good package, use constant temperature and humidity equipment for storage. Do a good job of PCB Factory reliability test, for example: thermal stress test in PCB reliability test, the supplier in charge takes more than 5 times of delamination as the standard, which will be confirmed in the sample stage and each cycle of mass production, while the general manufacturer may only require two times, and only once in a few months. The IR test of simulated mounting can also prevent the outflow of defective products, which is necessary for excellent PCB factories. In addition, PCB board TG should be selected above 145 degree Celsius, which is more safe.

Reliability test equipment: constant temperature and humidity box, stress screening cold and hot shock test box, PCB reliability test equipment.

Poor solderability ofPCB board

Cause:

too long storage time, leading to moisture absorption, the plate was polluted and oxidized, black nickel abnormal, solder proof scum (shadow), anti solder pad.

Solution: we should pay close attention to the quality control plan of PCB Factory and the standard of maintenance. For example, for black nickel, it is necessary to see if the PCB production plant has chemical gold out of the factory, whether the concentration of the chemical solution is stable, whether the analysis frequency is enough, whether the regular gold stripping test and phosphorus content test are set to detect, whether the internal solder test is well performed, etc.

PCB bending and warping

Cause:

unreasonable supplier selection, poor control of heavy industry, improper storage, abnormal operation line, obvious difference in copper area of each layer, and not firm enough production of broken holes.

Solution: the sheet is pressurized with wood pulp board and then packaged for shipment, so as to avoid deformation in the future. If necessary, clamp is added to the patch to prevent the device from bending under excessive pressure. To avoid the phenomenon of over bending of PCB before and after the furnace packaging.

Poor impedance of PCB board

Cause: the impedance difference between PCB batches is large.

Solution: the manufacturer is required to attach batch test report and impedance bar when delivery, and provide the comparison data of inside board wire diameter and board edge line diameter when necessary.

Anti welding blistering / falling off

Cause: there are differences in the selection of solder proof ink, abnormal solder proofing process of PCB board, rework or high chip temperature.

Solution: PCB suppliers should formulate PCB reliability test requirements and control them in different production processes.

Cavanyl effect

Cause: in the process of OSP and dajinmian, electrons will dissolve into copper ions, resulting in potential difference between gold and copper.

Solution: manufacturers should pay close attention to the control of potential difference between gold and copper in the production process.