PCB, commonly known as printed circuit board, is an indispensable part of electronic components and plays a core role. In a series of PCB production processes, there are many matching points. If you are not careful, the board will have defects. If you pull one hair and move the whole body, PCB quality problems will emerge one after another. So after the circuit board is manufactured, the test experiment becomes an essential link. Let's share the problems and solutions of PCB.
1. Delamination often occurs in PCB application
Causes: (1) material or process problems of the supplier
(2) Design material selection and insecure copper surface distribution
(3) The storage time is too long. The PCB board is damped after the storage period
(4) Improper packaging or preservation, damp
Solution: select good packaging, use constant temperature and humidity equipment for storage. Do a good job of PCB ex factory reliability test, for example: for the thermal stress test test in PCB reliability test, the supplier in charge takes more than 5 times of non stratification as the specification, and will recognize it in the sample stage and each period of mass production, while the general manufacturer may only require 2 times, and only once in a few months. The IR test that imitates the mounting can also avoid the outflow of defective products, which is necessary for excellent PCB factories. In addition, the Tg of PCB board should be selected above 145 ℃, which is more safe.
Reliability test equipment: constant temperature and humidity box, stress screening cold and hot impact test box, special equipment for PCB reliability test
2. Poor solderability of PCB
Causes: too long storage time, moisture absorption, plate pollution, oxidation, abnormal black nickel, anti welding scum (shadow), anti welding pad.
Handling method: pay attention to the quality control plan of PCB Factory and the proposed specification for maintenance when purchasing. For example, for black nickel, it is necessary to see whether the PCB board manufacturer has the external release of chemical gold, whether the concentration of chemical gold liquid is stable, whether the analysis frequency is met, whether the regular stripping test and phosphorus content test are set to detect, and whether the internal solderability test is well performed, etc.
3. PCB bending warpage
Reasons: unreasonable selection of suppliers, poor control of heavy industry, improper storage, abnormal operation flow line, obvious difference in copper area of each layer, weak manufacturing of broken holes, etc.
Solution: use wood pulp board to pressurize the sheet and then pack it for shipment, so as to avoid future deformation. If necessary, add clamps on the patch to avoid over pressing and bending of the equipment. Before packaging PCB, it is necessary to simulate the IR condition of mounting for experiment, so as to avoid the bad phenomenon of plate bending after furnace.
4. Poor PCB impedance
Reason: the impedance difference between PCB batches is large.
Solution: the manufacturer is required to attach batch test report and impedance strip when delivering goods, and provide the comparative data of the internal wire diameter and the side wire diameter of the board if necessary.
5. Anti weld blistering / falling off
Cause: there are differences in the selection of anti welding ink, abnormal anti welding process of PCB board, high temperature of rework or chip.
Solution: PCB supplier shall formulate reliability test requirements for PCB and control them in different production processes.
6. Metalvani effect
Reason: the potential difference between gold and copper is caused by the electron dissolving into copper ion in the process of OSP and big gold surface.
Solution: manufacturers need to pay close attention to the control of potential difference between gold and copper in the manufacturing process.
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