What Are The Common Faults Of Printed PCB Circuit Boards?

- Dec 03, 2018-

1. Layering reasons often occur in the use of PCB circuit boards:

(1) Material or process problems of suppliers

(2) Design material selection and poor copper surface distribution

(3) Preservation time is too long, beyond the shelf life, PCB circuit board is damp.

(4) improper packing or preservation, dampness

Responding measures: Choose good packaging, use constant temperature and humidity equipment for storage. For example, thermal stress test in PCB reliability test, the supplier takes more than five non-stratified tests as the standard, and confirms them at the sample stage and every cycle of mass production, while the general manufacturer may only require two tests and only confirm them once in a few months. Simulated IR test can also prevent more defective products from flowing out, which is necessary for excellent PCB factories. In addition, PCB sheet Tg should be selected above 145 C, so as to be safer.

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

2. Poor solderability of PCB sheet

Reasons: too long storage time, resulting in moisture absorption, page contamination, oxidation, black nickel abnormal, anti-welding SCUM (shadow), anti-welding PAD.

Solutions: When choosing and purchasing, we should pay close attention to the quality control plan of PCB plant and the standard of overhaul. For example, black nickel, we need to see whether the PCB plate factory has gold externalization, whether the concentration of gold wire is stable, whether the analysis frequency is enough, whether regular gold stripping test and phosphorus content test are set up to detect, whether the internal solderability test is well carried out, etc.

3. PCB plate bending.

Reasons: unreasonable selection of suppliers, poor control of heavy industry, improper storage, abnormal operation pipeline, obvious differences in copper area of each layer, fabrication of broken holes is not strong enough, etc.

Responding measures: Pressure the sheet with wood pulp board and then pack it for shipment, so as to avoid later deformation. If necessary, fixture is added on the patch to prevent the device from overweight bending the sheet. PCB needs to simulate the IR condition before packaging, so as to avoid the bad phenomenon of back plate bending.

4. Poor impedance of PCB board

Reason: Impedance difference between PCB batches is large.

Response measures: manufacturers are required to attach batch test reports and impedance bars when delivering goods, and to provide comparative data of in-board diameter and edge diameter when necessary.

5. Anti-welding blistering/shedding

Reasons: There are differences in the choice of anti-welding ink, abnormal anti-welding process of PCB board, heavy industry or high temperature of patch.

Response measures: PCB suppliers should formulate reliability testing requirements for PCB boards and control them in different production processes.

6, the methylene effect

Reason: Electrons dissolve into copper ions in the process of OSP and large gold surface treatment, resulting in potential difference between gold and copper.

Response measures: manufacturers need to pay close attention to the control of potential difference between gold and copper in the production process.