Microwave Tech - PCB board failure and its solution measures

PCB, commonly known as the printed circuit board, is an indispensable part of electronic components, plays a core role. In a series of PCB production processes, there are a lot of matching points. If you are not careful, there will be defects on the board, which will affect the whole body, and PCB quality problems will emerge endlessly. So in the circuit board production molding, detection test becomes an essential link.

1. PCB board is often layered in use

The reason:

(1) Supplier material or process problems

(2) Poor material selection and copper surface distribution

(3) The storage time is too long, exceeding the storage period, and the PCB board is affected by moisture

(4) Improper packaging or storage, moisture

Countermeasures: choose good packaging, use constant temperature and humidity equipment for storage. For example, in PCB reliability test, the supplier in charge of the thermal stress test takes more than 5 times of non-stratification as the standard and will confirm it in the sample stage and every cycle of mass production, while the general manufacturer may only require 2 times and confirm it once every 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, THE Tg of the PCB board should be above 145 degree Celsius, so as to be relatively safe.

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

2, PCB board solder poor

Cause: placed for too long, resulting in moisture absorption, layout pollution, and oxidation, black nickel abnormal, anti-welding SCUM (shadow), anti-welding PAD.

Solution: pay close attention to the quality control plan and maintenance standards of the PCB factory. For example, for black nickel, it is necessary to see whether the PCB board manufacturer has external gold plating, whether the concentration of gold wire liquid is stable, whether the analysis frequency is enough, whether the regular gold stripping test and phosphorus content test is set up to detect, whether the internal solder test is well-executed, etc.

3, PCB board bending board warping

Reasons: unreasonable material selection of suppliers, poor control of heavy industry, improper storage, abnormal operation line, obvious difference in the copper area of each layer, not strong enough to make the broken hole, etc.

Countermeasures: pack and ship the thin plate after pressurizing it with a wood pulp board, so as to avoid deformation in the future. If necessary, add a fixture on the patch to prevent the device from bending the board under heavy pressure. PCB needs to simulate IR conditions for testing before packaging, in order to avoid the undesirable phenomenon of plate bending after passing the furnace.

4. Poor impedance of PCB board

Cause: The impedance difference between PCB batches is relatively large.

Solution: the manufacturer is required to attach the batch test report and impedance strip to the delivery, and if necessary, to provide the comparison data of plate inner diameter and plate edge diameter.

5, anti-welding bubble/off

Cause: the selection of anti-welding ink is different, PCB board anti-welding process is abnormal, heavy industry or patch temperature is too high.

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

The Cavani Effect

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

Solution: PCB manufacturer need to pay close attention to the control of the potential difference between gold and copper in the production process.