PCB News - Analysis of common failures of multilayer circuit boards

Analysis of common failures of multilayer circuit boards

The double-sided circuit board is the middle layer of medium, and both sides are wiring layers. A multi-layer circuit board is a multi-layer wiring layer, and there is a dielectric layer between every two layers, and the dielectric layer can be made very thin. Multilayer circuit boards have at least three conductive layers, two of which are on the outer surface, and the remaining layer is integrated into the insulating board. The electrical connection between them is usually achieved through plated through holes on the cross section of the circuit board. In a series of PCB board production processes, there are many matching points. If you are not careful, the board will have defects, which will affect the whole body, and the quality of the PCB board will be endless. Therefore, after the circuit board is manufactured and formed, the inspection test becomes an indispensable link. Let me share with you the faults of PCB circuit boards and their solutions.

1. What delamination often occurs in the use of multilayer circuit boards
1. Supplier material or process issues;
2. Improper packaging or storage, damp;
3. Poor design material selection and copper surface distribution;
4. The storage time is too long, the storage period is exceeded, and the PCB board is damp.

Countermeasures: Choose the packaging and use constant temperature and humidity equipment for storage. Do a good job of PCB factory reliability test, for example: thermal stress test test in PCB reliability test, the responsible supplier is to use more than 5 times of non-layering as the standard, and it will be confirmed in the sample stage and each cycle of mass production. The general circuit board manufacturers may only require two times, and only confirm once a few months. The IR test of simulated placement can also prevent the outflow of defective products more, which is a must for an excellent PCB factory. In addition, the Tg of the PCB board should be selected above 145°C, so that it is safer.

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

2. Poor solderability of multilayer circuit boards

Reasons: too long storage time, resulting in moisture absorption, contamination and oxidation of the layout, abnormal black nickel, solder resist SCUM (shadow), and solder resist PAD.

Solution: Strictly pay attention to the quality control plan of the PCB factory and the standards for maintenance when purchasing. For example, black nickel, you need to see whether the circuit board manufacturer has chemical gold out, whether the chemical gold wire solution concentration is stable, whether the analysis frequency is sufficient, whether there is a regular gold stripping test and phosphorus content test for testing, and whether the internal solderability test is Have good execution and so on.

3. Poor impedance of multilayer circuit boards
Reason: The impedance difference between PCB batches is relatively large.
Countermeasures: The circuit board manufacturer is required to attach batch test reports and impedance strips when delivering goods, and if necessary, provide comparative data of the inner wire diameter and the board edge wire diameter.

Four, multi-layer circuit board bending and warping
Reasons: unreasonable material selection by the supplier, poor control of heavy industry, improper storage, abnormal operation line, obvious differences in copper area of each layer, and insufficient production of broken holes.
Countermeasures: pressurize the thin board with wood pulp board before packaging and shipping to avoid deformation in the future. If necessary, add a clamp to the patch to prevent the device from bending the board excessively. The PCB needs to simulate the mounting IR conditions for testing before packaging, so as to avoid the undesirable phenomenon of plate bending after the furnace.

Five, solder mask blistering/falling off
Reason: There are differences in the selection of solder mask inks, the solder mask process of multilayer circuit boards is abnormal, caused by heavy industry or excessively high patch temperature.
Countermeasures: PCB suppliers should formulate reliability test requirements for multilayer circuit boards and control them in different production processes.

Six, the Civanni effect
Reason: In the process of OSP and Dajinmian, electrons will dissolve into copper ions, resulting in a difference in potential between gold and copper.
Countermeasures: PCB manufacturers are required to pay close attention to the control of the potential difference between gold and copper in the production process.