PCB News - What is the cause of blistering on the circuit board?

What is the cause of blistering on the circuit board?

Printed Circuit Board Factory Editor: The blistering of the circuit board surface is actually a problem of poor bonding force of the PCB board surface, and then it is the surface quality problem of the board surface, which contains two aspects:

1. The cleanliness of the circuit board surface;

2. The problem of surface micro-roughness (or surface energy).

The blistering problem on all circuit boards can be summarized as the above reasons.

The bonding force between the coatings is poor or too low, and it is difficult to resist the coating stress, mechanical stress and thermal stress generated during the production process in the subsequent production process and assembly process, which will eventually cause different degrees of separation between the coatings.

Now some factors that may cause poor board quality in the production and processing process are summarized as follows:

1. The problem of substrate process treatment:

Especially for some thinner substrates (generally less than 0.8mm), because the rigidity of the substrate is poor, it is not suitable to use a brushing machine to brush the plate. This may not be able to effectively remove the protective layer specially treated to prevent the oxidation of the copper foil on the board surface during the production and processing of the substrate. Although the layer is thin and the brush is easier to remove, it is more difficult to use chemical treatment, so in production It is important to pay attention to control during processing, so as to avoid the problem of blistering on the board caused by poor bonding between the copper foil of the board substrate and the chemical copper; this problem will also cause blackening and browning when the thin inner layer is blackened. Poor, uneven color, partial black browning and other problems.

2. The phenomenon of poor surface treatment caused by oil stains or other liquids contaminated with dust during machining (drilling, lamination, milling, etc.) of the circuit board surface.

3. Bad sinking copper brush:

The pressure on the front grinding plate of the sinking copper is too large, causing the hole to be deformed, brushing out the copper foil rounded corners of the hole or even leaking the base material of the hole, which will cause the hole to bubble during the process of plating, spraying and soldering of the sinking copper; The board does not cause leakage of the substrate, but the heavy brushing board will increase the roughness of the hole copper, so during the process of microetching roughening, the copper foil at this place is very easy to produce excessive roughening, and there will also be a certain quality. Hidden dangers; therefore, it is necessary to strengthen the control of the brushing process, and the brushing process parameters can be adjusted to the best through the wear scar test and the water film test;

4. Washing problem:

The electroplating treatment for copper deposits has to go through a lot of chemical treatments. There are many chemical solvents such as various acid and alkali, electrodeless organic and so on. The circuit board surface is not clean with water. Especially the copper deposit adjustment degreasing agent will not only cause cross-contamination, but also It will cause poor partial treatment of the PCB surface or poor treatment effect, uneven defects, and cause some bonding problems; therefore, attention should be paid to strengthening the control of washing, mainly including the flow of washing water, water quality, washing time, and Control of the dripping time of the panels; especially in winter when the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the strong control of the washing;

5. Micro-etching in the pre-treatment of copper sinking and the pre-treatment of pattern electroplating:

Excessive micro-etching will cause leakage of the substrate in the orifice and cause blistering around the orifice; insufficient micro-etching will also cause insufficient bonding force and cause blistering; therefore, it is necessary to strengthen the control of micro-etching; general micro-etching before copper The corrosion depth is 1.5-2 microns, and the micro-etching before pattern plating is 0.3--1 microns. If possible, it is better to control the thickness of the micro-etching or the corrosion rate through chemical analysis and simple test weighing method; in general, micro-etching The surface of the etched board is bright in color, uniform pink, without reflection; if the color is not uniform, or there is reflection, it means that there is a hidden quality problem in the pre-processing; pay attention to strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the tank, and the load capacity, Microetching agent content, etc. are all items to be paid attention to;

6. Poor rework of heavy copper:

Some copper-immersed or reworked boards after pattern transfer may cause blistering on the board surface due to poor fading, improper rework methods or improper control of the micro-etching time during the rework process, or other reasons; if the rework of the copper-immersed board is found online Poor copper sinking can be directly removed from the line after washing with water and then reworked directly without corrosion after pickling; it is best not to re-degrease and micro-etch; for plates that have been thickened by the board, they should be deplated in the micro-etching tank. Pay attention to time control. You can use one or two plates to roughly estimate the deplating time to ensure the deplating effect; after the deplating is completed, apply a set of soft brushes and lightly brush the plate, and then sink the copper according to the normal production process, but the corrosion is slight. The eclipse time should be halved or adjusted if necessary;