PCB Tech - What is the cause of blistering on the PCB surface?

PCB circuit board quick proofing,The blistering of the circuit board surface is actually a problem of poor bonding of the board surface, and then the problem quality of the PCB surface, which contains two aspects:

1. The cleanliness of the 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 generated during the production and processing during the subsequent production and processing and assembly processes.

Mechanical stress and thermal stress, etc., eventually cause different degrees of separation between the coatings.

Some factors that may cause poor board quality during PCB production and processing are summarized as follows:

1. The problem of substrate processing:

Especially for some thin substrates (generally below 0.8mm), it is not suitable to use a brushing machine to brush the plate because of the poor rigidity of the substrate.

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 not to cause board surface substrate

The problem of blistering on the board surface caused by the poor bonding force between copper foil and chemical copper; this problem will also cause poor blackening and browning when the thin inner layer is blackened, uneven color, and partial blackening and browning. First class question.

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

3. Poor sinking copper brush plate:

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 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 process for copper sinking has to go through a lot of chemical treatments. There are many chemical solvents such as various acid, alkali and organic chemicals. The surface of the board is not clean with water. Especially the copper sinking adjustment degreasing agent will not only cause cross-contamination, but also cause cross-contamination. Poor partial treatment or poor treatment effect on the board surface, uneven defects, causing some bonding problems; therefore, we must pay attention to strengthen the control of washing, mainly including the flow of washing water, water quality, washing time,

And the control of the dripping time of the panel; especially in winter, 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 plating: Excessive micro-etching will cause the hole to leak the base material 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; generally the depth of micro-etching before copper sinking is 1.5-2 microns, and the micro-etching before pattern electroplating is 0.3--1 microns. If possible, it is best to pass chemical analysis and simple The test weighing method controls the micro-etching thickness or the corrosion rate; under normal circumstances, the surface of the micro-etched board is bright in color, uniform pink, without reflection; if the color is uneven, or there is reflection, it means that there is a hidden quality risk in the pre-processing; note; Strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the bath, the load, the content of the micro-etching agent, etc. are all items to be paid attention to;

6. Poor rework of sinking 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 boards to roughly measure the deplating time to ensure the deplating effect; after the deplating is completed, use a brushing machine and a set of soft brushes to lightly brush and then sink the copper according to the normal PCB production process. The micro-eclipse time should be halved or adjusted if necessary