Analysis of the causes of foaming on the board of PCBA circuit board

The foaming of the board surface of the PCBA circuit board is actually a problem of poor binding force of the board surface, and then it is extended to the surface quality of the board surface. This includes two aspects.：

1.The problem of board cleanliness；

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

The board surface foaming problem on all PCBA circuit boards can be summarized as the above reasons.

The binding 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 and processing process in the subsequent production and processing process and assembly process, resulting in different degrees of separation between the coatings. Phenomenon.

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

1.Problems with substrate process treatment：

Especially for some thinner substrates (generally below 0.8mm), because the rigidity of the substrate is poor, it is not advisable to use a brushing machine to brush the board. This may not be able to effectively remove the protective layer specially treated to prevent the oxidation of the copper foil on the plate during the production and processing of the substrate. Although the layer is thinner and the brush plate is easier to remove, it is more difficult to use chemical treatment. Therefore, it is important to pay attention to control in the production and processing to avoid the problem of foaming on the plate surface caused by the poor binding force between the copper foil and the chemical copper on the substrate; This kind of problem will also exist when the thin inner layer is blackened. Poor blackening and browning, uneven color, and poor local blackening and browning.

2.The phenomenon of poor surface treatment caused by oil pollution or other liquid pollution and dust pollution caused by the machining of the board surface (drilling, lamination, milling, etc.).

3.Poor sinking copper brush plate：

The pressure of the grinding plate before sinking copper is too high, causing the orifice to be deformed, the rounded corners of the copper foil at the orifice to be brushed out, and even the orifice to leak the substrate, so that the orifice foaming phenomenon will be caused in the process of sinking copper electroplating, tin spraying, welding, etc. Even if the brush plate does not cause leakage of the substrate, the excessive brush plate will increase the roughness of the orifice copper, so in the process of micro-etching and roughening, the copper foil can easily produce excessive roughening, and there will be certain quality risks; therefore, attention should be paid to strengthening the control of the brush plate process, and the process parameters of the brush plate can be adjusted to the minimum through the wear mark test and the water film test. best；

4.Washing problem：

For the electroplating treatment of submerged copper, a large number of chemical potions are required to be treated. There are many kinds of acid-base, organic and other pharmaceutical solvents, and the board surface is not cleanly washed, especially the degreasing agent of submerged copper, which will not only cause cross-contamination, but also cause poor local treatment of the board surface or poor treatment effect, uneven defects, causing some binding force problems; Therefore, attention should be paid to strengthening the control of washing, including the control of the flow of cleaning water, water quality, washing time, and the dripping time of the board; especially in winter, when the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the strong pair. Washing control；

5.Micro-etching in the pretreatment of submerged copper and the pretreatment of graphic electroplating：

Excessive micro-etching will cause the orifice to leak the substrate, causing foaming around the orifice; insufficient micro-etching will also cause insufficient binding force and cause foaming; therefore, it is necessary to strengthen the control of micro-etching; generally, the depth of micro-etching before copper immersion treatment is 1.5-2 microns, and the micro-etching before electroplating treatment is 0.3-1 micron. If there are conditions, it is best to control the thickness of micro-etching or the rate of etching by chemical analysis and simple test weighing method; Under normal circumstances, the color of the plate after micro-etching is bright, it is uniform pink, and there is no reflection; if the color is uneven, or there is reflection, it means that there is quality in the pretreatment of the process. Hidden dangers; pay attention to strengthen inspection; in addition, the copper content of the micro-etching tank, the temperature of the tank liquid, the load, and the content of the micro-etching agent are all items to be paid attention to.；

6.Poor rework of submerged copper：

Some submerged copper or reworked plates after the graphics are transferred will cause foaming on the surface of the plate due to poor fading during the rework process, incorrect rework method, improper control of micro-etching time during the rework process, etc. or other reasons; if the rework of the submerged copper plate is found on the line, the copper can be directly removed from the line after washing and pickled and reworked directly without corrosion; it is best not to re-degrease, micro-etching; for plates that have been electro-thickened, the micro-etching groove should be removed now, pay attention to the time control, you can first use one or two plates to roughly calculate the fading time, to ensure The effect of fading plating; after the fading plating is completed, a set of soft grinding brushes after the brushing machine is applied, and then the copper is sunk according to the normal production process, but the etching and micro-etching time should be halved or necessary adjustments should be made.