In the process of PCBA
circuit board assembly, causing a large reason for the foaming of the circuit board surface is the problem of poor binding force, that is, the surface quality of the board, which contains two aspects: the cleanliness of the board; The problem of surface microscopic roughness (or surface energy). Basically, all the problems of the board surface foam on the circuit board can be summarized into these two reasons. The poor or too low bonding force between the coatings is due to the difficulty in resisting the coating stress, mechanical stress, and thermal stress generated in the subsequent production and processing process and the PCBA
assembly process, which eventually leads to different degrees of separation between the coatings.
The following is a summary of some factors that may cause poor panel quality during PCB manufacturing and PCBA assembly.
1.The substrate process processing problems: especially for some of the thinner substrates (generally below 0.8mm), because the substrate rigidity is poor, should not be used to brush the plate machine brush.
So maybe unable to effectively remove the substrate in order to prevent the surface oxidation of copper foil in the process of production and processing and special processing layer, while the layer is thinner, brush plate is easy to remove, but the chemical processing is difficult, so important to pay attention to control in the production processing, lest cause panel substrate copper foil and copper chemical bonding force between the surface bubbles caused by bad; This kind of problem in the thin inner layer of melanization, there will also be poor melanization and Browning, color imbalance, local black and brown is not equal.
2.The surface in machining (drilling, lamination, milling edge, etc.) : in this process caused by oil or other liquids contaminated with dust pollution surface treatment of poor phenomenon.
3.The copper brush plate is not good: the pressure of the grinding plate before the copper sink is too large, resulting in the deformation of the orifice, brushing out the orifice copper foil fillet and even the orifice leakage base material, so in the process of copper sink electroplating, tin spray welding, it will cause the orifice bubble phenomenon. Even if the brush plate does not cause leakage of the substrate, the heavy brush plate will increase the roughness of the orifice copper, so in the process of micro-erosion and coarsening, the copper foil is easy to produce the excessive coarsening phenomenon, and there will be a certain quality hidden trouble.
Therefore, attention should be paid to strengthening the control of the brushing process, and the brush process parameters can be adjusted to the best through the wear mark test and water film test.
4.Washing problem: Due to heavy copper plating process to go through a large number of chemical liquid medicine treatment, so all kinds of acid-base the non-polar organic solvent such as drugs, board face wash not clean, especially heavy copper adjustment in addition to the agents, not only can cause cross-contamination, also will cause the board faces local processing bad or poor treatment effect, the defect of uneven, some PCBA assembly binding force in the aspects of the problem; Therefore, attention should be paid to strengthening the control of water washing, mainly including the control of water flow, water quality, water washing time, and board water-dropping time, etc.
Especially when the temperature is low in winter, the effect of washing will be greatly reduced, and more attention should be paid to the strong control of washing.
5.Micro-erosion in the pre-treatment of copper precipitation and graphic electroplating: micro-erosion should not be excessive, otherwise it will cause leakage of the base material of the orifice and cause bubbles around the orifice. The lack of micro erosion will also cause the lack of binding force, causing the phenomenon of foaming. Therefore, it is necessary to strengthen the control of micro-erosion; Generally, the micro erosion depth before the copper deposition is 1.5– 2 microns, and the micro erosion depth before graphic electroplating is 0.3—1 microns. If possible, it is best to control the micro erosion thickness or rate by chemical analysis and simple test weighing method.
Under normal circumstances, the surface of the micro-etched bright color, uniform pink, no reflection; If the color is not uniform or reflective, it indicates that there are quality hazards in the process pretreatment; Pay attention to strengthen inspection. In addition, the copper content of the micro-corrosion tank, the temperature of the tank, the load, the content of the micro-corrosion agent, and so on should be paid attention to.
6.Copper rework is poor: some copper or graphics after the rework of the reworked plate in the rework process because of poor fading, rework method or rework process of improper control of micro-corrosion time, and some other reasons will cause the surface bubble. The rework of the sunk copper plate can be directly reworked if the copper is found to be bad on the line after washing and directly removed the oil from the line after pickling without micro-corrosion.
It is best not to remove oil, micro-erosion; For the plates that have been electrically thickened, the micro-etched groove should be faded now. Pay attention to time control. You can use one or two plates to roughly measure the fading time to ensure the effect of the plating.
After the plating is finished, brush lightly with a group of soft grinding brushes followed by the brush machine and then sink the copper according to the normal production process, but the corrosion time should be halved or adjusted as necessary.
7.The surface in the production process of oxidation: if the immersed copper plate in the air oxidation, not only may cause no copper hole, the surface is rough, the same may cause the surface of the board foaming. The submerged copper plate in the acid storage time is too long, the surface will also be oxidized, and the oxidation film is very difficult to remove. Therefore, in the production process, the copper plate should be thickened in time. It should not be stored for too long. Generally, the copper plating should be thickened within 12 hours at the latest.
8.The activity of the copper bath is too strong: the copper bath newly opened cylinder or bath three-component content is too high, especially the copper content is too high, will cause the bath activity to be too strong, the chemical copper deposition is rough, hydrogen, cuprous oxide in the chemical copper layer caused by excessive inclusions in the coating quality decline and poor bonding force defects; Can be appropriate to take the following methods can be: reduce the content of copper, the appropriate increase in complexing agent, stabilizer content and appropriate to reduce the temperature of the bath.
9.Insufficient washing after developing in the process of graphic transfer: too long time after developing or too much dust in the workshop will cause poor cleanliness of the board, and the effect of fiber treatment is slightly poor, which may cause potential quality problems.
10.Electroplating tank organic pollution: especially oil, for the automatic line is more likely to appear.
11.Copper plating before leaching tank should pay attention to timely replacement: too much pollution or copper content is too high in the tank solution, not only will cause the cleanliness of the board, but also cause the surface roughness and other defects.
12.Winter factory production in the case of no bath heating: pay more attention to the production process and PCBA assembly plate electrified into the tank, especially with air stirring plating tanks, such as copper and nickel. For the nickel cylinder in winter, it is best to add a warm water bath before nickel plating (the water temperature is about 30-40 degrees), to ensure that the nickel layer is deposited in the initial dense good.
Some of the above can be said to be in the actual circuit board production and PCBA circuit board assembly process, the more common cause of the board foaming. Of course, there are many reasons for the foaming of the board, and for different manufacturers of equipment technology levels may be caused by different reasons for the foaming phenomenon, so this needs to be analyzed on a case-by-case basis.