In fact, the blistering of circuit board surface is the problem of poor bonding force of board surface, which further extends to the problem of surface quality of board surface, including two aspects:
1. Board surface cleanliness;
2. Surface micro roughness (or surface energy).
All the blistering problems on the board can be summed up as the above reasons.
It is difficult to resist the coating stress, mechanical stress, thermal stress and so on in the subsequent production and assembly process due to the poor or too low binding force between the coatings, resulting in different degrees of separation between the coatings.
This paper summarizes some factors that may cause poor quality of board surface in the process of production and processing as follows:
1. Problems in substrate processing:
Especially for some thin substrates (generally less than 0.8mm), because of the poor rigidity of the substrates, it is not suitable to use the brush machine to brush the plates.
In this way, it may not be able to effectively remove the protective layer specially treated to prevent the oxidation of the copper foil on the board during the production and processing of the base plate. Although this layer is thin and easy to be removed by brushing the board, it is difficult to use chemical treatment. Therefore, it is important to pay attention to the control during the production and processing to avoid the foaming problem caused by the poor binding force between the copper foil on the board and the chemical copper In the case of blackening of thin inner layer, there are also some problems, such as bad blackening and browning, uneven color and poor local blackening and browning.
2. Oil contamination or other liquid contamination caused by board surface machining (drilling, laminating, edge milling, etc.) and poor surface treatment.
3. The brush plate of copper sink is poor:
If the pressure of the grinding plate before copper deposition is too large, it will cause the deformation of the orifice and brush out the round corner of the orifice copper foil or even the leakage of the base material from the orifice, which will cause the blistering of the orifice in the process of copper deposition, electroplating, tin spraying and welding; even if the brush plate does not cause the leakage of the base material, the heavy brush plate will increase the roughness of the copper at the orifice, so the copper foil is prone to over roughening in the process of micro erosion and coarsening, which will also exist Therefore, it is necessary to strengthen the control of the brush plate process, and adjust the parameters of the brush plate process to the best through the abrasion test and water film test;
4. Water washing:
Due to the large amount of chemical water treatment, many kinds of chemical solvents such as acid-base inorganic organic and so on, the water washing of the board surface is not clean, especially the adjustment of oil remover for copper deposition will not only cause cross pollution, but also cause the local treatment of the board surface to be poor or the treatment effect to be poor, uneven defects, resulting in some problems in the binding force; therefore, it is necessary to pay attention to strengthen the water treatment The control of washing mainly includes the control of washing water flow, water quality, washing time, and plate dripping time; especially in winter when the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the control of washing;
5. Micro corrosion in copper deposition pretreatment and pattern electroplating pretreatment:
Excessive micro etching will cause leakage of base material around the orifice and bubble phenomenon around the orifice; insufficient micro etching will also cause insufficient bonding force and bubble phenomenon; therefore, it is necessary to strengthen the control of micro etching; generally, the micro etching depth of the pre-treatment of copper deposition is 1.5-2 μ m, and the micro etching depth of the pre-treatment of graphic electroplating is 0.3-1 μ M. if possible, it is best to control the micro etching thickness by chemical analysis and simple test weighing method Corrosion rate: generally, the color of the micro etched plate is bright, uniform pink, without reflection; if the color is uneven, or there is reflection, it indicates that there is a quality risk in the pre-processing of the process; pay attention to strengthen the inspection; in addition, the copper content of the micro etched groove, the temperature of the groove, the load, the content of the micro etchant, etc. are all items to be paid attention to;
6. Poor rework of copper sink:
Some reworked plates after copper deposition or graphic transformation will cause blistering due to poor peeling off, wrong rework method, improper control of micro etching time in the rework process or other reasons; if poor copper deposition is found in the reworking process, it can be directly removed from the line after washing, pickling and no direct reworking without corrosion; it is better not to remove oil and micro etching; for For the plates that have been electrically thickened, the micro etching bath should be removed now. Pay attention to the time control. One or two plates can be used to roughly measure the time of removal to ensure the effect of removal. After the removal, a group of soft grinding brushes after the plate brush machine shall be used to light brush, and then the copper shall be deposited according to the normal production process, but the time of micro etching shall be halved or adjusted as necessary;
7. The board surface is oxidized in the production process:
If the copper plate is oxidized in the air, it may not only cause no copper in the hole, rough surface of the plate, but also foam on the plate surface; if the copper plate is stored in the acid solution for a long time, the plate surface will also be oxidized, and this kind of oxide film is difficult to remove; therefore, the copper plate shall be thickened in time during the production process, rather than stored for a long time, and the copper plating shall be completed at the latest within 12 hours;
8. The activity of copper precipitation solution is too strong:
The high content of the three components in the new cylinder or bath solution, especially the high content of copper, will lead to the strong activity of the bath solution, rough deposition of chemical copper, excessive inclusion of hydrogen and cuprous oxide in the chemical copper layer, resulting in the degradation of physical properties and poor adhesion of the coating; the following methods can be taken properly: reduce the copper content, (supplement pure water into the bath solution), including three major components, appropriate When the content of complexing agent and stabilizer is increased, the temperature of bath solution is reduced properly;
9. In the process of graphic transfer, insufficient water washing after development, too long placing time after development or too much dust in the workshop will cause poor cleanness of the board surface and poor fiber treatment effect, which may cause potential quality problems;
10. Organic pollution, especially oil pollution, occurs in the electroplating tank, which is more likely to occur for the automatic line;
11. Before copper plating, the pickling tank shall be replaced in time. Too much pollution or too high copper content in the tank solution will not only cause the cleanness of the board surface, but also cause the roughness and other defects of the board surface.
12. In addition, in winter, when the bath solution is not heated in the production of some factories, it is necessary to pay special attention to the electrified entering of the plates in the production process, especially the plating bath with air agitation, such as copper and nickel; for the nickel cylinder, it is better to add a warm water washing bath before the nickel plating in winter (the water temperature is about 30-40 ℃), so as to ensure that the initial deposition of nickel layer is dense and good;
In the actual production process, there are many reasons for the foam on the board surface. The author can only make a brief analysis. For different manufacturers' equipment and technical level, different reasons may cause the foam phenomenon. The specific situation should be analyzed specifically. It is not allowed to generalize and copy mechanically. The above reason analysis is not divided into primary and secondary reasons and is basically based on the production process. In this series, only Is to provide you with a solution to the direction of the problem and a broader vision, I hope you can play a role in the process of production and problem-solving!
Oct 12, 2019
