Liquid photo resist in PCB pattern transfer and its fabrication (5)

6. Developing

The development removes (dissolves) the non-photosensitive, non-patterned wet film, leaving the photohardened graphic portion. The method is generally manual development and machine spray development.

The working conditions of this process are the same as the coating process.

Machine Development Formula and Process Specification
Na2CO3 0.8 to 1.2%
Antifoaming agent 0.1%
Temperature 30±2°C
Development time 40 ± 10 seconds Spray pressure 1.5 ~ 3kg/cm2

Brek Point Control is controlled from 1/3 to 1/2 during operation. In order to ensure the development quality, it is necessary to control the developer concentration, temperature, and development time within an appropriate operating range. Temperatures that are too high (above 35°C) or development times that are too long (more than 90 seconds) can result in reduced film quality, hardness, and chemical resistance.

After development, there are more glues, most of which are related to the process parameters. There are mainly the following possibilities:

1 the development temperature is not enough;
2Na2CO3 concentration is low;
3 spray pressure is small;
4 The transmission speed is faster and the development is not complete;
5 overexposure;
6 stacked plates.

Operation procedure precautions

(1) If a wet film enters the hole during production, it is necessary to increase the ejection pressure and lengthen the development time. After development, carefully check whether the hole is clean. If there is residue, rework should be repeated.

(2) After the developer has been used for a period of time, the capacity has dropped and new fluid should be replaced. Experiments have shown that when the pH of the developer drops to 10.2, the developer has lost its activity. To ensure the image quality, the plate-making capacity at PH=10.5 is defined as the cylinder change time.

(3) Wash thoroughly after developing so that the alkaline solution is not brought into the etching solution.

(4) If open circuit, short circuit, exposed copper and other phenomena occur, the reason is generally that there is damage or debris on the film.

7. dry

In order to make the film have excellent anti-corrosion and anti-plating ability, it should be dried after developing. The conditions are temperature 100°C and time 1 to 2 minutes. The cured film hardness should reach 2H ~ 3H.

8. Check revision

The revised version is actually a self-inspection. Its purpose is mainly to repair the defects on the graphics circuit and remove the parts that are not related to the graphics requirements. That is, the removal of extraneous burrs, glue spots, etc., and make up for missing holes such as pinholes and gaps. , broken lines and so on. The general principle is to scrape after make up, so that it is easy to guarantee the quality of revision.

The commonly used cleaning solutions include shellac, asphalt, and acid-resistant inks. The simplest one is the shellac solution. Its formula is as follows:

Shellac 100~150g/l
Methyl violet 1～2g/l
Amount of anhydrous ethanol

Revision requirements: the pattern is correct, the alignment is accurate, and the accuracy is in accordance with the process requirements; the conductive pattern has neat and smooth edges, no residue, oil, fingerprints, pinholes, notches and other impurities, and there are no residual film and foreign matter on the hole wall; 90% of the repairs The workload of the plate is caused by the uncleanness of the exposure tool. Therefore, the film should be frequently inspected during the operation, and the sunscreen and film should be cleaned with alcohol to reduce the amount of revision. Care should be taken in the revision of the gloves to prevent sweat contamination of the layout. If the first two processes are done very well, there is almost no revision, and the revision process can be omitted.

9. Strip

After etching (Etching) or plating (plating) is completed, the protective film must be removed. Usually, a 4-8% NaOH solution is used to remove the film, and the film is heated and expanded to achieve differentiation. Methods include manual film removal and machine spray coating.

Spraying machine is used to spray the film. Its injection pressure is 2 ~ 3kg/cm2. The quality of the film is good, the removal is clean, and the production efficiency is high. Increasing the temperature can increase the speed of film removal, but the temperature is too high and black holes are easy to occur. Therefore, the temperature should generally be 50-60°C.

After the film is removed, it must be cleaned. If there is residual glue on the surface after removing the film, the main reason is that the process parameters of the baking process are not correct, and the overbaking is generally excessive.

In the above discussion, some of them represent personal experience. In sum, strict control of process conditions is a prerequisite for ensuring product quality. Only according to the company's process equipment and technology level, the use of effective operating techniques and process methods, and the strengthening of total quality management (TQM), can greatly improve the product's pass rate.

At present, the rapid development of integrated circuit and packaging technology, the higher and higher requirements for the fineness of the PCB circuit. In summary, the use of a liquid photoresist pattern transfer process for the crucible can not only improve the fineness of the production line, but also reduce the production cost, and can also utilize the existing equipment, and the operating process can be easily grasped. The liquid photoresist pattern transfer process has become a graphic manufacturing process suitable for high precision and high density requirements. We believe that through the production practice, it will make its process more perfect.

Source: PCB Information Network