two. Liquid photoresist pattern transfer
Liquid photoresist process:
The previous process → Pretreatment → Coating → Prebake → Positioning → Exposure → Development → Drying → Inspection → Etching or Plating → Stripping → Crossing
1. Pre-cleaning
The main purpose of the pretreatment is to remove Grease, Oxidized Layer, Dust and Particle residues, Moisture, and Chemicals, especially Alkaline, on the copper surface. ) To ensure the cleanliness and roughness of the copper surface, to produce a uniform and suitable copper surface, and to increase the bonding force between the photoresist and the copper foil. The requirements for the wet film and the dry film are different. It is more focused on the cleanliness.
The methods of pretreatment include mechanical grinding, chemical pretreatment, and a combination of both.
1) Mechanical grinding
Plate condition:
Pickling time: 6 ~ 8s.
H2SO4: 2.5%.
Washing: 5s~8s.
Nylon Brush: 500 to 800 mesh, most of which uses 600 mesh.
Grinding plate speed: 1.2 ~ 1.5m/min, interval 3 ~ 5cm.
Water pressure: 2 to 3 kg/cm2.
Strictly control the process parameters to ensure that the board surface drying effect, so that the board surface without impurities, traces of glue and oxidation. It is best to carry out anti-oxidation treatment after grinding the board.
2) Chemical Pretreatment
For the MLB inner layer board (Inner Layer Board), due to the thin substrate, it is not appropriate to adopt the mechanical grinding method and often adopt the chemical pretreatment method.
Typical chemical pretreatment process:
Degreasing → Cleaning → Microetch → Cleaning → Drying
remove oil:
Na3PO4 40～60g/l
Na2CO3 40~60g/l
NaOH 10～20g/l
Temperature: 40～60°C
Mi-croetehing:
NaS2O8 170～200g/l
H2SO4 (98%) 2%V/V
Temperature: 20～40°C
The chemically treated copper surface should be pink. Whether using mechanical or chemical pretreatment methods, they should be dried immediately after treatment.
Inspection method: Water film test is used. The principle of water film rupture test is based on the interface chemistry between liquid and liquid phases or between liquid and solid phases. If you can maintain the water film 15 ~ 30s is not broken that is clean.
Note: The cleaned board should be worn with clean gloves and immediately coated with photo resist to prevent reoxidation of the copper surface.
2. Coating
Coating refers to uniformly covering the copper surface with a layer of liquid photoresist. There are many methods for this, such as centrifugal coating, dip coating, screen printing, curtain coating, roller coating, and the like.
Screen printing is a commonly used coating method, which requires low equipment, simple and easy operation, and low cost. However, it is not easy to coat both sides at the same time, the production efficiency is low, and the uniformity of the film cannot be completely guaranteed. In general screen printing, full-page printing uses 100 to 300 mesh screens, and electroplating uses 150 mesh screens. This method is welcomed by most small and medium manufacturers.
Roll coating can realize double-sided coating at the same time. It has high automation production efficiency and can control the coating thickness. It is suitable for large-scale production of various specifications, but requires equipment investment.
Curtain coating is also suitable for large-scale production, but also can uniformly control the thickness of the coating layer, but the equipment requirements are high, and can only be painted on one side before coating the other side, affecting the production efficiency.
Photo-induced coating film is too thick, easy to produce underexposure, lack of development, high pressure sensitivity, easy to stick the film; film is too thin, prone to overexposure, poor resistance to plating insulation and easy to produce metal plating film phenomenon, Slow film removal.
Working conditions: Clean room under yellow light, room temperature is 23 ~ 25 °C, relative humidity is 55 ± 5%, the workplace is kept clean, avoid sunlight and direct sunlight.
(to be continued)