What is the image transfer

Dry film photoresist structure

Dry film photoresist consists of polyester film, photoresist film and polyethylene protective film. The polyester film is a support for the photosensitive layer, which is coated to form a film, and its thickness is usually about 25 μm. The polyester film is removed before development after exposure to light to prevent oxygen from diffusing to the resist layer during exposure, destroying free radicals, and causing a decrease in sensitivity. The polyethylene film is a protective film covering the photosensitive adhesive layer to prevent the dirt and the like from contaminating the dry film and avoiding the mutual adhesion of each layer of the resist film when the film is wound. The polyethylene film generally has a thickness of about 25 μm. The photoresist film is the main body of the dry film, and is mostly a negative photosensitive material. The thickness of the photoresist film is different depending on its use. There are several types of specifications, and the thinnest film can be a dozen micrometers, and the thickest one can reach 100 μm.

The dry film photoresist is prepared by first applying the pre-prepared photoresist to a polyester film on a high-precision coater under high cleanliness conditions, drying it through a drying tunnel, and cooling. On polyethylene protective film, wound on a roll core.

★ The main components and functions of the photoresist layer: A large number of water-soluble dry films are used in China. The composition of the all-water-soluble dry film resist is introduced here.

Print etching process:

Under the material → plate surface cleaning → wet film → exposure → development (paste film → exposure → development) → etching → removal of film → enter the next process Chop-shaped plating process is summarized as follows:
Blanking → Drilling → Hole Metallization → Pre-Copper Plating → Clean Plate → Apply Wet Film → Exposure → Develop (Dry Film → Exposure → Develop) → Form Negative Phase Image → Pattern Copper Plating → Pattern Electroplated Metal Resist Layer → Removing Film → Etching → Entering Next Process
There are two methods for image transfer, one is screen printing image transfer and the other is photochemical image transfer. Screen printing image transfer is cheaper than photochemical image transfer, especially in the case of large production batches, but screen printing resist printing materials usually can only produce greater than or equal to o. 25mm printed conductors, and the photo-resistors used for photochemical image transfer produce sharp images with high resolution. The content described in this chapter is the latter method. Photochemical image transfer requires the use of photoresist. Here are some basic knowledge about photoresist.

4) Plasticizers can increase the uniformity and flexibility of dry film resists. Triethylene glycol double acetate can be used as a plasticizer.
5) Tackifier The chemical binding force between the dry film photoresist and the copper surface can be increased to prevent the defects such as warping and plating of the film due to loose bonding. Commonly used tackifiers such as benzotriazole.
6) Thermal Inhibitor In the production and application of dry film, many steps need to receive thermal energy, in order to prevent thermal energy from adding thermal inhibitor to the polymerization of dry film. Such as methoxy phenol, hydroquinone, etc. can be used as thermal inhibitor.
7) Pigment To make the dry film show a vivid color, it is easy to modify and check and add color material. For example, malachite green and Sudan III are added to make the dry film vivid green, blue and so on.
8) Solvents Solvents must be used to dissolve the above components. Acetone and alcohol are usually used as solvents. In addition, some kinds of dry films are also added with photochromic agents to increase or decrease color after exposure to identify exposure. This kind of dry film is also called discoloration in films.

Author: Yuan Bin Source: PCB network city