In PCB manufacturing, the precision guarantee of film production is a key link to ensure the quality of circuit boards, and its precision directly affects the circuit accuracy and performance of PCBS. The following are the key points for ensuring the precision of film production in PCB manufacturing:
The key role of film production in precision
The precision basis of graphic transfer: As the carrier of graphic transfer, the precision of film directly determines the accuracy of PCB circuits. In the film drawing stage, through computer-aided design (CAD) data, the circuit patterns are precisely drawn on the film using a dedicated plotter. The plotter controls the laser or inkjet device to form patterns on the photosensitive emulsion layer of the film. The precision of this process determines the accuracy of the final work.
The importance of dimensional stability: The film must have extremely high dimensional stability, as any slight dimensional change may affect the circuit accuracy and performance of the final PCB product. During the graphic transfer stage, the film is closely adhered to the copper clad laminate. When exposed to ultraviolet light, the transparent area on the film allows ultraviolet light to pass through, causing a photochemical reaction in the corresponding photosensitive material on the copper clad laminate and forming a latent image consistent with the circuit pattern. If the film size is unstable, it will cause latent image position deviation, which in turn affects the line accuracy.
Measures to ensure the accuracy of film production
Material selection and quality control
The base material of the film: The base of the film is usually made of polyester material, providing stable physical support for the film and ensuring that it is not prone to deformation during the production process. Meanwhile, the film material should have good dimensional stability, that is, the dimensional changes caused by variations in environmental temperature and humidity should be small.
Photosensitive emulsion: Photosensitive emulsion is the key for film to achieve image recording, and its main components include silver halide particles and gelatin. Silver halides undergo photochemical reactions under the action of light, thereby recording image information. It is necessary to ensure the quality and performance stability of the photosensitive emulsion to guarantee the accuracy of image recording.
Production process optimization
Drawing accuracy control: The plotter precisely controls the laser or inkjet device based on the design data to form patterns on the photosensitive emulsion layer of the film. The plotter should be calibrated and maintained regularly to ensure its drawing accuracy.
Exposure and development control: During the graphic transfer stage, strictly control the process parameters of exposure and development, such as exposure time, ultraviolet intensity, developer concentration and temperature, etc., to ensure the formation of latent images and development effects, thereby ensuring the accuracy of the line pattern.
Environment and Storage Management
Storage environment control: Film has very high requirements for the environment and must be stored under constant temperature and humidity conditions to prevent deformation and aging. The temperature should usually be between 20 and 25 degrees Celsius, and the humidity should be between 50% and 60%. Air conditioners and dehumidifiers should be installed in the storage room to ensure a stable environment.
Dust-proof and pollution-proof: Film should be kept away from dust and contaminants. When stored, it should be in a dedicated storage box and its surface should be kept clean. Regularly clean the storage room and storage boxes to prevent the intrusion of dust and contaminants.
Inspection and Maintenance
Regular inspection: Conduct a comprehensive inspection of the stored films once a month to ensure their quality and condition are good. The inspection items include the cleanliness, flatness and whether there are any signs of aging of the film, etc.
Maintenance and care: Timely maintenance and care should be carried out on the films with problems found to prevent the problems from escalating. Scrap films that are severely aged or irreparable to ensure production quality.
Strategies for dealing with precision issues such as film expansion and contraction
Controlling heat exposure: The heat exposure time during the PCB manufacturing process is one of the main factors causing the expansion and contraction of the film. In order to reduce the degree of expansion and contraction, it is necessary to control the time and temperature of hot exposure. In each step of PCB manufacturing, especially during copper plating and thermoplastic pressing processes, the time of hot exposure needs to be strictly controlled to reduce the thermal impact of the film material.
Material selection: Different types of film materials have different expansion and contraction properties. During the process of PCB design and manufacturing, appropriate film materials should be selected based on specific requirements, and materials with stable expansion and contraction performance should be chosen as much as possible. For example, the use of film materials with a high glass transition temperature (Tg) can reduce the degree of expansion and contraction.
Compensation design: In PCB design, some compensation designs can be introduced to address the issue of film expansion and contraction. For instance, in the routing planning, a certain amount of space and margin should be reserved to ensure sufficient fault tolerance when the film expands or contracts. In addition, special wiring methods can also be adopted, such as controlling the direction and length of the traces, to minimize the impact of film expansion and contraction on the PCB.
