The film bottom plate is the leading process in the production of printed circuit boards. The quality of the film bottom plate directly affects the quality of printed board production. When producing a printed circuit board, there must be at least one corresponding film base. Each conductive pattern (signal layer circuit pattern and ground, power layer pattern) and non-conductive pattern (solder resist pattern and characters) of the printed board should have at least one film negative. The various graphics are transferred to the production sheet by a photochemical transfer process.
The use of the film bottom plate in the production of printed boards is as follows:
Photomask pattern in graphics transfer, including line patterns and photo solder, resist patterns.
Fabrication of screen stencils in screen printing processes, including solder mask graphics and characters.
Machining (drilling and profile milling) CNC machine tool programming basis and drilling reference.
Modern printed board production requires that the film bottom plate needs to meet the following conditions:
The dimensional accuracy of the film base must be consistent with the accuracy required for the printed board and should be compensated for by variations in the manufacturing process.
The graphics of the film should conform to the design requirements and the graphic symbols are complete.
The edge of the film of the film bottom is straight and tidy, and the edges are not faint; the contrast between black and white is large, which meets the requirements of the photosensitive process.
The material of the film base should have good dimensional stability, that is, the dimensional change due to changes in ambient temperature and humidity is small.
The film bottom plate of the double-panel and multi-layer boards requires the coincidence accuracy of the pad and the common pattern.
Each layer of the film's bottom plate should be clearly marked or named.
The film base can transmit the required wavelength of light, and the wavelength range required for general light sensing is 3000-4000A.
When making the film bottom plate in the past, it is generally necessary to first make a photographic base map, and then use the camera or pirated to complete the production of the film bottom plate. This year, the use of advanced laser light painting technology has greatly improved the production speed and quality of the bottom plate, and can produce high-precision, thin wire patterns that could not be completed in the past, making the CAM technology for printed board production perfect.
2. Substrate material
Copper Clad Laminates (CCL), referred to as copper clad laminates or copper clad laminates, are substrate materials for the manufacture of printed circuit boards (hereinafter referred to as PCBs). The PCBs currently produced by the most widely used etching method are selectively etched on a copper clad sheet to obtain a pattern of the desired wiring. The copper clad board is mainly used for the functions of conduction, insulation and support on the entire printed circuit board. The performance, quality and manufacturing costs of printed boards depend to a large extent on copper clad laminates.
3. Basic manufacturing process
The printed board can be divided into single-sided, double-sided and multi-layer printed boards according to the number of layers of the conductor pattern.
The basic manufacturing process for a single panel is as follows:
Foil Sheet-->Unloading-->Bake Plate (Preventing Deformation)-->Molding-->Washing, Drying-->Foil (or Screen Printing)->Exposure Development (or Anti-corrosion Ink) - -> Etching -> De-filming ---> Electrical continuity detection --> Cleaning treatment --> Screen printing resistance welding pattern (printed green oil) --> curing --> screen printing symbol --> curing - ->Drilling --> Shape processing --> cleaning and drying --> inspection --> packaging --> finished products.
The basic manufacturing process of the double panel is as follows:
Typical processes are the SMOBC method and the pattern plating method. Process wire methods are also used in certain specific situations.
1) Graphic plating process
Foiled Foil-->Unloading-->Drilling Datum Hole-->CNC Drilling-->Inspection-->Deburring-->Chemical Plating Copper-->Electroplating Thin Copper-->Inspection--> Brush plate --> film (or screen printing) --> exposure development (or curing) --> inspection plate ---> pattern plating (Cn ten Sn / Pb) --> remove film --> etching - ->Inspection repair board-->Plug nickel plating gold plating-->Hot melt cleaning-->Electrical continuity test-->Cleaning treatment-->Screen printing resistance pattern-->Cure-->Screen printing symbol- -> Curing -> Shape Processing -> Cleaning and Drying -> Inspection -> Packaging -> Finished Product.
In the process, the two processes of "electroless copper plating --> electroplating thin copper" can be replaced by a process of "electroless copper plating", both of which have advantages and disadvantages. Graphic Plating - The etched double-faced metallization plate is a typical process in the 1960s and 1970s. In the 1980s, the bare copper solder mask process (SMOBC) was gradually developed, and it has become a mainstream process especially in precision double panel manufacturing.
2) bare copper solder mask (SMOBC) process.
The main advantage of the SMOBC board is that it solves the solder bridging short circuit between the thin lines, and because of the constant ratio of lead to tin, it has better solderability and storage than the hot melt board.
There are many methods for manufacturing SMOBC plates. There are standard pattern electroplating subtraction method to remove lead-tin SMOBC process; tin plating or immersion tin instead of electroplating lead-tin subtractive pattern plating SMOBC process; plugging or masking hole method SMOBC process Addition method SMOBC process, etc. The following mainly introduces the SMOBC process and the plugging method SMOBC process flow of the lead plating tin after the pattern plating method.
The SMOBC process for replating lead-tin by pattern plating is similar to the pattern plating process. Change only after etching.
Double-sided copper clad plate--> according to the pattern plating process to the etching process--> lead-free tin--> check---->clean---> solder resist pattern--> plug nickel-plated gold--> Plug tape -> hot air leveling ----> cleaning ---> screen printing symbol ---> shape processing ---> cleaning and drying ---> finished product inspection --> packaging --> finished products.
The main process flow of the plugging method is as follows:
Double-sided foil-->Drilling-->Chemical copper plating-->Whole plate electroplating copper-->Break hole-->Screen printing image (positive image)-->etching-->Go to the screen printing material, To block the hole material --> cleaning --> solder mask graphics --> plug nickel plating, gold plating --> plug tape --> hot air leveling --> the following process and the same as the finished product.
The process steps of this process are relatively simple, and the key is to block the holes and clean the plugged ink.
In the hole-blocking process, if the plugging ink plugging and screen printing imaging are not used, a special masking type dry film is used to cover the holes, and then exposed to form a positive image, which is a masking hole process. Compared with the plugging method, there is no longer a problem of cleaning the ink in the hole, but there is a high requirement for masking the dry film.
The basis of the SMOBC process is to first produce a bare copper hole metallized double panel and then apply a hot air leveling process.