What is PCB Manufacturing Process?
The full name of PCB is printed circuit board, as it is evidently manufactured through a printing process.
The PCB manufacturing process involves transferring the PCB graphic onto a copper-clad board according to the designed circuit pattern. Then metalize the through holes and print solder mask ink to protect the copper foil and traces. Finally, the exposed pads are surface treated to form the circuit board that is required.
The raw material of the circuit board is copper-clad laminate, which is an insulating board with a thin layer of copper foil on the surface.
A printed circuit board serves as the platform for attaching and installing electronic components, while also providing a means of communication between these components to create an electrical conduction pathway.
Below is PCB manufacturing Process Flow Chart:
PCB Manufacturing Process
(i) Innerlayer
1. Preliminary Treatment:
Removes the anti-tarnish coating,dirt,grease,from the copper clad laminate.
2. Dry Film Lamination:
Application of an UV sensitive dry film to cleaned surface of the copper laminate. Utilizes a fully automated Cut Sheet Laminator (CSL) which applies dry film on both sides of the copper laminate through controlled heat and pressure.The line includes material surface preparation,CSL,loader and Stacker.
3. Dry Film Exposure:
A negative phototool or artwork is imaged into dry film, on both sides of the copper clad,through UV light exposure leaving a positive image in the dry film.During exposure the UV energy is absorbed by the dry film directly underneath the clear areas of the overlaying artwork,causing it to polymerize and harden.The film covered by dark areas of the artwork remains soft
4. Dry Film Developing:
After the dry film is imaged, the unexposed soft areas of the film are dissolved away while the hardened dry film remains unaffected.
5.Copper Etch：
The remaining hardened dry film on the copper acts as a “resist” and the unprotected copper is chemically dissoloved or etched.
6.Strip Resist:
The hardened dry film is stripped from the copper leaving the desired copper pattern reproduced from the artwork, The inner-layer image transfer process has been completed.
7. Automated Optical Inspection(AOI):
Inner-layer cores are inspected with the use of a computer aided optical inspection system to locate any pattern defect that may have occurred during the image transfer process.The AOI process uses a data file generated at CAM, the machine compares the image scanned versus a graphic computer file. AOI benefits consist of early detection of process deviations, reduction of final test fallout’s, consistent line width and tolerances.
8.Inner-layer Oxide:
This process is designed to intentionally create a coating of copper oxide onto the copper circuitry to enhance the surface topography.This will increase the bond strength between the core and the bonding materials used in the multi-layer lamination.
9.Vaccum Press Lamination:
Lamination is the process of bonding cores together to form a multi-layer panel. Inner-Layer oxidized cores are stacked up with prepreg and copper foils,depending on the type of build.
Outer Layer
1. NC Drilling:
Panels arriving from the vacuum press will be drilled to create interconnections between the different layers of the circuitry.The drills are CNC controlled and receive files from CAM which contain the number of hits,holes sizes,and the path for the drill head to follow. Panels from the lamination presses are first routed and edge beveled to clean up the edges of panels. The tooling holes are spot faced to allow the panels to lie flat on the drill table.
2. Electroless Copper
It’s a chemical metalization process intended to metallize the surface of dielectric material at the hole wall
and institute electrical connection between all exposed copper surfaces. The process deposits a very thin
(75 micro-inches），fragile coating of pure copper over the entire surface of the panel.this includeds the drilled
hole walls and the external surfaces.
3.Dry Film Lamination:
Just as in inner layer,photosensitive dry-film is laminated on both sides of the panel.
4.Dry Film Exposure:
A positive image is used to create a negative(reverse) image of the external circuitry onto the
Dry-film,note that the dark areas of the artwork cover the panel holes. The film and the artwork are exposed to UV light and the external image is created.
5. Dry-Film Developing:
The unexposed areas of the dry-film are dissolved away.The dry-film creates a “channel” for copper pattern plating to take place.
6. Copper and Tin Plating:
Copper plating is electrodeposited onto the copper foil that is outlined by the dry film.Copper is plated on the surface and in the holes of the panel.The panel are suspended in an acid-copper bath along with copper anode balls.Current from a DC rectifier drives copper to be consumed from the anodes and deposited on the plated surfaces.Organic compounds are also introduced to the plating baths to control deposition rates.
Tin Plating is immediately after copper plating, a thin layer(0.003”) of tin is electroplated on the surface of the copper.Tin will act as etch resist in a future manufacturing process.
7.Dry Film Strip:
Removes the plating resist exposing the base copper underneath.The plated copper remains,protected by the tin
Plating etch resist.
8.Copper Etch:
The exposed copper is removed through an etching process,while the plated tin acts as a resist- protecting the plated copper from the etchant.
9.Tin Strip:
The tin plate etch resist is stripped off and the external circuitry is exposed.
10. Soldermask:
Solder mask is an insulative protective coating that is applied to the external circuitry after the SES process.
11. Solder mask Exposure:
PISM acts similarly to a Dry-Film,a negative artwork artwork is used to create the image of the solderable areas like SMT pads, PTH. The solder mask is exposed to UV light in a controlled environment such as in inner or outer-layer.
12.Soler mask Developing:
The unexposed PISM is developed away,leaving the solderable pads exposed.
13.Silkscreens(Idents):
After the application of the board finish,the legends are added onto the panel through screen printing of
The identification ink which is available in different colors,UV or thermally cured.
14.Solderable Finishes:
Hot Air Solder Leveler(HASL),ENIG, OSP are the most commonly used finish because of its good electrical
Continuity,excellent shelf life,and mechanical bonding properties.
15. NC Routing:
– Individual boards are cut from manufacturing panel
– Use NC Router, similar to NC Drilling equipment
– Typically 0.093” cutting tool(0.030”,0.062”)
16. Q.C. Inspection
Electrical Testing(Bare Board Test):
– 100% electrical test for open circuit,short circuit
– Universal test equipment with customized fixtures
– Double sided access
– Test to electrical netlist generated from gerber data
Visual Inspection:
– Detect any cosmetic defects according to IPC-A-600.
(i.e. scratches,chips,uneven solder)
– Rework- soldermask touch-up,solder touch-up
– Typically 100% inspection
QC Audit Inspection:
– Verification of all dimensions:
Registration
Annular Ring
Board Thickness
Warp & Twist
– Review product to customer specification
– Measurement of all metalization thicknesses(Cu,SN/PB,Au,Ni)
– Special Requirements(cleanliness,microsection,TDR)
