Manufacturing process of Printed Circuit board

1. Pre-production Engineering
- The process starts when the customer’s PCB orders, the orders will go to the engineering
department to ensure smooth production. The checking of the Gerber file is through:
o The reviewing of the design files sent by the customer. The contents that are
reviewed are if:
 The contents are complete
 The production information is clear
 The circuit design is reasonable
 There is any requirement beyond the capability of the company
 Other issues
- Preparation of instructional materials and processing program for production

The content of manufacturing instruction:

 Material cutting
 Inner layer
 Press
 Drill
 PTH
 Panel Plating
 Outer Layer Wiring
 Pattern Plating
 Etching
 AOI
 Soldermask
 Silkscreen
 Surface Finish
 Routing + Washing
 E-test
- Forwarding of the instruction document to the different production department
2. Board Cutting
- The cutting of the board in the panel plating department starts with the determination of
the additional proportion of the materials:
o Number of layers
o Copper thickness
o Trace width
o Trace spacing
o Surface finish

The limitation of the PCB equipment of the PCBWay company in board cutting process

PCB Capabilities
Number of Layers 1-10
Material FR-4, Aluminum
 Max. Size 500x1100mm
Min. Size 5x6mm
Board Thickness 0.2 – 2.4mm
Min. Trace 0.1mm/4mil
Min. Spacing 0.1mm/4mil
Surface Finish HASL with Lead
HASL lead free
Immersion gold
OSP
Where:

Copper Clad Laminate – type of materials made from electronic glass fiber cloth or other

reinforcing materials dipped in resin, laminated with copper foil on one or both sides and heat

pressed.

Mil – equal to 0.001 in

FR-4 – a printed circuit board that is made from a flame-retardant epoxy resin and glass fabric

Composite. (FR means flame retardant, 4 means woven glass-reinforced epoxy resin)

Qualities:

operating temperature (50 to 115 deg. C)

Higher glass transition temp value (180 deg. C)

Cost-friendly when compared to other materials.

HASL – Hot air solder level, immersing circuit boards in molten pot of a tin/lead alloy then

removing the excess solder by using “air knives”, which blows hot air across the surface

of the board

OSP - Organic solderability preservative, it is anti-tarnish to prevent copper from being oxidized,

picking up thermal shock, or being affected by moisture.

- Sheet material cutting involves two stages:

o Copper Clad Laminate cutting
 Cutting of the Copper Clad Laminate into processing size
o Board grinding and baking
 Before image transferring the sheet material are grinded and baked
 Corners of the board will be rounded and edged to remove the glass
fibers at the end of the board during cutting to reduce scratch issues
on the board surface or other hidden quality problems.
 Baking the board helps removes the moisture and volatile on the
board to increase the dimensional stability and mechanical strength
of the material.
3. Print Inner Layers
- The printing of inner layer involves stages:
o Pre-treatment
 Removing of impurities attached to the surface of copper and increase
surface roughness to ensure good adhesion between dry film and surface to
avoid film stripping and short circuit or diffusion coating cause by
inadequate film lamination
o Dry film lamination
 Applying or coating the surface of a treated copper sheet with special
photographic film that can produce a polymerization reaction and form a
stable substance attached to the surface of the copper when exposed to UV
lights. Thus, blocking plating and etching in the next process. The process
must be carried out in a dust free and brown light room.
o Exposure
 Each layer has a corresponding film image in order to avoid offsetting the
position of the image, the film need to be aligned with a substrate laminated
with a film before exposure. Under UV light exposure the light-transmitting
part of the film undergoes a photopolymerization reaction and is cured to
form a macromolecular structure that is insoluble in dilute alkali
o Developing, Etching and Stripping (DES)
 Technicians firstly uses a developing solution to wash off the dry film that
has not been polymerized while the film that has been polymerized remain
on the board surface as a protective layer against erosion during etching.
Next, the inner layer panels of the multilayer PCBs enter the etching area
the unexposed drying film is removed by the developer and the copper
surface is then exposed. The exposed copper surface gets dissolved and
etched away in the copper chloride to obtain the desired trace. The stripping
step is to strip off the exposed dry film protecting the copper surface with a
sodium hydroxide solution. Operators remove any remaining resist to ensure
that no substances affect the conductivity of the copper. After stripping is
completed, the entire PCB circuit of the inner layer has been shaped. Then,
the panels are transferred to the optical inspection department to check the
consistency between the etched circuit pattern and circuit in the design
4. Etch Inner Layers
-
5. Inner Layer Automatic Optical Inspection (AOI)
- During the etching process, the edging method, the etching rate, the types and PH value of
the etchants or other factors directly affect the quality of the circuits. If these factors are not
properly controlled. Defects such as short circuit, open circuit, circuit width defects and
copper residues will be caused. Therefore, the boards after etching need to be carefully
inspected. Automatic Optical Inspection is a common method that can effectively control the
scrap rate and improve product quality. In the AOI process, CAM/CAD data of PCB are often
used as reference for image comparison. The CAM/CAD data is firstly converted into image
data that can be recognized and stored by the AOI machine. Various light sources are filtered
 by optical lenses and then irradiated on the PCBs the lights are then reflected through
various filter lenses to the receiver that generates a corresponding electrical signal according
to the intensity of the light signal. Through its image processing card, the AOI machine
converts the electrical signal obtained by the Charge Couple Device camera, scanning the
ball surface into a computer-identifiable binary signal. Thus, obtaining a binary image of PCB.
The binary image will be compared with the board image data converted by the CAM stored
in the AOI machine. Defects will be reported at the positions of discrepancies. Finally, the
inspector confirms the discrepancies to complete the entire inspection process. Automatic
optical inspection can detect defects early. So, as to effectively prevent defective boards
from moving onto the next process. Thus, reducing material waste and cost.
6. Lay-up and bond (Lamination)
o Pre-liminary lay-up
 Prior to laminations, the surface of inner image layer needs to go through an
oxide process to roughen and passivate the copper surface, increase the
interaction surface area of resin, enhance the bond strength between the
copper layer and the prepreg to avoid problems such as delamination and
diffusion coating. Once inner layer has been confirmed as being defect-free,
they are ready for lamination. PCB lamination process mainly consist of
following steps:
o Lay-up
 Multi-layer boards with 6 layers or more require pre liminary lay-up, which
stacks and fixes core boards with etched circuit pattern and prepreg
together in a certain order. In this step, inner layers are fixed by riveting or
fusing to ensure that the traces of each layer will not cause open or short
circuit because of misalignment. Lay-up step is to stack copper foil prepreg
inner layers after preliminary lay-up and other materials in the proper order
for lamination
o Lamination
 The inner layers, which are clamped by iron plates, are placed on stands and
then fed into a vacuum heat press machine for lamination. Under high
temperature and pressure, the resin in the prepreg melts and flows to fill
the core board and laminated layers together. Once finished, operators
remove the top iron plate of the stacked layers and then take away the
bearing aluminum plate. Only three or more layers of PCBs need to be
laminated while single- and double-sided panels do not require.
o Post treatment
 After lamination, the boards are processed by beveling targets drilling, edge
milling, and other processes for subsequent production. Among the
processes, layer deviation checking by x-ray and hole milling are the most
important parts.
7. Drilling the PCB
- To make the circuit of each layer connected the board needs to go through the drilling
process to make the corresponding holes according to the specifications in the drill files. For
single and double-sided boards, drilling process follows directly after the board cutting.
While multi-layered boards are drilled after lamination. We can generally divide the PCB
drilling process into the following 4 steps:
o Drilling location holes
 Location holes serves as the positioning points in the PCB production and
testing process. Before drilling, the back-up board, the substrate, and the
aluminum sheet are first put on the high-speed drilling machine table from
the bottom to up. According to the manufacturing instruction, 3 to 4 around
3.2 millimeters location holes are drilled on the edge of the board.
o Inserting pins
 In order to increase production efficiency, several boards are stacked for
drilling. But these boards need first to be taped on the drilling machine table
through the pins with the backing board and covering plate together to
avoid shifts and dislocation
o Drilling holes
 The drilling process is controlled by a computer program, so it simply
requires to input the CAM-converted drilling parameter files to drill the
corresponding holes. Mechanical drilling is a commonly used method to drill
holes in the PCB manufacturing process. The drill is rotated at a high speed
through spindle and create a cutting force to drill a number of different
types of holes, including Plates Through Holes (PTH), Non-Plated Through
Holes and Via Holes. Before drilling a backing board is placed underneath
the board to protect the surface of the drilling machine and an aluminum
sheet is also laid on the top to make the holes in the copper foil flatter and
prevent the bit from overheating.
o Holes inspection
 After drilling the hole location and aperture of the first sample of the board
should be inspected. After making sure that there are no problems such as
extra holes, missing holes, or hole shift, then it is ready for the next
production process.