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The manufacturing process of a PCB

What is a PCB?

A printed circuit board, also called PCB, serves, in simple terms, as a carrier for the components and the connections of the components to each other and to the outside, which together form the circuit. In most cases, the carrier material serves as an insulator, while the connection between the components is made by copper tracks.

Here, the PCB combines mechanical attachment and electrical connection as its most important properties. PCBs are used as an irreplaceable base in almost all electronic devices.

Carrier material and connections on the PCB

Glass fibre fabric (FR4/5), polyimide foil (Flex), aluminium, Teflon and ceramics are used as the electrically insulating carrier material of the PCB.

Electrical connections consist mainly of copper tracks for SMD components or wiring for THT components.

Components and assembly

The majority of components are soldered onto this surface as SMD (Surface Mounted Device) components or THT (Through Hole Technology) components are mounted via through-hole assembly.

The term PCBA (Printed Circuit Board Assembly) or "electronic assembly" from PCB assembly refers to the printed circuit board equipped with components. By embedding components, the PCB is no longer just a carrier of components but has sometimes become part of the circuit itself.

Types of PCBs

A PCB can be single-sided , double-sided or consist of several layers. If a PCB has several layers, it is called a multilayer. With multilayers, each layer offers space for its own circuit, so that much more complicated circuits can be realised.

Double-sided and multilayer PCBs are the most common type, with multilayers being used for more complicated applications. Flexible PCBs are used to save space and to make flexible connections between mechanical parts.

The data required to create the PCB is entered in layout programs such as EAGLE, Altium or TARGET 3001! (downloadable free of charge from this page) and sent to the PCB manufacturer or, as on the Beta LAYOUT page, processed by drag & drop.

The process is described here for rigid PCBs, flexible PCBs, which Beta LAYOUT also sells, require a modified process.

Cam editing
The data records from the various software solutions supported in the PCB-POOL are standardized in the Ext. Gerber Format (RS 274X).
The processed output file in Ext. Gerber Format can be supplied as preview.
A pre-production preview of the PCB layout can be supplied in PDF format.

Order tracking

Material Preparation
The copper-clad panels along with the drill entry material & a back-up-board are then cut to size.
The standard panel comprises of a 0.062 inch thick base material, with a coating of 0.5 ounce (18µm) copper on each side.

Drilling and pinning
At this stage the reference & tooling holes are drilled. The PCB-POOL panel is then pinned onto the CNC machine.

CNC Drilling
With the help of CNC drill machines the through-hole plated and component drills are produced. During this process, spindle speeds of up to 230,000 revolutions per minute are recorded.

WATCH''ur''PCB Step

Through-hole plating
Now an electrographic film (e.g. Palladium) is electroplated to the wall of the drill cavity, this allows for galvanisation with copper to occur at a later stage.

Brushing
Because PCBs must be completley free of grease and dust, they are subjected to rigourous cleaning (e.g. by brushing) before proceeding to the next stage.

Resist laminating
Under extreme temperatures and pressures the entire PCB-POOL panel is laminated with a photosensitive dry resist (LAMINAR 5038).

Resist exposure
Using the previously generated photoplots the resist is exposed to UV light.

WATCH''ur''PCB Step

Resist development
Through cyclic construction the exposed panel is developed in a 1% sodium carbonate solution. The PCBs are now ready for plating.

Structure of the conductor pattern in electroplating

Electroplated Conductor Configuration
The tracks and pads which are developed, free of photo resist, are copper-plated to a thickness of approx. 1,378mil (35µm) and fused with a 0,24mil - 0,39mil (6µm -10µm) tin film, protecting the tracks and pads during the final etching process.

Resist stripping and removing tin from the circuit board

Resist stripping
The photoresist is stripped away with a 2.5% caustic potash solution. This lends itself to the immersion and spray coat processes.

Etching
The next step is the spraying on of a coat of ammonia solution onto the copper film, getting rid of any excess copper, while the galvanised tin protects the tracks and pads.

Tin stripping
Only then will the tin be removed using a nitric acid based tin-stripper. This lends itself to the dipping or spraying processes.

WATCH''ur''PCB Step

Applying the solder resist to the circuit board

Soldermask application
The soldermask can be applied as a dry film or a liquid lacquer in a hanging casting implement. After this comes the screen-printing and spraying processes.

Soldermask exposure
Finally, using the previously generated photoplots the soldermask is exposed to light.

Soldermask development
The development of the exposed PCB is in turn achieved through a cyclic construction in a 1% sodium solution. Hence all soldering points and pads, which are to be tin plated later, are cleared of soldermask.

Apply silk screen to printed circuit board

Silkscreen
Using a Direct Legend Printer, the silkscreen is immediately printed onto the soldermask. In this process the printhead sprays the screen-print, defined by Gerber data, directly onto the PCB.

Burning in the solder resist on the circuit board

Burning-in
At a temperature of 302°F (150°C) the soldermask is tempered over a period of approx. 60 minutes.

WATCH''ur''PCB Step

Application of the ENIG Hal surfaces to the boards

Surface finish

Chemical Nickel-Gold (ENIG)
The pads freely developed by the solder paste are coated with Chemical Nickel-Gold together with the surface by means of vertical baths. The gold layer is used to protect the nickel surface to ensure solderability.
The advantages as opposed to HAL are stress-free coating and the flat surface.

Hot Air Levelling (HAL)
On the surface coating the pads are tin plated in a hot-air tin-plating system at a temperature of around 518°F (270°C). During this process the PCB-POOL panel is immersed in liquid tin which is blown off with preheated air under a pressure of approx. 72,5 psi (5 Bars).
The technical specifications sheet for the lead-free tin which is used can be found by clicking on the following link: Specifications.

WATCH''ur''PCB Step

Pinning
To prevent the panel from moving during routing, it is pinned down onto the routing machine bed.

Milling the panel of printed circuit boards

Routing
In the final stages, the individual PCBs are routed from the PCB-POOL panel with the aid of a CNC Routing machine. This operation involves spindle speeds of over 40,000 revs per minute and a feed rate of 1m/min.

Resist laminating
Under extreme temperatures and pressures the internal layers are laminated with a photosensitive dry resist (LAMINAR 5038).

Resist exposure
Using the previously generated photoplots the resist is exposed to light.

Resist development
Through cyclic construction the exposed inner layers are developed in a 1% sodium carbonate solution.

Pressing
Only at this stage are the individual layers pressed in a Multi-layer press at a max. temperature of 175°C and a cyclic time of 90 minutes for the layer structure.

The next stage is drilling. The following manufacture process is equally valid for both multi-layer and double-sided PCBs.