PCB Manufacturing Process: how are PCBs made
PCB holes and vias
Holes, often called via holes or vias are needed within a PCB to connect the different layers together at different points. Holes may also be needed to enable leaded components to be mounted on the PCB. Additionally some fixing holes may be needed.
Normally the inner surfaces of the holes have copper layer so that they electrically connect the layers of the board. These “plated through holes” are produced using a plating process. In this way the layers of the board can be connected.
Drilling is then accomplished using numerically controlled drilling machines, the data being supplied from the PCB CAD design software. It is worth noting that reducing the number of different sizes of holes can help reduce the cost of the PCB manufacture.
It may be necessary for some holes to only exist within the centre of the board, for example when inner layers of the board need to be connected. These “blind vias” are drilled in the relevant layers prior to the PCB layers being bonded together.
PCB solder plating and solder resist
When a PCB is soldered it is necessary to keep the areas that are not to be soldered protected by a layer of what is termed solder resist. The addition of this layer helps prevent unwanted short circuits on the PCB boards caused by the solder. The solder resist normally consists of a polymer layer and protects the board from solder and other contaminants. The colour of the solder resist is normally deep green or red.
In order to enable the components added to the board, either leaded or SMT to solder to the board easily, exposed areas of the board are normally “tinned” or plated with solder. Occasionally boards, or areas of boards may be gold plated. This may be applicable if some copper fingers are to be used for edge connections. As the gold will not tarnish, and it offers good conductivity it provides a good connection at a low cost.
PCB silk screen
It is often necessary to print text and place other small printed idents onto a PCB. This can help in identifying the board, and also in marking component locations to aid in fault finding, etc. A silk screen generated by the PCB design software is used to add the markings to the board, after the other manufacturing processes for the bare board have been completed.
PCB prototype manufacturing process
As part of any development process it is normally advisable to make a prototype before committing to full production. The same is true of printed circuit boards where a PCB prototype is normally manufactured and tested before full production. Typically a PCB prototype will need to be manufactured quickly as there is always pressure to complete the hardware design phase of the product development. As the main purpose of the PCB prototype is to test the actual layout, it is often acceptable to use a slightly different PCB manufacturing process as only a small quantity of the PCB prototype boards will be needed. However it is always wise to keep as close as possible to the final PCB manufacturing process to ensure that few changes are made and few new elements are introduced into the final printed circuit board.
The PCB manufacturing process is an essential element of the electronics production life cycle. PCB manufacturing employs many new areas of technology and this has enabled significant improvements to be made both in the reduction of sizes of components and tracks used, and in the reliability of the boards.