Printed Circuit Boards (PCB)

LPKF is a collection of machines used to make Printed Circuit Boards (PCBs). PCBs are found in almost all electronic devices, and the Process listed below talks about all the steps needed to make a PCB.

0.25mm (10 mil) trace width

0.25mm (10 mil) trace spacing

0.4mm (15 mil) vias

Below is a list that gives a general overview of all the steps for the process of making a PCB. The LPKF system lets us create boards that are up to 8 layers thick; however, simpler 2 layer boards are much more common.

FR4 is the most common material used for PCB manufacturing. It is comprised of two layers of copper separated by an insulating fiberglass layer. Copper is drilled and routed away to make the circuit board.

Starting with a blank sheet of FR4, the first step is to drill all the through holes, including vias. A via is a hole that connects the top layer to the bottom layer. They are commonly used to tunnel a trace from one layer to the other in order to get around intersecting traces. Vias can also be used to connect ground planes on the top and bottoms layers which helps prevent capacitive effects between the layers.

The insides of the vias that were just drilled get plated with a thin layer of copper. This connects the top and bottom layer together.

The board gets placed back onto the router where the tracks on the top layer are routed. The tracks are the connections between all the components on a PCB. The board gets flipped over and the same process is completed for the bottom layer.

The solder mask is what makes most PCBs look green. It serves two purposes: 1) Act as an insulating layer for the top and bottom to protect the board, and 2) Repel solder. Solder mask helps to avoid bridging tightly spaced components because solder will get repelled in the areas between copper pads.

The silk screen is pretty much the same as the solder mask. The same process is used, but it is white and is used to print text on the board. Text can include everything from labels for what component goes where, to company logos, or even dates of manufacture for the board.

Stencils are used to help apply solder paste. A stencil is a polyimide sheet that has holes cut in it that line up with the pads of components on the board. For this system, the stencil is routed similar to the boards.

There is a jig in the LPKF system that helps align the stencil with the board and makes it easier to apply solder paste. A glob of solder paste is placed on the stencil and is spread over the pads of the PCB.

A pick and place machine is used to place all components on the board after the solder paste has been applied.

A reflow oven is able to get hot enough to melt solder but not damage the board. After reflowing, the board is complete.

The ProtoMat is the board router. This machine is used to drill and route the PCB and make the Stencils used when applying solder paste.

This is the CAM software used to control the S64 and set up jobs.

This is the through hole plater used to copper plate vias. There is also a setting to tin plate pads to make them look more of a silver shiny rather than copper.

Solder mask kit used to apply the solder mask.

Silkscreen kit used to apply silkscreen graphics.

Pick and place machine. It used compressed air to pick components up and place them on the board. This method is easier and more precise than doing it by hand.

This is the jig used to align the stencil to the board. From here, solder paste can easily be applied to all the pads.

This is the reflow oven used for melting the solder paste. It is also used for curing the solder mask and silk screen.

The abbreviated process is as follows:

1. Drill vias (ProtoMat S64)
2. Plate vias (Contac S4)
3. Drill traces (ProtoMat S64)
4. Apply solder mask and silkscreen (ProMask/ProLegend kits, ProtoFlow S N2, UV Lamp)
5. Solder components (ProtoPrint S, ProtoPlace S, ProtoFlow S N2)

PCB - Printed Circuit Board

SMD/SMT - Surface Mount Device/Surface Mount Technology (components that attach by being soldered to pads on one side of the board)

Through Hole - Hole that goes through the board

Through Hole Component - Component that uses through holes

Via - Plated hole that connects different layers in a board

Trace/Track - Basically a wire on the board that connects one component to another

Fiducial - Holes used for tracking and picking up the position of the board

Solder mask - Insulating layer that repels solder and protects the board. Commonly green.

Silkscreen - Layer of printed text. Commonly white.