Eurocircuits offer two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.
We plate the hard gold onto the PCBs after the soldermask process and before we apply the surface finish to the rest of the board. Hard-gold plating is compatible with all the other surface finishes we offer.
We first plate 3 – 6 microns of nickel onto the edge connector fingers and then on top of that 1 – 2 microns of hard gold. The plated gold is not 100% pure; it contains some cobalt to increase the wear-resistance of the surface.
We normally bevel the edge connectors to ensure easy insertion. Bevelling can be specified in the order details.
To make sure that the gold fingers align exactly with the edge-connector profile, we rout the vertical edges of the connector on the first drill run. The edges of the connector are then exactly aligned to the printed image.
In some cases one or more gold fingers are shorter than the rest, so that the longer pads connect first when the PCB inserted into the connector. This means that the shorter pads cannot be connected vertically to the plating bar. They have to make the connection needed for electroplating in another direction (see illustration. Here the blue lines represent the profile added at first drill stage and the green the final profiling).
After plating we check the adhesion of the plated nickel and gold with an industry-standard tape-test. We measure the thickness of the plated layers with a non-destructive X-ray measuring machine.
Limitations of the technology
The plated pads have to be on the edge of the PCB, as this is an electroplating process. There has to be an electrical connection between the plated pads and the production panel frame.
The maximum length of the plated pads is 40 mm as we use a standard shallow plating bath .
Inner layers have to be free of copper at the edge of PCB. Otherwise the bevelling could expose the copper.
If you want your PCBs delivered in a customer panel, the panel frame/border must be open on the edge connector side to allow us to make the connection for electroplating.
We can plate hard gold on two sides of PCB. But if the connectors are on the opposite sides of the PCB there has to be a minimum 150 mm between them.
To ensure optimum quality surface-finish, do not place any plated holes (PTH), SMD or other pads closer than 2.00 mm (80 mil) to the gold fingers – see drawing.