Edge plating - how to draw it? New KiCAD user

[sugarcoated]

Thank you for the thoughts. Yes, it does appear as though the original has been bent around the plate. I don’t know if it was laser cutting, as the switch piece is from the late 1970s. It was likely a special and I don’t know a way to make it apart from manually cutting the contacts and somehow adhering them to the board. It doesn’t sound like edge-plating is the way to make it happen.

I’ve sent an e-mail to PCBWay as I read they have a good UK support service, so perhaps they’ll tell me how it’s prohibitively expensive!

I’ve looked at castellations and they won’t work as they will go straight through the board to the opposite contact. This would be fine for the majority of the contacts that simply wrap right over the top of the board, but the ones that are offset have to have a contact that in some way travels along the edge.

For another switch of the same decade, I manually etched two pieces of copper-clad board, but that one didn’t have contacts that were electrically connected between each side of the board. Attached is a picture of the same failure mode on this other switch that necessitated the repair. The hole at the end holds a crossbar that prevents the switch spring from pulling the contact piece out of the front panel, so it’s under strain whenever the switch is disengaged. It appears this strain causes failure at this point.

The design with the edge plating is subsequent to this nylon example, longer, and appears to be more robust - interestingly, it’s made from two layers of PCB material, like my repair! They must have thought it a good idea too.

[paulvdh]

If it was from the '70ies then etching is more likely.

Etching is a regular process to be used on sheet metal. Lots of nameplates for example are deep etched (or cast instead), then filled with enamel powder and baked in an oven. Etching can also be used for very fine details such as 1000 slots in an encoder disk.

It does not look like it can be made with a “Standard” PCB process. This probably means you have to find a PCB manufacturer that does special jobs, or modify the design so most can be done in a standard process and then modify it yourself to get to a finished product.

A possible way is to design a PCB which is edge plated over the whole side, and then cut slots in them with either a dremel, x-acto knife, a saw or similar to separate the pads, and possibly fill the cuts again with epoxy.

[Aris_Kimi]

My suggestion would be to read carefully manufacturer’s requirements about how your drawings should be.

After some changes that they will probably apply into your uploaded(proper drawed) files, and maybe also some explaining emails with images like the above, you should be able to confirm the result into their 3D viewer.

In some cases it does worth the trouble…

[Meterman2026]

I recently handled a board that was completely plated around the edges except for the breakaways where it was attached to runners during the SMT placement / wave solder phases (RF shielding).

The edges were nowhere near as smooth as would be expected for switch contacts.

I would be inclined to say that the easiest method to make these would be to have the PC boards made with the edge bare, but with vias connecting the sides as needed. Then for the edge itself, have some thin sheet copper laser-cut then bent over a form to get a series of ‘fingers’ and which would then be lap-soldered in place.

[Sprig]

@Meterman2026

Then for the edge itself, have some thin sheet copper laser-cut then bent over a form to get a series of ‘fingers’ and which would then be lap-soldered in place.

This looks to me to be a better solution. The copper alloy/thickness of the material could be selected for the best balance of wear/conductivity/corrosion; something that could not likely be done with edge PCB electroplating.

[paulvdh]

Non-ferrous metal sheets such as copper and brass up to around 0.2mm are relatively easy to cut with a normal pair of scissors.

If you’re curious how well this work, then start with a normal soda can (Aluminimum) which are easily available in supermarkets or just lying around in the street.

Every time my stock runs low I start looking around a bit when cycling into town to grab a few lying around. Avoid the “red bull” cans, they stink enormously, and the smell does not go away easily.

[ZASto]

If you do not have fixed sliders on the narrow edge then your design with vias would be totally OK.
IMHO, you should place vias at the place wheres free of fixed contacts. Gold plating as a must.

[SembazuruCDE]

@Meterman2026

have some thin sheet copper laser-cut

Caution with this. Many laser cutting shops will refuse to cut copper. One vendor that I was in contact with told me that the reason why is their lasers use copper for mirrors (copper is an excellent IR reflector). You would need to find a laser cutting shop that has the correct equipment and processes for cutting copper.

I’m not saying that it is impossible, but the lower cost laser cutting houses might not have the specialized equipment available. Check this link for a white-paper-like explanation of the challenges and techniques to overcome laser cutting copper:

Fiber Laser Cutting vs. Traditional Sheet Metal Cutting

[sugarcoated]

I guess Sprig’s prophecy was innacurate based on the discussion this has caused!

I’ve just had a reply from PCBWay. It was somewhat lacking in English (who uses txt speak when replying to an inquiry?!) but the gist was that they do edge plating and it must be included in the Gerber. So there must be a way to define it.

I’ve looked harder at the switch, and considered the interesting and thoughtful replies in the thread. Yes, it’s likely the original is bent metal rather than plated. Presumably the bending over the top of the switch adds strength.

There are no mechanical contacts with the upper thin surface of the switch - these folds are purely to provide electrical continuity to the other side. However, there are only two that are offset and need special consideration. The rest connect to the contact opposite so could be done with vias, if it’s not too much to place a via on every pad. Not having done a PCB before with one of these services, the whole process of production appears rather magical and crazy.

So that leaves two that could be edge plated (each plating perhaps 5mm long) or linked manually subsequently. My reservation with this is the bulk of the extra material interfering with the sliding of the switch past the contacts.

I’m not too concerned with wear and tear. I can’t imagine a bit of sliding wearing through the contacts in a short time. It’s not like the record switch is in constant use. If it works, the PCB switch version could be replicated easily, and perhaps be made with thicker copper.

I don’t think the cutting out approach will work, simply because of the effort involved in accurately cutting and positioning the conductors. While possible with scissors and time, I am unsure about the adhesive working against the sideways sliding pressure, and about burnishing the edges down so that it slides properly. I’m sure I could do it, but I was hoping for a less labour-intensive method which the PCB houses seemed poised to provide. I have a house to build and about 6" of desk space to do repairs on when I push my keyboard back in my temporary office, and that space is being competed for by about a dozen projects!

However, thank you for all the thoughts. These are really sparking my imagination!

[Sprig]

@sugarcoated

I guess Sprig’s prophecy was innacurate based on the discussion this has caused!

@Sprig

It may be do-able at this point time, but I don’t know how to tell you how to do it.

Unless you meant this one:

@Sprig

You may not get very many replies to your post.

This topic isn’t very common on the forum; which most of the time does not generate many replies; I’m glad to have been wrong!

[paulvdh]

Think about how PCB’s are made.
(Some Youtube vid’s may help, Euro Circuits has some nice video’s)

How double sided PCB’s are made:

• Start with FR4, which is fully plated with thin, copper (typically 17.5um) on both sides.
• All plated holes (and side plating routing is done.
• Inside of the holes are made slightly conductive with some “carbon substance”.
• The whole panel with PCB’s is put into a bath, and with electrolysis copper is added on all conductive surfaces. Top & Bottom is thickended to 35um, all (conductive) holes get approx 17.5um copper.
• The places where copper must stay is covered with some acid resistant “paint”. (This includes the holes and the side plated area’s.)
• The PCB is etched in a bath.
• Etch mask is removed, Solder mask added, etc.

(I have omitted a few steps here, youtube explains it better.

The problem is with your intermittent edge plating. The step of making the sides conductive and adding copper with electrolysis are not selective. They work over all exposed area’s. Your PCB will also be made from a big panel with lot’s of PCB’s in it, and your side plating will be made in a narrow routed slot.
This slot is only accessible from the top side, and a router bit that creates the slot is round. That bit can not reach into the corners between your intermittent edge cut parts.

End result is that even manufacturers who do side-plating will probably not make this PCB for you.

This image comes close. It also has milled out gaps after the side plating. Maybe it is good enough for you.

I found it after a search for:
https://duckduckgo.com/?q=PCB+selective+side+plating&t=h_&ia=web

And the website was:
https://www.multi-circuit-boards.eu/en/pcb-design-aid/drills-throughplating/pcb-sideplating.html

[Meterman2026]

Good to know! Thanks.

There is something I would like to have cut from sheet copper as soon as I can get a proper CAD drawing made, so when I get ‘a round tuit’, I’ll look at having it cut via water jet instead.

[Amit_Bahl]

Edge plating can be achieved by placing the through holes on the edge of the PCB such that the inner wall of the through-hole coincides with the grid line as shown in the images below.


In order to get the flat line in the hole coinciding with the grid, the hole shape should be selected as oval as shown below.

[eelik]

That’s not reliable, I guess the manufacturer will ask about your intention. SMD pads could be used for the same purpose.

[sugarcoated]

Thank you - that is very similar to what I need. I could have the whole edge plated, then file the gaps myself if it’s the intermittency that’s the problem. I can move the relevant contacts back from the edge by whatever distance the copper will overlap, and if the ones already connected with vias are joined it won’t matter, but the offset ones that have to be connected along the edge of the board won’t interfere with their neighbours.

I’ll enquire further with some firms and see what requirements they need. Otherwise, I could do just the normal front and back sides, and manually solder the two extra pieces on.

I can upload the KiCAD file if someone would be able to look it over for me, and say which files need to be together for it to be comprehensible by another computer.

[sugarcoated]

After a recommendation, I have been in contact with Eurocircuits and so far I am extremely impressed. Despite being an inexperienced hobbyist, the UK representative has called me twice to discuss the requirements and offered advice which I am going to spend this weekend working into the board design. It appears basically possible to do this switch using round-edge-plating, but there may be a bit of jiggery-pokery required like drilling on the board edge to separate the contacts. I’ll report back.

I realise it will be significantly more expensive than one of the Chinese firms, but having read their blog post on why the prices are what they are, I agree entirely.

[sugarcoated]

I have been having some really useful feedback from Steve Jones at Eurocircuits, and the specialist who has been investigating ways to help me make this switch as a PCB. I’ve been blown away by the customer service - it’s one of those things that just makes one happy to engage, and it’s been a delight, even as an idiot who doesn’t understand the KiCAD programme and hasn’t any experience with PCB manufacture.

It appears it might be possible to make the switch using vias in the centre of the board, which is a contact dead-zone. The specialist thinks this is easier than edge plating parts of the board, or trying to lap-solder manually after the PCB has been made.

However, it requires re-drawing my KiCAD PCB and I wondered if anyone had any resources that would help me. The specialist’s feedback is:

He should use “pads” and “traces” to make the design.

He does not do so, and now there is no distinction in his design between copper pads, and hence the pads that we can free of soldermask, and traces that connect the pads, which could be covered with soldermask).

Basically customer has made 1 giant customer footprint in his library for the complete slider….with different pin connections:

In the above pic, area marked as 13 is “one complete” pin connection, while in fact it consists of 3 pads, 2 smaller ones and a longer on, connected with traces.

Basically the customer made his pcb design in the footprint editor of Kicad, while he should use the footprint editor to define the “FootPrint”, and then use Kicad itself to make the pcb design, being a connected bunch of components. Where in this case the components are the individual connection pads…

So I would not design the footprints as customer did, I would make 2 SMD footprints in general:

• one for the smaller version of the connection pad à like pad 11 in above pic
• one for the larger version of the connection pad à like pad 9 in above pic

Looking at it further, it is probably ONLY needed to create the Small version of the footprint.

Because I think that the “long” version of the footprint is in fact nothing more then 2 adjacent small footprints, connected with a wide trace.

With these 1 small (or 2?) footprint you can create an – or 1 - SMD component.

And then you add as many as needed of that SMD component to the design.

You then place the SMD components where they are needed on top and bottom,

and you connect them as needed by traces, small and big ones, you can use vias, etc…

To create the copper areas on the left and right of the slider pcb, you can use copper fill, or copper pour.

Of course, if you first draw the schematic – defining the components and their connection between them - then designing the pcb is a piece of cake.

Of course, in this instance there is no schematic as there are no components. I was drawing in a CAD drawing programme as I was following an online tutorial on how to make unusually shaped pads.

[sugarcoated]

I’m back on this and have struggled my way through what could be a suitable PCB method.

I’ve made an SMD footprint from a set of lines, a polygon and a pad, combined to form a new pad. I hadn’t grasped that using the lines and polygon tools like a paintbrush, rather than for creating a single shape with a fill was a valid option. I was struggling to get the curved edges with the polygon, as of course it only does straight lines.

I’ve used the footprint of the smaller of the two contact types, connecting two of them with a wide trace to make the larger ones.

[bson]

Another option, if you actually need an edge contact surface, is wrap a flexible film PCB around a piece of plastic and putting some foam behind the contact edge. Have mechanical holes in the film and plastic holder and fix it with a plastic rivet. See for example this EEVBlog video (HP-41CV teardown, though I think that’s an HP-41CX PCB actually) at 7:10:

EEVblog #582 - HP41CV Calculator Teardown