Every PCB Has Its Place

Everyone has their favorite process for PCB fabrication, as long as you’re a happy hacker I don’t think it really matters. But in this post I thought it might be interesting to describe my personal process, and some of the options available.

Making your own at home

The Dirty Electronics Skull Etching Synth a great looking maskless board.

Etching is the classic PCB fabrication option for the home hacker. It’s been many, many years since I etched a PCBs but it can produce interesting results. Some people don’t like it, and I’d personally tend to avoid it as a messy and finicky process. But, if you only need 1 or 2 layer boards with large features (through-hole components are best of course) it can be a viable option. In some cases, I think etched boards look awesome and are a great fit. One example is the skull etching shown to the right. The oxidation and discoloration of the boards adds to the design aesthetic in this case.

A simple design milled on an Accurate CNC

For those with a bigger budget a professional milling machine might be a viable choice. I’ve used an Accurate CNC in the past (LPKF and others make mills too), but this is an expensive option (no online pricing, but if $10,000 USD is a lot for you don’t bother). The accurate mill is pretty awesome, it can be fitted with a vacuum bed, automatic tool changer and vision system for alignment. The mill can produce high quality two layer boards with all the holes and vias drilled out. The final step of filling the vias is however manual, but compared to etched boards the results are pretty professional (the mill itself uses milled PCBs!). They claim a 0.1mm (4 mil) track size, I’ve never tried tracks this small but surface mount components were not a problem.

While a fun toy, it’s worth considering if you really need a PCB mill. The only case where they’re really valuable is if you want to be able to iterate over a design with less than a days turn around. This can be useful in RF or low noise designs where you might want to experiment with different layouts, but for other projects the price of a good mill can pay for quick turn around (1 or 2 days from order submission to delivery) on a lot of boards.

Commercial Fabrication

Years ago commercial fabrication used to be a very expensive and finicky process. For the most part you’d need to order a full panel putting the service outside of most hobbyists reach. Generating gerbers and drill files to the fabs specification could also be a process fraught with complication.

These days services that aggregate designs onto a single panel and break them out for distribution are common. For my work I mostly stick with OSHPark and SeeedStudio whose services complement each other well. I’ve also used Itead and found them compatible with Seeed (with the added benefit that they supply free boards for open projects).

Using OSHPark gives me the warm fuzzies. A child of the hacker community, born out of DorkbotPDX, all OSHPark’s boards are fabbed in the US (check out the great amphour interview for more details). Their services are limited to either 2 or 4 layer boards (always in purple, and always coated with gold (ENIG)), in 6×6 (6 mil traces with 6 mil spacing) or 5×5. I rarely attempt BGA boards so the 2 layer service works out great for me. OSHPark’s minimum order is 3 boards, which is perfect for prototyping. The gold plating also provides a nice finish, which both protects the board from oxidation and provides a nice surface to solder to. The main reason I use OSHPark however is that they’re cheap for small boards and have a relatively fast turn around (I recently purchased 3 tiny 20x15mm boards for $2.40 including shipping which was unbeatable). From OSHPark in the US to the UK my boards take about 2 weeks to arrive. They’ve also automatically upgrade boards to their super-swift service for free when there’s spare capacity. Their service is pretty slick, and provides a rendering of the gerbers prior to ordering as a final check which comes in very handy.

Zigbee to esp8266 interface fabricated by Seeed (left) and OSHPark (right) (more complex boards here)

Seeed on the other hand are much cheaper for larger size boards and volume orders. They also provide more color and finishing options. The cheapest option at Seeed is green PCBs with HASL finish (hot air solder leveling). From Seeed, my boards usually take about a month to arrive (there are a few delivery options, but in my experience this is about as fast as it gets and faster shipping services often make using Seeed less attractive).

The image to the right shows a couple of very simple boards I had manufactured at both OSHPark and Seeed. I’ve never had a fabrication issues with boards from either service (though I prefer the ENIG finish).

Partly due to the limitations imposed by using commercial fabs I pipeline my projects. I send projects out to fab early in the design process and then switch to another design. When the board comes back I bring it up, bodge as required, and iterate over the layout. This works well with a two-week turn around, so I mostly use OSHPark while prototyping.

My boards also tend to be quite small (Arduino shield size or a little bigger). With small boards like this OSHPark is usually on-par or cheaper than ordering from Seeed (whose minimum quantity is 10 boards). With boards of about 100x100mm or larger I consider Seeed as they become significantly cheaper.

As a hobbyist I also rarely need huge numbers of boards, but for workshops when I need 10 or 20 boards I order from Seeed based on the final iteration of my prototypes. This is not only much cheaper than OSHPark, but I can get boards in a variety of colors to make workshops more interesting too.

This post has described some of the available options and my personal process. I hope it’s been interesting, but I’d love to hear about your favorite fabrication techniques, services and experiences both good and bad too. Please comment below!

DIY Circuit Boards Look Professional

Professional Looking DIY PCB Boards

Making PCBs at home is a great means to get your prototype up and running without having to wait weeks for a professionally made board. Regardless if these prototype boards are milled or etched, they are easily identified as ‘home brew’ due to their ‘unfinished’ appearance. [HomeDIY&Stuff] has put together a little how-to on the process for making DIY PCBs look a little closer to a professionally manufactured board.

The process starts out with designing the board in a PCB program. There are a lot of these programs available. Eagle is a popular choice and has a free version available. Once the layout it finalized, the design is printed out on a transparent sheet of plastic. A blank copper-clad PCB board that already has a UV sensitive coating applied are available for purchase and is what is used in this example. The transparency is placed over the PCB blank and then exposed to UV light. The coating on the PCB cures where ever the UV light passes through the open areas of the transparency.

Once the transparency is removed, there is a noticeable difference in coating color where it has cured. This board is now placed in a developer solution that removes the un-cured UV sensitive coating. A Ferric Chloride acid bath then etches away at the now-exposed copper. The cured coating from the previous step protects the copper at the trace locations during the etch process. The result is a board with copper where you want it and none where you don’t. If the board has any through-hole components, this would be the time to drill those holes.

Up to this point the process has been pretty standard for homemade PCBs and the next part is certainly the most interesting but, unfortunately, is also the worst documented step; the solder mask and silk screening. It appears that two silk screens are produced, one for the solder mask and one for the silk screen. The artwork for making the silk screens can be output from the PCB design software. There is no mention of the solder mask material used but oil-based silk screen ink is specified. Although the details are lacking, the photos show that it works pretty well. If you have had any experience with silk screening DIY PCBs, let us know in the comments.

Exposing PCBs with a home made laser printer

Making your own printed circuit boards – as useful as it is – is a pain. Using the very popular toner transfer method requires a dozen steps that have to go perfectly the first time, and milling boards on a CNC machine creates a lot of mess. The most industrious hackers are able to bodge up a direct-to-board printer from an old inkjet printer, but these builds are usually a little kludgy. [Tixiv]’s LaserExposer board printer is one of the first builds we’ve seen that does away with all the negatives of the other techniques of PCB manufacturing and turns making your own boards into a very, very simple process.

The LaserExposer uses photosensitive copper board, like many of the other PCB printers we’ve seen. Instead of printing out the board artwork to a transparency or mask, [Tixiv] used a 1 Watt 445nm blue laser with a hexagonal mirror to directly expose the artwork onto the board, line by line.

The entire device is built around an old flatbed scanner that slowly crawls over the PCB, exposing the traces of copper to be etched away. This required reverse engineering the mirror motor control board from an 90s-era laser printer and building a circuit to precisely control the timing of the laser. [Tixiv] eventually got everything working and after etching had some of the most professional looking home-brew boards we’ve ever seen.

[Tixiv] put up a demo video of his build (after the break, German audio, YouTube has captions…). Anyone have an old flatbed scanner lying around?

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