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PROTOTYPE PC BOARDS There is an easier way . . . If you’re a small manufacturer, design lab or college without in-house PC board prototyping facilities, who do you turn to? It’s a problem a lot of organisations face – even SILICON CHIP – but there are answers out there . . . C ommercial prototyping services are not new – they’ve been around pretty much since PC boards started being used extensively in, what, the 1960s? By and large, they’ve concentrated on the one-off board as an adjunct to their main game – commercial PC board manufacture. A potted PC board history When PC boards first came out, producing artwork for the pattern was a labour-intensive and exacting process. First of all, the pattern had to be worked out by the designer or engineer, then hand-drawn by a skilled draftsman (yep, very few girls back then) using black ink on either film or paper. I well remember one such draftsman where I worked who had all-but finished such a drawing – a rather large one at that – and then knocked over his bottle of ink (guess where!). A week’s work, literally in the bin . . . Once the drawing was finished, checked and checked again, a photographic negative had to be produced, usually involving a trip to a photo lithographer. Then the board had to be produced using one of several photo-sensitive processes. Later came drafting tapes and pads, which allowed the board pattern to be laid out on film and used directly with positive photo resists. However, track widths (or more specifically track gaps) by Ross had to be kept quite wide so that the siliconchip.com.au photo resists (and production processes) of the day could handle them. Another memory from way back then is the late Ron Bell, founder of RCS Radio (and one of Australia’s early PC board gurus!) complaining bitterly to the project designers at Electronics Australia when we used “25 thou” tapes and spacing instead of his minimum of “35 thou”! “No-one in Australia can produce boards with that spacing,” he said. Imagine how Ron would be today with 5-thou tracks and spacing over multiple layers! PC board PC software It must have been the late 1980s or early 1990s when software for printed circuit board design started appearing (remember Autotrax?) Since then, there have been lots of board layout packages brought out – some excellent, some average and some, well . . . Some were so expensive they were way beyond the home constructor but believe it or not, some were actually freeware or shareware. OK, so you’ve designed your masterpiece on the computer and even had the software check it out to make sure there are no mistakes. Where to from here? As you might imagine, SILICON CHIP faces this dilemma with just about every project we design, as the vast majority are based on PC boards. We’ve been down the path of the Tester D-I-Y prototype PC board – we’ve even May 2008  29 Here’s how you’ll receive your “panel” of PC boards from IMP. There are ten boards on this standard-size (417 x 264mm) panel and we could have squashed another in if required. The boards are all drilled, plated, solder masked and screened with a component overlay on the reverse. Each of the individual PC boards is about 95% cut out but remains secured to the panel as shown above (highlighted by the yellow circle). Even these lands are themselves drilled with a series of small holes to make removal of the board from the panel an easy task . . . published several articles about it. And we’ve achieved some very good results, particularly with today’s photosensitive PC board blanks. For the hobbyist, we stand by everything we said in those articles – it’s still a perfectly viable process. However, we have to say it can also be a messy process, particularly the etching side. One un-noticed splash of etchant on a shirt and it’s off to shirt heaven (or more likely to shirt hell with the expletives undeleted!). What’s more, under- or over-etching is far too easy to do, with shorts between tracks or breaks in tracks too common. Again, they’re easy to miss and Murphy says they’ll only show up when the smoke escapes at first turn-on. We’ve even tried a milling process, where a computercontrolled mill grinds off the unwanted copper and even drills the holes. It works . . . but it takes time. And the mill is not exactly cheap! Speaking of holes, all bar the milled boards must be drilled. If it’s a large, complicated board, that Murphy bloke again says you’re bound to miss one or two and only discover them when a chip won’t fit in! So what we needed was a prototyping service that wasn’t too expensive and provided reasonably quick turnaround. It needed to handle electronic lodgement of computer files. We think we’ve found such a service! In fact, we’ve used it quite a number of times now and cannot fault the end result – except where they tell us that the end result has a fault (more on that in a moment). And lest you think that we at SILICON CHIP get a cut rate for mentioning them, we can assure you that we pay the same rates as everyone else! It’s just that we have found the service so good, we thought we should tell everyone about it! IMP PC offer a range of prototyping services, from a lightning-fast 24 hour priority through to the one we generally use, a 5-day sample and prototype panel service. They’re an RoHS-compliant manufacturer and can offer boards with either leaded or lead-free solder, depending on the customer’s requirements. In fact, they can also offer immersion silver finish and even immersion gold finish. That word “panel” requires a little explanation. It’s not a front or rear panel as we’re used to – rather, it’s a panel of PC boards, as many as will fit on their standard sheets: 417 x 264mm useable area. They also have a large sheet with 493 x 290mm useable area. This gives you a clue to the way they work. Rather than produce just one PC board at a time, they offer the customer the opportunity to have a number made at the one time. They could be duplicates of the one PC board or they could be completely different boards. We generally get two boards of each board made – just in case – and then fill the panel with other project prototype boards or even get some boards made that we need. The boards that come back to us come still attached to the panel – but cutting them out is very easy (most of the board edge is cut – or more accurately, it’s milled – but just a few “bridges” of blank [etched] fibreglass hold the board on the panel. See the photo series above. Enter the Gladiators . . . It’s called IMP Printed Circuits Pty Ltd, a member of the Codan Group and is based in Cavan, a northern suburb of Adelaide, SA. These days, with high-speed broadband and fast courier services, that’s as close as the office next door! With more than 40 years experience in the PC game (the company was established in 1964), they’re now recognised as one of the leaders in the industry. 30  Silicon Chip This board has a flaw (in this case a broken track) – so when IMP send it to the client, it has a highlight – a huge arrow marking the spot. As it is a prototype, such imperfections are easily cured! siliconchip.com.au . . . and this is how it’s done. The long hair and hand belong to SILICON CHIP’s Mauro Grassi, who is shown here removing one of the individual PC boards by cutting through the land with a hacksaw blade. As we said before, this already has a series of holes drilled to mke it easy. You don’t even have to cut through all four sides to remove the board. We normally find cutting through two sides is enough; a bit of thumb-power is all that’s needed to break it free. The slightly rough edges are very easy to clean up with a file. The boards are not simply etched – they are drilled, plated, solder-masked and a component overlay is silkscreened on the reverse side. In other words, they’re complete ready to use once removed from the panel. do this to establish an account or arrange credit card payment for your first order How many boards? How long is a piece of string? It all depends on the size of the individual boards. They’re fitted onto the panel for minimum wastage allowing, of course, for a small space between each board. The accompanying photo of a recent panel we had made give you a good idea. How many layers? IMP PC’s sample and prototype service can produce any board from single sided and double sided right through to eight layers. Naturally, as the number of layers goes up, so do the prices. Yield We hinted before that PC board production is not an exact science. It’s pretty good, but with the thin tracks used on today’s boards, there will be times when the boards aren’t absolutely 100% perfect. We’ve only struck this once or twice but it so happened that one of the boards we recently received had a flaw in it. It’s not like the days of yore when you had to go over your own produced board with a magnifying glass – IMP PC do it for you. If they find anything wrong, they highlight it with a big yellow arrow. You might wonder why they don’t redo the panel if it has errors: surely you want your PC boards perfect. Remember, we are talking prototype boards and it is highly likely that there will need to be mods anyway, so a repaired track is not a significant problem. However, they will redo the panel if it doesn’t achieve their pre-agreed yield standard. Lodging board patterns Like most PC board houses, IMP PC work from Protel PC board files which are electronically submitted. They do have their own specific requirements for lodgement so it’s worth a look at their website (or call them) before you send in your first batch. In fact, you’ll need to siliconchip.com.au How much? The standard prototyping service, with 5-day turnaround, costs $285 for the standard sheet and $335 for the large sheet (for a single-sided board). OK, at first glance this sounds expensive but look at what you get: while they’re called “prototype” boards, they’re every bit as good as the production boards IMP PC will also be glad to talk to you about! (IMP PC also work with several quality overseas suppliers who can produce volume boards at the right price). Even if that was for just one board, that’s chicken feed for most companies – they would have spent many, many thousands of dollars developing the project and probably paid several thousand dollars for their PC board software to boot (you like that pun?). What’s more, have a look at the photo of the panel of boards above that we had made recently. Count ’em – there are ten reasonable-size boards on that panel with space for at least one more. $335 divided by 11 is just over $30 per board. So cost really isn’t an issue. Time (5 working days) shouldn’t be an issue with the right planning – and if a board really is required urgently IMP PC offer a 24-hour service. Yes, you’ll have to pay extra for that – but if it really is that urgent . . . With the “rush” service, if the PC board file is received prior to 10AM, the finished panel will be despatched from the factory by midday next day. Incidentally, if you want extra panels produced at the same time as your first, they will cost $75 for the standard panel and $95 for the large. And if you need more advanced boards, IMP PC can handle just about any requirements. They have a freecall number in both Australia (1800 888 543) and New Zealand (0800 441 500) for technical enquiries. SC For more information, contact IMP Printed Circuits Pty Ltd, 6CB Fisher Drive, Cavan SA 5094 Tel: (08) 8262 1444 Fax: (08) 8262 2044 Website: imppc.com.au May 2008  31