EiED Online>> Fast PCB Prototyping

Feb. 7, 2005
Need fast prototype turnaround? Try building your own printed circuit board. Also, reviews of some embedded books.

It's not often that I see something really new and revolutionary. But that's the reason why I'm writing about the S-Series ProtoMat circuit board plotter from LPKF Laser & Electronics. While it uses plotter technology, the system is really a printed circuit board (PCB) generator that does not employ the chemicals normally associated with PCB creation. Combined with LPKF's ProConduct system for plated-through holes, designers can have prototype boards in one afternoon instead of shipping the design out to a prototype shop.

Most designers currently send work to prototype shops because the process for creating a board is fraught with chemicals and critical steps. Two-day turnaround times are possible with air shipments, and the LPKF solution beats that easily. LPKF's approach is very economical for prototypes and even very small production runs. It is also a good way to provide custom boards.

This is how it works.

Staying Between The Lines The ProtoMat S62 is a self-contained circuit board generator that interfaces to a PC via a USB connection (Fig. 1). It's a desktop unit that is relatively quiet. An internal vacuum system handles dust generated by the system. Overall, it's about as big and innocuous as a heavy-duty laser printer and not much harder to use.

You start by placing a blank circuit board in the ProtoMat S62. Next you import the Gerber files for your board design into the ProtoMat software and let it run.

The S62 grabs the necessary milling tool. The system supports up to ten milling tools at a time (Fig. 2). It then starts grinding away the surface copper. This is the same process used by most milling machines, but the depth is the same across the PCB. The job is only partially done if double-sided or multiple-layer boards are needed. In the former case, the board is manually flipped and the process is repeated. In the latter case, a double-sided board is created for each pair of layers, and then the boards are stacked and pressed together. Holes are drilled, and then it's time to make plated through holes.

Making Plated Through Holes The holes are not plated using the usual messy electroplating method. Instead, LPKF has the ProConduct process. It starts by covering both sides of the board with a removable film and drilling the holes. The board is then placed on a vacuum table and a squeegee is used to push silver polymer paste into the pre-drilled holes (Fig. 3). The board is flipped and the process repeated. Then the film is removed, leaving paste in the holes (Fig. 4). After film removal, the board is placed into an oven for 30 minutes (Fig. 5). The heat converts the paste into solid metal (silver) on the sides of the hole in about half an hour. Resistance is only 20 to 60 mO. Minimum hole size is 0.4 mm.

Time needed for the whole PCB generation process depends upon the size of the board and the complexity of the milling, but an average turnaround time for a double-sided board is a few hours, including plated through holes. That is hard to beat.

The LPKF system is ideal for colleges, prototyping shops and individual companies that do system designs in-house. The latter is the largest market and the target for the S62.

An in-house approach has significant benefits including fast turnaround, keeping a design secure, and providing an atmosphere of experimentation. Why order a dozen prototypes when one or two can be fabricated quickly and tested, and another set created based upon feedback from current testing? A system could be potentially designed in the morning, built over lunch, and tested in the afternoon without even working overtime.

The cost for the S62, including cabinet and tool change, is just under $18,900. A complete milling system based on the S62 with all the bells and whistles, including an automatic fiducial camera and vacuum table, is less that $25,000. That is a lot of prototype boards for a small outfit, and larger companies can afford multiple systems. Prototype PCB houses may also want to check out the S62 to provide even faster turnaround than with chemical-based solutions.

The S62 would be a great product even if PCBs were the only thing it could create. However, it can also do other milling jobs such as creating cases, overlays, and other items that need to be milled, drilled, or etched. It can create solder masks and a host of other items often required for a finished prototype.

This approach to PCB manufacturing will not be applicable to mass production of thousands of boards. The industry has that solution down. Still, for prototypes and small production runs, the S62 is hard to beat.

I recently did an Electronic Design webcast about the system with Jim Greene of LPKF Laser & Electronics. Check it out if you want to hear more about the S62.

The Latest Read I have been looking at a number of books during my travels and finally had some time to write up what I thought. So here they are.

First is a book entitled Wireless Sensor Networks: An Information Processing Approach by Fend Zhao and Leonidas Guibas from Morgan Kaufman Publishers (ISBN 1-55860-914-8). If you want to see what Zigbee and low-cost, low-power micros can do, then check it out. The book is actually very general and addresses things such as infrastructure, tracking of multiple objects, and network databases. It is a good teaching book, although its coverage of real-world examples does not go into details. Still, it's an excellent book to read if you need an overview of this type of technology.

Threadx is a popular embedded real time operating system from Express Logic. The book Real-Time Embedded Multithreading Using ThreadX and ARM by Edward Lamie from CMPBooks (ISBN 1-57820-134-9) provides a good overview of Threadx and a minor overview of ARM processors. There is a single case study about a video/audio/motion (VAM) recording system that builds on the initial presentation. The introduction to an RTOS, more specifically Threadx, is good. However, the accompanying CD does not contain a way to build Threadx applications, making the instruction work best if you have Threadx on-hand. The appendices divide up Threadx application programming interfaces (APIs), definitely making it a handy item for those needing to learn Threadx quickly.

The Embedded FreeBSD Cookbook by Paul Cevoli from Newnes Publications (ISBN 1-5899-5004-6) is an interesting contrast between the basics and nit picking details of how to get FreeBSD running on an embedded system. The CD included with the book contains an eBook version as well as FreeBSD tools. You will likely want to download the latest FreeBSD sources from the Internet if you plan on using FreeBSD on a prototype or production system.

FreeBSD is one of the first open source operating systems, and like most BSD implementations, has played second fiddle to Linux. FreeBSD does have many advantages when it comes to building a compact and secure system.

The book revolves around the digital input-output (DIO) server appliance, a system with a PC architecture and third-party data-acquisition boards. It makes a good case study and it does cover all the bases from using secure shell (SSH) for remote management and debugging to the use of the Tomcat Java web server for delivering of Java server page (JSP) pages.

One of my favorites is the Open-Source Robotics and Process Control Cookbook by Lewin Edwards (ISBN 0-7506-7778-3). It is sort of a case study about the E2, a submarine robot project that Edwards was developing. It uses a Mini-ITX (see EiED Online>> Building A Mini-ITX System, ED Online ID #9327) running Linux along with some microcontrollers for various subsystems. The book provides the overall system architecture and delves into various aspects even to the point of briefly discussing the video-based object detection system. The CD contains source code and schematics, but this is definitely not an E2 How-To, so don't put on your scuba gear yet. It is an interesting look at system design by example and it touches on a number of robotic aspects. Don't pick this up as your first book on robotics, but it is great for roboticists that want some insights into an interesting project.

Finally, some thoughts on another book from Newnes, Programming PIC Microcontrollers With PicBasic by Chuck Hellebuyck (ISBN 1-5899-5001-1). Microchip's 8-bit PIC microcontrollers are popular because of their low power, high performance, and compact size. Hard core developers bang away with assembler while others try to get a C compiler to generate decent code. Micro Engineering Labs' PicBasic compiler provides an alternative that is more friendly to new PIC developers. It also generates code suitable for production work and it's great for quick projects. PicBasic uses the same syntax as PBASIC from Parallax, the originator of the Basic Stamp. The big difference is that the latter runs an interpreter while the PicBasic compiler generates machine code that runs 10 to 15 times faster. It will also handle a wide range of PIC chips and interfaces such as I2C (Pro version). The CD that comes with the book has all the source code examples but no copy of the compiler. That will run you at least $99, although most will opt for the $250 Pro version.

Although some of these books have been around for awhile, their contents are well worth a look if the topic interests you. Let me know if you come across a useful book so we can spread the good word.

Related Links Electronic Design LPKF Laser & Electronics Webcast Archive

Express Logic

LPKF Laser & Electronics

Micro Engineering Labs



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