The general process of circuit board assembly goes like this: You order your PCBs. You also order your components. For surface mount components, you apply solder paste to the pads, put the components on top, and then heat the board up so the solder paste flows and makes a bond. Then for through hole components you put the leads through the holes, and solder them with an iron or a solder wave or dip. Then you do an inspection for defects, program any microcontrollers, and finally test the completed board to make sure everything runs.
The tricky part is in volumes. If you’re only doing a few boards, it’s usually easiest to assemble them by hand. In the thousands you usually outsource. But new tools, and cheap hacked tools, have made it easier to automate small batches, and scale up into the thousands before outsourcing assembly.
In this new series which we’re calling Tools of the Trade we’ll be covering a variety of tools used for building products, and we’re starting with circuit board assembly. Let’s investigate our tools of the trade: solder paste dispensing. Continue reading “Tools of the Trade – Solder Paste Dispensing”
There’s a lot of little things that can go wrong before you get great results out of a process. We like to read build logs to learn from the mistakes made. [Marc Liyanage] bought a Nomad CNC machine from Carbide3d, and after a bit of learning has gotten some very nice PCBs out of it.
The first trip up he encountered was not setting the design rules in EagleCAD to check for gaps too small for his router bit. After he sorted that, and worked around an issue with Carbide not supporting R values for curves; instead opting for IJK, he made a nice TQFP to DIP break out board.
The next board was a more complicated double-sided job. He cleverly had the machine drill two holes all the way through the PCB to give him a space for two alignment pins. Unfortunately this didn’t work out exactly as planned and he had a slight misalignment with some of the via holes. It looked alright and he began assembling. To his dismay, the clearances were off again. It was a bit of deja vu for us.
We’ve made lots of boards on a CNC machine, and can attest to the task’s finicky nature. It’s certainly quicker than the photoresist technique for boards with lots of little holes. It will take someone quite a few tries before they start having more successes than failures, but it’s very rewarding.
Over the last few years we’ve seen a few commercial products that aim to put an entire PCB fab line on a desktop. As audacious as that sounds, there were a few booths showing off just that at CES last week, with one getting a $50k check from some blog. [Connor] and [Feiran] decided to do the hacker version of a PCB printer: an old HP plotter converted to modern hardware with a web interface with a conductive ink pen.
The plotter in question is a 1983 HP HIPLOT DMP-29 that was, like all old HP gear, a masterpiece of science and engineering. These electronics were discarded (preserved may be a better word) and replaced with modern hardware. The old servo motors ran at about 1.5A each, and a standard H-Bridge chip and beefy lab power supply these motors were the only part of the original plotter that were reused. For accurate positioning, a few 10-turn pots were duct taped to the motor shafts and fed into the ATMega1284p used for controlling the whole thing.
The final iteration of hardware wasn’t exactly what [Connor] and [Feiran] had in mind, but that’s mostly an issue with the terrible conductivity of the conductive ink. They’ve tried to fix this by running the pen over each line five times, but that introduces some backlash. This is the final project for an electrical engineering class, so we’re going to say that’s alright.
Continue reading “Circuit Plotting With An HP Plotter”
A common way to create a custom PCB at home is to do what is called the Toner Transfer Method. In this process, the trace layout of the board is printed out on a piece of special toner transfer paper that allows the ink to come off in the following step. The toner transfer paper is then put print-side-down on a copper clad PCB blank, heated and pressed with an iron. The heat and pressure from the iron transfers the toner from the paper to the copper. The exposed copper then is chemically removed, the previously applied toner protects the copper in the pad and trace areas. The toner is then removed using paint thinner.
That is a long process with many critical steps. [mlerman] wondered why no one was printing the toner directly to the PCB. He has been tinkering with printing directly on PCB blanks for 4 years now. He’s made hundreds of boards over that time and can now make a PCB in under 15 minutes.
The obvious route to take would be to modify a current laser printer to accept the much-thicker-than-paper PCB boards. A few printer models were tried but [mlerman] feels the Lexmark E260 works the best due to the cost, internal mechanical components and an easily modifiable manual feed system. There is also a Local Printer Utility that allows the majority of the printer parameters to be adjusted.
Continue reading “PCB Toner Transfer Method, Now Without The Transfer”
After making your first PCB, you’re immediately faced with your next challenge – drilling the holes. It’s a doable task with a small drill press, but a lot of makers already have a small CNC mill or router, but how to make that work the first time? [Alessio] has you covered with a technique that uses a CNC-mounted webcam and some linear algebra for perfect through-holes the first time and every time.
A few months ago we saw [Alessio]’s work with transform matrices and PCB drills. The reasoning behind this technique is if a PCB isn’t exactly aligned to a CNC mill’s axes, or if the scaling for a toner transfer board is a bit off, automating the drilling process will only end in pain, with holes going through traces and a whole host of other nasty things. The application of linear algebra gets around this problem – taking a measurement off of two or three known locations, it’s easy to program a CNC machine to drill exactly where it’s supposed to.
[Alessio]’s new project takes the same mathematical techniques and applies them to a very sleek application that uses a drill-mounted webcam. After taping his homebrew PCB down to the mill, [Alessio] simply marks off a few known points, imports the drill file, and lets a computer calculate where to drill the holes. The results are remarkable – with a soldermask and silkscreen equipment, these handmade boards can be just as good as professionally manufactured boards,
There are Windows and OS X binaries for [Alessio]’s tool available on his page, with a video demo available below.
Continue reading “Drilling PCBs with cameras and math”
PC board houses are getting more accessable and less expensive all the time. Some of us are even getting very, very good at making our own circuit boards at home. There are times, though, when a project or prototype requires an extremely cheap custom board right now, something etching a custom board won’t allow. [KopfKopfKopfAffe] has a unique solution to this problem, able to create custom boards in under an hour without any nasty chemicals.
Instead of starting his build with copper-clad board, [KopfAffe] used every rapid prototyper’s friend, simple one-sided perf board. The shape of the board was milled out on a CNC machine, and both the top silk screen and bottom layer were marked off using the toner transfer method. After that, a custom circuit is just a matter of placing components and putting solder bridges between all the marked pads.
[KopfAffe] is only using this technique for single-sided boards, but we don’t see any reason why it couldn’t be employed for simple double-sided boards. This would still have the problem of making vias between the layers, but that’s still a problem with proper, home-etched double sided boards.
[Christian Aurich] wanted to use his Eagle CAD circuit board design in a proper CAD program in order to design enclosures. There are already a few options along these lines, but they didn’t quite fit his needs so he developed a script to import Eagle boards into FreeCAD. The script is packaged as a python macro for FreeCAD.
In describing the shortcomings of what’s already out there [Christian] does mention the use of EagleUp to model boards in Google SketchUp. But he feels the way the data is produced by SketchUp makes these models work well with 3D printing, but says they’re not easy to use with mechanical design CAD software. He also feels that the photo-realistic renderings are useless when developing enclosures.
It’s worth mentioning that this approach is only possible because CadSoft’s migration to XML makes it dead simple to get at the data.