MightyOhm

Soldering surface mount (SMT) components is tricky, particularly if you can’t see what you are doing due to the small scale of most SMT parts.  Since I started working with SMTs at home I have suffered with a 10x magnifier ring-light.  It works, but it’s tricky to use, mainly because the working distance is so small that getting a soldering iron on a part and keeping that part in focus are almost mutually exclusive.

The right tool for this job is a stereo microscope.  Stereo microscopes use two separate optical paths to provide you with depth perception, very helpful for working with 3-dimensional objects like printed circuit boards.  Even better is a stereo zoom microscope, where the magnification factor can be changed by turning a knob instead of swapping out lenses.

Until now I assumed that a stereo zoom microscope would be way out of my price range, at least several hundred or a thousand dollars for a very basic setup.  However, some searching on eBay showed that good deals can be had, and a used microscope with a boom stand suitable for surface mount work can be found for as little as $200-$300.  New microscopes are available for $400-$500, although there is some debate regarding the quality of low-cost imported microscopes.  Caveat emptor.

For surface mount soldering, 7-30x magnification is reasonable (that’s 10x eyepieces * a 0.7-3x objective), and a 4″ or greater working distance makes using tools under the microscope a lot easier.

I ended up buying an American Optical (AO) model 569 with an illuminator and boom stand, shown below.  Total cost was just over $200 with shipping.

Combined with the PID controlled hotplate I just put together this is a very powerful setup for doing rework of very tiny components – I could probably work with 0402′s, maybe even 0201′s if I was careful.  Using this setup, 0805′s are easy. (and they look huge!)

The scope is very old, it was made in the late 1970s, but it has survived in extremely good condition.  Upon receiving it, I tightened some setscrews and regreased the slides and it’s as good as new, despite being over 30 years old!

There are a few more photos of the microscope setup on flickr.

The image quality is excellent.  Here are a couple pictures of my SYBA USB-Audio Adapter taken with the microscope and my Sony DSC-V1 digital camera.  I held the camera up to one eyepiece, set it into macro mode, and snapped the shutter – these images are straight off the camera with no retouching.

Click to enlarge.

When you finish a PCB design, you typically use the CAM export function of your layout tool to generate a set of gerber files to send to the PCB manufacturer.  To avoid errors in the finished board, it’s usually a good idea to review the files before you click send.

Enter gerbv, a free, open source gerber viewer that is available for many platforms, including Debian and OS X (via fink).

I recently upgraded to version 2.0 (I was using the really outdated version 1.0 on Macports) and I am really impressed by the improvements in the GUI and overall usability.

gerbv is a part of the gEDA suite, which also includes layout and schematic capture tools that are slowly becoming more popular vs. more established non-free tools like Eagle.

Update: I missed an interesting update to a post over on My 2uf, not everyone seems to like the rest of the gEDA suite.

gerbv screenshot

AVR HV Programmer Shield PCB Layout

What’s this???

In response to the continued demand for a PCB version of my Arduino-based AVR High Voltage Programmer, I just released a first cut to BatchPCB and should have a prototype within 3-4 weeks.

This design is an improvement upon the original HV programmer shield in the following areas:

• Onboard 12V boost converter eliminates the need for an external 12V power supply
• Support for two of the most common families of AVR microcontrollers, the ATmega48/88/168 and ATtiny2313
• Separate Ready and Burn indicators
• Protection resistors on every single data, control, and supply line to the target AVR, meaning that your Arduino and AVR should survive any mishaps during programming, including inserting the AVR backwards or off by 1 pin.

I hope to have kits for sale in early February.  Sorry for the delay in getting these made, but I wanted to make the best possible shield I could!

Let’s say you are designing a printed circuit board in Eagle, and you need to place a component that you’ve never used before.  In Eagle, before you can use a new component, you need a land pattern, a schematic symbol, and a mapping between them to fully define the part.  Often, you can search through Eagle’s included libraries and find what you need (or something close enough).  But what if that fails?

The symbol and pin definitions are usually pretty easy – just copy the datasheet.  The hard part is the land pattern: the collection of copper traces, soldermask openings, silkscreen, and other features that define the part on the PCB.

To come up with a land pattern, you usually have a few options:

1. Someone else may have done you a big favor by creating a part definition and uploading it to the Eagle library directory.  Caveat: Use it at your own risk.  Surface mount parts tend to be particularly hard to use right out of the box – often someone else’s land pattern won’t even pass your DRC.  Whose process were they using, anyway??
2. Look through the datasheet for the part to try and find a recommended land pattern. (Good luck!  Increasingly these are not included, but may be somewhere else on the manufacturer’s website.  Google is your friend!)
3. Take a guess based on the geometry of the part, assuming you have a mechanical drawing or a physical sample somewhere.
4. Skip 1-3 and use an IPC-7351 land pattern generator.

IPC-7351 is a standard for printed circuit board land pattern designs.  The standard attempts to, well, standardize land patterns to try to discourage every PCB designer from having his or her own custom library of land patterns.  IPC takes known good land patterns and combines them with accepted manufacturing tolerances to produce a land pattern that will work for most people most of the time.  Increasingly you will see references to IPC-7351 in datasheets instead of a land pattern drawing, so access to the standard is becoming more important over time.

Cool, right?  Well, the bad news is that while you can browse through the table of contents/introducton for free, downloading the standard costs big bucks.

Fortunately, PCB Matrix has a free IPC-7351 Land Pattern Calculator (direct download link here) that you can use to generate land patterns based on the standard.  You don’t need to own a copy of the standard to benefit from it.

The calculator is somewhat tricky to use but if you click the right buttons you can get something like what is shown below (click to enlarge).

PCB Matrix IPC-7351 Land Pattern Calculator Screenshot

X and Y are the dimensions of the recommended pads for an 8-lead Thin SOT-23, which happens to be the package for the LT3464.

With this information, you can return to Eagle and create a land pattern for your device.  PCB Matrix will also sell you premade Eagle libraries, but from their site it was not clear how much they cost.  Based on their other products, my guess is several hundred dollars and a yearly maintenance contract – I’ll draw my own, thanks.

Unfortunately, the calculator is Windows only, so Mac guys like me need to use VMware Fusion or similar to use it.  Can someone create a web version, please?

I am using this tiny USB-audio adapter as part of my Wifi Radio project.  It’s a ridiculously cheap $8 at Newegg.com and contains a C-Media CM119 chip targeted at VoIP applications.  I have no idea why they chose to use a VoIP chip for this application because it contains a lot of bells and whistles that are not being used in this device, such as support for a matrix keypad!

Unfortunately, I have not been able to locate a datasheet for the CM119 so for now I will be using it only for it’s intended application – adding an audio output to a wireless router with USB.  Come to think of it, that is probably not it’s intended application, but it’s close enough.  Hooray for embedded Linux!