Wednesday, January 7, 2015

Soldering the micro-USB

The previous post raised some questions about how difficult it is to deal with the micro-USB connector.  The connector in question is an FCI 10103593, a devilishly tiny little thing but really, not all that hard to deal with.

Top view of the connector

Bottom view of the connector
The pads on the PCB in question are only complete for the power and ground pins

PCB pad

Before starting, it can be helpful to bend the required pins down a little, and the unnecessary pins up and out of the way
Bent pins

The first step is to tack down one corner with the pins properly aligned.  
Step 1

Then, you can take a close look with a magnifying glass and verify that the pins are aligned.  With only one corner tacked down it is easy to re-heat the pad and re-position the jack.

Once you are comfortable that the pins are properly aligned, tack down the other three corners so the part is now secure.
Step 2
Finally, heat the Vdd pad and flow a little solder onto the pad.  Wait a bit with heat on the pad and the pin will heat up and wick the solder onto the pin. 
Step 3
If you should get a little heavy on the solder, desoldering braid is a wonderful thing!

Tuesday, January 6, 2015

A PIC Development Helper

When I first got into playing with PICs, my programmers were all homebrew, mostly based on the Tait family.  For years I used the NoPPP (no-Parts PIC Programmer).  It worked fine for small PICs, and back in the day, real serial ports were ubiquitous.

When I discovered in-circuit programming, I went through various "standards" for connecting my target to the programmer, none especially satisfying.  When I got an ICD2, I was impressed with the convenience of the RJ12 connection, both to the project and to the programmer.  The problem is, the RJ12 is very unfriendly when you are working on a perfboard or a solderless breadboard.

Now the nice thing about the RJ12 approach is that it is pretty simple to make up a cable, but the project end can be a problem, especially for solderless breadboards.  Often you end up with a mess like this.

At some point I got an ICD2-LE, which is basically an ICD2 in a PICkit package.  It turns out that the PICkit style connector is pretty convenient for perfboards, but doesn't help a lot for solderless breadboards.
It is convenient, but I still lusted after a way to conveniently use the RJ12.  I also like cell phone chargers as power supplies for PIC projects.  They are adequate to power most projects, and can be had for around three bucks on Amazon.  But the teeny micro-USB connector is tough enough on a printed circuit board, maddening on a perfboard.  Still, many of my perfboards have micro-USB connectors in spite of the soldering frustration.

For some time I envisioned a small PCB with an RJ12, micro-USB and PICkit connector that I could easily attach to a perfboard or solderless breadboard.  I even laid out a PCB design.
PCBs tend to be expensive for the first one, though, and I don't see myself as going into the board selling business, so that sat on the shelf for years.

Recently, a hero on the PIClist posted a link to PCBshopper, a site that takes your board specs and gives you prices from dozens of suppliers.  At the time I was getting ready to have a PCB made (my first) for a graphics TFT project.  I sent out that design (still debugging it) to Accutrace, who in very short order made me 10 beautiful boards for quite a reasonable price.

Another supplier, Maker Studio, had very good prices but not so great shipping times.  It hit me that perhaps that was the way to make my little programming/power adapter board.

In studying that, tho, I learned something very significant.  Tiny, tiny changes can have a huge impact on the price.  My TFT board was 4"x3", a size that many suppliers will make at a reasonable price.  Maker Studio will make boards up to 10x10cm dirt cheap.  4 inches is a hair over 10cm, so for a 4" board, their price wasn't any better than Accutrace but their delivery was three weeks instead of 8 days, so they fell off the radar.

Anyway, it hit me that I could do 5 of my little adapter boards within the 10x10cm outline, so I laid out an array of boards:

I knew most suppliers had an upcharge for panelized boards, even if they are not going to shear them.  But it wasn't clear from Maker Studio's web site just how that would work, so I sent in the gerbers with no explanation.

China, of course, is about as far away in time zones as you can get, so a day later they emailed me that they needed more money, so I emailed back that their price was acceptable, then next day they said they would create a product that I could pay against, eventually it was probably 5 or 6 days before everything was all settled.  I was quite surprised when, 20 days after the original order, in spite of all the delays, a package of 10 boards arrived from China.  (Their expected delivery was 20 days).  And this was right before Christmas when I suspect the mails aren't especially fast.

I got another surprise.  The USB connector is designed to mount on the rear of the board, and I had forgotten to remove the bottom silk from the zip file of gerbers.  But the outline of the USB connector was screened on the bottom of the board!  I don't know if they always do the bottom silk, most suppliers charge extra for that, sometimes a lot.  Or maybe the upcharge for a paneled board included it, but basically I got 50 of my little adapter boards for less than 50 cents each.  OK, I gotta shear them, but since I have a shear I use for making cases, that's no big deal.

The populated board looks a little odd, but works as intended
Probably the PICkit connector was overkill, and if I had to do it again I would put the RJ12 in the middle so I could shear off the PICkit if I wanted.  I designed the foil so I could shear off the USB in case all I wanted was power.
This is nice on a perfboard, but really nice on a solderless breadboard

And the power-only thing works on a solderless breadboard, too

Comparing the two vendors, I have the feeling that the Accutrace board is a little higher quality, but that may be simply because I paid more.

Both boards are heavy, rigid boards, both have thick copper and masks that seem impervious to abuse with a soldering iron, both have nice, crisp screening.  The Accutrace boards have slightly rounded corners while the Maker Studio boards have sharp corners.  The Accutrace solder mask seems a little less opaque, but that could just be the color.

Given how painless and cheap the process was, I will probably make more boards in the future.  I tend to be impatient, so I might lean towards Accutrace, but on the other hand, I'm cheap, and $15 for 10 PCBs seems like a bargain.