Building the ELM329 CAN Device - Part I

After a lot of digging I had finally found a supplier for the device enclosure that offered the exact enclosure I had based my design on. They were (of course) in China, but I decided to just go for it, since after doing some research they did appear like an official business. I had placed my order on a Thursday evening, and I had not heard anything by that Monday so I contacted them to see what the status was, fully expecting it would take another week or so before they'd even ship the product etc. To my surprise they did not only provide me with a valid tracking number right away, when checking the number on UPS it showed the package was already in California and making it's way up here so I would receive them the next day! Consider me impressed!

Device Enclosure with USB Cable

Meanwhile I also ordered a handful of the ELM329 chips from ElmElectronics.com. At $21 a piece they're not cheap, but hopefully I can recoup some of the cost by selling a few devices after I've confirmed this design actually works OK etc. (For those of you leaving comments interested in the Eagle files etc - I haven't decided yet if I will - or when, but I may simply sell some ready-built devices on GRRRR8.net or Ebay)

Now it was time to start building the PCBs - I basically watched a bunch of tutorials and figured - how hard can it be? so I dove straight in. First I started with the bottom side of the board. Since I have 2 layer PCB with both the Top AND Bottom populated, I'll have to bake the board twice - once per each side. Based on this I figured I'd do the side with the smallest / lightest components first so that once it comes time for the 2nd bake I wouldn't have the large chip etc hanging upside down and possible re-flowing to the point of falling off. Supposedly the surface tension will hold on any of these components just fine, so that will be an interesting 2nd session.

Usually you want to put your board somewhere solid (desk/workbench/counter) and in a frame so that it doesn't move. Because I didn't bother making a custom frame I used the common trick of making two L-Shapes out of extra PCBs and taping those down to the work area. They are the same thickness so there are no weird bumps when it's time to apply the paste. Next I put a piece of tape on my bottom-side OharaRP Kaplan Stencil and secured it so that it lined up just right, and I could still lift it up on one side.

Frame out of Extra PCBs & Stencilon top of PCB - Ready for the paste!

I had purchased a small jar of Lead-Free solder paste which was thicker than I thought it would be. It roughly had the consistency of grout you use with ceramic tiles etc while I was expecting it to be runnier for some reason (perhaps I had seen too many videos of people using the syringe paste..). Now normally you need some kind of tool to spread the paste on - Some places sell a $50+ specialty solder paste applicator, while others use a $5 homedepot spackle/putty knife. I went super cheap and used an old plastic card much like a credit card. This actually worked beautifully: I scooped some paste out of the jar and basically smeared it over the area. Then I ran the edge of my 'tool'  at a shallow horizontal angle to work the paste into the openings in the stencil. A second run over it, but this time more vertical cleaned 98% of the paste right off the stencil and left the pads nicely coated and I simply scraped the excess back into the little jar.

Paste applied through the stencil

Stencil lifted away showing the gray solder paste on the pads

After this it was time to place the components. For my SWCan ELM327 I had used 1206 components which took some getting used to. This time we were down to 0805 size components - If I had to hand-solder this stuff I would probably stick with 1206, but since all I really had to do was place them on the board for the reflow they weren't that bad to work with at all. I did notice that I probably should've made my silkscreen font a LITTLE bit bigger because at times it was hard to tell what the component was supposed to be.. (Is it R8 or R9??). After some work with the tweezers I ended up with this:

All components placed and ready for baking

Next step was to actually bake the board. I had gotten a small 1000W toaster oven (cheapest I could find) that went up to 450 degrees Fahrenheit. I didn't bother with getting a special controller for reflow profiles etc since these things take a while to heat up anyway. So, Instead I went at it barebones like many others have done. Basically pop in the board, turn on the oven to 400-450 and simply wait for solder to reflow, wait a few seconds, then turn it off and pop open the door to let it cool off.

Baking away

Cookies are done!

The end result looked really good - I would never guess this was done by some amateur in their kitchen vs a professional PCB house. Now the wait is on for the mail to deliver the ELM329 chips so I can try the other side and hopefully not screw up :)