Surface-Mount Prototyping (AXL 335 & SFH 7050)

Question

I'm working on a senior project and I'm having some trouble prototyping with surface mount components. I know you can find SMT adapters out there for most SMT chips and components, but I've been having some trouble finding adequate ones. Additionally, I'm new to using surface mount technology to begin with so I don't know if I'm even looking for the right things.

Here are datasheets to the two components:

http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL335.pdf

http://www.osram-os.com/Graphics/XPic7/00187722_0.pdf/SFH%207050,%20Lead%20(Pb)%20Free%20Product%20-%20RoHS%20Compliant.pdf

Any help would be appreciated!

Thanks in advance.

Answer 1

Your first go at it should be to try to find these or suitable replacements in an already-mounted format, either in dev boards, or from a prototyping supplier like SparkFun.

Second, you can try to make your own circuit boards. These packages are challenging because it is very, very difficult to just use an iron.

There are two ways you can go on this IMO:

1) Reflow paste. Because these are no-lead packages, you'll need to control the paste thickness carefully, which pretty much means a solder stencil. Once you have the paste down, put your part on, preheat the board to a particular temperature and apply hot air. You can also use the hot-plate method that @Robherc mentions.

2) Try a soldering iron anyway. I noticed that the ADXL doesn't require you to solder down the center pad, so you might be able to get away with extending the footprint pads out a little beyond the recommended pad size, just enough to get an iron and a dob of solder on. This hopefully will wick up into the pad and make contact with the component lead.

3) Give it to a professional rework shop. It's expensive, but you might be able to get the 'student discount' if you are pleasant enough.

Obviously all of these require you to design a custom circuit board, which you may not be able to get away from...

Answer 2

Your first step needs to be looking near the end of the datasheets for "recommended solder pad" designs. Have a good look at the pattern they're showing, paying particular attention to the measurements involved.

From a cursory look-through, it looks like your 2nd component wouldn't be too hard to attach with a regular soldering station with precision tip on the iron. You'd need to pre-tin the pads with solder, but then it could be held in place while melting each solder pool to attach it. This is a method I've personally used with about an 85% "first time go" success rate.

As for your first component, the mfgr wants the central pad on the bottom soldered, so if you can't get that thing in a different package, you'll end up needing to work with a hot plate to melt the solder pools from behind the pcb (reflow soldering) to get a proper connection on that one.

Answer 3

SMT adapters work fine for TQFP, 805 and above, SOT-223, and pretty much anything that has leads and can be picked up with tweezers. The chips you are trying to do have the pads underneath the chip itself and are designed to go through reflow ovens. If you are in a tight spot you could turn the chip upside down and solder magnet wire to the pins but the chip is very small, so you will run into some frustration if you're not adept with a soldering iron (you might end up spending more time assembling a prototype than you anticipated.)

I would recommend designing a PCB in KiCad and ordering PCBs; kiCad will only take a couple days to learn. These are both very small components (one is 4mm) so you are also looking at solder paste and a reflow oven. There are multitudes of assembly/PCB fabs that would etch and place the parts and run a probe test. The time and peace of mind gained is worth it in my opinion. As far as etching this in your garage at home, I wouldn't attempt something like that with parts like these (the pads are underneath the chip and if you get a bridge in the wrong place then you might as well throw away the burned out component.) Your turn around will be 1 to 2 weeks. You don't have to provide the fab with your entire BOM in case you want to do mods or revisions on easier to solder parts (lay out the pcb with test/mod pads and the ability to cut traces if necessary.) Good luck.