# Soldering a SMD sensor - options without etching PCB?

I would like to break out this sensor. I don't have the equipment to design and etch my own PCB.

Do most sensors come in standard dimensions, such that a pre-made break out PCB could be obtained? How would I go about finding such a break out PCB?

The dimensions are listed in the datasheet (below), as well as a notation of 5-SMD, but I haven't been able to find an appropriate board.

Am I approaching this wrong? It has no leads, but I assume the solder will flow under the pads just fine.

Thanks.

Update: I ended up doing both - the spacings were compatible with standard protoboard so initially I soldered to that. But ultimately I learned to use Eagle and got a board fabricated for about 20 bucks. Definitely recommended.

• Is there anything the prevents you from laying out the PCB, and having the outside PCB fab make the PCB for you? – Nick Alexeev Feb 5 '17 at 19:58
• Solder 30AWG wire to the pads and glue it upside down to something solid. – Daniel Feb 5 '17 at 19:59
• @NickAlexeev Only my lack of experience and time. Is this how you would do a one-time PCB layout? – nate Feb 5 '17 at 20:14
• @nate: It's a skill that can be learned like any other. While it isn't free, I've found i spend way less time having a board fabbed than fooling around trying to make alternatives work. – whatsisname Feb 6 '17 at 3:23
• If you have time, I would suggest laying out a pcb and have it professionally manufactured. It's a good skill to know, and pcb manufacturing can now be had really cheap! Oshpark.com, for example, charges $5 per square inch for a high quality board, and you get three copies of the board for that price. And free shipping :) Although it will take a few weeks to get them made. In your case, you could easily fit the IC and breakout headers on a 1x1" board. 3 boards for$5; that's less expensive than prototyping material. – bitsmack Feb 6 '17 at 5:11

Given the 0.1" multiple spacing, you could quite simply solder it to some veroboard/busboard (stripboard).

To do this you could place it against the solder side of the board, making sure to cut gaps in the strips below the IC, and then solder to the strips. This shouldn't be too difficult as from the images in the datasheet it appears that the pads extend up the sides of the IC.

Alternatively, you could place it on the component side of the board. For this you would need to solder short lengths of wire between the pads on the IC and through the holes in the veroboard.

As a side note it is worth taking care in how you place the sensor. Given that it is an accelerometer, placing it as square and parallel with the surface as possible is advised as it will make it easier to work out how X/Y/Z relate to the board.

When I am desperate, I take an Xacto knife to a sheet of blank circuit board and cut as needed to give me a pattern where I can solder the device. Or, this sensor might sit on a pre-etched perfboard having 0.1" solder pads. Solder wires to the pads after you solder the sensor to the pads.

• ...you don't even have to be desperate. It's a valid quick proto-typing technique. This particular item has the relative joy of really comfortably wide spacing at 0.200 inches, so it should be a piece of cake. – Ecnerwal Feb 5 '17 at 20:16
• I'm "desperate" so these are good ideas. Could you elaborate a bit more on the Xacto solution. I'm reading: metal free, hole free PCB, which I cut grooves into and then flow solder along? – nate Feb 5 '17 at 20:17
• @nate He's talking about copper-clad board - so it's a continuous layer of copper on fibreglass. You cut through the copper with a knife/Dremel to make the gaps between the 'tracks' which are formed by the remaining copper. – user1844 Feb 5 '17 at 20:36
• One more: use permanent marker or nail polish or model paint to draw resist patterns on raw clad PCB. Use Ferric Chloride or Ammonium Perchlorate or some other etchant to etch away the unprotected copper. There may be more benign etchants available now, I haven't done this in decades! – Paul Elliott Feb 5 '17 at 21:37
• For sure! The speed and low cost of on-line PCB fab houses is pretty amazing. I use them for surface-mount as well as through-hole designs. Email them your CAD files and get back some boards in a few days. – Paul Elliott Feb 6 '17 at 4:30

Here is an example of the "cut islands in all-copper PCB and solder on" method (it's not beautiful.)

This one also has a recommended capacitor installed, so the "ground" island makes an L under the device to permit the capacitor (small brown item on bottom edge) to be installed as near the device as practical.

• It is, apart from the molten-back wire insulation. – rackandboneman Feb 6 '17 at 15:10

This sensor is a DFN (dual flat no-lead). Pads are on bottom, and it seems there are also dimples on the sides that are tin-plated and connected to the pads.

Check out SparkFun or AdaFruit, they may have the breakout board with correct pad pitch. The sensor has pads at 200mil apart so 50-mil breakout board for SOIC chips should line up with pads quite well. The challenge would be to find a proto board with correct spacing between rows.

If you don't have a prototyping board with pads at right spaces, the easiest is to 'dead-bug' the sensor. The sensor is not a humidity sensor so it does not need fresh air and turning it upside down will only invert some motion axis.

Another thing you can try is to use a through-hole board, put 18-24 AWG solid wires like staples through the board in right places to match the pads, and then solder the sensor pads to these wires. Wires will lift the chip up from the surface of the board so you can put solder under the chip with sharp soldering iron tip. Surface tension will pull the solder between pads and wires, and the gap between pads is wide enough so you don't have to worry about shorting anything. If the dimples are plated, you can also use them to test continuity when soldering the wires.

Just glue the sensor upside down to something flat and solder thin wires to the pads. I’ve done it even for more complex parts like this tiny bluetooth module (a PAN1326 with 0.6mm pads):

Unfortunately I don’t have a picture of the finished solder job but you wouldn’t see much because it’s covered in hot glue.