Saturday, 1 October 2011

Electronics: Easy SMD Soldering (Surface Mount Devices)

Well the time has come I guess I have to start using SMD components for some of my projects such as the Arduino.

Although I haven’t embraced them fully in to my designs as you can see from the photo above I etched a small board to convert the SOIC footprint to DIP.

Eagle PCB Design files INC PDFs are available in the files section

I have seen various methods of reflow some use ovens,cooker top hotplates and even DIY hot airguns in a similar way to "hot air reworking stations" which is actually the prefered professional way when reflowing or prototyping using a small hot air tip.

I chose the Household Iron Method of reflow which basically involved holding an old iron upside down with the hotplate facing upwards but there are much safer ways!. There are a few things to watch out for here and most of them are to do with safety but as with anything to do with soldering, electrics and molten metal’s common sense will save you ,these are all hazards of DIY electronics so if you are unsure about anything look away now.

Safety First... this is just the obvious stuff.
I take no responsibility if you ruin your Mums, Partners or Wife’s best iron or damage yourself or property do this at your own risk !

If your a young tinkerer ask permission from the old man!

Make sure that there is no water inside the iron beforehand!

Preferable use an old iron that is still in a safe good working order condition!

Make sure nothing is around you work area except the stuff you really need!

Keep the iron turned off at the socket till you ready!

Watch your swivel chair when move around when it spins round it might touch the iron (this one nearly got me)!

As the iron doesn’t like been on its back just like a turtle it will try and right its self burning everything in its path so I used a small vice to hold the iron firmly by its handle while still being able to get to the heat controls.

I placed a small amount of solder paste on each SOIC pad on the board using a paper clip .I then used a pair of tweezers to place the chip evenly on the pads.

Before starting i measured the maximum temperature the iron would reach with my multimeter it turned out to be around 220°C (428°F) solder melts around 185°C (365°F) .A good quick test is to lay some solder in the iron hotplate and wait for it to melt, although the PCB its self will insulate the heat by a small amount so i ended up using the iron on full to get enough heat into the pads to melt the solder paste quickly.

Turn the iron on and not leaving it unattended let it heat up about 1/2 then using some tweezers place the board on the Iron sole plate.If you have enough heat in the PCB the process should only take a few minutes.

Paying close attention to the paste you should see it turn from grey goo to shiny silver at this point check all the pads are shiny leave it 5-10 seconds longer turn the iron off at the socket and using tweezers slide the board off the iron on to a bit of cardboard to cool.

And heres the finished PCB.

If you want to see a reflow in extremely close detail you can watch it here