In my previous post I wrote about the QRP-Labs QCX-mini amateur radio kit which only has through-the-hole components to be soldered by the enthusiast but had problems with some of the surface mounted op-amps and my desire to learn how to remove those surface mounted devices (SMD) and install new ones. To learn how to do that I bought a handful of kits to practice on.
First up is the Gikfun DIY SMD SMT Welding Practice Soldering Skill Training Board Ek7028 which was a pretty great kit to assemble, when finished it isn’t much to share as it just blinks some lights in the middle of the circuit board, but it comes with 124 LEDs, capacitors, and resistors and 2 ICs to solder to the board. I even practiced correcting “tombstoning” and removing then replacing components. The 1206 and 805 sized components were pretty easy, I did those with my Hakko 888 fine tipped soldering iron, but the 603 and 402 components I used the hot-air rework station.
The Gikfun kit was a challenge but it also gave me a lot of confidence to get the fancier SMD kits assembled.
I purchased 2 kits from Evil Mad Scientist, The 555SE Discrete 555 Timer and The 741SE Discrete 741 Op-Amp which when finished make great desk toys/conversation starters and can even be used to make working circuits.
I actually assembled the 555 Timer first, I followed the provided instructions by installing components as they were stored in their packaging a few at a time. I applied a dab of Chip Quik SMD291AX REWORK SOLDER PASTE 5CC 63/37 NO CLEAN SOLDER on each pad and then used the hot-air rework station to melt the solder. It worked really well and by the end of the kit I was full of confidence.
At the top of the page is the completed Op-Amp and below you can follow along with the steps I used to assemble it. Unlike with the 555 Timer I applied paste to the entire board by hand, a solder mask is not supplied with the kit.
Then I placed each component. The solder paste did a decent job holding the components in place, I developed a rhythm of getting the component onto the board with a bit of it stuck in the paste then maneuvering it into its correct position followed by a tap on the top to set it down into the paste.
And finally, I moved the hot-air rework station’s wand across the entire board moving quickly at first to warm up the entire board then more slowly and finally concentrating on each component until the solder flowed.
The finished kit puts a big smile on my face, I am very excited to do more SMD kits.
The only thing that bothers me about using the hot-air rework station and soldering paste is that the soldering paste has an expiration date. I have been told that it is good for about 6 months and if refrigerated can be used up to a year, but after that it doesn’t work as expected. I have solder wire that is 30 plus years old and works as well today as it did the day I bought, that won’t be the case with solder paste.