Soldering components to the PCB and teaching YOU how to solder

A project log for The UnbreakaBLE Micro Drone

Use any Bluetooth 4.0(BLE) device to control this agile little modular drone.

Anshul SanamvenkataAnshul Sanamvenkata 07/24/2017 at 04:040 Comments

I am going to have an horrendous time soldering this PCB. I have soldered SMD passives before, and I find them generally pretty easy, but I have never soldered QFN before, and this is my first time. I will document my journey of soldering QFN components here. Make sure you have a fine tip soldering iron, and a hot air station. The one I ordered was extremely cheap, and was a Hakko knockoff from Amazon. Here's the link for people who are interested.

First Attempt:

My first attempt was a total failure. I tried to go the cheap route without solder paste and stencils, and used the video below to help me. 

It looks so easy right? Wrong! I only soldered components essential for the microcontroller, and the microcontroller itself. My ISP programmer couldn't even recognize it because the pins weren't all soldered correctly. I desoldered the microcontroller and kept trying over and over, reballing the QFN pads every time. I finally got the ISP to recognize and program the microcontroller. Huzzah!

My victory ended there however, because I soon discovered I could not reprogram through the USB, and the sample LED blink program wasn't working. I reasoned it was once again bad soldering because the schematics were perfect.

Second Attempt:

Realizing going the cheap route wouldn't work, I ordered myself some solder paste, and hunted for cheap stencil manufacturers.

After some digging I found a website called oshstencils which despite similar naming is NOT related to OSHPark. The order process was incredibly easy, and the stencil itself was quite cheap. Only $5.63!, in fact the shipping cost more than the stencil itself with USPS Priority Mail costing $7. 

After receiving the needed materials, I set to work using the below video as a guide.

With the combination of a hot air station, a solder stencil, and a tube of solder paste, I got the microcontroller working on the first try! Everything worked perfectly including the USB and outputs.

Once the hard part is done, soldering the passive components is pretty easy with a fine tip soldering iron, and the SOT 23-5 packages in the form of voltage regulators are very easy to solder as well.