Hot air soldering recommendations for STM32L031G6U6 (UFQFPN28)

[zizou_1221]

Hello,
I’m a master’s student soldering an STM32L031G6U6 (UFQFPN28) onto my own PCB using a hot air station, and I’d like to do it correctly. My first attempt (no solder paste, no extra flux, about 400 °C) left the chip unable to connect over SWD, so I suspect poor joints or heat damage.
Could you please advise:
1. Do the package pins carry enough solder on their own, or should I apply solder paste/flux on the PCB pads?
2. What hot air temperature, airflow, and heating time do you recommend, and what is the maximum temperature/time the part tolerates?
3. Is there a recommended reflow profile or preheating for this package (e.g. JEDEC J-STD-020), and any ESD or handling precautions?
Thank you in advance for your help.

[mfgkw]

There is no solder by ST on the UFQFPN28 package.
You have to supply solder+flux or paste. 

Somewhere in the data sheet you will find the exact requirement how about the recommended process. But while soldering manually you wil have no tools to check the conditions (I assume).
It is possible to solder this package manually, but this requires some experience and will never be 100% reliable. I recommend to use some cheap prototyping boards and chips (not necessarily your STM controller) for training.

There are different approaches, depending on your situation. You might use paste and heat from all sides, or paste and heat only from bottom side. There are many youtube tutorials about this (more or less useful).

Since the audience here is probably more professional you might earn some objection on your attempts. But with some training and sense of materials it is possible. Buy a bunch of cheap ICs and see how solder flows. Then spare the IC from unnecessary heat while having the solder flowing.

BTW LQFP28 is much easier to solder by hand than UFQFPN28.

 

[TDK]

You will be unable to do this without flux. Get a flux pen or bottle of flux.

Put as much solder on the pads on the board as you can using a soldering iron. Use flux. The pins do not have solder.

Put more flux on the board around the pads. Use tweezers and hold the chip in the correct spot and heat it up with the hot air gun. The temperature is not critical, 660 F / 350 C is fine for leaded solder. Eventually the solder will melt and the chip will suck down to the board. Ensure all pads are reflowed and then remove the heat.

 

Yes, there is a reflow profile in the data sheets. You will be unable to replicate it with a hot air gun.