Good evening, could you please tell me how many watts a soldering iron is recommended for soldering electronic cards?

As an addition to tell you to use quality tin, it is so important or even more important that the soldering iron itself use a quality tin, with a bad tin even having a quality soldering iron you will never get good welds. The best thing is a soldering station that has soldering iron and hot air, there are more or less economical ones such as those of the BAKU brand that are not bad in value for money and have spare parts for tips, resistors, etc. in case you need to repair or put a new tip in the long run; If you are looking for a soldering iron for generic use, buy a brand like Weller or JBC they are more expensive but you will weld better and if you take care of the tips they will last you a lot. The economic soldering tips get black soon and then it is impossible to weld with them.

With a 35W tinner you could do the job well but you have the risk of burning the track if you apply heat for a long time, it is normal to use a 20W or hot air station that is used for SMD welding. I hope to be helpful.

Braian; In addition to the Watts, it is recommended that you look at the specifications about the insulation of the power grid that has the captive, A solder that induces some AC to the circuit in which it is being used can cause a lot of damage, especially in CMOS components.