Yes, you can solder on Type K soft copper. Here are the steps:
• Heat up soldering iron to an appropriate temperature for the job.
• Clean and tin both surfaces of the copper piping with flux and solder.
• Place heat on joint area until it is hot enough for soldering.
• Touch solder wire to joint and let it flow into the gap between two metals as they cool down.
Once completed, your new joint should be strong and airtight!