I was working on making my own PCB but faced a problem during etching. I used an iron to transfer the circuit to the copper board, some of the sketch wasn't fine so I used a permanent marker to make it clear. After putting in the ferric chloride and copper removed I found that the copper was perfectly removed and the traces were fine. But as I used a thinner to remove the black markings, even though they were covered, many traces had holes and gaps. This was unexpected as the markings after removal from the ferric chloride solution were fine but after using a thinner, the copper inside was missing. I dont know where is the problem. Is there any problem with the use of permanent marker or with thinner??? Kindly help me as this is the third time I am facing these results. The image is shown below:
I am using solder now to fill the gaps.