A while ago I bought some cheap perfboard from AliExpress. Once when I was trying to solder with it, dark brown stuff started coming out of nowhere (I guess it was coming from whatever the board was made out of) and covering the pads and when it covered a pad, it was no longer possible to solder to it). Has anyone else experienced this? I guess it's because the material the board was made from is just not resistant to the temperature? I think a proper material is called "phenolic paper" but I suppose this was something different.