The copper is covered with solder-mask, a sort of resin. You need to scrape it off, or use sharp pointed probes.
Because the method you describe, and it's advantage, is really a disadvantage. Not only is it harder to place smd parts on unevenly tinned pads, it prevents the main advantages of solder paste.
The first is that solder paste holds a piece in place, ever so slightly, before being reflowed. It is a paste of tiny solder beads and flux. The smd parts are suspended in place.
The second being surface tension. When freshly reflowed, free of oxidation and contaminants, there is high surface tension. The parts are not likely to move without external force. Second and third reflows result in lower surface tensions, as well as cold joints.
And the last advantage is capillary action. Between the flux, the surface to surface contact of the pad and the pin, capillary action pulls the pin to the center of the liquid solder. Multiple pins doing this, makes a smd part self center. And as long as you have solder mask between the pins, this is even more effective, of course, only if there is not excessive paste on the pads.
And most importantly, industry leaders have probably tried your method, and having not adopted it, it probably didn't sit well with them. Probably.
Best Answer
You want transparency sheet pressed on PCB as flat as possible, no bubbles or gaps and you want it toner side to PCB. What i mean is you want toner to be as close to UV sensitive coating as possible, otherwise youll get shadows with blury edges.
Overexposure might be a problem too as UV does get thru toner in the long run. I usually lay two copies of a print for one side of PCB (as ideally aligned as possible of course)
Another opposite thing - you mention you are using a photoframe. Does it have a glass or plexiglass in it? UV is filtered out by glass, you need a plexiglass as it's more transparent for UV.
Edit: I usually use two copies of artwork and water - wet transparencies want to stick togeather because of water surface tension. The same for "glueing" it to PCB. It's just a matter of pushing air bubbles from under transparency - i use a couple of cotton balls - one hand to hold board in place and other to swipe bubbles to the sides.