Sorry to hear you are having so much trouble. You really need to measure the temperature of the board to ensure you are even close to a useful preheating. You can just get a cheap thermocouple and use it with a DMM. Your DMM might have a temperature range but it is really just reading mV and displaying the corresponding value. If you don't have such a range you can just follow the datasheet on the thermocouple and convert from mV to °C. The probe should be less than $5.00USD including shipping.

One other thing is the surface. Is there a heavy oxide layer? If so you may have to remove that mechanically before the flux is useful. Very fine sandpaper or a fiberglass spot sanding pen will do the trick. If the copper has a dark red color, you'll need to do something. Be gentle obviously, and you don't need to remove the oxide from any place you don't need solder to wet.

 

Sorry to hear you are having so much trouble. You really need to measure the temperature of the board to ensure you are even close to a useful preheating. You can just get a cheap thermocouple and use it with a DMM. Your DMM might have a temperature range but it is really just reading mV and displaying the corresponding value. If you don't have such a range you can just follow the datasheet on the thermocouple and convert from mV to °C. The probe should be less than $5.00USD including shipping.

One other thing is the surface. Is there a heavy oxide layer? If so you may have to remove that mechanically before the flux is useful. Very fine sandpaper or a fiberglass spot sanding pen will do the trick. If the copper has a dark red color, you'll need to do something. Be gentle obviously, and you don't need to remove the oxide from any place you don't need solder to wet.

Thanks so much for your time and advice. Actually I did scrape the pads gently in the beginning, thinking perhaps the type of solder used during manufacturing was in the way of getting it all to heat up enough. But after watching videos on how PCBs are assembled in the factory, I now know the grainy looking solder I was looking at was likely "solder paste", tiny granules of solder suspended in a paste, that is supposed to heat up to the point where it all melts to a shiny solder finish as normal - what I was seeing was probably solder paste that wasn't heated up high enough and I could still see granules and is the reason the components popped off during gentle handling.

In any case, in the beginning I had already scraped the pads down to a mixture of shiny metal, and also copper showing through, where I probably scraped away a bit of the pad too by accident. This didn't help at all. It was after that point I started posting for help online.

From your last reply I concluded - I just don't have the equipment required to do this and rather than invest further money and time, write it off as a learning experience. If I encounter this kind of scenario again in the future, I at least know enough to turn it down, or weigh up the cost of buying the heating plate and some way of knowing the temperature of the board.

I appreciate your advice, I've definitely learned from it, so it amounts to something after all