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Very cool idea!

I don't have all the tools needed for tapping holes for the legs, so I drilled holes for some 3" wood screws I had. The holes were .010" smaller than the screw threads and it was still a battle to screw them into the 6061 Al block. I find myself using the micrometer all the time... It's now level and I've finished the wiring of the elements and powered up the PID controller. The 4 300W 120V elements are in parallel and will be wired in series with the 25A SSR. A couple more wires and I fire this baby up and watch the lights dim. Oh, I still have to drill the TC hole...
One thing I'll be watching is the time it takes to get up to temp. I've tried to outdo you enso!

Ive drilled the TC hole too deep by mistake. Looks like it's over by about .090". I'm going to fill it with some leftover metal shavings and thermal paste. This may be a blessing in disguise as now the PID TC feedback sensor is reading data through similar barriers as the elements.

I'm going to drink a beer, recheck the wiring and throw the switch... 120VAC scares the hell out of me!

If it works, I will have to bring home my laser IR temp gauge to verify temps.

Hmm, not working... I hear the internal PID controller relay clicking after reset, but no voltage to the SSR. TC is reading correctly and rises in temp to the touch

It's not as bad as 230V.

LOL @ Arlet. Once one gets stung by household AC voltage, one won't forget it! 230 even more so!

So I was reading up on this POS PID controller I got from EBAY. I need to modify it. Shouldn't be too difficult. The internal control signals that operate the internal relay need to be brought out to the SSR.

So, I made the most rudimentary modification to this PID board, by removing the internal relay and routing the 2 signals offboard, and the SSR is lighting up. Now time to hook up the load. And just 1 more beer...

EDIT:We've got heat! I love modern digital electronics. PID controller, element wires and SSR very cool. Hotplate up to 145deg Celcius. About 1 degree per sec, steady.

SSR getting warmer after 15 mins. Shutting down and putting device on a cookie tray to cool down. Success! Tried to show some steam, it floated to the left of monitor. Legs were getting too warm on the wooden desk. Had to shut down

Congratulations! Now it's time to destroy some expensive BGA chips!

Arlet, I do have a USB camera just like that one. I've been meaning to set it up on a taller stand.

If you ever do check the temperature with an infrared thermometer, do let us know how well the PID display correlates.

Be aware that IR thermometers don't work well on aluminum, at least not without adjusting. I'd put an empty PCB on the hotplate, and measure that instead.

I was once told by an American colleague that the problem with 110V is that the shock it gives can make you grab and hold onto the conductor (giving you a prolonged shock) where as 230V shocks tend to cause your hand to be kicked back.

When he was in the US Navy he'd be taught to escape from smoke filled submarine compartments using the back of his hand to feel his way around in case there were any live cables.

I can testify that 230-240V gives you quite a kick.

A PCB with lots of little vias would be more interesting. FR4 is not a great heat conductor, so vias play an important role in heat transfer from the hotplate up to the balls. I even read in some design guide a recommendation to place the dogbone pattern on unused pins to increase the heat mass of the upper level for even heating. It might even be a good idea to put vias on unused pins to move more heat up.

On a different note, I believe that solder balls are 63% tin and 37% xxxsolderxxx lead. According to wikipedia https://en.wikipedia.org/wiki/Soldering#Solders, this mix is eutectic, meaning that it has a melting point of 183C (not a range) - it transitions straight to liquid from solid.

There is a slight heat gradient between the heating elements (my heaters are 80mm apart). This will require setting the temperature a little higher. If there is a next time, I will probably put more heating elements spaced closer together. The current set up is workable, but I have to figure out the temperatures - right now I am just guessing.

In my later, successful experiments, I jammed the plate temperature way up, to 250C. This melts the balls in around 15-20 seconds (I will time it next time). The board then has to be removed quickly (and carefully) to avoid smoking the FR4.

I would like to lower the temperature a little. I know that at around 200 it seemed to take forever to heat it. I had no luck until I set it to 220 or so.

Looking at some profiles on the Internet... I see wave soldering going up to 260C, IR heating to 230C, etc... Perhaps I am not that far off.

Given the complete lack of calibration of any kind, this is not very helpful. I should spring for a thermometer, or at least verify with another thermocouple setup (I am thinking about a PID-controlled toaster oven next).

You mean "lead", I suppose. However, due to the EU RoHS directive, many devices are lead-free now. This is annoying, because the lead-free solders have higher melting temperatures, and I generally find them inferior in their soldering ability. I think the best thing would be to perform a number of test runs to see which temperature setting works best. An IR thermometer could be useful to measure how even the temperature is. Although with the big slabs of aluminum you are using, I would expect decent results. However, the aluminum may be heated evenly, you still need a good board design to make sure the balls all reach the same temperature.

Yes, this is going to be the challenge I'm starting to realize. I've been away from board design for more than 6 months, so some stupid questions:
Is it possible to have a via for every pin of a BGA package? I would think so off the top of my head...
I have a desoldering station which has a hot air gun. Maybe this, in conjunction with the hotplate, would help bring the temps up quicker without cooking the FR4 board material. Not sure if air blowing would move the BGA package though...