Think of it this way. You could have one big board with spots to put in upgrades, camera, memory graphics, whatever. Soldering can get things pretty small, and

Think of it this way. You could have one big board with spots to put in upgrades, camera, memory graphics, whatever. Soldering can get things pretty small, and pretty close together. Home soldering is possible, but requires some tools, and a steady hand. if you want people to solder, you'll probably need to make the connections a little bigger and further apart than what you would need for a nice smt with mask in a shop. Soldering is is also kind of hard to reverse. Any mechanical fastener is easy to undo, but much more bulky than soldering. i'm thinking little plastic clips, but there are alternatives. in any case, they're going to be bigger. That leaves maybe some kind of conductive epoxy and a solvent to remove it. that should be pretty comparable to soldering, but seems like it would have the same problems, you'd want bigger surface mount pads. mechanical fasteners are the way to go, you don't need any (or many) expensive tools to get it right. but mechanical fasteners are big, and that's space that could go to more battery, bigger screen or whatever. further apart means slower bus speed, and probably other problems. The other options require special tools. So phone plus $200 or whatever for the tools just isn't worth it. (and making the process super reliable for novices isn't easy)