How do they get all those little copper tubes stuck in a board?
I've heard through-hole electroplating (not exactly sure how they do that, but a post I found when I googled the phrase says that you dab on a drop of a certain solution on the inside of the via and then plate onto this priming layer.
I've also heard that you can get what are basically rivets which you put through the board and then solder on both sides. The budget version of this is to stick a copper wire / pipe through of the appropriate diameter. Actually, if you drill the holes the right size, you could probably press fit in a few pieces of pipe and have it stay in nicely (though you'd probably still have to solder to make reliable connections.
Yes, it is basically electroplating; it is not that difficult in theory but I doubt there are any sensible DIY solutions.
Using "rivets" is one but the ones I've seen are little more than piceces of copper wire; they are primarily meant for correcting errors on prototype boards or for hobbyists.
The current methods are proprietary but the original way was to drill holes through the board and soak the board in an electrolyte. This was done before the board was etched for the traces. Ultrasound may be used to get the electrolyte to penetrate into the holes. Then the board is electroplated. Again ultrasound is used to keep the electrolyte circulating through the feed throughs.
I actually didn't know how this was done, when I asked. Working with this stuff all my adult life, I've had an entertaining time asking. Speculation and answers have included inserted little tubes in the board, and dusting the holes with graphite, then electroplating.
You all seem much better informed. Thanks.
If the graphite was ever done, it doesn't seem to be used any more.