So, I use an intermediary method for my prototyping boards. I put flux on the board, then I put solder on the pads with a soldering iron. Just dragging the soldering iron horizontally over the pads seems to deposit just the right amount (except for central QFN pads where I cover only the center of the pad). Then I flux again and place components. It's very easy to do because there's no paste and you can easily nudge them into the position with a stick.
Aha. So Northguy. BTW, I agree with 99% of everything you ever post concerning just about anything. Total respect. And a question.
Have you ever tried this:
Flux the pads. Then just drop the 0402 parts on there without caring about rotation. Keep going until you have dropped on all your 0402's that are say, left-right. Just make sure they stick to the flux somewhere over/near the pads. (The only reason you are pre-placing them at all is so you don't have to switch back and forth between pickup tool and tweezers, and you don't have to switch between microscope and naked eye, and you don't have to have long pause between making joints to allow the tinned tip to oxidize; it has nothing to do with accuracy/alignment; These inefficient maneuvers are a big part of why soldering can be so much less efficient than paste and place, but we don't have to do it that way). Now after you get them all "placed," you put down the pickup tool. You pickup the tweezers in your left hand. You pickup your iron in the right hand. Knife tip preferred for me. Loaded with solder.
Now you look under the microscope, and you align the part with the tweezers in your left hand while you tack it with the preloaded knife tip. Alignment is done, and the part ain't moving. Usually for resistors, if there's enough room, I can easily do both sides with a knife tip. (I have sanded away a tiny bit of the chrome on the back of the point, to aid in this maneuver). But oftentimes, due to pad size or other pads/parts, it is difficult. If the latter, just tack one end and move on. Keep going until you run out of solder, then pick up a new blob. (Knife tip can hold enough solder to do a lot of SMD resistors, prolly 6-30 joints without getting out of control, depending on pad size and PCB finish). All this time, you are not putting down the tweezers, ever. You are not letting go the iron, ever. You are just once in a while having to look away to pick up more solder. After done, flip the board and touch the iron to the other end of the parts. IOW, why pretin the pads when that could have been you making the joints? This way, the first time you ever make any attempt to align a part is definitely the last. There is no way the part will stick to the tweeers/stick when you withdraw it. There's no way you'll put your hand on it and smoosh things. There's no need to put it in the oven, after. There's no inspection, later.
We gots two hands, and using only 1 of them to play Jenga/Operation, and having to do it under mag lamp (or having to look in/out of the microscope to pickup every single part) is very weird to me. I still don't get it, and I have tried. I have bought an oven and done dozens of boards with stencil and hand placing, because it is so popular. And there is a definite advantage on the passives, in particular. But the time saved is more eye strain, cuz it's way more efficient to do it with naked eye. And wherever I (and some folks surely have better eyes and hands) need the microscope, which is fine pitch IC's, mainly, it don't work so hot. And with larger board/panel size, you don't need a manual PnP or to fiddle with a handrest. You just flux and drop the parts in area you can work on without accidentally pasting your palms. And after soldering them, you do the next stage.
And yeah, I do 0402. Did something like a hundred of them this past week.
With the right software link from the pcb software to the PNP machine programming takes no more than fife minutes. (If there are some single parts not mounted in feeders I place it by hand.)
With a PnP, now we're talking. I think this is going to be better suited to batch production, though. Or does this include loading all the parts? Damn nice to have one of these things, I'm sure.
I'm definitely open to trying, again, but I wonder if it's really worth it. Maybe someone who traditionally stencil pastes and hand places parts, and who has a microscope, can try it "my way." I am sure I am not the only person to ever think of this. I'm not advocating people don't do paste/reflow. I'm trying to figure out why my $200.00 reflow oven is in storage.
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